&EPA
United States
Environmental Protection
Agency
Building Retrofits for Increased
Protection Against Airborne
Chemical and Biological Releases
REPORT
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National Homeland Security Research Center
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June 2007 EPA 600/R-07/157
NISTIR7379
Building Retrofits for Increased
Protection Against Airborne
Chemical and Biological Releases
Jacky Rosati
Andrew Persily
Robert E. Chapman
Steven J. Emmerich
W. Stuart Dols
Heather Davis
Priya Lavappa
Amy Rushing
Building and Fire Research Laboratory
Prepared for:
U.S. Environmental Protection Agency
Research Triangle Park, NC
Funded under IAG DW-13-93010301-0 by the U.S. EPANational Homeland Security Research Center
(NHSRC), Decontamination and Consequence Management Division (DCMD)
*fATES O* *•
U.S. Department of Commerce
Carlos M. Gutierrez, Secretary
Technology Administration
Robert Cresanti, Undersecretary of Commerce for Technology
National Institute of Standards and Technology
William A. Jeffrey, Director
Office of Research and Development
National Homeland Security Research Center, Decontamination and Consequence Management Division
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Abstract
Due to concerns about potential airborne chemical
and biological (chembio) releases in or near buildings,
building owners and managers and other decision makers
are considering retrofitting buildings to provide some
degree of protection against such events. A wide range of
technologies and approaches are being proposed with varying
levels of efficacy and cost, as well as varying degrees of
applicability to particular buildings and ventilation systems.
This document presents the results of an effort to evaluate
chembio retrofit options for buildings. A number of retrofit
options are identified, and their potential to protect building
occupants from a number of generic contaminant releases is
evaluated, using building airflow and contaminant transport
modeling. In addition, a case study is presented in which
specific retrofit options were considered for two actual
buildings and preinstallation designs and cost estimates were
developed. Based on the analyses performed, the results of
the case study and other available information, guidance
on the application and effectiveness of various retrofits is
presented. An economic analysis software tool employing
life-cycle cost analysis techniques was developed as part of
this project, and its use is described in an appendix to this
report.
The retrofit options considered fall into two categories,
the first being stand-alone technologies or devices such
as enhanced paniculate filtration that are installed and
implemented as purchased. The second category includes
retrofit approaches that employ operational strategies or
building modifications to increase building protection, such
as outdoor air purging or building envelope airtightening.
The guidance section describes each retrofit technology and
approach in some detail, presenting relevant performance
data and the level of protection that might be expected
from the retrofit. Potential disadvantages and knowledge
gaps are also discussed for each technology. The retrofit
technologies considered include enhanced particle filtration,
sorbent-based gaseous air cleaning, ultraviolet germicidal
irradiation, photocatalytic oxidative air cleaning, and work
area air capture and filtration equipment such as mail
handling tables. The approaches include ventilation system
recommissioning, building envelope airtightening, building
pressurization, relocation of outdoor air intakes, shelter-in-
place (SIP), isolation of vulnerable spaces such as lobbies,
system shutdown and purge cycles, and automated heating,
ventilating, and air conditioning (HVAC) operational
changes in response to contaminant sensing. The filtration
and air cleaning options are noted to have the advantage
of always being operational, which is an advantage as
long as the systems are properly designed, installed, and
maintained. However, the lack of standard test methods for
sorbent-based gaseous air cleaning and other air cleaning
approaches is identified as a critical issue in the application
of these technologies. Building envelope air sealing and
pressurization can be quite effective in protecting against
outdoor releases as long as effective filtration against the
contaminant of concern is also in place. The protection
provided by operational changes such as system shutdown
and purging are shown to be very dependent on the timing
of their implementation, with the possibility of increasing
occupant exposure if the timing is inappropriate. Isolating
vulnerable zones and other system-related modifications
are highly dependent on the building layout and system
design, and their implementation must be well conceived
to be effective under the range of conditions that exist in
buildings. Finally, many retrofits are noted as also providing
the additional benefits of increased energy efficiency and
improved indoor air quality, which should be included in the
life-cycle cost comparison of different options to the degree
possible.
Keywords: air cleaning, building protection, CBR, chembio,
filtration, indoor air quality, life-cycle costs, terrorism
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Use of Non-Si Units in a NIST Publication
The policy of the National Institute of Standards and (HVAC) industries, certain non-Si units are so widely
Technology is to use the International System of Units (SI used instead of SI units that it is more practical and less
units) in all its publications. However, in the North American confusing to include values in non-Si units in portions of this
construction and heating, ventilating, and air conditioning publication.
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Table of Contents
1. Introduction 1
1.1. Project Description 1
1.2. Retrofit Options 1
1.2.1 Retrofit Technologies 2
1.2.2 Retrofit Approaches 3
2. Technical Evaluations 5
2.1 Description of Simulations 5
2.1.1 Building Models 5
2.1.2 Contaminants and Release Scenarios 6
2.1.3 Retrofits 7
2.1.4 Simulations and Analysis 11
2.2 Results of Simulations 11
2.2.1 Single-zone Model 11
2.2.2 Two-story Office Building 15
2.2.3 High-rise Office Building 26
2.3 Summary of Simulation Results 33
3. Case Study 35
3.1 Description of Buildings and Retrofits Considered 35
3.2 Retrofit Design 36
3.3 Economic Evaluation 37
3.4 Technical Evaluation 39
3.5 Discussion of Case Study 42
4. Guidance 45
4.1 General Guidance 45
4.1.1 Understand the Buildings 45
4.1.2 Understand the System 46
4.1.3 Inspect the System 46
4.1.4 System Tune-Up 46
4.2 Retrofit Technologies 46
4.2.1 Enhanced Particle Filtration 46
4.2.2 Sorption-based Gaseous Air Cleaning 53
4.2.3 Ultraviolet Germicidal Irradiation (UVGI) 56
4.2.4 Photocatalytic Oxidation Air Cleaning (PCO) 57
4.2.5 Work-area Treatment 58
4.3 Retrofit Approaches 58
4.3.1 System Recommissioning 59
4.3.2 Envelope Tightening 60
4.3.3 Building Pressurization 63
4.3.4 Relocation of Outdoor Air Intakes 65
4.3.5 Shelter-in-place 67
4.3.6 Isolation of Special-use Spaces 68
4.3.7 System Shutdown and Purging 69
4.3.8 Automated HVAC Response 70
4.4 Guidance Summary 71
5. Conclusions 75
6. Acknowledgements 77
7. References 79
Appendices 83
A. Life-Cycle Cost Analysis Tool for Chem/Bio Protection of Buildings: Software Primer 83
B. Case Study Retrofit Design Documentation 107
C. Case Study Retrofit Costs per Unit of Floor Area 115
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List of Acronyms
A&E: architectural and engineering, with reference to firms that do both types of design work
ASHRAE: American Society of Heating, Refrigerating, and Air Conditioning Engineers
ASZM-TEDA: military grade carbon sorbent, impregnated with copper, silver, zinc, molybdenum,
and triethylenediamine
BASE: Building Assessment, Survey, and Evaluation (EPA study of 100 U.S. office buildings)
BFRL: Building and Fire Research Laboratory (part of NIST)
CMU: concrete masonry unit (type of wall construction block)
CONTAM: NIST-developed multizone airflow and contaminant dispersal simulation program
CSEPP: Chemical Stockpile Emergency Preparedness Program (a FEMA program)
ELA: effective leakage area
EPA: Environmental Protection Agency
FEMA: Federal Emergency Management Agency
GPAC: gas-phase air cleaning
HEPA: high-efficiency paniculate air filters
HVAC: heating, ventilating, and air conditioning
IAQ: indoor air quality
LCAT: Life-Cycle Cost Analysis Tool (NIST-developed software for comparing retrofit options)
LCC: life-cycle cost (method for economic comparison of retrofit options)
MERV: Minimum Efficiency Reporting Value (metric of particle filtration efficiency based on
ASHRAE Standard 52.2)
NIST: National Institute of Standards and Technology
OAE: Office of Applied Economics (part of BFRL)
PCO: photocatalytic oxidation
PVNS: present value of net savings (method for economic comparison of retrofit options)
SIP: shelter-in-place
TAB: testing, adjusting, and balancing (procedure for confirming ventilation system operation
relative to design)
ULPA: ultra low-penetration air filters
UV: ultraviolet
UVC: C-band wavelength of UV radiation, generally less than 280 nm
UVR: UVGI rating value
UVGI: ultraviolet germicidal irradiation
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1.0
Introduction
Due to concerns about potential airborne chemical and
biological (chembio) releases in or near buildings, building
owners and managers and other decision makers are
considering retrofitting buildings to increase protection
against such events. A range of technologies and approaches
are being proposed with varying levels of efficacy and cost,
as well as varying degrees of applicability to particular
buildings and ventilation systems. While a number of useful
guidance documents have been published (ASHRAE 1993,
NIOSH 2002 and 2003), most of these do not address the
selection of appropriate and cost-effective retrofits for
specific buildings. In order to address this need for better
guidance on building retrofits to increase protection against
chembio releases, the Building and Fire Research Laboratory
(BFRL) at the National Institute of Standards and Technology
(NIST) undertook the project described in this report.
1.1 Project Description
The purpose of the project is to provide building owners,
managers, engineers, and other decision makers with
information about retrofit options to improve the safety
of buildings against airborne hazards and with economic
analysis tools for use in selecting cost-effective approaches to
mitigating those hazards. This project was organized around
a number of tasks, the first two of which were to identify
the retrofit options to be considered in the project and to
establish the methods to use in the technical and economic
evaluations of these options. The next task was to conduct a
technical evaluation of the protection impacts of the retrofits,
using building airflow and contaminant transport simulations.
This evaluation is described in Section 2 of the report. These
simulations involved the analysis of three buildings subjected
to generic particle and gaseous releases to determine the
reduction in occupant exposure as a result of implementing
the various retrofits. Section 3 of the report presents a case
study in which specific retrofit options were investigated for
two buildings and preinstallation designs and cost estimates
were developed. Finally, guidance on the application and
effectiveness of various retrofits is presented in Section 4.
A key effort within the project was to formulate methods
for economic analysis that provide life-cycle cost (LCC)
information about retrofit options to assist decision makers
in choosing how to improve the safety of their buildings. An
economic analysis software tool was developed (available
for download at www2.bfrl.nist.gov/software/LCCchembio/
index.htm). with a software primer included in Appendix A to
this report. The economic analysis methodology includes the
following considerations: the assumptions and information
requirements necessary to compute the costs of each retrofit
option; the methodology for combining information about
first costs with operations, maintenance, and repair costs
and with other costs to compute the LCCs of the retrofit
options; and specification of the appropriate circumstances
for applying this methodology to cost analyses of the options.
The economic analysis methodology includes two metrics of
the cost effectiveness of alternative investments, LCC and
present value of net savings (PVNS).
It is important to note that each building and its ventilation
system and each contaminant release scenario is unique.
Therefore, the information presented here must be
considered in the context of a specific building's
characteristics, including layout, system type and
design, and occupancy. The level of protection in a given
situation is highly dependent on these characteristics and
the nature of the contaminant release, and it is extremely
difficult to make general statements about which strategies
will be effective in a given situation and to what degree.
Nevertheless, this project is based on the philosophy that
better protection is a worthy goal, even if the degree of
protection cannot be characterized in general terms.
1.2. Retrofit Options
The first task in this project was to identify candidate retrofit
options for consideration in the technical evaluations of the
study and for potential inclusion in the resultant guidance
itself. These options are divided into two basic categories,
specific technologies, such as filtration and air cleaning
devices, and more generic approaches to increasing building
protection, such as building pressurization strategies and
isolation of areas of potential concern (e.g., mail rooms).
These options have been identified based on information
in the published literature, information from vendors, and
interactions with researchers, consultants, government
agencies, building contractors, HVAC experts, and other
knowledgeable individuals. The options that are considered
are limited to engineering-based retrofits as opposed to
building and personnel management options such as building
security and evacuation. Obviously, building management
practices can play a major role in increasing building
protection, but they are not within the scope of this project.
In addition, the options considered are restricted to those that
are "off-the-shelf or commercially available today. While
much research and development currently in progress will
result in more options in the future, only currently available
technologies are being considered.
This section presents the technologies and approaches
that have been identified and includes a discussion of the
performance data that are relevant to the simulations planned
for the project and a summary of other issues related to the
retrofit that are relevant to the study.
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1.2.1 Retrofit Technologies
A number of technologies have the potential to increase
building protection against chembio contaminant releases.
Most of these are in the particle filtration and gaseous
air cleaning categories. Other technologies for building
protection include systems for use in mail rooms and other
spaces that may be more vulnerable to contaminant releases.
These systems are designed to capture and remove the
contaminants before they are able to migrate to other portions
of the building.
Enhanced particle filtration
Particle filtration is currently employed in most commercial
and institutional buildings, primarily to limit dirt buildup
on cooling coils and other wetted surfaces in order to
reduce the potential for microbial growth and to maintain
good heat transfer between the air and the coil surfaces.
However, typical levels of filtration are not always very
effective in removing particles of the sizes associated with
many biological contaminants, i.e., on the order of 1 ^m.
Nevertheless, dramatic increases in removal rates can still be
achieved through enhanced filtration without the use of very
high levels of efficiency (NIOSH 2003). Particle removal
efficiencies are fairly well established based on the use of
ASHRAE Standard 52.2 (ASHRAE 1999), which provides a
rating method referred to as Minimum Efficiency Reporting
Value (MERV).
The implementation of enhanced filtration involves a number
of important issues. First, the particle size of interest must
be considered. Biological contaminants vary in size, but
the bacteria and spores of most interest are generally on the
order of 1 ^m to 10 ^im. In addition, the installation of more
efficient filters will generally result in an increase in the
pressure drop across the filter. Depending on the increase in
filter efficiency and the type of filter installed, the increase in
pressure drop may or may not be particularly large. In some
cases, the air handling equipment will need to be modified
due to the increased pressure drop.
Sorption-based gaseous air cleaning
Sorption-based gaseous air cleaning is currently employed
in a number of applications to control odorous, corrosive,
or otherwise undesirable gases generated within or outside
of buildings. A variety of sorbents are employed, including
activated carbon, alumina, and sorbents impregnated with
compounds to enhance their ability to remove specific
contaminants (NIOSH 2003, ASHRAE 2003). These sorbents
have varying degrees of removal effectiveness depending
on the particular sorbent-contaminant combination, and they
capture contaminants through either physical adsorption
or chemisorption. Some sorbents employing the former
mechanism can be regenerated through heating or other
processes. Adsorbents using a chemisorption process
generally rely on catalytic (continuously self-regenerating)
reactions that chemically decompose the threat gases into
less toxic or nontoxic gases. The effectiveness of sorbent-
based air cleaners also depends on temperature, humidity,
the concentrations of the contaminant of interest as well as
other contaminants, and the residence time of the air stream
in the air cleaning unit. Gaseous air cleaning devices are not
typically employed in commercial and institutional buildings
but are seeing increasing use in a number of applications.
There are no standard test methods for determining the
contaminant removal efficiency of gaseous air cleaning
equipment for use in selecting and sizing these systems.
Manufacturers have performance data and experience that
can be useful, but efforts to develop the equivalent of a
MERV rating for gaseous air cleaning are still being pursued.
In general, gaseous air cleaning systems are associated
with a more significant pressure drop than particle filtration
devices and require more space than typical filtration
equipment. These increased pressure drops can in turn affect
system airflow rates and may require significant system
modifications. These devices must be changed at intervals
that depend on their capacity, the concentrations to which
they are exposed, and the degree of temperature and humidity
control in the system.
Ultraviolet germicidal irradiation (UVGI)
UVGI systems have been used for many years to kill airborne
infectious contaminants in healthcare facilities and other
venues, primarily to control the transmission of tuberculosis.
These devices use ultraviolet irradiation in the 250 nm to 260
nm wavelength range and are generally installed in the upper
portions of a room with shielding to protect the occupants
or in ductwork where such shielding is not required. This
application is distinct from the use of UVGI to kill biological
contamination on exposed cooling coils resulting from dirt
accumulation and condensation.
The effectiveness of these devices is primarily a function
of device geometry, intensity of the light source, microbial
resistance, and residence time of the contaminants of
concern. Inactivation or "kill" rates can be predicted with a
fair level of reliability based on these parameters (VanOsdell
and Foarde 2002). However, there is no standard test method
for determining the effectiveness of these devices and
they are not generally supplied with the performance data
to determine kill rates. These devices are associated with
electrical energy consumption and require some level of
maintenance to keep them operating effectively.
Photocatalytic oxidation air cleaning (PCO)
PCO is an air cleaning approach in which titanium dioxide
(TiO2) acts as a photocatalyst when irradiated by UV light,
removing organic chemicals including both chemical and
biological contaminants. If the photocatalytic reaction is 100
percent complete, the by-products include water and carbon
dioxide, but complete conversion is difficult to achieve in
practice.
Various PCO devices are available as either portable, stand-
alone units or in-duct devices. However, the lack of test
methods for gas or biological removal limits the availability
of performance data.
PCO systems generally have low pressure drops in
comparison to particle filters and sorption-based gaseous
air cleaning. However, questions exist as to the useful life
of the catalysts in practice and the production of undesirable
by-products associated with incomplete photochemical
reactions.
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Work area treatment
A variety of devices are available for capturing and removing
particulates from work areas, e.g., mail opening stations.
These devices are essentially air capture hoods combined
with high-efficiency filtration systems. Some of these devices
also incorporate antimicrobial elements, gaseous air cleaning
components, and UVGI.
The performance of these devices is generally expressed as
a filter efficiency at a specific particle size and an airflow rate.
Units with antimicrobial or gaseous air cleaning capabilities
are impacted by the lack of standard test methods noted
earlier. Another important parameter is the contaminant
capture effectiveness, but this is not generally covered in the
product specifications.
1.2.2 Retrofit Approaches
In addition to the specific technologies described above,
there are a number of retrofit approaches that also have the
potential to increase building protection against chembio
releases. This section describes approaches that do not
involve a specific technology but rather a general strategy
for building and system design or operation.
System recommissioning
Assessing the vulnerability of a building to a chembio release
and using the ventilation system as part of a protective
strategy require that the system design be understood and
that the system be operated as intended. Ventilation system
recommissioning is a process by which a system's operation
is brought into line with its design intent. Depending on the
system, recommissioning can involve a number of items
including the following: testing and balancing airflow;
calibrating temperature, humidity, and other sensors used
to control system operation; checking dampers for proper
operation; reviewing system operating schedules; and
confirming system capacity relative to current loads.
The impacts of a recommissioning effort will depend on the
design of the ventilation system and the degree to which the
system has "drifted" away from its design specifications.
In addition to increasing building protection, building
recommissioning can also increase energy efficiency,
improve indoor air quality, and extend equipment life.
Envelope tightening
According to the available data, the exterior envelopes of
U.S. commercial and institutional buildings are fairly leaky
(Emmerich and Persily 2005). This leakage in combination
with indoor-outdoor pressure differences caused by weather
and system operation can lead to significant infiltration rates
and the entry of exterior chembio contaminants without
the possibility of removing them through filtration or air
cleaning. Therefore, tightening of building envelopes has the
potential to increase building protection.
Envelope tightening can also improve building energy
efficiency by reducing heating and cooling loads due to
infiltration (Emmerich et al. 2005a and 2005b, Emmerich and
Persily 1998). In addition, building indoor air quality can be
improved by reducing unfiltered and uncontrolled infiltration.
Building pressurization
This approach involves protecting a building against
outdoor chembio releases through the overpressurization
of the building interior relative to outdoors and the removal
of the outdoor contaminant from the intake air via filtration or
air cleaning. The idea behind this strategy is for the building
to be pressurized continuously under normal operation, not as
a response strategy in the event of a release. To be effective,
the amount of air must be sufficient to overcome negative
pressures that can be induced by weather and the operation
of other systems. This approach is more likely to be effective
in a building with a tight envelope than a leaky one.
This approach is characterized by the net amount of
outdoor air intake relative to exhaust or spill air, the
envelope airtightness, the weather conditions, and the filter/
air cleaner removal efficiency. The cost and maintenance
issues associated with filtration are also relevant to this
approach. In addition, ventilation system airflow rates and
controls may need to be modified to achieve the desired
levels of pressurization. As with envelope tightening, this
approach can have a positive impact on indoor air quality
(IAQ) by reducing infiltration of contaminated air.
Relocation of outdoor air intakes
Unless otherwise protected, ground level air intakes are
more likely to be exposed to the intentional release of a
chembio contaminant relative to more inaccessible intakes.
One potential solution is to relocate the intake to a higher
elevation that will presumably be harder to access.
There is no quantity that characterizes the degree of
accessibility of an air intake, but presumably an intake that
is located at a higher elevation is less likely to be subject
to a ground level release. Locating outdoor air intakes well
above ground level also reduces the entry of contaminants
associated with landscaping and other activities. There is
clearly a cost associated with relocating air intakes, which
in some cases can be quite significant. In addition, the
relocation may modify the airflow resistance associated with
the intake, thereby requiring other modifications to the air
handling system.
Shelter-in-place (SIP)
In the event of an exterior release, and in some cases an
interior release, the building occupants can move to a
designated space that is isolated from the rest of the building
and offers protection from the airborne contaminant. The
degree of protection will increase if the space is well isolated
in terms of airflow by having tight boundaries and even more
if it is equipped with a filtration and air cleaning system
to remove contaminants that have entered the space. Serf-
contained filtration and air cleaning systems for use in SIP
spaces are currently commercially available.
The primary variables inherent in this approach include the
airtightness of the interior partitions and, if filtration or air
cleaning is employed, the supply airflow rate to the space and
the filter/air cleaner removal efficiency. There is some cost
involved in setting up such an arrangement, particularly in
terms of any airtightening involved and the equipment costs
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for an oversupply and cleaning system. The system will also
require some maintenance to ensure it will function properly
in the event it is needed.
Isolation of special-use spaces
Due to the potential vulnerability of mail rooms, loading
docks, and lobbies to chembio releases, keeping these spaces
at a lower pressure than adjacent portions of the building
can provide some protection. Such isolation can be achieved
through ventilation airflow control, e.g., exhaust fans, and
will generally be easier to achieve if these spaces are served
by a dedicated system. This approach is more likely to be
successful if the boundaries between the vulnerable space
and the rest of the building are tight.
There may be some initial costs associated with airtightening
or with modifications of system airflow rates to achieve
the desired pressure relationships. The latter will require
maintenance in terms of periodically checking the system
balancing to verify that these pressure relationships are still
in effect. In some cases, a new air handling system may need
to be installed. Controls to modulate the system airflows in
response to the real-time pressure monitoring between the
space and an adjacent space may also be needed.
System shutdown and purging
In some circumstances, shutting down a building ventilation
system or operating it at 100 percent outdoor air intake
(purging) may help protect the building occupants from
exposure to a chembio release. However, realizing these
benefits requires knowledge that the release has occurred
and that one of these options is the appropriate response,
and switching to the desired ventilation mode quickly. A
dedicated control that implements the operational strategy is
one means of making the change relatively quickly, though
a fast shutdown requires quick-acting and tight-sealing
dampers, fan braking mechanisms and specially-constructed
ductwork to prevent ducts from collapsing, all of which are
not typically employed in commercial building ventilation
systems. Also, running a building in a purge mode can result
in pressure differences that make it difficult for building
occupants to open and close doors.
Automated HVAC response
Given a timely and reliable signal from a contaminant
sensor, or perhaps an occupant-generated signal, a building's
automated control system could modify the ventilation
system operation in a manner that contains the contaminant
in the zone of release, or prevents it from entering a building
in the case of an outdoor release, and maintains the rest of the
building and egress paths at low contaminant concentrations.
These modifications could include stopping and starting fans,
repositioning dampers, or securely closing doorways. This
is the concept behind automated smoke control systems that
have been used for many years (Klote and Milke 2002) to
contain smoke in the fire zone and provide a safe evacuation
route for the building occupants. The manner in which a
system's configuration and operation should be modified
depends on the building and system design and layout, and
the nature of the contaminant release.
In theory, if the sensors and system capabilities were
available, and the building and system airflow dynamics
were well understood, this approach would be able to provide
a high level of protection. However, sensors that are fast,
reliable, and inexpensive enough are not currently available
for any applications other than very high security buildings
where the costs are justified.
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2.0
Technical Evaluations
In order to support the guidance to be developed as part of
this project, technical evaluations of the retrofit options were
conducted to estimate the impacts of the retrofits on occupant
exposure. These evaluations employed simulations of generic
building and system configurations, with contaminants
intended to represent generic chembio contaminants, as
described below.
2.1 Description of Simulations
The technical evaluations of the retrofits involved simulations
of airflow, contaminant transport, and occupant exposure in
selected buildings, using the multizone airflow and indoor
air quality model CONTAM (Walton and Dols 2005). The
general concept of the evaluations is to simulate generic
contaminant releases within or outside a building and calculate
the occupant exposure, and then to repeat the process for the
same building and release scenario with one or more retrofits
in place. The cases without the retrofits are referred to as the
baseline cases. The measure of retrofit performance is based
on the change in occupant exposure, i.e., the retrofit exposure
as a percentage of the baseline exposure.
Table 1 Simulated Buildings
The CONTAM simulation program was used based on
its demonstrated ability to model multizone airflow and
contaminant transport in building systems, as well as on
the project team's familiarity with the program. CONTAM
considers a building as a system of interconnected volumes
or zones, each at a uniform temperature and contaminant
concentration. These zones can be rooms, hallways, floors
of a building, stairwell shafts, etc. Airflow paths between
zones, and between zones and the outdoors, are specified in
the building model along with other relevant information
such as ventilation system airflows, weather, and wind
pressure coefficients on exterior surfaces. Using these inputs,
CONTAM calculates airflow rates between each zone, under
either steady state or transient weather and system operation
conditions, based on a simultaneous mass balance of air in
each zone. Given additional information on contaminant
sources and removal mechanisms and outdoor contaminant
concentrations, CONTAM determines contaminant
concentrations in the zones based on the calculated airflow
rates and contaminant-specific information.
Building # of Stories Floor Area, m2 (ft2) System Type
1 (Single-zone)
2 (Office)
3 (Office)
1
2
14
1,000 (10,800)
2,600 (28,000)
11,900 (128,000)
Simple air handler
Single air handling system
Central air handling systems
2.1.1 Building Models
The project focus on commercial and institutional buildings
served to define the buildings studied in the simulations,
which are described in Table 1.
Building #1 is a simple, single-zone model included to
examine the first-order effects of ventilation, filtration,
and infiltration without the complexities of weather, interior
zoning, etc. The various airflow rates are input to the model,
rather than calculated as in the other building models. Only
some of the retrofits apply in this building, but its simplicity
makes it easier to understand the impacts of each option. The
two-story office building model is more detailed, including
some interior zoning such as stair and elevator shafts and
ceiling return plenums, a more realistic ventilation system,
and the calculation of weather-driven infiltration associated
with envelope leakage. Building #3 contains a lobby, mail
room, and loading dock, and is modeled with central air
handling systems.
In order to create CONTAM models of these buildings, a
number of factors need to be defined, including the building
zoning, occupancy levels, airtightness of the exterior and
interior walls, and ventilation systems. The manner in which
these factors are handled in each of the buildings is described
below.
Zones
While the number of stories of each building is listed in
Table 1, the subdivision of these stories into zones in the
CONTAM representation of each building must also be
defined. In addition, some of the simulations involve lobbies,
mail rooms, and loading docks, which must also be specified
in each building model. The buildings are zoned as described
below:
1-zone building: single zone, with no lobby, mail room, or
loading dock
2-story office: two levels per floor, the occupied space and
the return plenum above the suspended ceiling; two toilet
rooms with exhaust airflow on each floor; an elevator and a
stair shaft in the building core, both of which are two stories
tall; a lobby zone and loading dock door on the first floor, but
no mail room; and a conference room on the second floor
-------
High-rise office: two levels per floor, the occupied space and
the return plenum above the suspended ceiling; two toilet
rooms with exhaust airflow on each floor; two elevator shafts
and two stair shafts, all of which extend from the basement
to the 11th floor and one stairway that extends through the
13th floor; a mezzanine level that houses the mechanical
ventilation systems between the 1st and 2nd floors; a 12th floor
mechanical room and 13th floor elevator room; a main lobby
on the 1st floor; a mail room with a loading dock door on the
basement level; and conference rooms on all occupied floors
from the basement through the 11th floor.
Airtightness
Values for the baseline airtightness of the exterior walls are
based on an existing database of airtightness values obtained
from building fan pressurization testing (Emmerich and
Persily 2005, Persily 1999). While there is less information
on the airtightness of interior partitions, the available data
were used as a basis for the values in the models (Ivy and
Persily 2001). In the analysis, the exterior wall leakage
value (effective leakage area at 4 Pa reference pressure
normalized by wall area) in the model of the two-story
office was 5 cnvYm2 of wall area (0.07 inVft2). For the high-
rise building, the exterior wall leakage value was 8.7 cnvYm2
(0.13 inVft2). These leakage values are fairly typical for office
buildings, based on the limited measurements that have been
made. Interior partitions are assumed to be leakier, with an
effective leakage value of 20 cmVm2 (0.29 in2/ft2). For the
one-zone building model, all airflow rates are defined, so no
airtightness values are employed to calculate pressure-driven
airflows.
Occupancy
The number of people in each occupied zone was based on
the default occupant density values in ASHRAE Standard
62.1-2004, i.e., 5 people per 100 m2 (1000 ft2) in office space
(ASHRAE 2004). The corresponding number of people is
located in each CONTAM zone for the duration of each
simulation, except in cases where shelter-in-place strategies
are evaluated and the people move during the simulation
period.
Systems and system models
While the system types in each building are genetically
identified in Table 1, the details of the system airflows are
based on current ASHRAE Standards (ASHRAE 2004), the
results of the EPA BASE ventilation data analysis (Persily
and Gorfain 2004), and actual design values in the case of
the high-rise office building. CONTAM has three options
for modeling ventilation systems (constant airflows to or
from the outdoors; simple air handling systems that allow for
recirculation; and full duct models that include all the details
of duct resistance and fan performance curves). Simple air
handling system models were determined to be sufficient for
these simulations, based on their ability to adequately handle
system filtration and their ease of use relative to complete
duct models.
The single-zone building model has constant airflow rates,
with the outdoor air intake rate equal to 20 percent of an
assumed supply airflow rate per unit floor area of 5 L/s«m2
(roughly 1 cfm/ft2 '*). These values correspond to typical
office building system designs, consistent with those seen
in the EPA BASE buildings (Persily and Gorfain 2004).
The envelope infiltration rate is also modeled as a constant
airflow corresponding to an air change rate of 0.2 fr1. The
baseline system is assumed to have a MERV 6 particle filter
in the outdoor air intake and in the recirculated airstream
(equivalent to the filter being in the mixed airstream), with
a particle removal efficiency of 16.4 percent for particle
diameters of 1 \im, but no gaseous air cleaning capability.
The MERV ratings throughout this report are defined by
ASHRAE Standard 52.2 (ASHRAE 1999).
The two-story office building model was developed to
be more realistic than the single-zone case, with envelope
infiltration rates calculated by CONTAM, based on weather
and system-induced pressure differences and envelope
leakage areas. The outdoor air intake rate of the system
was about 10 percent of the supply airflow rate, which
corresponds to about 9.2 L/s (19 cfm) per person for the
130 occupants assumed to occupy the building. The supply
airflow rate to the building zones is based on roughly
5 L/s«m2 (1 cfm/ft2) of floor area. The baseline building
model has a MERV 6 filter in the mixed airstream,
impacting both the outdoor air intake and recirculation air.
The high-rise building model is based on, though not
identical to, a portion of an actual office building. The system
outdoor and supply airflow rates are based on the design
specifications for that building, with a minimum outdoor air
intake of approximately 23 percent of the supply airflow rate
of 4.9 L/s«m2 (0.96 cfm/ft2) of floor area. The systems are
assumed to have MERV 6 filters in the mixed airstream, with
no gaseous air cleaning.
2.1.2 Contaminants and Release Scenarios
The simulated contaminants include generic paniculate
and gaseous contaminants rather than any specific chembio
contaminants. The paniculate and gaseous contaminants are
referred to as contaminant P and G, respectively. The particle
is modeled as monodispersed with a diameter of 1 [im,
and the gaseous contaminant is assumed to be nonreactive.
Particle removal by deposition on surfaces, including
filtration of infiltrating air by the building walls, is not
included in the analysis. Release locations both inside and
outside the building are considered, including the following:
• Exterior release distant from building
• Exterior release at outdoor air intake(s)
• Interior release in lobby
• Interior release in mail room
• Interior release into ventilation system return
• Exterior release in vicinity of loading dock, with loading
dock door closed
]t cfm is the conventional non-Si unit for volumetric airflow
rate and refers to cubic feet per minute.
-------
The simulated releases are described in Table 2. The
outdoor release is represented by a constant, elevated
outdoor concentration for a period of 60 s. The release at
the intake and the loading dock are modeled as a localized
increase in the outdoor concentration at that specific location,
again lasting 60 s. The indoor releases are expressed as
contaminant release rates per unit of time and once again
last for 60 s in the designated location.
Only two release scenarios are used for the single-zone
building model, indoor and outdoor. There are more release
scenarios for the two-story office building, given its more
detailed representation. In addition to the outdoor general
release, there is also a release at the outdoor air intake and
at the loading dock door. Indoor releases occur in the lobby
and into a ventilation system return vent on the first floor.
In addition to these releases, the high-rise office building
Table 2 Contaminant Release Rates
simulations include a release in the mail room instead of
at the loading dock.
The calculated concentrations and the assumed release rates
have no significance in relation to any particular chembio
contaminant but were chosen to yield indoor concentrations
in a reasonable range of interest. Given the generic nature
of these contaminants and releases, and in keeping with the
purpose of the project, the calculated concentrations cannot
be used to estimate health impacts. As a result, the results
in terms of the relative concentration or exposure among
the various simulated cases are of far more relevance than
the absolute concentration and exposure values themselves.
Also, while radiological contaminants are not specifically
considered in this study, the results for the paniculate
contaminant can be considered to represent the impacts on
radiological contaminants of the same particle size.
„,.,„,,„ . Outdoor Air Intake and . , .
Contaminant Outdoor General . ,. ~ . Interior
Loading Dock
G, gas
P, particle
1 mg/m3
109 particles/m3
10 g/m3
109 particles/m3
16.7 g/s
109 particles/min
2.1.3 Retrofits
Like the contaminant releases, the retrofits and the manner
in which they are implemented in the simulations depend on
the building in question. The list of retrofits considered in the
simulations is as follows:
1. Air cleaning and filtration options: Separate analyses
are performed for these systems located in the outdoor
air intake and in the mixed air (downstream of where the
outdoor and recirculation airstream merge).
a. Enhanced particle filtration: increase from baseline
MERV value to retrofit value.
b. Gaseous or gas-phase air cleaning (GPAC): include a
gaseous air cleaner in the ventilation system with none
assumed present in the baseline case; since there is no
standard test method for these devices or values provided
by manufacturers, the contaminant removal efficiency is
only an estimate for the purposes of the simulations.
2. HVAC system options: The following retrofits include
changes in HVAC operation.
a. System shutdown: model by turning off all ventilation
systems including exhausts, thereby reducing outdoor air
intake to zero; include different initiation times to account
for varying degrees of warning based on automatic, visual,
or other means of detection; note that when the system is
shut down, envelope infiltration continues to occur based
on weather effects.
b. Purging: model by running the ventilation systems with
100 percent outdoor air intake; include different initiation
times to account for varying degrees of warning.
c. Ventilation system recommissioning: assume the
baseline case is consistent with design intent and model
condition(s) that are "off-design" including the following:
reduce the outdoor air intake by 50 percent (referred to
as 5 percent intake since the "design" value is assumed
to be 10 percent); increase the return airflow relative to
the supply such that there is 5 percent less supply to the
building than return (referred to as 5 percent undersupply);
increase the return airflow from the ventilated space to
100 percent of the supply, i.e., 100 percent recirculation;
and allow 10 percent of the airflow intended to pass
through the filter to bypass the filter (10 percent filter
bypass). Note that recommissioning cases are applied
only to the two-story building.
d. Relocation of outdoor air intakes: simply assume that the
contaminant does not enter the building if the intake is
moved and all exposures are zero; applies only to release
at the intake.
3. Envelope and pressurization options:
a. Envelope tightening: tighten the building envelope, but
do not modify the ventilation system operation.
b. Envelope tightening/filtration: combine the envelope
tightening and enhanced particle filter in the outdoor air
intake.
c. Envelope tightening/GPAC: combine the envelope
tightening and outdoor air intake GPAC retrofit.
d. Envelope tightening/filtration/pressurization: combine
envelope tightening and enhanced particle filter retrofit in
the air intake with an attempt to pressurize the building by
doubling the outdoor air intake relative to the minimum
design value.
e. Envelope tightening/GPAC/pressurization: combine
envelope tightening and air intake GPAC retrofit with
an attempt to pressurize the building.
-------
4 Local options:
a. Shelter-in-place: move occupants from office space to
selected shelter locations in each building, and turn off
all ventilation systems at a specified time; shelters have
tighter interior partitions; after a two-hour sheltering
period, the occupants leave the building and the systems
are operated with 100 percent outdoor air.
b. Shelter-in-place with air cleaning: same as shelter in place,
but with a recirculating filtration and air cleaning system
operating in the shelter during the sheltering period.
c. Lobby and mail room isolation: isolate these spaces
through combinations of interior partition tightening and
using ventilation systems to induce lower pressures in
these spaces relative to the rest of the building; applied
only to high-rise building.
The manner in which these retrofits were implemented in
each of the building models is described below.
Single-zone model
Table 3 presents the retrofits applied to each of the release
scenarios for the single-zone model. Almost all of the retrofits
were applied to both the outdoor and indoor releases, even
though not all of them were expected to have a beneficial
impact. For example, shutting down a system in the event
of an indoor release would be expected to increase rather
than to reduce exposure. Nevertheless, all possible cases
were analyzed to explore the impacts of both "good" and
potentially "bad" actions.
Table 3 Retrofit and release scenarios for single-zone model
Release Scenario
Retrofit
Enhanced outdoor air filtration
Enhanced mixed air filtration
System shutdown
Purging
Envelope tightening
Envelope tightening and outdoor air filtration
Outdoor
X
X
X
X
X
X
Indoor
-
X
X
X
X
X
Enhanced Outdoor Air Filtration: The MERV 6 paniculate
filter on the outdoor air intake is replaced with a more
efficient filter, specifically a MERV 13 filter. This change
is reflected in an increase in the particle removal efficiency
at 1 [im from 16.4 percent to 89.6 percent. In addition, a
gaseous air cleaner with a removal efficiency of 95 percent
is located in the outdoor air intake; in the base case, there
was no gaseous air cleaning. Note that this retrofit does not
account for the existence of any bypass around the filter.
Mixed Air Filtration: The MERV 6 particulate filter in the
mixed airstream is replaced with a MERV 13 filter, again
with no bypass. In addition, a gaseous air cleaner with a
removal efficiency of 95 percent is added to the mixed
airstream.
System Shutdown: The outdoor air intake is reduced to
zero for 2 h, starting 6 s, 30 s, 1 min, and 5 min after the start
of the contaminant release. At the end of the 2-h shutdown
period, the system operates at 100 percent outdoor air intake.
Outdoor Air Purge: The outdoor air intake is increased
from the minimum value of 10 percent outdoor air intake
to 100 percent intake, beginning 30 s prior, 30 s after, 1 min
after, and 5 min after the start of the release and continuing
for the remainder of the simulation.
Envelope Tightening: The constant envelope infiltration rate
is reduced from 0.20 fr1 to 0.01 fr1.
Envelope Tightening and Enhanced Filtration: The
reduced infiltration rate and the enhanced outdoor air
filtration are combined.
Two-story office model
Table 4 presents the retrofits applied in the two-story office
building simulations.
Enhanced Outdoor Air Filtration: The MERV 6 particulate
filter on the outdoor air intake is replaced with a MERV 13
filter, and a gas phase air cleaner (with a removal efficiency
of 95 percent) is added to the air intake. This retrofit was not
applied to the indoor releases since it would not impact the
resulting exposure.
Mixed Air Filtration: A MERV 13 particle filter replaces
the baseline MERV 6 filter in the mixed airstream, and a 95
percent efficient gaseous air cleaner is added to that airstream
as well.
System Shutdown: The outdoor air intake is reduced to zero
for 2 h, starting 6 s, 30 s, 1 min, and 5 min after the start of the
exterior contaminant release. However, envelope infiltration
still continues during the shutdown, as determined by the
outdoor weather conditions. At the end of the 2-h shutdown
period, the system operates at 100 percent outdoor air intake.
Outdoor Air Purge: The outdoor air intake is increased
from the minimum value to 100 percent outdoor air intake,
beginning 30s prior, 30s after, 1 min after, and 5 min after
the start of the release and continuing for the remainder of
the simulation.
-------
Envelope Tightening: The exterior wall leakage is reduced
from 5 cmVm2 (0.07 inVft2) to 0.7 cmVm2 (0.01 irf/ft2).
Envelope Tightening and Enhanced Outdoor Air
Filtration: The improved envelope airtightness and the
enhanced outdoor air filtration are combined. This applies
only to the general outdoor release and the release at the
intake since the results for the indoor releases are no
different from the envelope tightening retrofit alone.
Envelope Tightening, Enhanced Outdoor Air Filtration,
and Building Pressurization: The increased envelope
airtightness and the enhanced outdoor air filtration are
combined with a doubling of the outdoor air intake fraction
to 20 percent in order to pressurize the building and reduce
infiltration of outdoor releases.
Envelope Tightening and Enhanced Mixed Air Filtration:
The improved envelope airtightness and the enhanced mixed
air filtration are combined.
Envelope Tightening, Enhanced Mixed Air Filtration,
and Building Pressurization: The increased envelope
airtightness and the enhanced mixed air filtration are
combined with a doubling of the outdoor air intake fraction
to 20 percent.
Shelter-in-place: Occupants are moved to a shelter-in-place
zone in the second floor conference room. Four different
cases are included, corresponding to different times at which
the occupants move to the shelter: 30 s before the release,
and 30 s, 1 min, and 5 min after the release starts. During
the sheltering period, the shelter-in-place zones are "sealed"
by reducing plenum and door leakage, and all ventilation
systems are turned off. Two hours after the start of the
release, all occupants are moved out of the building, i.e., they
are no longer exposed to the contaminants, and the systems
are run at 100 percent outdoor air.
Shelter-in-place with Air Cleaning: This is the same as the
shelter-in-place case with the addition of an air cleaner to
each shelter zone. The air cleaners recirculate air within the
room and have an airflow rate of roughly 5 L/s«m2 (1 cfm/ft2)
of floor area with MERV 15 particle filters (99.75 percent
removal efficiency for 1 ^im particles) and a removal
efficiency of 95 percent for the gaseous contaminant.
Recommissioning: Five cases represent a system that isn't
operating properly in order to estimate the potential benefit
from a recommissioning effort. These cases include the
following: 100 percent recirculation (no outdoor air intake);
reduction of the outdoor air intake to 5 percent from the
baseline value of 10 percent; an unbalanced system with
5 percent more return air from the space than supply air to
the space; 10 percent of the supply air bypassing the baseline
mixed air filters; and 10 percent of the supply air bypassing
the enhanced mixed air filters.
Table 4 Retrofit and release scenarios for two-story office building model
Release Scenario
Retrofit
Enhanced outdoor air filtration
Mixed air filtration
System shutdown
Purging
Envelope tightening
Tightening and enhanced outdoor air filtration
Tightening, OA filtration, and pressurization
Tightening and enhanced mixed air filtration
Tightening, MA filtration, and pressurization
Shelter-in-place
Shelter-in-place with filtration
Outdoor
General
X
X
X
X
X
X
X
X
X
X
X
Outdoor
Intake
X
X
X
X
X
X
X
X
X
X
X
Indoor,
Lobby
~
X
X
X
X
~
X
X
X
X
X
Indoor,
Return Vent
~
X
X
X
X
~
X
X
X
X
X
Loading
Dock
~
X
X
X
X
~
X
X
X
X
X
Recommissioning
100% recirculation
5% outdoor air intake
5% undersupply
10% bypass of baseline filter
10% bypass of enhanced mixed air filter
X
X
X
X
X
~
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
-------
High-rise model
Table 5 presents the retrofits applied to each of the five
release scenarios for the high-rise model. As this is a
relatively complex model, not all retrofits were applied
to all the releases.
Enhanced Outdoor Air Filtration: As in the single-zone
and two-story models, the MERV 6 paniculate filters on
the outdoor air intakes of all three air handling systems are
replaced with MERV 13 filters. Gaseous air cleaners having
removal efficiencies of 95 percent are also installed in the
intake. Again, this retrofit was not applied to the indoor
release cases.
Mixed Air Filtration: A MERV 13 particle filter replaces the
MERV 6 baseline filter in the mixed airstream, and a 95 percent
efficient gaseous air cleaner is added to that airstream as well.
System Shutdown: Four different shutdown scenarios are
considered. All systems are turned off, starting 6 s, 30 s, 1 min,
and 5 min after the start of the exterior contaminant release.
Two hours after the release begins, the systems are turned
back on and operated at 100 percent outdoor air intake for
the remainder of the simulation. The occupants are assumed
to remain in the building throughout the changes in system
operation. Note that envelope infiltration continues during the
shutdown, as driven by the outdoor weather conditions.
Table 5 Retrofit and release scenarios for high-rise office building model
Release Scenario
Retrofit
Enhanced outdoor air filtration
Mixed air filtration
System shutdown
Purging
Envelope tightening
Envelope tightening and OA filtration
Tightening, filtration, and pressurization
Shelter-in-place
Shelter-in-place with filtration
Lobby partitions
Lobby partitions and HVAC isolation
Mail room undersupply
Mail room undersupply and return air filtration
Outdoor
General
X
X
X
X
X
X
X
X
X
~
~
~
~
Outdoor
Intake
X
X
X
~
X
X
~
~
~
~
~
~
~
Indoor,
Lobby
~
X
~
X
~
~
~
~
~
X
X
~
~
Indoor,
Return Vent
~
X
~
X
X
~
~
~
~
~
~
~
~
Mail
Room
~
X
~
~
~
~
~
~
~
~
X
X
Outdoor Air Purge: The outdoor air intake of all three
systems is increased from the minimum value to 100 percent
outdoor air intake, beginning 1 min after the start of the
release and continuing for the remainder of the simulation.
Envelope Tightening: The exterior wall leakage is reduced
from 8.7 cmVm2 (0.13 inVft2) to 0.7 cmVm2 (0.01 irf/ft2).
Envelope Tightening and Enhanced Outdoor Air
Filtration: The improved envelope airtightness and the
enhanced outdoor air filtration are combined. This retrofit is
applied only to the general outdoor release and the release at
the intake since the results for the three indoor releases are no
different from the envelope tightening retrofit alone.
Envelope Tightening, Enhanced Outdoor Air Filtration,
and Building Pressurization: The increased envelope
airtightness and the enhanced outdoor air filtration are
combined with an increase in the outdoor airflow rate.
Shelter-in-place: Occupants are moved to shelter-in-place
zones on their respective floors of the building. Four different
cases are included, corresponding to different times at which
the occupants move to the shelter: 30 s before the release,
and 30 s, 1 min, and 5 min after the release starts. During
the sheltering period, the shelter-in-place zones are "sealed"
by reducing plenum and door leakage, and all ventilation
systems are turned off. Two hours after the start of the
release, all occupants are moved out of the building, i.e., they
are no longer exposed to the contaminants, and the systems
are run at 100 percent outdoor air.
Shelter-in-place With Air Cleaning: This is the same as
the shelter-in-place case with the addition of an air cleaner
to each shelter zone. The air cleaners recirculate air within
the room and have an airflow rate of roughly 5 L/s«m2
(1 cfm/ft2) of floor area with MERV 15 particle filters
(99.75 percent removal efficiency for 1 ^im particles)
and a removal efficiency of 95 percent for gas G.
Lobby Partitions: The lobby is partitioned off from the rest
of the first floor with walls having the same leakage rate as
the rest of the interior walls and two doors. The lobby is still
-------
served by the same ventilation system that serves the rest of
the first floor.
Lobby Partitions and HVAC Isolation: In addition to a
separate lobby, this retrofit includes an air handling system
dedicated to the lobby. The lobby system has approximately
10 percent more return airflow than supply in an attempt to
depressurize this zone relative to the rest of the building.
Mailroom Undersupply: Adjust the mail room return
airflow to be 10 percent greater than the supply in an attempt
to depressurize this zone relative to the adjacent zones.
Mailroom Undersupply and Enhanced Return Air
Filtration: In addition to the undersupply, filter the mail
room return air with a MERV 15 particle filter and a
95 percent gas filter.
2.1.4 Simulations and Analysis
Simulations were performed for the building models and
retrofits described above. These simulations were run for
12 h with a 5 s time step. For the two-story and high-rise
buildings, cases were run with no wind speed or indoor-
outdoor temperature difference, i.e., no weather-induced
envelope infiltration. To study infiltration effects, additional
cases were run with a wind speed of 5 m/s (11 mi/h) and an
indoor-outdoor temperature difference of 20 °C (36 °F).
The simulations yield contaminant concentrations as a
function of time in each building zone. The concentrations
were subsequently used to determine occupant exposures.
The exposure of an individual building occupant is the
average contaminant concentration to which he or she is
exposed over the simulation period in units of mg-min/m3
for the gaseous contaminant G and number-min/m3 for the
paniculate contaminant P. In the shelter-in-place cases, the
exposure is based on the occupants' initial location in the
building and then their exposure after moving to the shelter.
They are assumed to leave the building 2 h after the release,
at which point there is no additional contribution to their
exposure. The two-story office building is assumed to have
130 occupants, evenly split between the two floors. The high-
rise office building has a total of 285 occupants distributed
among the various floors.
The average exposure for all occupants of the building is then
determined from the individual occupant exposures. These
exposures are calculated over 6 h, starting 1 h before the
release and continuing 5 h after. For each retrofit simulation,
the average building exposure is compared with the baseline
exposure to determine the exposure as a percentage of the
baseline.
2.2 Results of Simulations
The simulation results for each of the building models are
presented in this section in terms of the exposure reduction
for each retrofit case relative to the baseline exposure without
any of the retrofits included. In addition, representative plots
of concentration versus time are included for selected cases
to help explain the impacts of the retrofits.
2.2.1 Single-zone Model
Figure 1 is a plot of the calculated concentrations for the
single-zone baseline and retrofit cases subject to the outdoor
particle release. As described earlier, this release corresponds
to an increase in the outdoor concentration from 0 to 109
particles/m3 occurring at t = 1 h and lasting for 1 min.
Therefore, all the concentrations are zero for the first hour.
The baseline case is the solid line with a peak concentration
of 2xl04 particles/m3. The other lines show the impacts of
selected retrofits, with the combination of enhanced outdoor
air filtration and envelope tightening resulting in the lowest
peak concentration. Envelope tightening alone has a less
significant impact due to the low baseline infiltration rate
relative to the outdoor air intake rate and the low baseline
filter efficiency. Less contaminant enters the building at the
lower infiltration rate, so the initial concentration is slightly
lower than the baseline case. However, the lower air change
rate causes the contaminant to remain in the building for
a longer time, resulting in similar concentrations to the
baseline case after about 45 min. The enhanced outdoor air
filter significantly reduces contaminant entry and therefore
concentration, while the enhanced mixed air filter reduces
concentration even further due to the continued filtration of
the recirculation airstream.
The four shutdown cases show the importance of timing,
with timely implementation of the shutdown having a much
more significant impact than a delayed shutdown. (Note
that the shutdown cases all exhibit a discontinuity at a time
of 3:00 when the system resumes operation at 100 percent
outdoor air intake.) The 6-s and 30-s shutdowns reduce
contaminant entry and the initial concentrations, but the
lower ventilation rate during the shutdown leads to higher
contaminant concentrations than the baseline case later on
during the shutdown. The two late shutdown cases, 1 min
and 5 min, result in significantly higher concentrations than
the baseline case because the ventilation rate is reduced after
the contaminant has entered the building. The purge retrofit
doesn't reduce the initial concentration, but the increased
ventilation rate the contaminant at a relatively high rate. The
timing of the purge cycle also impacts the concentrations,
but only the 1 min purge results are displayed in this figure;
the other results are presented below in Table 6. Analogous
transient concentration data exist for the gaseous contaminant
G and for the indoor release scenarios. These results are also
summarized in Table 6.
The single-zone exposure reductions, relative to the
baseline case, for the indoor and outdoor particle releases
are presented in Table 6 and plotted in Figures 2 and 3. The
exposures are presented as a percentage of the baseline
exposure; therefore, a retrofit that does not change the
exposure corresponds to a value of 100 percent. Lower
percentages correspond to a reduction in exposure. As noted
in the discussion of Figure 1, the combination of outdoor
air filtration and decreased infiltration results in the lowest
initial concentrations for the outdoor release, but the mixed
air filtration retrofit results in the lowest exposure. Envelope
tightening alone increases exposure to the indoor release
due to the lower dilution rate but has only a small impact on
-------
exposure to the outdoor release. Retrofits that are particularly
effective, i.e., decreasing exposure to about one-third or less
of the baseline, include outdoor air filtration (for the outdoor
release), mixed air filtration, envelope tightening with
outdoor air filtration (outdoor release), outdoor air purge for
an indoor release, and purging after the release is complete.
The 6-s shutdown reduces exposure to the outdoor releases
by about one-third, but the later shutdowns actually increase
exposure to the outdoor release. These results indicate
that unless a shutdown can be implemented very early in
response to an outdoor release, it may be better to leave the
system running. All the shutdowns increase the exposure to
an indoor release, as would be expected, pointing out the
importance of reacting to an event based on good awareness
of the circumstances. The change in exposure for the purge
cycle given an indoor source is not strongly dependent on
timing, but it is for an outdoor release. Of course, purging is
not a reasonable response to an outdoor release, but it could
conceivably happen, given poor awareness. After an outdoor
release is over, however, purging is an effective means of
removing the contaminant that did enter the building. Figures
2 and 3 display the relative exposures for the gaseous and
paniculate contaminants, respectively. The results are similar
in the two figures, with the only differences resulting from
the lack of a gaseous air cleaner in the baseline case and
differences in the removal efficiencies for the paniculate and
gaseous filter retrofits.
2.0K+04
Figure 1 Single-zone simulation results for an outdoor particulate release
I.5E+04
I I.OK+04
5.0E+03
O.OE+QO
0:00
Baseline
OA nitration
A Mixed air filtration
Envelope tightening
•^—OA filter and envelope
• 6-s shutdown
30-s shutdown
• I-min shutdown
• 5-min shutdown
- Purge, I min
1:00
2:00
Time (h:min)
3:00
4:00
-------
Table 6 Single-zone retrofit effectiveness values
Case
OA filtration
Mixed air filtration
Shutdown (6 s)
Shutdown (30 s)
Shutdown (1 min)
Shutdown (5 min)
Purge (30 sec prior)
Purge (30 sec after)
Purge (1 min after)
Purge (5 min after)
Envelope tightening
Envelope + OA filtration
Indoor
Source
100.0
19.7
220.7
220.6
219.7
208.7
22.6
22.8
23.6
30.5
115.3
115.3
Outdoor
Source
18.4
3.6
68.1
135.5
219.6
208.8
100.1
62.6
23.6
30.5
99.9
5.8
Indoor
Source
100.0
35.2
171.9
171.5
170.0
158.7
33.2
33.6
34.7
44.5
108.5
108.5
Outdoor
Source
26.8
9.4
58.8
108.3
170.0
158.8
144.0
90.6
34.6
44.5
91.7
12.1
250
Figure 2 Single-zone exposure results for gaseous contaminant G
Outdoor release
Indoor release
-------
200
Figure 3 Single-zone exposure results for particulate contaminant P
Outdoor release
Indoor release
Table 7 Single-zone sensitivity analysis results
Parameter Varied
Indoor
Release
Outdoor
Release
Indoor
Release
Outdoor
Release
Baseline
Zone volume
OA intake rate
Infiltration rate
Filter efficiency
Release amount
Release duration
0
9
1
-
-10
-10
0
0
0
~
-10
-10
0
5
1
4
-10
-10
0
o
-5
-i
6
-10
-10
Retrofits
Outdoor air filter efficiency
Mixed air filter efficiency
Reduced infiltration rate
~
30
0
44
57
0
~
9
0
33
45
0
-------
In order to determine the importance of the input parameters
in the single-zone simulations, a simple sensitivity analysis
was performed in which the baseline and retrofit simulations
were repeated with selected inputs varied (decreased) by
10 percent. The results of that analysis are presented in
Table 7, with the impacts on the baseline case exposures in
the upper portion of the table and the impacts on the retrofits
in the lower portion. In the latter cases, the parameters
associated with the retrofit (e.g., filter efficiency) were
decreased by 10 percent and the value in the table is the
change in exposure relative to the retrofit case. Most cases
show either essentially no impact of the variation or an
approximately linear (i.e., about 10 percent) impact. For
example, varying the zone volume has no impact since it
increases both the contaminant concentrations and the air
change rate, resulting in no change in exposure. Larger
differences are seen for the filter efficiency retrofits, for
example, a 44 percent increase in exposure for the gaseous
contaminant and a 33 percent increase for the paniculate
contaminant for an outdoor release in the case of the outdoor
air filter retrofit. This "amplified" sensitivity occurs because
the exposure is impacted by 1 minus the removal efficiency,
and therefore a 10 percent change in the efficiency is a larger
change in 1 minus the efficiency.
2.2.2 Two-story Office Building
Figure 4 is a plot of the calculated concentrations
for the two-story office building subject to the outdoor
particle release with no weather effects (i.e., zero wind
speed and no indoor-outdoor temperature difference).
As described earlier, the outdoor release corresponds
to a 60-s increase in the outdoor concentration from
0 to 109 particles/m3 at t = 1 h. The concentrations for
the baseline case are shown by the solid black line with a
peak concentration just below 7.5xl06 particles/m3, which
begins to decay immediately after reaching that peak. The
concentrations for the envelope tightening case are identical
to those for the baseline case because there is no infiltration
under no-weather conditions. The lack of weather-induced
pressures in combination with the building being positively
pressurized (i.e., supply airflow greater than return plus
exhaust) leads to no infiltration through the envelope. The
other lines in the plot show the impacts of selected retrofits,
with the mixed air filtration retrofit (open black triangles)
resulting in the lowest concentrations. Combining envelope
tightening with outdoor air or mixed air filtration yields
identical results to enhanced filtration alone, again because
there is no envelope infiltration. Therefore, these two cases
are not shown in the figure. Tightening the envelope and
increasing the outdoor air intake to induce pressurization
increases the concentration for both filtration cases because
the additional outdoor air brings more contaminant into the
building. Given that the building is already pressurized and
there is no infiltration, there is no reduction in contaminant
entry due to reduced envelope leakage.
The four shutdown cases show the importance of timing such
actions. (Note that the shutdown cases in Figure 4 all exhibit
a discontinuity at a time of 3:00 when the system resumes
operation at 100 percent outdoor air.) The contaminant
concentration is constant during the shutdown period because
there is no air change under no-weather conditions. The 6-s
shutdown significantly reduces contaminant entry, and once
the purge begins, the contaminant is quickly removed from
the building. The 30-s shutdown also reduces contaminant
Figure 4 Two-story simulation results for an outdoor particle release (no weather)
8.00E+06.
6.00E+06-
4.00E+06 -
2.00E+06 -
O.OOE+00
-Baseline
OA filtration
Mixed air filtration
Envelope tightening
OA filter, envelope, pressure
MA filter, envelope, pressure
6-s shutdown
30-s shutdown
1-inin shutdown
5-min shutdown
Purge, 1 miii
0:00
1:00
2:00
3:00
Time (h:min)
4:00
5:00
6:00
-------
entry and the initial concentration relative to the baseline
case, but the contaminant concentrations are higher than the
baseline later during the shutdown. The two late shutdown
cases, 1 min and 5 min, result in significantly higher
concentrations than the baseline because the shutdown retains
the contaminant in the building. Only the results for the purge
case starting 1 min after the release are shown, and these
exhibit a quick reduction in the contaminant concentration as
expected. Analogous concentration data exist for the gaseous
contaminant G and for the indoor releases.
Figure 5 is a plot of the two-story office building
concentrations subject to the outdoor particle release with
weather effects included, i.e., a nonzero infiltration rate.
The concentration for the baseline case is the solid black
line that peaks around 1.25xl07 particles/m3. Note first
that this peak is higher than in the no-weather case because
more contaminant enters the building due to infiltration.
The building air change rate for the no-weather case is
0.38 h"1, while it is 0.60 h"1 with weather-induced infiltration.
The roughly 60 percent increase in air change rate is close
to the increase in the peak concentration. Upgrading the
outdoor air filtration efficiency from MERV 6 to MERV 13
reduces the concentrations by about one-half relative to the
baseline case, while upgrading the filtration in the mixed
airstream reduces the concentration even further. Tightening
the envelope, which reduces the building air change rate from
0.60 h'1 to 0.39 h'1, decreases the concentrations somewhat
but not as much as filtration. The combination of enhanced
outdoor air filtration and envelope tightening (solid red line)
significantly reduces the concentration, while locating the
filter in the mixed air (solid blue line) reduces it even more.
While not shown in the figure, increasing the outdoor air
intake in an attempt to induce pressurization increases the
concentration relative to the other outdoor air filtration cases
because the additional outdoor air brings more contaminant
into the building. The four shutdown cases once again show
the importance of the timing of the shutdown. However,
the existence of significant envelope infiltration reduces the
effectiveness of shutdown strategies relative to that seen in
Figure 4 with no weather because contaminant continues to
enter the building during the shutdown. Again, only the purge
case starting 1 min after the release is shown, which exhibits
a quick reduction in the contaminant concentration after the
release. Analogous transient concentration data exist for the
gaseous contaminant G and for the indoor release scenarios.
Tables 8 through 11 present the exposure reductions for all
the retrofit cases for the two-story building, with the first
two covering contaminant P (particle) and the second two
covering contaminant G (gas). Each value in the table is
the change in occupant exposure over 6 h relative to
the baseline case. Therefore, a value below 100 percent
corresponds to an exposure reduction, while a value
greater than 100 percent means the retrofit actually
increases exposure. Table 8 contains the relative exposure
for contaminant P with no weather effects, i.e., no envelope
infiltration. There are no entries in the loading dock column
(with one exception noted below) because with the outdoor
air intake rate exceeding the exhaust airflow rate and no
weather to drive air into the building, no contaminant enters
at the loading dock door. Upgrading the outdoor air filtration
from MERV 6 to MERV 13 reduces occupant exposure by
almost 90 percent for the outdoor releases. The results for
the general and intake releases are identical since there is no
envelope infiltration. This filter upgrade has no impact on
Figure 5 Two-story simulation results for an outdoor particle release (with weather effects)
LOOEfOT-
O.ODE^-00
-Baseline
Outdoor air filtration
a Mixed air filtration
- Indoor, return vent
OA filter and envelope
MA filter and envelope
6-s shutdown
30-s shutdown
° 1 -min shutdown
» S-min shutdown
+ Purge, 1 min
0:00
1:00
2:00
3:00
Time (h:min)
4:00
5:00
6:00
-------
exposure to the two indoor sources, and therefore these cases
were not run. Using a MERV 13 filter in the recirculation
airstream is more effective in reducing exposure, with the
retrofit exposure less than 5 percent of the baseline. The
mixed air filter has a larger impact than the intake filter on the
outdoor sources because now the recirculation air is filtered
on each pass through the air handler. The upgraded mixed air
filter also results in similar exposure reductions for the indoor
sources.
Envelope tightening has almost no impact on exposure for
any of the sources, given the lack of any weather-induced
driving pressures. Combining enhanced outdoor air filtration
with envelope tightening is therefore identical to the
filtration retrofit alone, as is the case for enhanced mixed
air filtration plus tightening with only a minor exception
for the lobby release. As noted in the discussion of Figure
4, supplementing these retrofits with increased outdoor air
intake in an attempt to pressurize the building increases
exposure to outdoor sources. However, combining outdoor
filter enhancement and pressurization reduces exposure to the
indoor sources by roughly one-third due to the increased air
change rate. Adding pressurization to the mixed air filtration
and envelope retrofit roughly doubles the exposure relative
to these combined retrofits with no pressurization for the
outdoor sources but has little effect for the indoor sources.
Table 8 Two-story retrofit effectiveness values (contaminant P, no weather)
Exposure Relative to Baseline (%)
Retrofit
Outdoor air (OA) filtration
Mixed air (MA) filtration
Envelope tightening
Envelope, OA filtration
Envelope, OA filter, pressure
Envelope, MA filtration
Envelope, MA filter, pressure
100% recirculation
5% OA intake
5% undersupply
10% baseline filter bypass
10% MA filter bypass
6-s shutdown
30-s shutdown
1-min shutdown
5-min shutdown
Purge - 30 s prior
Purge - 30 s after
Purge - 1 min after
Purge - 5 min after
SIP - 30 s prior
SIP - 30 s after
SIP - 1 min after
SIP - 5 min after
SIP AC -30s prior
SIP AC -30s after
SIP AC - 1 min after
SIP AC -5 min after
Outdoor,
General
12.4
3.3
100.0
12.4
19.7
3.3
7.1
65.7
85.8
151.0
108.5
6.8
31.7
155.0
303.0
236.2
262.8
146.0
24.3
27.3
0.1
137.6
269.5
215.2
0.0
12.2
24.9
28.4
Outdoor Air
Intake
12.4
3.3
100.0
12.4
19.7
3.3
7.1
53.2
76.6
108.5
6.8
31.7
155.0
303.0
236.2
262.8
146.0
24.3
27.3
0.0
137.5
269.5
215.2
0.0
12.2
24.9
28.4
Indoor,
Lobby
4.2
98.3
63.4
3.8
3.3
120.9
108.8
69.9
108.3
7.6
0.9
1.2
2.9
46.5
0.9
0.9
1.0
4.8
0.0
1.2
4.3
49.8
0.0
0.3
0.6
5.9
Indoor,
Return Vent
3.3
100.0
73.1
3.3
3.3
115.5
106.4
66.1
108.5
6.8
30.7
154.1
302.1
236.2
0.0
11.8
24.3
27.3
0.0
136.7
268.7
215.3
0.0
12.1
24.9
28.4
Loading Dock
9.1*
* Exposure relative to the baseline outdoor air intake case
-------
The five "recommissioning" cases appear in Table 8 after the
various "envelope" retrofits. The 100 percent recirculation
case has roughly 20 percent higher exposures for the two
indoor releases due to the lower total air change rate. There
is a roughly one-third reduction for the outdoor general case
because the reduced contaminant entry has a larger impact
than the lower dilution rate. The situation is similar for the
5 percent outdoor air intake case for both the general
outdoor release and the intake release, i.e., less entry is
more significant than less dilution, leading to a decrease
in exposure. The indoor sources have somewhat higher
exposures due to the decrease in the building air change
rate. When there is 5 percent less supply than return, the
infiltration rate increases from 0.0 fr1 to 0.40 fr1, and the
total air change rate roughly doubles. In this case, the
outdoor general exposure increases because of the increased
contaminant entry, but the exposure decreases for the intake
and two indoor source cases due to the higher dilution rate.
Because the building is now depressurized, contaminant
enters at the loading dock, which results in nonzero exposure
even with no weather. In this case, the 9.1 percent exposure
metric is relative to the baseline intake source case since
there is no baseline loading exposure for comparison.
Assuming 10 percent bypass around the baseline filter
increases exposure by about 10 percent in all cases. If the
same bypass fraction is assumed for the mixed air filtration
retrofit, the exposure relative to the baseline is still low, but
the exposure relative to the mixed air retrofit itself roughly
doubles.
As noted in the discussion of Figure 4, the earlier shutdowns
are more effective than those that are delayed. In fact, only
the 6-s shutdown reduces the exposure below the baseline
case for all but the lobby source. The later shutdowns for the
other sources actually increase the relative exposure, with
the 1-min shutdown exposure being three times the baseline
value. In this particular case, the system shuts down after the
contaminant has entered the building and the dilution rate
reduces to essentially zero. The 5-min shutdown is also not
very timely, but there are 4 min of ventilation and filtration
after the release ends and before the shutdown begins. The
indoor lobby releases have much lower exposure because
there are no occupants in the lobby when the release occurs,
and the contaminant is not as effectively transported to the
rest of the building from the lobby as it is from the return.
The impacts of the purge cycle are also a strong function
of timing. Early purges are more effective for the indoor
releases. However, as expected, purging is not effective for
the outdoor releases when done before or during the release,
as such timing brings more contaminant into the building.
Later purging does help clear the outdoor contaminant from
the building and reduces exposure by about 75 percent.
Again, less contaminant spreads from the lobby to the rest of
the building when the purge cycle begins, and therefore the
purge is more effective in removing the contaminant for this
case. Note that purging reduces exposure more than system
shutdown for the interior releases.
The shelter-in-place cases, like the shutdown and purge
cases, show the importance of timing. For all sources,
moving the occupants to the shelter 30 s before the release
occurs eliminates essentially all exposure due to the lack
of weather-driven air movement in the building. Instigating
the shelter strategy halfway through the release increases
exposure by about 40 percent, with the exception of the
lobby source because of the contaminant that enters the
shelter space and then remains there during the low air
change sheltering conditions. In the lobby case, the source
is not transported effectively to the shelter, and therefore
the exposure decreases for that case. The 1-min and 5-min
cases also increase exposures for other than the lobby
source. However, adding a recirculating air cleaner to the
shelter reduces exposure significantly in all cases, with
later initiation of sheltering resulting in greater exposure.
Table 9 contains the exposure relative to the baseline for
contaminant P with weather included, i.e., a wind speed
of 5 m/s and an indoor-outdoor temperature difference of
20 °C. The existence of weather-driven pressure differences
results in an envelope infiltration rate of 0.22 h"1, which when
added to the outdoor air intake rate of 0.38 h'1 yields a total
air change rate of 0.60 h"1. With the existence of infiltration,
contaminant from the loading dock source now enters the
building, and the rightmost column of the table contains
results. The existence of infiltration results in a difference
between the impacts for the outdoor general and outdoor air
intake sources for the outdoor air filtration retrofit. The former
case has less of an exposure reduction because contaminant
entering the building via envelope leakage is not filtered,
while the reduction for the intake source is identical to the
no-weather case. Adding a MERV 13 filter to the mixed
airstream is again quite effective in reducing exposure, with
similar reduction values as those seen in the no-weather
cases. However, the reductions are smaller for the outdoor
general release because of unfiltered contaminant entry due
to infiltration. The reduction for the loading dock release
is smaller because of the exposure that occurs before the
contaminant gets to the mixed air filter.
Envelope tightening now reduces the exposure for the outdoor
general source because less contaminant enters via infiltration.
However, for the intake case, the same amount of contaminant
enters the building as in the baseline case, but the dilution rate
is lower with the tighter envelope and the exposure therefore
increases. The situation for the two indoor sources is similar,
and the exposure also increases by about 20 percent. Because
tightening the envelope increases the level of building
pressurization, less contaminant enters at the loading dock
door and there is a large exposure reduction for that case.
Combining enhanced outdoor air filtration with envelope
tightening increases the exposure reduction for the outdoor
general source relative to the no-weather condition due to
the reduced contaminant entry. There is less reduction for the
intake source because of the lower dilution rate. Increasing
the outdoor air intake in an attempt to pressurize the building
increases the relative exposure for both the outdoor general
and intake sources, relative to tightening and filtration alone,
because more contaminant enters. Increasing outdoor air to
-------
pressurize the building eliminates all contaminant entry at
the loading dock door, resulting in zero exposure. Combining
envelope tightness with enhanced mixed air filtration reduces
exposure for the outdoor general and loading dock cases,
relative to enhanced filtration alone, and has little impact
on the other three cases. The exposure reductions for these
combined retrofits are much more significant than those for
envelope tightening alone. Increasing outdoor air intake
for pressurization again increases exposure for the two
outdoor sources, relative to tightening and enhanced mixed
air filtration alone. The combination of these three retrofits
has little impact on the two indoor sources, but the addition
of pressurization does eliminate contaminant entry at the
loading dock.
The results for the first two of the five "recommissioning"
cases, 100 percent recirculation and 5 percent outdoor air
intake, are similar to those for the no-weather cases. The
100 percent recirculation case has roughly 20 percent higher
exposure for the two indoor releases, and there is a roughly
25 percent reduction for the outdoor general case. The
loading dock exposure increases significantly because the
building is at a lower pressure with no outdoor air intake.
Under 5 percent outdoor air intake for the general outdoor
release and the intake release, the decrease in contaminant
entry is more significant than the decrease in ventilation,
leading to a decrease in exposure. The indoor and loading
dock sources have somewhat higher exposures due to the
Table 9 Two-story retrofit effectiveness values (contaminant P, with weather)
Exposure Relative to Baseline (%)
Retrofit
Outdoor air (OA) filtration
Mixed air (MA) filtration
Envelope tightening
Envelope, OA filtration
Envelope, OA filter, pressure
Envelope, MA filtration
Envelope, MA filter, pressure
100 % recirculation
5 %OA intake
5 % undersupply
10 % baseline filter bypass
10% MA filter bypass
6-s shutdown
30-s shutdown
1-min shutdown
5-min shutdown
Purge - 30 s prior
Purge - 30 s after
Purge - 1 min after
Purge - 5 min after
SIP - 30 s prior
SIP - 30 s after
SIP - 1 min after
SIP - 5 min after
SfP AC -30s prior
SfP AC -30s after
SIP AC -1 min after
SIP AC - 5 min after
Outdoor,
General
48.6
15.4
72.4
9.9
14.1
2.7
5.1
75.8
88.3
118.4
106.4
18.9
160.5
184.5
211.7
177.3
190.3
111.3
28.8
33.0
16.5
106.1
196.5
187.5
2.7
11.4
22.2
30.8
Outdoor Air
Intake
12.4
3.8
121.8
15.1
24.0
4.1
8.7
54.5
85.4
107.3
7.8
21.4
105.2
207.0
171.5
304.0
169.1
28.2
31.7
0.0
156.9
308.5
255.7
0.0
15.6
32.1
36.8
Indoor,
Lobby
4.9
120.3
78.4
4.7
4.2
124.8
112.5
78.1
107.2
8.8
13.0
14.1
17.2
55.3
1.1
1.2
1.3
5.8
24.2
26.6
33.4
97.9
4.8
5.1
5.9
13.6
Indoor,
Return Vent
3.8
121.6
89.3
4.0
4.0
118.9
109.2
73.7
107.3
7.8
20.5
103.6
204.5
170.0
0.0
13.6
28.0
31.7
0.0
155.8
307.3
255.4
0.0
15.5
32.0
36.7
Loading
Dock
35.7
4.3
0.0
1.3
0.0
180.6
125.0
83.0
104.9
38.3
391.7
343.3
278.2
220.8
33.4
33.4
33.5
36.7
42.2
35.6
40.8
75.3
7.9
6.8
12.4
10.8
-------
decrease in the building air change rate. When there is
5 percent less supply than return, the infiltration rate roughly
doubles, and the total air change rate increases by about one-
third. In this case, the outdoor general exposure increases
because of the higher entry, but the exposure decreases for
the other cases due to the higher dilution rate. Assuming
10 percent bypass around the baseline filter increases
exposure by somewhat less than 10 percent in all cases.
If the same bypass fraction is assumed for the mixed air
filtration retrofit, the exposure is still reduced relative to the
baseline, but the exposure relative to the mixed air retrofit
itself increases by as much as 100 percent.
The shutdown cases again show the impact of timing.
However, the early shutdown does not reduce exposure
for the outdoor general and loading dock sources because
contaminant enters the building at a higher rate after the
shutdown starts. The contaminant entry increases with the
system off because the system flows tend to pressurize
the building relative to outdoors. The reductions for the
6-s shutdown are similar for the intake, lobby, and return
vent sources relative to the no-weather cases. The two later
shutdowns have less relative exposure than the no-weather
case for all but the lobby source, given the higher post-
Table 10 Two-story retrofit effectiveness values (contaminant G, no weather)
Exposure Relative to Baseline (%)
Retrofit
Outdoor air (OA) filtration
Mixed air (MA) filtration
Envelope tightening
Envelope, OA filtration
Envelope, OA filter, pressure
Envelope, MA filtration
Envelope, MA filter, pressure
100 % recirculation
5 %OA intake
5 % undersupply
10 % baseline filter bypass
10% MA filter bypass
6-s shutdown
30-s shutdown
1-min shutdown
5-min shutdown
Purge - 30 s prior
Purge - 30 s after
Purge - 1 min after
Purge - 5 min after
SIP - 30 s prior
SIP - 30 s after
SIP - 1 min after
SIP - 5 min after
SIP AC -30s prior
SIP AC -30s after
SIP AC -1 min after
SIP AC -5 min after
Outdoor,
General
5.0
5.0
100.2
5.0
5.7
0.6
1.2
79.0
93.6
113.1
1.8
13.9
67.9
132.8
106.4
115.1
64.0
10.7
12.2
0.0
60.3
118.1
96.9
0.0
5.6
11.4
13.2
Outdoor Air
Intake
5.0
5.0
100.2
5.0
5.7
0.6
1.2
61.7
58.7
1.8
13.9
67.9
132.8
106.4
115.1
64.0
10.7
12.2
0.0
60.2
118.1
96.9
0.0
5.6
11.4
13.2
Indoor,
Lobby
0.9
98.7
46.1
0.8
0.7
145.4
115.9
54.2
2.1
0.3
0.5
1.2
20.6
0.3
0.3
0.4
2.1
0.0
0.4
1.6
21.5
0.0
0.1
0.2
2.6
Indoor,
Return Vent
0.6
100.2
52.5
0.6
0.6
139.8
113.8
50.6
1.8
13.4
67.5
132.4
106.4
0.0
5.2
10.6
12.2
0.0
59.9
117.8
96.9
0.0
5.5
11.4
13.2
Loading
Dock
5.8*
* Exposure relative to the baseline outdoor air intake case
-------
release dilution rates due to the extra infiltration airflow.
Again, the indoor lobby releases have lower relative
exposures under shutdown because there are no occupants in
the lobby and the contaminant is not effectively transported
to the rest of the building.
The two early purge cycles increase exposure for the outdoor
sources because more contaminant enters the building. The
exposure reductions for the later purge cycles are similar to
those seen in the no-weather cases. It is interesting to note
that the reductions for the loading dock source are relatively
independent of timing. The exposure changes and timing
trends for the shelter-in-place cases are similar to those
seen for the no-weather cases, except that infiltration causes
contaminant to enter the building for the cases in which
the shelter strategy is implemented before the contaminant
release starts. Therefore, the exposure reduction for the
30s prior case is no longer 100 percent, except for the
outdoor air intake and return vent sources. In the latter
case, the contaminant released into the vent does not
migrate to the rest of the building before the purge is
implemented. Adding a recirculating air cleaner to the
shelter again reduces exposure significantly in all cases,
Table 11 Two-story retrofit effectiveness values (contaminant G, with weather)
Exposure Relative to Baseline (%)
Retrofit
Outdoor air (OA) filtration
Mixed-air (MA) filtration
Envelope tightening
Envelope, OA filtration
Envelope, OA filter, pressure
Envelope, MA filtration
Envelope, MA filter, pressure
100 % recirculation
5 %OA intake
5 % undersupply
10 % baseline filter bypass
10% MA filter bypass
6-s shutdown
30-s shutdown
1-min shutdown
5-min shutdown
Purge - 30 s prior
Purge - 30 s after
Purge - 1 min after
Purge - 5 min after
SIP - 30 s prior
SIP - 30 s after
SIP - 1 min after
SIP - 5 min after
SIP AC -30s prior
SIP AC -30s after
SIP AC -1 min after
SIP AC -5 min after
Outdoor,
General
40.0
6.3
91.0
5.6
5.1
0.6
1.1
87.6
96.2
102.9
7.8
75.3
90.8
108.9
94.0
104.1
60.4
14.8
17.4
7.6
57.5
107.5
104.8
1.3
6.4
12.5
17.2
Outdoor Air
Intake
5.0
0.8
142.8
7.1
8.2
0.8
1.7
65.2
75.9
2.4
11.0
53.6
105.5
90.6
156.1
86.8
14.5
16.7
0.0
80.6
158.5
90.6
0.0
8.4
17.3
20.0
Indoor,
Lobby
1.2
140.5
66.5
1.1
1.0
159.2
123.3
69.9
2.9
5.7
6.1
7.6
26.8
0.5
0.5
0.6
2.9
10.5
11.6
14.6
46.6
2.2
2.3
2.7
6.7
Indoor,
Return Vent
0.8
142.6
75.2
0.8
0.8
152.8
120.3
65.5
2.4
10.5
53.2
105.2
89.9
0.0
7.0
14.4
16.7
0.0
80.1
158.0
135.0
0.0
8.4
17.2
20.0
Loading
Dock
18.3
5.0
0.0
0.7
0.0
235.8
135.3
149.5
19.6
205.5
183.1
148.2
119.9
17.8
17.8
17.9
19.9
22.5
19.0
20.2
50.8
4.4
3.7
6.8
6.4
-------
with later initiation of sheltering resulting in greater
exposure but still with reductions over 80 percent relative
to the baseline case.
Tables 10 and 11 present the relative exposures for the no-
weather and weather cases for the gaseous contaminant G.
These results are very similar to those seen in Tables 8
and 9 for contaminant P, except as impacted by the different
gaseous removal efficiencies for the baseline and retrofit
efficiencies relative to those for the particle filters. For
example, the exposure reductions for the outdoor air and
mixed air retrofits are larger for contaminant G because the
gas filter has a higher efficiency than the enhanced particle
filter and the baseline gaseous removal efficiency is zero. In
general, the relative exposures for contaminant G are lower
than for the paniculate contaminant, but there are a few
exceptions such as the 100 percent recirculation and 5 percent
outdoor air intake "recommissioning" cases, which accentuate
the lack of gaseous air cleaning in the baseline case.
The impact of envelope infiltration on contaminant entry
and, in some cases, retrofit effectiveness has been mentioned.
Table 12 shows the impact of weather-induced infiltration
more explicitly by comparing the exposure to contaminant P
Table 12 Ratio of exposure with weather to exposure without, contaminant P
Exposure Relative to Baseline (%)
Retrofit
Outdoor air (OA) filtration
Mixed air (MA) filtration
Envelope tightening
Envelope, OA filtration
Envelope, OA filter, pressure
Envelope, MA filtration
Envelope, MA filter, pressure
100 % recirculation
5 %OA intake
5 % undersupply
10 % baseline filter bypass
10% MA filter bypass
6-s shutdown
30-s shutdown
1-min shutdown
5-min shutdown
Purge - 30 s prior
Purge - 30 s after
Purge - 1 min after
Purge - 5 min after
SIP - 30 s prior
SIP - 30 s after
SIP - 1 min after
SIP - 5 min after
SIP AC -30s prior
SIP AC -30s after
SIP AC -1 min after
SIP AC -5 min after
Outdoor,
General
546.5
648.9
101.0
111.2
100.0
113.5
100.0
161.0
143.5
109.4
136.9
388.3
706.7
166.1
97.5
104.7
101.1
106.3
165.3
168.8
36859.9
107.6
101.7
121.6
39241.1
131.1
124.0
151.1
Outdoor Air
Intake
81.8
94.2
99.6
99.6
100.0
99.9
100.0
N/A
83.8
91.1
80.9
93.7
55.2
55.5
55.9
59.4
94.6
94.7
94.7
95.1
*
93.3
93.6
97.2
*
105.2
105.3
105.8
Indoor,
Lobby
96.0
99.5
100.5
98.7
104.7
83.9
84.0
90.9
80.4
94.2
1214.1
915.1
488.2
96.7
106.9
106.7
105.7
97.8
*
1841.6
632.5
159.7
*
2349.2
805.5
187.3
Indoor,
Return Vent
94.1
99.5
100.0
99.9
100.0
84.3
84.0
91.3
81.0
93.6
54.7
55.1
55.4
58.9
*
94.5
94.7
95.1
*
93.3
93.6
97.2
*
105.2
105.3
105.8
Loading
Dock
147.9
* The exposure with no weather is zero, and therefore the ratio is infinite.
-------
with weather to the exposure without weather. The entries in
this table do not compare the relative exposure to the baseline
for each retrofit, but rather compare the exposures for each
case with and without weather. The outdoor general source
shows the greatest impact of weather-induced infiltration
with only a few exceptions. The two filtration retrofits have
more than five times greater exposure due to the unfiltered
contaminant entry when infiltration is occurring, while
the cases with filter bypass have less dramatic increases in
exposure with weather impacts included. The two cases with
reduced outdoor air entry (100 percent recirculation and
5 percent outdoor air intake) are also strongly impacted by
weather-induced contaminant entry. The two early shutdown
cases have increased exposure for the outdoor general source
and the lobby source. In the first case, the increased exposure
is due to contaminant entry with the infiltration air, even after
the shutdown occurs. In the lobby case, the weather induces
airflow within the building, which moves the contaminant
to the occupied zones more effectively than it does without
weather. The 30 s prior SIP cases show dramatic increases
in exposure due to interzone airflow driven by the weather-
induced pressures in the building. Some cases have reduced
exposure with weather versus without, but none of the
reductions are particularly large.
Figures 6a through 6c present the two-story office building
particle exposures, relative to the baseline case, for the
with-weather condition. Figure 6a presents these results for
the filtration retrofits for all five source locations. Figure
6b presents the results for the shutdown and purge retrofits,
while Figure 6c presents the SIP results. Examination of
these figures leads to some broad categories of exposure
reduction. While the divisions are somewhat arbitrary, the
following categories of exposure level relative to baseline are
helpful in considering the results: 25 percent or less, about
50 percent, about 100 percent, and more than a 25 percent
increase in exposure. The only retrofits that consistently fall
in the lowest exposure category, roughly 25 percent or less
of baseline, are envelope tightening with enhanced outdoor
air or mixed air filtration, the fastest implementation of
sheltering without air cleaning, and the two fastest with air
cleaning. The only exception is for the loading dock source,
in which early sheltering increases contaminant entry into
the building. The purging response is fairly consistently in
the 25 percent or less category for the two later purge times,
except in the case of the lobby source in which purging is
more effective.
Outdoor sources, both general and air intake, are of particular
interest in buildings with good perimeter security and those
that may not be targets themselves but may be near a target.
For the two outdoor sources, retrofits that reduce exposure to
roughly 25 percent or less of baseline include the following:
mixed air filtration alone; envelope tightening combined with
400
Figure 6a Relative exposure for filtration retrofits with weather, particle releases
350-
150
• Outdoor general
• Outdoor air intake
• Lobby
• Return vent
• Loading dock
in Case not relevant
OA filtration
Mixed air
filtration
Envelope
tightening
Envelope,
OA niter
Retrofit
Envelope,
OA filter,
pressure
Envelope,
MA filter
Envelope,
MA filter,
pressure
-------
outdoor or mixed air nitration; the two later purging cycles;
the earliest implementation of SIP without air cleaning;
and all but the very slowest implementations with air
cleaning. The intake release, but not the outdoor general
release, falls in this lowest relative exposure category for
outdoor air filtration alone and for the earliest shutdown.
Outdoor air filtration reduces the relative exposure by
roughly 50 percent for the outdoor general release. Most
of the other retrofits result in only small, 20 percent or less,
reductions in the relative exposure for the outdoor releases,
while several cases actually increase exposure, in some cases
by a significant amount.
Another distinction worth noting is the consistency in the
exposure reductions across sources. For example, mixed air
filtration has a fairly consistent reduction for all five sources,
as does the shelter-in-place with air cleaning. Most of the
other retrofits are beneficial for some sources but not for
others.
40ft
Figure 6b Relative exposure for system operation retrofits with weather, particle releases
Outdoor
Outdoor air intake
Lobby
Return vent
Loading dock
Shutdown Shutdown Shutdown Shutdown Purge Purge
6s after 30 s after I mm after 5 min after 30 s prior 30 § after
Retrofit
Purge Purge
I min after 5 min after
The recommissioning cases were run to investigate
the importance of system installation, operation, and
maintenance on exposure. While only a small number were
considered, and only for specific values of the relevant
parameters, they do provide some useful insight. Figure 7
shows the relative exposure for the five recommissioning
cases for the particle releases with weather effects. For
10 percent bypass around the baseline filter, there is an
increase in exposure relative to baseline for all releases,
but due to the low baseline filter efficiency, the increase is
small. However, with the same 10 percent bypass around
the higher efficiency retrofit filter, the increases are larger,
particularly for the intake, lobby, and return vent releases.
The last three recommissioning cases all relate to system
airflow controls. If there is no outdoor air intake (100 percent
recirculation), the relative exposure increases for the two
indoor sources and especially for the loading dock release.
The outdoor general source is associated with less exposure
because there is no outdoor air intake, which also makes
the intake source irrelevant to this case. If the outdoor air
intake is reduced by 50 percent of its intended value, the
exposure to outdoor sources is reduced accordingly while the
exposure to indoor sources increases, given the lower rate
of dilution. Finally, if the building becomes more negative
due to an undersupply of 5 percent relative to the return
flow, there is more contaminant entry for the outdoor general
source, but all other exposures are reduced, given the higher
overall air change rate of the building. The important point
of the recommissioning cases is that filter bypass and poor
airflow control can increase exposure, presumably by much
larger amounts than shown in these cases if the problems are
particularly bad. These results demonstrate the importance of
operating a system as designed and the value of good system
maintenance.
-------
400
Figure 6c Relative exposure for SIP retrofits with weather, particle releases
Outdoor general
Outdoor air intake
Lobby
Return vent
Loading dock
--
250
SIP SIP SIP SIP SIPAC SIPAC SIPAC SIPAC
30s prior 30 s after 1 min after 5 min after .UK prior 30 s after 1 min after 5 min after
Retrofit
Figure 7 Relative exposure for recommissioning cases with weather, particle releases
Outdoor general
Outdoor air intake
Lobby
Return vent
Loading dock
iir Case not relevant
10 % filter bypass 10 % bypass
relative to baseline relative to MA
retrofit
100 % 5 % outdoor air 5 % undcrsupply
recirculation intake relative to relative to baseline
relative to baseline baseline
Retrofit
-------
2.2.3 High-rise Office Building
Figure 8 is a plot of the calculated concentrations in the high-
rise office building for selected cases subject to an outdoor
particle release with no weather-induced infiltration. Note
that in the high-rise building, the average exposure includes
occupants of the lobby, mail room, and other spaces that can
have a large impact on the average, depending on the source
location and contaminant transport dynamics. The baseline
results correspond to the solid line that peaks around
3xl04 particles/m3 and decays immediately thereafter. The
building air change rate for the baseline case with no weather,
i.e., driven by mechanical intake alone, is 1.12 fr1. Forthe
no-weather conditions, the results for the tight envelope
case are identical to those for the baseline case, as indicated
in the plot's legend. Tightening the envelope has no effect
on the air change rate for the no-weather case because the
system flows already pressurize the building. Enhancing the
outdoor filtration decreases the concentrations significantly.
Those results are also identical to the results for the case
that combined envelope tightening and enhanced outdoor air
filtration, and are barely distinguishable from the case that
combines outdoor filtration, tightening, and pressurization
with additional outdoor air intake. Increasing the mixed air
filtration efficiency decreases the concentration more than
the enhanced outdoor air filter. The impact of the shutdown
cases is similar to the impact seen in the other buildings, with
timing being critical.
3UE+04
Figure 8 High-rise simulation results for an outdoor particle release (no weather)
2JOE+04-
1-QE-HM-
0 DEHJO
Baseline (also envelope)
Outdoor air filtration (also envelope)
A Mixed air filtration
a OA filter, envelope pressure
* 6-s shutdown
30-s shutdown
• 1 -inin shutdown
» 5-min shutdown
0:00
1:00
2:00
3:00
Time (h:miit)
4:00
5:00
6:00
Figure 9 shows the same cases as Figure 8 but with weather
conditions inducing envelope infiltration. In this case, the
building air change rate is 1.35 fr1, an increase of 0.23
fr1 relative to the no-weather case. The peak baseline
concentration of just over 3xl04 particles/m3 is slightly
higher than the no-weather case because the nonzero
infiltration results in more contaminant entry. The peak
concentration for the envelope tightening case is just
barely lower than that of the baseline case because the
decreased contaminant entry tends to balance the decreased
dilution rate. The four filtration retrofits all decrease the
concentrations significantly, with the mixed air filter resulting
in the greatest reduction. The four shutdown cases now show
the concentration decaying during the 2-h shutdown.
The high-rise building is more complex than the other two
buildings due to its mix of systems, the nonuniform occupant
distribution in the building, and the existence of the lobby
and mail room. These features lead to somewhat unique
contaminant transport and exposure patterns. For example,
Figure 10 shows the concentrations in the lobby and the
first and second floors for a lobby release of contaminant P
with no weather. The baseline case has no interior partitions
between the lobby and the rest of the first floor, and the
concentration peaks around 2.5xl05 particles/m3 as indicated
by the solid black line in the figure. Almost none of the
contaminant released in the lobby is transported to the rest of
the building, and therefore no line is seen for the second-floor
baseline concentration. Partitions that separate the lobby from
-------
Figure 9 High-rise simulation results for an outdoor particle release (with weather)
3.0E+04-
2.0E+04-
!
l.OE+04-
O.OE+00.
Baseline
Outdoor air filtration
* Mixed air filtration
- Em-dope tightening
OA filter and envelope
••• OA filter, envelope, pressure
° 6-s shutdown
° 30-s shutdown
» 1-min shutdown
5-mi» shutdown
2:00 3:00 4:00
Time (h:min)
5:00
6:00
Figure 10 Lower levels of high-rise building for lobby release of contaminants P (no weather)
2.0E+06
1.5E+06-
LOE+06-
S.OE+05
O.OE+00.
a
a
s
a
n
o
^—1st Floor (baseline)
2nd Floor (baseline)
° Lobby (^partitioned)
1st Floor (partitioned)
2nd Floor (partitioned)
° Lobby (isolated)
1st Floor (isolated)
2nd Floor (isolated)
2:00
3:00
Time (h:min)
4:00
5:00
6:00
-------
the rest of the first floor increase the lobby concentrations
(open blue squares) to a peak concentration of almost
2xl06 particles/m3 and decrease the concentrations on the
rest of the first floor (solid blue line) relative to the baseline
case. However, after about 15 min, these concentrations are
the same as in the baseline case. Again, the concentrations on
the second floor are so low that no line is seen. Finally, when
the lobby is further isolated through the use of a dedicated
ventilation system, the lobby concentrations (open red
squares) are slightly higher than in the partitioned case. Now
the concentrations on the rest of the first floor, as well as on
the second floor, are zero. Therefore, as the cases progress
from baseline to partitioned lobby to HVAC isolation of
the lobby, the lobby concentrations and the exposure for
the small number of lobby occupants increases, but the
concentrations and exposures in the rest of the building
decrease. The difference between average and local exposure
is highlighted in Table 13, which shows the average exposure
for the occupants of the lobby, the rest of the first floor, the
second floor and above, and the entire building for the lobby
release and retrofits. In the baseline case, there is only a
single zone on the first floor, i.e., the lobby is not a separate
zone. There is some exposure throughout the building due
to contaminant transport upward from the lobby. Installing
partitions increases the exposure of the three lobby occupants
but reduces it for the rest of the first floor occupants and
those in the higher floors. Finally, isolating the lobby through
ventilation reduces the exposure outside the lobby to zero.
Table 13 High-rise exposures for lobby source and retrofits (contaminant P, no weather)
Average exposure (particle»min/m3)
. ,, D , , 1stri 2nd Floor and r ,. D ....
Lobby Rest of 1st Floor ., Entire Building
Number of occupants
Baseline
Lobby partitions
Lobby partitions and HVAC isolation
3
6.38 x 106 *
1.71 x 107
1.73 x 107
22
6.38 x 106
4.52 x 106
0
230
1105
758
0
285
5.60 xlO5
5.30 x 105
1.81 x 105
* In the baseline case, the lobby is not a separate zone but is part of the first floor zone.
Tables 14 through 17 present the relative exposure for all
the retrofit cases for the high-rise office building, with the
first two covering P (particle) and the second two covering
G (gas). Each value in the table is the average occupant
exposure over 6 h, relative to the baseline case expressed
as a percentage. Therefore, a value below 100 percent
corresponds to a reduction in exposure. Given the varied
occupancy and complex zoning of this building, there is
a range of exposure values among the various occupant
locations that is not revealed by the average exposure,
as noted in the discussion of Table 13.
Table 14 contains the relative exposure for contaminant
P with no weather-induced infiltration. Enhanced outdoor
air filtration decreases exposure to about 12 percent of the
baseline value, with no difference between the general
outdoor and intake releases. A mixed air filter is more
effective. This retrofit is not particularly effective for the
mail room release because the filters are in the main
handlers that don't serve this space and because the mail
room exposures are so high. The shutdown cases show the
impact of timing discussed previously, but even the fastest
shutdown reduces exposure to the outdoor sources by only
about 25 percent. Purging reduces exposure by about 70
percent, while envelope tightening has little impact on the
outdoor sources. Shelter-in-place is fairly effective, with
timelier sheltering being moreso. Adding filtration to the
shelter greatly increases the exposure reduction. The mail
room retrofits prevent contaminant from moving to the rest
of the building, but the exposure of the mail room occupants
is still high, leading to only a 15 percent reduction in the
average exposure.
Table 15 contains the exposure reductions for contaminant
P with weather effects, i.e., a nonzero envelope infiltration
rate. The exposure reduction associated with enhanced
outdoor air filtration in the general case is now lower than for
the intake release. Most of the other cases are not impacted
very significantly by the inclusion of weather, with some
exceptions. The mail room release with the mixed air filter
has a more significant reduction in the exposure, though the
relative exposure is still fairly high. All of the shutdown cases
are impacted by infiltration, with an increase in exposure for
the 6-s shutdown for the general release but a larger decrease
for the intake source. All of the other shutdown cases have
lower exposures relative to the baseline than the no-weather
cases due to the nonzero dilution rates during the shutdown
periods. Envelope tightening reduces exposure from the
outdoor general release due to less contaminant entry via
infiltration but increases exposure from the other three
sources due to the lower outdoor air dilution rate. The shelter-
in-place reductions are also lower, particularly without the
filtration and air cleaning systems.
-------
Table 14 High-rise retrofits effectives values (contaminant P, no weather)
Exposure Relative to Baseline (%)
Retrofit
Outdoor air nitration
Mixed air nitration
6-s shutdown
30-s shutdown
1-min shutdown
5-min shutdown
100 %OA purge
Envelope tightening
Envelope, OA nitration
Envelope, OA filter, pressure
SIP - 30 s prior
SIP - 30 s after
SIP - 1 min after
SIP - 5 min after
SIP AC -30s prior
SIP AC -30s after
SIP AC - 1 min after
SIP AC - 5 min after
Lobby partitions
Lobby partitions, HVAC isolation
Depressurize mail room
Depressurize mail room, filter return
Outdoor,
General
12.4
4.9
72.7
350.8
677.2
471.1
36.9
100.2
12.4
13.5
5.1
8.6
16.7
41.1
0.4
0.1
1.7
26.1
Outdoor Air
Intakes
12.4
4.9
72.7
350.8
677.2
471.1
100.2
12.4
Indoor,
Lobby
32.0
26.0
91.1
94.6
32.4
Indoor,
Return Vent
4.0
29.2
95.5
Mail Room
92.1
86.6
86.6
-------
Table 15 High-rise retrofits effectives values (contaminant P, with weather)
Exposure Relative to Baseline (%)
Retrofit
Outdoor air nitration
Mixed air nitration
6-s shutdown
30-s shutdown
1-min shutdown
5-min shutdown
100 %OA purge
Envelope tightening
Envelope, OA nitration
Envelope, OA filter, pressure
SIP - 30 s prior
SIP - 30 s after
SIP - 1 min after
SIP - 5 min after
SIP AC -30s prior
SIP AC -30s after
SIP AC - 1 min after
SIP AC -5 min after
Lobby partitions
Lobby partitions, HVAC isolation
Depressurize mail room
Depressurize mail room, filter return
Outdoor,
General
24.5
9.4
140.7
268.2
418.8
321.1
38.3
93.8
11.6
12.6
34.8
32.0
38.6
63.8
3.2
3.1
3.9
24.4
Outdoor Air
Intakes
12.4
5.2
41.9
204.2
397.8
302.3
108.9
13.5
Indoor,
Lobby
33.3
30.4
104.3
99.5
27.4
Indoor,
Return Vent
4.1
30.5
107.8
Mail Room
73.3
87.8
69.6
Tables 16 and 17 contain the contaminant G results, without
and with weather, for the high-rise building. As was the case
in the two-story office building, the results are essentially
identical to the results in Tables 14 and 15 for contaminant P,
except as impacted by the different removal efficiencies for
the gas relative to the particle. For example, the outdoor air
and recirculation retrofits have lower relative exposures for
contaminant G because the gas filter has a higher efficiency
than the enhanced particle filter.
-------
Table 16 High-rise retrofits effectives values (contaminant G, no weather)
Exposure Relative to Baseline (%)
Retrofit
Outdoor air nitration
Mixed air nitration
6-s shutdown
30-s shutdown
1-min shutdown
5-min shutdown
100 %OA purge
Envelope tightening
Envelope, OA nitration
Envelope, OA filter, pressure
SIP - 30 s prior
SIP - 30 s after
SIP - 1 min after
SIP - 5 min after
SIP AC -30s prior
SIP AC -30s after
SIP AC - 1 min after
SIP AC - 5 min after
Lobby partitions
Lobby partitions, HVAC isolation
Depressurize mail room
Depressurize mail room, filter return
Outdoor,
General
5.0
1.2
47.7
230.2
445.0
324.4
24.2
100.2
5.0
5.0
2.8
5.4
11.0
27.7
0.2
0.1
1.2
14.4
Outdoor Air
Intakes
5.0
1.2
47.7
230.2
445.0
324.4
100.2
5.0
Indoor,
Lobby
16.5
14.1
88.5
95.9
27.7
Indoor,
Return Vent
0.8
15.9
92.4
Mail Room
85.5
80.6
80.6
-------
Table 17 High-rise retrofits effectives values (contaminant G, with weather)
Exposure Relative to Baseline (%)
Retrofit
Outdoor air nitration
Mixed air nitration
6-s shutdown
30-s shutdown
1-min shutdown
5-min shutdown
100 %OA purge
Envelope tightening
Envelope, OA nitration
Envelope, OA filter, pressure
SIP - 30 s prior
SIP - 30 s after
SIP - 1 min after
SIP - 5 min after
SIP AC -30s prior
SIP AC -30s after
SIP AC -1 min after
SIP AC -5 min after
Lobby partitions
Lobby partitions, HVAC isolation
Depressurize mail room
Depressurize mail room, filter return
Outdoor,
General
17.2
3.9
86.0
176.3
283.5
226.3
26.2
99.7
5.0
5.0
20.2
19.4
24.4
42.7
2.0
1.9
2.6
17.0
Outdoor Air
Intakes
5.0
1.4
28.9
140.6
274.2
217.7
114.3
5.7
Indoor,
Lobby
18.7
17.9
113.5
102.2
34.7
Indoor,
Return Vent
0.9
18.0
120.1
Mail Room
58.2
83.6
55.4
-------
2.3 Summary of Simulation Results
Multizone airflow and contaminant transport simulations
were performed in three buildings to estimate the impacts of
selected retrofits on occupant exposure to generic chembio
contaminants. The general approach of these simulations is
to model a generic contaminant release within or outside a
given building and calculate the average occupant exposure
to the contaminant and then to repeat the process for the
same building and release scenario with one or more retrofits
in place. Therefore, the measure of retrofit performance
is based on the change in average occupant exposure
relative to the baseline case. As noted earlier, the assumed
contaminant release rates and the calculated concentrations
have no particular significance in relation to any particular
contaminant, and therefore the calculated concentrations
cannot be used to estimate any health impacts. Nevertheless,
they do provide useful insights into the impact of the retrofits
considered and the factors (e.g., weather, building features)
that determine these impacts.
One key issue to note is that the results presented and the
conclusions reached are strongly dependent on the particular
building models, sources, systems, and other features of the
simulations. While a large number of cases were examined,
it is always true that each building, system, and retrofit
application is unique, and the effectiveness in any particular
circumstance needs to be determined based on the associated
details. Note also that the changes in exposure reported here
are based on average exposures, and the effectiveness of a
particular retrofit can be locally quite variable in the case of
an indoor source. In addition, the modeling approach used in
these analyses does not consider within-room concentration
gradients.
The results for all three building models showed that the
most significant and consistent exposure reductions were
associated with enhanced filtration, either of the outdoor
airstream alone for exterior releases or the mixed airstream
for indoor and outdoor releases. The benefits of filtration
were also evident in the shelter-in-place strategies. The
size of the reduction depended primarily on the removal
efficiencies of the baseline and retrofit filters. Because
the amount of contaminant that passes through the filter,
and therefore contributes to exposure, depends on 1 minus
the removal efficiency, small changes in efficiency can
have relatively large impacts on exposure. For example, a
1 percent absolute reduction in the efficiency of a 90 percent
efficient filter (resulting in 89 percent removal) increases the
associated exposure by 10 percent.
While filtration can be quite effective, the impact of
filtering the intake air can be degraded by the presence of
envelope infiltration in the case of a general outdoor release
(not localized to the outdoor air intake). The importance
of infiltration has been identified previously as an issue
with building protection strategies based on outdoor air
filtration (Persily 2004). Due to the strong dependence
of infiltration on building envelope airtightness, weather
conditions, and ventilation system airflow rates, the extent
of such degradation cannot be generalized. Strategies based
on building pressurization to minimize infiltration will be
similarly impacted by envelope leakage. Effective filtration
and pressurization strategies require low envelope leakage
values. Envelope tightening alone is not a particularly
effective retrofit but achieves its value when combined with
effective air filtration.
The impacts of shutdown strategies are highly dependent
on their timing relative to the start of a release, with higher
effectiveness for earlier implementation. This unsurprising
result leads to the question of how a building manager or
operator knows when a release is occurring, or has just
occurred, and that a system shutdown may be advised. Given
the current state of sensing technology and the inherently
unpredictable nature of such releases, it is unclear how
realistic it is to rely on a shutdown strategy. And as noted
in the simulations, a late shutdown retains the contaminant
in the building and increases exposure. Therefore, the risk
of implementing a system shutdown too late in the event
timeline needs to be considered in response planning.
The use of 100 percent outdoor air purging, while potentially
effective in removing a contaminant, is also a function of the
timing of implementation relative to the release. However,
purging was found to be more effective than a system
shutdown for most cases simulated. The "ideal" strategy for
many cases might be a shutdown before or during a release
followed by a purge once the release is over. However,
implementing such a two-stage approach would again
require knowledge of the timing of the release, which in
general is not expected to exist. In contrast, one reason for
the effectiveness of the filtration strategies as modeled is that
they are "always on." In other words, contaminant removal
occurs as soon as the source begins since filtration requires
no human or automated intervention. Some have proposed
strategies in which the air cleaning capability would be
available in an alternate HVAC flow path, which would
require, for example, switching the affected airstream from
one duct to another. The effectiveness of such a system would
therefore again rely on the timing of implementation.
The use of shelter-in-place is generally effective in reducing
exposure but far moreso when a recirculating filtration/air
cleaning system is employed in the shelter. While early
implementation of sheltering is more effective than later
sheltering, timing appears to be somewhat less critical than
for a shutdown response. Again, these conclusions are true
for average exposures, and there can be localized impacts
that result in much higher exposures in certain zones of a
building. Therefore, quicker sheltering is better, which raises
the same notification questions identified in the discussion
of system shutdown. Also, while later sheltering still might
be effective on average, there can be an issue with exposed
occupants bringing contaminant into the shelter on their
persons, which is not addressed in this analysis. Additionally,
knowledge of when to leave a shelter would be required as
eventually occupants in a shelter without air cleaning receive
the same exposure as unsheltered occupants.
-------
-------
3.0
Case Study
A case study was conducted as part of this project to
investigate the application of building protection retrofits
in two actual buildings. Specifically, the case study involved
identifying and designing retrofits to these buildings given
their particular floor plans and HVAC system designs.
The performance of the retrofits was evaluated using the
simulation approach employed in the technical evaluation
of the retrofits. The case study also included an economic
analysis in which the costs of the retrofit measures were
identified and quantified. The cost data were estimated for
illustrative purposes as well as to provide sample data for
the economic evaluation software developed as part of the
project. Two office buildings, with very different floor plans
and ventilation system designs, were selected for the case
study. One is a high-rise office building with central air
handling systems, in addition to other features of interest,
including intakes near ground level, a loading dock, a mail
room, and a public-access lobby. The other building is a one-
story office building with multiple rooftop air handling units
and no spaces other than offices.
The retrofit design and cost estimation were performed
by an architectural and engineering (A&E) firm and were
based on a list of candidate retrofits identified by NIST. The
A&E firm then proceeded with the design work, producing
detailed designs for implementing the retrofits. As part of this
effort, the A&E firm reviewed the existing mechanical and
control systems in the two buildings, including all original
architectural, structural, mechanical, and electrical plans and
any modifications of these plans. The firm also conducted
field inspections of the buildings and systems and then
performed the design work and prepared detailed descriptions
and drawings of the proposed retrofits. Cost estimates for the
retrofit work include the following:
• Retrofit installation costs (including equipment, materials
and parts, required demolition, labor, and performance
testing)
• Annual filter replacements costs (including material costs
and labor, based on an assumed frequency of replacement)
• Cost of additional electricity associated with filtration
options that significantly increase system pressure drop
These retrofits, and the associated cost estimates, are specific
to the buildings examined in terms of the available options
and the details of implementation. While the designs and
costs are of interest to the general question of building
protection, they cannot be applied to other buildings.
Determining retrofit options, designs, and cost estimates for a
specific building always requires consideration of the unique
features of that building.
3.1 Description of Buildings and Retrofits
Considered
High-rise Office Building
The high-rise office building is part of a larger complex
of buildings built in the early 1960s. In addition to the
office space, the building has an elevator penthouse,
basement, and subbasement with a total floor area of about
12,100 m2 (130,500 ft2). The east and west facades of the
building are faced with grey face brick; insulated porcelain
spandrel panels and fixed aluminum frame windows enclose
the north and south facades. There are six field-assembled
air handlers located on the mezzanine level of the building
(above the second story). Each unit has a mixing box with
outdoor air louvers and dampers (including minimum
outdoor air dampers) and a return air duct. These units also
have a filter rack upstream of the coils and accessible from
the mixing box, with 10 cm (4 in) deep pleated filters rated at
MERV 6 (ASHRAE 1999). The outside air intake louvers for
these air handlers are located about 6 m (20 ft) above ground
level. The temperature controls are pneumatic, and each unit
is started and stopped manually or by means of time clocks.
However, the systems operate 24 h every day of the year.
The building has a lobby area with a 4.3-m (14-ft) ceiling
and a floor area of about 325 m2 (3500 ft2). The lobby has
glass curtain walls on two sides and marble-finished walls
on the other two and is accessed from a glass-enclosed
14-m2 (150-ft2) vestibule with a series of two rows of four
balanced glass doors. The lobby is open to the elevator bank
serving the building and another wing of the complex. The
lobby does not have a dedicated air conditioning system
but is served by one of the six air handlers located on the
mezzanine, which also serves the corridors adjacent to the
lobby.
The building has a mail room in the basement, with a
floor area of about 334 m2 (3600 ft2). The mail room has
a suspended acoustical ceiling system and is enclosed by
concrete masonry unit (CMU) walls and modular metal
partitions. One wall is solid to the ceiling, two walls have
doors to interior corridors, and the fourth wall is an exterior
wall with a roll-up door to a loading dock area. The mail
room does not have a dedicated air handler and is served by a
unit in a basement mechanical room that also serves several
adjacent spaces. The basement mechanical room contains six
other air conditioning units, serving other basement and first-
floor spaces and is fairly crowded with storage tanks, pumps,
ductwork, and other services. The ceiling plenum above the
mail room is also very congested with ductwork, piping, and
other services.
-------
One-story Office Building
This building is a contiguous group of large, one-story
trailers that have been joined to form a single building of
about 1600 m2 (17 000 ft2). The building is about 4.6 m
(15 ft) tall with six exterior doors, 67 fixed double-glazed
windows, and a crawl space containing electrical and
plumbing services. The building is served by 28 rooftop heat
pump units that provide heating, cooling, and ventilation.
Each unit has a 2.5 cm (1 in) MERV 4 filter and is controlled
by a single thermostat in the occupied space.
Candidate Retrofits
Based on an initial assessment of the buildings, NIST
provided the A&E firm with the following lists of candidate
retrofits for consideration in the two buildings.
High-rise building:
• Enhanced particle filtration consistent with
current air handlers (currently MERV 6)
• Enhanced particle filtration with air handler
modifications to handle increased pressure drop
• Enhanced particle filtration and gaseous air
cleaning with air handler modifications
• Envelope tightening
• Quick shutoff switch
• Quick purge switch
• Shelter-in-place: tighten shelter spaces, local
filtration/air cleaning units
• Isolate/depressurize lobby: install partitions,
dedicated system to depressurize
• Isolate/depressurize mail room: tighten interior
partitions, dedicated system to depressurize
• Relocate ground level intakes to higher elevation
• HVAC system testing, adjusting, and balancing
One-story building:
• Enhanced particle filtration consistent with current
air handlers (currently MERV 4)
• Enhanced particle filtration with air handler
modifications to handle increased pressure drop
• Enhanced particle filtration and gaseous air
cleaning with air handler modifications
• Envelope tightening
• Quick shutoff switch
• Quick purge switch
• Shelter-in-place: tighten shelter spaces, local
filtration/air cleaning units
3.2 Retrofit Design
Based on their review of the building design and condition,
along with the retrofits identified by NIST, the A&E firm
designed a number of retrofits for the two buildings. As
noted earlier, these retrofits and the associated cost estimates
are specific to the buildings examined in terms of available
options and the details of implementation. Determining
options and costs for a specific building always requires
consideration of the unique features of that building. Also
note that the list of retrofits considered is not comprehensive,
and none of these options should be interpreted as either
providing the best protection or the most cost-effective option
possible.
A number of options were considered for each building. For
the high-rise office building, the following retrofits were
considered and design work performed:
Filter upgrade #1: Replace all the MERV 6 paniculate
filters with MERV 11 filters. MERV 11 is the highest
efficiency that can be installed, employing existing filter
frames and requiring no changes to the existing fans or
motors.
Filter upgrade #2: Replace all the MERV 6 paniculate
filters with a three-stage filtration system, including a
10-cm (4-in) pre-filter (MERV 8), an 85 percent
intermediate filter (MERV 13), and a 99.97 percent
HEPA filter (MERV 17). This option requires the
installation of new HEPA filter frames, as well as
replacing the fans and motors of the air handlers to
handle the increased pressure drop and replacing the
main circuit breaker to handle the increased electrical load.
Filter upgrade #3: Replace all the MERV 6 paniculate
filters with a multistage filtration system including a
10-cm (4-in) pre-filter (MERV 8), an 85 percent
intermediate filter (MERV 13), a 99.97 percent HEPA
filter (MERV 17), an AZDM-TEDA grade carbon gas
phase filter, and a 5-cm (2-in) final filter (MERV 11). This
option requires the installation of new HEPA filter frames,
as well as replacing the fans and motors of the air handlers
to handle the increased pressure drop and replacing the
main circuit breaker to handle the increased electrical load.
Tighten the exterior envelope of the building: Seal
around interior and exterior of windows, doors, and
penetrations of the building envelope. (Note that it is not
possible to know the actual before and after airtightness of
the building without conducting fan pressurization tests of
building airtightness. There are often significant leaks in
commercial building envelopes at wall-floor and wall-roof
interfaces that might not necessarily be addressed by these
retrofits.)
Shutoff and purge switches: Install quick shutoff and
purge switches in a central location of the building, i.e.,
a guard office that is staffed 24 h/d.
Elevate outdoor air intakes: Extend the outdoor air
intakes from the mezzanine level to the roof. (Note that
this option would block more than 100 exterior windows
of the building because there is no available internal space
through which to run the new ductwork.)
Lobby retrofit with exhaust filtered to level #2: Isolate
the lobby from the rest of the building (other wings and
corridors) by providing tempered glass partitions with
self-closing glass doors. Also, install a new air handling
unit in the basement mechanical room to serve the lobby
-------
only, with level #2 nitration as described above. The design
also includes a new exhaust fan, drawing from the lobby,
and nitration level #2 installed in the outgoing airstream
to clean the air before it is exhausted to the outdoors. This
exhaust fan is sized to maintain 10 percent more exhaust
air from the lobby than supply air under normal operating
conditions. This retrofit requires a number of electrical
modifications to accommodate the new fans and motors.
Lobby retrofit with exhaust filtered to level #3: Same as
above, except the exhaust air from the lobby is filtered to
level #3.
Mail room retrofit with exhaust filtered to level #2: Air
seal the partitions between the mail room and all adjacent
zones. Upgrade the filtration in the air handler serving
the mail room to filtration level #2, which requires the
installation of HEPA filter frames. Add the same level
of filtration to the exhaust airflow out of the mail room
to prevent any contaminant released in the mail room
from impacting the rest of the building. The filtration
upgrade requires higher horsepower motors and electrical
modifications for both the supply and exhaust fans. The
system is to be operated with 10 percent more exhaust air
from the mail room than supply air.
Mail room retrofit with exhaust filtered to level #3:
Same as above, except the exhaust air from the mail room
is filtered to level #3.
Shelter-in-place: Designate a number of shelter-in-place
spaces in the building, with air sealing of the walls of these
spaces, plus a stand-alone, recirculating filtration and air
cleaning unit in each such space.
TAB: Test, adjust, and balance (TAB) the existing air
handling systems to ensure that they are being operated
at the designed airflow rates. This retrofit, while not
necessarily resulting in a direct reduction of occupant
exposure to contaminants, allows the system to be relied
on for other protection strategies with a greater degree
of confidence. The retrofit may also reduce energy
consumption and improve indoor air quality. However,
the impacts of such a TAB effort will depend on the as-is
condition of the system, specifically the magnitude of the
differences between system design and performance.
For the one-story office building, the following retrofits were
considered and design work performed:
Filter upgrade #1: Replace all the existing MERV 4
paniculate filters with MERV 11 filters, employing
existing filter frames and requiring no changes to fans
or motors.
Filter upgrade #2: Given the power and space limitations
of the rooftop units, it is not possible to upgrade the
filtration beyond MERV 11. Therefore, to provide a
higher level of filtration, the designer proposed installing
two dedicated outdoor air fans on steel platforms on the
roof, which would provide filtered outdoor air to the
rooftop units. These outdoor air units have filtration
consistent with option #2 for the high-rise office building,
specifically, a three-stage system including a 10-cm (4-in)
pre-filter (MERV 8), an 85 percent intermediate filter
(MERV 13), and a 99.97 percent HEPA filter (MERV 17).
In addition to the platform, fans, and filters, this option
requires electrical system upgrades.
Filter upgrade #3: Same as above, but with filter option
#3 in the two outdoor air fans. Specifically, this option
includes the new support platform, new fans, a multistage
filtration system including a 10-cm (4-in) pre-filter, an
85 percent intermediate filter (MERV 13), a 99.97 percent
HEPA filter (MERV 17), an AZDM-TEDA grade carbon
gas phase filter, a 5-cm (2-in) final filter (MERV 11), and
electrical system upgrades.
Tighten the exterior envelope of the building: Patch
roof leaks, seal around windows, provide doors with
gasket hardware, replace door thresholds, and seal around
pipe and conduit floor penetrations within the building's
crawl space. (Note that it is not possible to know the
actual airtightness level without a fan pressurization test.
As noted for the high-rise building, there are often other
significant leaks in commercial building envelopes that
might not be addressed by these sealing efforts.)
Shutoff switches: Install quick shutoff switches in the
reception area of the building. (The systems cannot be
operated in a purge mode. Therefore, no purge switch
option is considered.)
More detailed descriptions of the buildings and retrofit
designs are excerpted from the A&E report and presented in
Appendix B.
3.3 Economic Evaluation
The cost data provided by the contractor for each of the
retrofits consists of first costs (equipment and installation),
annual costs for maintaining the retrofit, and annual costs
of additional electrical power required for operation. These
costs are summarized in Table 18. The annual maintenance
costs consist of the materials and labor associated with filter
replacement. Table 19 expands on the maintenance cost
entries in Table 18 by providing cost per change (e.g., labor
and materials costs) and the assumed number of changes per
year for each filter option. The values in Table 19 are given
for each air handling unit, so the total maintenance costs are
those values multiplied by six. In actual application, the filter-
changing schedule is a complex function of the outdoor and
indoor conditions, and may be different from these assumed
frequencies in a specific building. The annual operating costs
are the increase above the base case electrical consumption.
More detailed breakdowns of the initial costs for the retrofits
are presented in Appendix C. In addition, life-cycle costs for
each retrofit option are included in the presentation of the
technical evaluation of the retrofits in the following section.
-------
Table 18 Summary of Retrofit Cost Estimates
Costs (thousands of $)
Retrofit
Initial Cost
Annual
Maintenance
Cost
Annual
Operating Cost
Increase
High-rise building
Base case
Filtration upgrade #1
Filtration upgrade #2
Filtration upgrade #3
Envelope tightening
Shutoff/purge switches
Extend intakes to roof
Lobby partitions
Lobby partitions and dedicated HVAC system
Lobby retrofits, with filtration level #2
Lobby retrofits, with filtration level #3
Mail room air sealing
Mail room air sealing, with filtration level #2
Mail room air sealing, with filtration level #3
Shelter-in-place spaces
System testing, adjusting, and balancing
0.0
71.4
291.8
1111.3
625.3
20.9
225.1
64.1
198.9
215.6
273.1
29.1
101.3
194.1
75.8
75.0
2.9
1.2
21.1
153.0
0.0
0.0
0.0
0.0
1.0
5.5
5.8
0.5
5.2
26.4
0.0
0.0
0.0
0.0
39.0
71.3
0.0*
0.0
0.0
0.0
1.5
8.1
10.5
0.0
18.5
35.6
0.0
0.0*
One-story building
Base case
Filtration upgrade #1
Filtration upgrade #2
Filtration upgrade #3
Envelope tightening
Shutoff switch
0.0
2.1
251.3
368.6
32.4
11.8
3.6
6.3
5.6
22.6
0.0
0.0
0.0
0.0
20.8
28.9
0.0*
0.0
* May reduce building energy consumption and associated operating costs.
-------
Table 19 Maintenance Cost of Filtration for High-Rise Building
..... Unit Cost .. .. Material Cost Labor Cost Total Cost _, ,,, Annual
Material ($) Units ($) ($) ($) Changes/Year Cost ($)
Baseline ("as-is") system
MERV6
5
20
100
20
120
4
480
Level 1 filtration: Limited participate filtration and no chemical air cleaning
MERV11
8
20
160
32
192
1
192
Level 2 filtration: Enhanced participate filtration and no chemical air cleaning
MERV8
MERV13
HEPA
5
125
300
20
20
20
100
2,500
6,000
20
500
1,200
120
3,000
7,200
1
0.33
0.33
TOTAL
120
1,000
2,400
3,520
Level 3 filtration: More enhanced participate filtration and chemical air cleaning
MERV8
MERV13
HEPA
Gas phase air cleaning
MERV11
5
125
300
4,500
8
20
20
20
20
20
100
2,500
6,000
90,000
160
20
500
1,200
18,000
32
120
3,000
7,200
108,000
192
1
0.33
0.33
0.2
2
TOTAL
120
1,000
2,400
21,600
384
25,504
3.4 Technical Evaluation
The degree of protection against generic chembio releases
provided by the case study retrofits was investigated through
multizone airflow and contaminant transport simulations
using the CONTAM program (Walton and Dols 2005). As
in the retrofit evaluations presented in Section 2, CONTAM
was used to estimate occupant exposure for generic indoor
and outdoor releases of both a gaseous and paniculate
contaminant, referred to as G and P, respectively. The
exposure was estimated for the baseline (as-is) building and
then for the building with the selected retrofits installed.
For the purposes of these estimates, the exposure was
calculated for the occupants over 6 h, with the release
of both contaminants occurring at the beginning of the
second hour. Note that potential particle removal processes,
such as deposition and filtration of infiltrating air by the
building walls, were not included in the analysis. While
these processes might be expected to impact the estimated
exposures, they will have a less significant impact on relative
exposures between cases than on the absolute exposure for
a single case. The results of these simulations are presented
in Tables 20a through 20c for the high-rise office building
in terms of the ratio of the exposure with the retrofit to the
baseline exposure without. Therefore, the values in the
tables are dimensionless, and the lower the value the greater
the reduction in exposure. The exposure ratios reported are
based on calculated average exposures of all occupants in the
building. Table 21 presents the average exposure ratios for
the one-story office building.
Life-cycle costs of the various retrofits are also reported in
Tables 20a, 20b, and 20c for the high-rise office building
and in Table 21 for the one-story office building. Cost data
from Tables 18 and 19 are used to calculate life-cycle costs.
The life-cycle cost figures in Tables 20 and 21 are based on
a 20-year study period and a 7 percent real discount rate.
The discount rate is used to adjust future costs for filter
replacements (i.e., annual maintenance costs) and additional
electricity (i.e., annual operating cost increases) to a present
value amount. All life-cycle cost figures are expressed in
thousands of dollars. It is important to note that the life-cycle
cost figures do not include any potential cost savings, such
as reduced energy consumption due to envelope tightening
or increased worker productivity due to improved indoor air
quality associated with enhanced filtration.
Table 20a presents relative occupant exposures for a generic
outdoor release for the high-rise office building. This outdoor
release was modeled as a step change elevation in outdoor
concentrations of both gaseous contaminant G (1.0 mg/m3)
and paniculate contaminant P (1.0 x 106 particles/m3) lasting
for 1 min. The selected retrofits studied for this release
included filtration option #1 (upgrade of existing system
filters from MERV 6 to MERV 11), filtration option #2
(three-stage filtration system, including 10-cm [4-in] pre-filter
[MERV 8], an 85 percent intermediate filter [MERV 13] and
a 99.97 percent HEPA filter [MERV 17]), filtration option #3
(multistage filtration system, including a 10-cm [4-in] pre-
filter [MERV 8], an 85 percent intermediate filter [MERV
13], a 99.97 percent HEPA filter [MERV 17], an AZDM-
TEDA grade carbon gas phase filter, and a 5-cm [2-in] final
filter [MERV 11]), sealing the building envelope, and then
each filtration upgrade option in combination with envelope
sealing. The weather conditions during the simulation period
-------
Table 20a Relative Exposure and Life-Cycle Cost for Selected Retrofits in High-Rise
Building (outdoor release with weather-induced infiltration)
Exposure Relative to Baseline (%)
Retrofit
Filtration option #1
Filtration option #2
Filtration option #3
Envelope sealing
Filtration #1 with envelope sealing
Filtration #2 with envelope sealing
Filtration #3 with envelope sealing
Contaminant G
(gas)
100
100
13
100
100
100
0
Contaminant P
(particle)
64
15
15
97
56
0
0
Life-cycle Cost
(thousands of dollars)
122
899
6,283
625
748
1,524
6,908
were an outdoor air temperature of 0 °C and a wind speed
of 5 m/s in order to induce a reasonable level of envelope
infiltration. The building envelope effective leakage area (at
a reference pressure of 4 Pa) was 5 cmVm2 before (0.07 in2/
ft2) and 0.7 cm2/m2 (0.01 inVft2) after sealing the envelope.
The baseline whole building air change rates were 0.23 fr1
due to infiltration and 1.12 fr1 due to outdoor air intake, for a
total of 1.35 fr1. The envelope sealing completely eliminated
infiltration under the conditions modeled, leading to a whole
building air change rate of 1.12 fr1.
As seen in Table 20a, the predicted exposure reductions for
an outdoor contaminant release vary widely from no impact
at all (100 percent relative exposure) to very nearly a total
elimination of exposure (0 percent relative exposure). For
the gas contaminant, the retrofit with the largest reduction is
filtration option #3, which includes a gaseous air cleaner in
the outdoor air intakes, combined with envelope sealing for
a predicted reduction in exposure of essentially 100 percent.
Without sealing the envelope, filtration option #3 is predicted
to have a smaller impact, with an exposure reduction of
87 percent. The lower reduction without tightening occurs
because of outdoor air entry via infiltration that is not
impacted by the air cleaning system. Envelope sealing alone
has no impact on exposure to contaminant G. The other
filtration options do not impact contaminant G because they
include only particle filtration.
For contaminant P, filtration option #2 (and #3 since it
provides equivalent particle filtration) combined with
envelope sealing is predicted to reduce exposure by essentially
100 percent. As with contaminant G, the impact of these
levels of filtration is lessened if the envelope is not sealed
with a predicted exposure reduction of 85 percent. The
lower filtration upgrade (option #1) has predicted exposure
reductions of 36 percent and 44 percent with and without
envelope sealing, respectively. Unlike contaminant G,
envelope sealing alone is predicted to have a small impact (3
percent reduction) on exposure because the baseline building
includes a particle filter.
Table 20b presents the relative exposure for a source in
the lobby of the high-rise office building. The contaminant
source was modeled as a 1-min contaminant release of
1-kg of gaseous contaminant G and 1.0 x 109 particles of
contaminant P. The selected retrofits studied for this release
include the following:
• Install partitions to separate the lobby from the remainder
of the first floor (modeled leakage of 1 cm2/m2 [0.01 in2/
ft2] at 4 Pa for lobby walls and 150 cm2 [23.2 in2] for each
of two doors).
• Install the internal partitions and a separate HVAC system
with 10 percent undersupply to depressurize the lobby
relative to the rest of the building.
• Install partitions and a separate HVAC system with
10 percent undersupply, plus filter the lobby return air
with filtration option #2 (addition of new outdoor air fans
with a three-stage paniculate filtration system).
• Install partitions and a separate HVAC system with
10 percent undersupply, plus filter the lobby return air
with filtration option #3 (addition of new outdoor air fans
with a four-stage filtration system, including a carbon gas
phase filter).
As seen in Table 20b, the predicted reductions in the average
6-h exposure to a contaminant release in the lobby vary
from a 1 percent increase to a 92 percent reduction. For
contaminant G, the retrofit with the largest reduction is
filtration option #3, which includes a gaseous air cleaner in
the lobby return, combined with the lobby partitions and
isolated HVAC. As stated earlier, the calculated exposure
ratios are based on the average exposure of all occupants
in the building. Adding lobby partitions alone results in an
increase in average exposure to both contaminants because
it increases exposure to occupants in the lobby while only
reducing exposure in the remainder of the building by 10
percent or less. Using isolated HVAC in combination with
the lobby partitions results in an average exposure reduction
of 66 percent for contaminant G with respect to the baseline
-------
Table 20b Relative Exposure and Life-cycle Cost for Selected Retrofits in High-Rise
Building (lobby release with weather-induced infiltration)
Exposure Relative to Baseline (%)
Retrofit
Lobby partitions
Lobby partitions and isolated HVAC
Lobby partitions and isolated HVAC
and return filtration option #2
Lobby partitions and isolated HVAC
and return filtration option #3
Contaminant G
(gas)
101
34
34
8
Contaminant P
(particle)
101
22
8
8
Life-cycle Cost (thousands of
dollars)
64
225
367
455
case. Adding filtration option #2 does not impact contaminant
G because it includes only particle filtration. HVAC isolation
combined with the lobby partitions results in a 78 percent
reduction in average exposure to contaminant P. Adding the
HEPA filtration (i.e., return filtration options #2 and #3) to the
other lobby modifications further improves the effectiveness
for an exposure reduction of 92 percent.
Table 20c presents relative occupant exposures for a
source in the mail room of the high-rise office building.
The contaminant source was modeled as a 1-min contaminant
release of 1 kg of gaseous contaminant G and 1.0 x 109
particles of contaminant P. The selected retrofits studied for
this release included the following:
• Seal the mail room (reduce wall, interior doors, exterior
doors and ceiling leakage to 1 cmVm2 [0.01 inVft2] at 4 Pa,
10 cm2 [1.6 in2] each, 5 cm2 [0.8 in2] each, and 2.5 cnvYm2
[0.04 inVft2], respectively), and modify the HVAC system
to depressurize the mail room with 10 percent undersupply.
• Seal the mail room as above, modify the HVAC system
with 10 percent undersupply, and filter the basement
recirculation air with filtration option #2 (addition of new
outdoor air fans with a three-stage paniculate filtration
system).
• Seal the mail room, modify the HVAC system, and filter
the basement recirculation air with filtration option
#3 (addition of new outdoor air fans with a four-stage
filtration system, including a grade carbon gas phase filter).
As seen in Table 20c, the predicted exposure reductions for
the mail room contaminant release are 22 percent for both
contaminants and all retrofits. However, as with the lobby
case, the exposure is the average for the mail room occupants
and the occupants of the rest of the building. The retrofits
increase exposure of the mail room occupants but reduce the
exposure of the occupants in the remainder of the building by
100 percent. As in the case of the lobby retrofits, sealing the
mail room and reducing the supply airflow tends to keep
the contaminant from migrating to the rest of the building,
thereby increasing the exposure to the mail room occupants.
The filtration upgrades do not provide additional protection to
the building occupants because they are located in the
system exhaust stream and serve only to prevent discharge
of contaminants to the ambient environment.
For the one-story building, CONTAM was again used to
estimate occupant exposure for a generic outdoor release for
the baseline building and then for the building with selected
retrofits. This outdoor release was modeled as a step change
elevation in the outdoor concentrations of both gaseous
contaminant G (to 1.0 mg/m3) and paniculate contaminant P
(to 1.0 x 109 particles/m3) that lasted for 1 min. The retrofits
studied for this building include filtration option #1 (upgrade
of existing system filters from MERV 4 to MERV 11),
Table 20c Relative Exposure and Life-Cycle Cost for Selected Retrofits in High-Rise
Building (mail room release with weather-induced infiltration)
Exposure Relative to Baseline (%)
Retrofit
Seal mail room and HVAC undersupply
Seal mail room and HVAC undersupply and
filtration option #2 in basement recirculation
Seal mail room and HVAC undersupply and
filtration option #3 in basement recirculation
Contaminant G
(gas)
78
78
78
Contaminant P
(particle)
78
78
78
Life-cycle Cost
(thousands of dollars)
34
362
895
-------
filtration option #2 (addition of dedicated outdoor air fans
with a three-stage paniculate filtration system), filtration
option #3 (addition of dedicated outdoor air fans with a
multistage filtration system, including a grade carbon gas
phase filter), sealing the building envelope, and each filtration
upgrade option in combination with envelope sealing. The
weather conditions during the simulation period were an
outdoor air temperature of 0 °C and a wind speed of 5 m/s
in order to induce a reasonable level of envelope infiltration.
The building envelope effective leakage area (at a reference
pressure of 4 Pa) is 5 cmVm2 (0.07 itf/ft2) before and 0.7
cmVm2 (0.01 inVft2) after sealing the envelope. The baseline
whole-building air change rates are 0.28 fr1 due to infiltration
and 0.89 fr1 due to outdoor air intake, for a total of 1.17
Ir1. The envelope sealing completely eliminates infiltration
in this building under the conditions modeled, leading to
a whole-building air change rate of 0.89 fr1. The filtration
removal efficiencies used in the simulations are 0 percent
for contaminant G and 5 percent for contaminant P for the
baseline case, 0 percent for contaminant G and 51.4 percent
for contaminant P for option #1, 0 percent for contaminant G
and 99.97 percent for contaminant P for option #2, and 99.5
percent for contaminant G and 99.97 percent for contaminant
P for option #3.
As seen in Table 21, the predicted reductions in the relative
exposure to an outdoor contaminant release vary widely from
no impact at all up to a greater than 99 percent reduction. For
the gas contaminant, the retrofit with the largest reduction
is filtration option #3, which includes a 99.5 percent gas air
cleaner in the outdoor air intakes, combined with envelope
sealing for a predicted reduction in exposure of over
99 percent. Without envelope sealing, filtration option #3
is predicted to have a somewhat smaller impact, with an
exposure reduction of about 84 percent. Envelope sealing
alone has almost no impact on exposure to contaminant G.
The other filtration options do not impact contaminant G
because they include only particle filtration.
For contaminant P, filtration option #2 (and #3 since they
provide equivalent particle filtration) combined with
envelope sealing is predicted to reduce exposure by over 99
percent. As with contaminant G, the impact of the improved
filtration is lessened if the envelope is not sealed, with
a predicted exposure reduction of about 82 percent. The
lower filtration upgrade option #1 has predicted exposure
reductions of about 40 percent and 54 percent with and
without envelope sealing, respectively. Unlike contaminant
G, envelope sealing alone is predicted to have some impact
(a 9 percent reduction) on exposure because the baseline
building includes a particle filter.
3.5 Discussion of Case Study
The primary goal of the case study was to apply simulation
and economic analysis to two real buildings, both to
demonstrate the analysis methodologies and to gain further
insights into the retrofits investigated. The case study has
provided useful information on the design, implementation,
and performance of selected chembio retrofits in two very
different buildings — a high-rise office building with
central air handling systems and a one-story office building
with multiple rooftop units. The technical and economic
analysis in the case study highlights the building-specific
nature of the design and analysis of the retrofit options, such
as multiple levels of filtration, and their associated costs
and other economic impacts. In addition, the case study
analysis shows the possibility of completely eliminating
exposure to a threat such as the outdoor release by applying
a combination of improved filtration and envelope sealing.
However, the economic analysis indicates the relatively high
cost of accomplishing this level of protection. Information on
potential performance and costs such as those presented here
are both critical to decision makers.
In some cases, examination of the results beyond average
exposures yields additional insight into the potential retrofit
effectiveness. For example, the lobby retrofits result in
Table 21 Relative Exposure and Life-Cycle Cost for Selected Retrofits in One-Story
Office Building (outdoor release)
Exposure Relative to Baseline (%)
Retrofit
Filtration option #1
Filtration option #2
Filtration option #3
Envelope sealing
Filtration #1 with envelope sealing
Filtration #2 with envelope sealing
Filtration #3 with envelope sealing
Contaminant G
(gas)
100
100
16
100
100
100
0
Contaminant P
(particle)
60
18
18
91
46
0
0
Life-cycle Cost
(thousands of dollars)
72
538
926
32
104
570
958
-------
reductions in average exposure of up to 92 percent, but the
average exposure after retrofit is distorted by differences
between occupant exposure in the lobby zone and occupant
exposure in the remainder of the building. The reduction in
exposure to occupants of nonlobby zones ranges from
97 percent to more than 99 percent for the cases that include
filtration option #3. Thus, this modification achieves nearly
complete isolation of the lobby, which is its intent. However,
the retrofit could not protect the lobby occupants from a
release in that zone.
The results also show the importance of considering
effectiveness and costs of potential combinations of retrofits.
For example, sealing the envelope of the one-story office
building has a minimal impact on occupant exposure to an
outdoor release of contaminant P and no impact on occupant
exposure to contaminant G. However, when combined
with filtration, envelope sealing substantially improves the
effectiveness of the filtration retrofits on both contaminants
while increasing first costs by less than 10 percent and
potentially decreasing operating costs by reducing building
heating and cooling loads.
-------
-------
4.0
Guidance
This section presents guidance on the application of
retrofits to better protect buildings from chembio releases.
The purpose of this guidance is to present available options
for retrofitting existing buildings for improved chembio
protection and to discuss where these options are most
applicable, the potential benefits and associated costs,
and the extent of our current understanding regarding
their application and performance. The information in
this section is based on information in the literature, other
guidance documents, and the results of the technical
evaluations conducted in this study.
When considering the retrofit of a specific building, it is
critical to note that the unique features of the building and
its systems must be considered when implementing the
retrofit and in forming expectations as to the level of
protection that will be realized. Also, while it is more
straightforward to define and design protection systems for
a particular release (primarily its location and timing), it is
rare that such advanced knowledge can be expected to exist.
The undefined nature of the threats that need to be considered
make retrofit selection and design far more challenging and
limit the ability to quantify or "guarantee" any particular
degree of protection. Nevertheless, this guidance is based
on the philosophy that increased protection is a goal worth
pursuing, even if the degree of improvement cannot be
quantified in advance.
In addition to achieving the improved understanding of
retrofit options that will result from the information presented
below, there is another key step in the decision-making
process regarding a specific building. Before one decides
which retrofit options to implement, it is critical to assess the
risks to which the building may be exposed. Risk assessment
is a well-established process and needs to be carried out
to determine the potential likelihood of an event and the
associated costs and other impacts if an event does occur.
While risk assessment methods and the linkage between
the outcome and the resulting actions are beyond the scope
of this report, there is some useful discussion in ASHRAE
(2003) and FEMA (2005).
This section is organized into three parts, beginning with
actions that generally make sense under any circumstance.
Most of these actions are consistent with good building and
system operation and maintenance and therefore may be
considered part of good practice. The next two groups are
organized into retrofit technologies and retrofit approaches.
As discussed in Section 1 of this report, the former category
refers to specific off-the-shelf technologies, such as filtration
and air cleaning devices, while the latter refers to more
generic approaches to increasing building protection, such
as building pressurization and isolation of spaces of potential
concern (e.g., mail rooms).
4.1 General Guidance
There are a number of actions that can be beneficial under
almost any circumstance. In many cases, they are associated
with only modest costs and sometimes yield additional
benefits in terms of reduced energy consumption and
improved indoor air quality. Many of these actions have
been advocated in prior publications on building protection
(ASHRAE 2003a, NIOSH 2002, Price et al. 2003). They tend
to focus less on specific threats and more on sound building
operation and maintenance practices that can support the
successful implementation of specific chembio protection
strategies and greatly increase the likelihood that any
particular response strategy will perform as intended.
4.1.1 Understand the Building
Regardless of the degree of risk to which a particular building
may be subject, it is always a good idea to understand the
building. In this case, the term "understand" refers to several
issues including the layout of the building, the activities
within, and what is going on outside the building. As every
building is unique to some degree, it is hard to develop a
general list of parameters to assess but the following list
provides some sense of the type of information that is
relevant. The EPA Building Air Quality manual also provides
useful guidance for characterizing a building (EPA 1991).
Building layout
Entrances: Identify where people enter the building,
including "nonstandard" entrances such as loading docks,
side entrances, and parking garages.
Ground level airflow paths: Identify accessible locations
where air can enter a building, including but not limited
to outdoor air intakes. Also consider entrances, loading
docks, and emergency doors where a negative pressure
will pull air into a building.
Space types and occupancy levels: Determine what
different types of spaces exist in a building (offices,
classrooms, meeting rooms, etc.) and where the occupants
are generally located.
Building activities
Occupancy patterns: Identify where and when people
arrive and leave the building. Is there a predictable
schedule? Be sure to consider evenings and weekends.
Occupant activities: Be aware of what people are
doing in the building, the activities likely to generate
contaminants that might be harmful or perceived as
harmful to occupants, and when these activities take place.
Outside the building
Pedestrian and motor vehicle traffic: Is the building
located in an area of high pedestrian or motor vehicle
activity?
-------
Nearby sources: Is the building close to other high-
profile buildings, or to industrial facilities, transportation
stations, roadways, or train tracks where an intentional or
unintentional release could occur?
In terms of building protection in particular, vulnerability
assessment methods that will address some of the security-
specific issues are being developed (LBNL 2004).
4.1.2 Understand the System
Whether or not one anticipates using the building ventilation
system as part of a protective strategy, it is important to
understand the system as it is designed to operate and as it is
actually operating. Again, each building and its ventilation
system is unique to some degree, but some basic information
needs to be assembled and understood. The EPA Building
Air Quality manual again provides some useful guidance
on ventilation system characterization (EPA 1991). In some
cases, these actions may require assistance from individuals
such as TAB contractors or engineering consultants, who are
not part of the building operating staff.
System design
Documentation: Assemble mechanical drawings and fan
specifications; these may not be on-site and are often out
of date; if so, current drawings and system specifications
are important resources that should be developed as soon
as resources can be acquired for such an effort, which
can be quite involved in many buildings; assemble any
existing TAB reports.
Air handler design information: Design supply, return,
and outdoor air intake airflow rates; areas served by each
air handler; and specified levels of filtration.
Exhaust systems: Design airflow rates, areas served,
operating schedules, and location of on/off controls.
Sequence of operations: Determine how systems are
intended to operate per time of day, outdoor temperature
and humidity, and season of the year, including
modulation of outdoor air intake and supply airflow rates.
This effort also includes understanding fire alarm systems,
smoke control modes, and any available purge cycles.
System operation
Airflow rates: Evaluate supply, outdoor, and exhaust
airflow rates relative to design values and modulation
of same, based on time of day and outdoor conditions,
again relative to design sequence of operations.
Building pressures: Assess indoor-outdoor pressure
differences at entrances and ground level airflow paths
under different conditions of weather and ventilation
system operation; at a minimum, assess the direction
of the pressure difference; assess pressure differences
between key spaces (e.g., lobbies, mail rooms, parking
garages, and loading docks) and the surrounding spaces
of the building to determine whether air will flow
from these spaces into the rest of the building (include
consideration of different weather conditions).
4.1.3 Inspect the System
Achieving good system operation requires inspecting the
system components to ensure that they are in good working
condition. Again, the Building Air Quality guidance
document (EPA 2001) contains sound recommendations on
the aspects of such an inspection. A more detailed inspection
protocol was developed for the EPA Building Assessment,
Survey, and Evaluation (BASE) Study (EPA 2003, Persily
1993). The components that should be considered in such an
inspection include the following:
• Outdoor air intakes: cleanliness, open per the
operating schedule
• Intake dampers and damper linkages: functioning
as designed, able to open and close
• Fans: general condition
• Cooling coils: general condition, including cleanliness
• Drain pans: cleanliness, rust, existence of standing
water and/or microbial growth
• Air filters: general condition, condition of seals
and existence of bypass
• Temperature, humidity, and pressure sensors used
by building control systems: general condition
4.1.4 System Tune-up
Based on the information gathered through these efforts to
understand the building and its systems, the next step is to
make the adjustments necessary to bring the system operation
in line with the original design intent and current needs. Such
"recommissioning" is likely to improve energy efficiency
and indoor air quality and is discussed as a retrofit option in
Section 4.3.
4.2 Retrofit Technologies
This section presents guidance on several specific retrofit
technologies. The guidance includes a brief description
of the technology, including how it functions and how it's
applied; a discussion of existing performance data, the
protective impact that can be expected from its application,
and the associated costs; and finally information gaps
regarding the technology. The information presented here
reflects the current state of knowledge, but much research
and other activity is currently occurring in the area of
building protection. It is expected that more information on
these technologies will be produced in the future and new
technologies will become available. Therefore, it is important
that building designers, owners, operators, and others
responsible for building protection stay abreast of current
developments in this rapidly changing area.
4.2.1 Enhanced Particle Filtration
Objective
To increase the removal of paniculate contaminants from
HVAC system airstreams through the use of higher efficiency
particle filters than those currently in place.
-------
Description
Assuming that an air handler has at least some minimal level
of particle filtration (generally used to keep cooling coils
and other system components clean), this retrofit involves
replacing the existing filters with higher efficiency particle
filters. There are two distinct situations in which this retrofit
can be implemented. In the first case, the new filters are
installed in the existing filter racks (perhaps with some slight
modifications), such that the pressure drop associated with
the higher efficiency filters is compatible with the existing
fans and motors. In other cases, the pressure drop associated
with the new filters is too high for the existing system and the
fans, motors, and/or electrical systems need to be modified.
A great deal of information is available on particle
filtration, including general discussions of the technology
and its application (ASHRAE 2000, NAFA 2001), as well
as guidance specific to chembio protection of buildings
(NIOSH 2003). As noted in these references, there are
three primary types of paniculate air filters: mechanical,
eletrostatically charged, and electronic. Mechanical filters,
which are sometimes referred to as media filters and include
familiar panel, bag, and pleated filters, capture particles
via three predominant mechanisms. The first mechanism
is impaction, where particles collide with the filter media
instead of flowing around the filter fibers and then become
attached to the media. Interception is similar to impaction,
but rather than colliding directly with the filter fiber, the
particle comes in close contact with the fiber as it moves
along with the airstream and the forces of attraction result in
the particle sticking to the fiber instead of continuing to move
with the airstream. Smaller particles can also be captured by
diffusion, where random movement of the particles relative
to the airstream causes them to come in contact with the
filter media and become attached. Figure 11 shows a generic
curve of particle removal efficiency as a function of particle
size or diameter. (An efficiency of 1.0 means that the filter
removes all of the paniculate matter that flows into the filter,
while a lower efficiency removes the corresponding fraction
of the incoming paniculate matter.) In general, diffusion is
most effective with smaller particles, while impaction and
interception are most effective at larger diameters. This
difference results in a dip in removal efficiency in the range
of 0.2 ^im, which is a particle size that tends to penetrate
fairly deeply into the human respiratory system.
The use of eletrostatically charged media can potentially
increase particle removal through the interaction of charged
media and naturally charged particles. There are multiple
approaches to charging the media, and in all cases the
performance can be impacted by humidity, time of service,
exposure to various airborne contaminants, and dust buildup
(or loading) on the filter. Electronic air cleaners employ
electrostatic precipitation in which an electric charge is
imparted to particles as they pass through an ionizing
section of the device. The particles are then collected onto
alternately charged plates downstream of the ionizing section.
The removal efficiency of these devices is impacted by
particle size, air speed, ionizing and collector plate voltages,
spacing of the ionizers and collector plates, and coating of
the ionizing wires with silicon dioxide over time. Another
important consideration with these devices is their potential
to emit ozone, particularly if the ionizing wires are damaged.
The particles that are relevant to building security cover
a potentially wide range, but the focus is primarily on
biological contaminants, including microbes such as bacteria
and fungi, as well as toxins. A great deal of information
is available on the range of bioagents and their unique
characteristics in terms of size, infectiousness, and lethality
(Kowalski 2003, Kowalski and Bahnfleth 1999). The
predominant size range of interest for these contaminants
is on the order of 1 ^m, but the particle size ranges from as
small as a few tenths of a micrometer to several micrometers.
The size range is important in relation to the dependence of
filter efficiency on particle size depicted in Figure 11. Most
mechanical filters have higher removal efficiencies in the size
range of interest, i.e., 1 ^im or greater, but the existence of
smaller particles can still be an issue for some contaminants.
Figure 11 Representation of filter efficiency dependence on
particle size (NIOSH 2003)
Filter collection mechanisms
1.0
0.8 -
0.6 -
« 0.4 -
1
| 0.2 H
t*.
0
Diffusion
Regime
Diffusion and
Interception
Regime
Inertial
Impaction
and
Interception
Regime
0.01
0.1 1.0
P;H tic le Diameter (microns)
-------
Available Performance Information
Particle removal efficiencies are fairly well established,
based on the use of ASHRAE Standard 52.2 (ASHRAE
1999), which provides a rating method referred to as
Minimum Efficiency Reporting Value (MERV). The MERV
ratings are based on particle size specific removal rates
and include the effects of filter loading over time, thereby
providing more information than contained in the dust spot
efficiency and arrestance values from ASHRAE Standard
52.1 (ASHRAE 1992). MERV values range from 1 to
20, with higher values having higher removal rates. For
reference, a 30 percent dust spot filter corresponds roughly to
a MERV 8 and a HEPA filter corresponds to values of MERV
17 or higher. Figure 12 shows some sample plots of removal
efficiency as a function of particle size for a range of MERV
values. Note that ASHRAE Standard 62.1-2004 requires the
use of at least a MERV 6 filter upstream of all cooling coils
or any other wetted surface. Historically, paniculate filters
have been installed in commercial buildings to keep system
components clean, which improves the performance of heat
transfer surfaces and reduces the likelihood of microbial
growth in ventilation systems. But more recently, concerns
about indoor air quality and now building security have
renewed the consideration of higher levels of filter efficiency
(Burroughs 2005a).
While the MERV rating system has been available since
1999, many users and vendors still speak in terms of dust
spot efficiency and arrestance, the performance parameters
determined with the earlier ASHRAE test method 52.1
(ASHRAE 1992). Table 22 compares the values of the three
parameters and presents some information on the types of
filters that provide the various efficiency values.
Figure 12 Representative curves of particle removal efficiency for
various MERV Levels (Kowalski and Bahnfleth 2002)
MERV Rattn
^^^^^^_
-4
-6
-8
-9
-10
11
| •)
12
-13
-15
16
0.01
OJO 1,00
Particle diameter (mm)
10.00
-------
Table 22 Comparison of generic particulate filter efficiency values
(ASHRAE 1999)
Approximate Values From
MERV Value per ASHRAE ASHRAE 52.! R|ter Jype
Dust Spot Efficiency Arrestance
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
< 20%
< 20%
< 20%
< 20%
< 20%
< 20%
25% to 30%
30% to 35%
40% to 45%
50% to 55%
60% to 65%
70% to 75%
80% to 90%
90% to 95%
> 95%
n/a
n/a
n/a
n/a
n/a
< 65%
60% -70%
70% -75%
75% - 80%
80% - 85%
85% -90%
> 90%
> 90%
> 90%
> 95%
> 95%
> 95%
> 98%
> 98%
n/a
n/a
n/a
n/a
n/a
n/a
Throwaway media filters,
washable panel filters,
electrostatic panel filters
Pleated filters (25 mm to 125 mm thick),
cartridge filters, throwaway media filters
Bag and box filters
HEPA/ULPA filters
There have been relatively few measurements of installed
filter removal efficiencies. A recent field study by Burroughs
(2005b) included measurements in several office buildings
over one year, using particle counts up and downstream of
filters of different MERV levels. The results did verify that
the MERV ratings translated to installed performance but
also found significant leakage at the filter seals. More such
measurements are needed to better understand the factors that
determine installed performance in order to support improved
installation, operation, and maintenance practices.
Protective Impacts
Enhanced particulate filtration can reduce the exposure to
bioagents, but the impact depends on the particle diameter
of the agent, the filter efficiency at that diameter, the airflow
rate through the filter, the quality of filter maintenance, and
the filter location relative to the contaminant source and the
occupants. Given the lack of prior knowledge of the particle
size to which one might be subjected and the prevalence of
bioagents in the 1 [im range, one should expect to realize
significant protection from upgrading filtration. And since
larger particles (greater than 1 ^m in diameter) are more
readily removed by filtration than smaller ones, high-
efficiency filters (i.e., HEPA) are not necessarily required
to remove close to 99 percent of 1 [im particles. Whether
this level of removal provides an adequate level of protection
is a separate, but important, issue. At the same time, filtration
systems must be properly installed and maintained, just
like any other building equipment, to perform as expected
over time.
Given the removal efficiency of an upgraded filter relative
to the pre-retrofit filter, it is relatively straightforward to
determine the potential protective impact. However, since a
filter will remove only contaminants that flow through it, the
filter location relative to the contaminant source is critical to
the exposure reduction that will be realized. The three generic
source locations of interest are outdoors, at the air intake,
and indoors. An outdoor release that increases the ambient
concentration surrounding a building for some period of time
will result in contaminant entering the building through the
intake (filtered) and through envelope leakage (unfiltered).
(Intake air that bypasses the filter due to poor filter sealing
is discussed below.) The amount of contaminant that enters
-------
the building with the intake air will be reduced by an
amount determined by the filter removal efficiency relative
to the pre-retrofit value, but the actual exposure reduction
will be impacted by the amount of envelope leakage or
infiltration relative to the amount of air intake. Assuming
that no contaminant is removed by the building envelope (a
conservative assumption because some contaminants will be
"filtered" by the envelope), and ignoring filter bypass as well
as particle loss due to deposition onto building surfaces, the
impact on the exposure reduction depends primarily on the
ratio of the envelope infiltration airflow to the outdoor air
intake airflow.
One can express the "effective" filter efficiency as a function
of the rated or nominal efficiency e of the filter and the ratio
of the airflow entering the building via infiltration QINF to the
airflow entering via the system intake QINT as follows:
Equation 1 g
Effective filter efficiency =
Q
INF
Q
+ 1
INT
The rated efficiency e is the removal efficiency of the
device itself (based on a test performed in accordance with
ASHRAE 52.2), again without any filter bypass, while the
effective efficiency is the removal efficiency on a whole-
building scale adjusted for the entry of unfiltered infiltration
air. In other words, the effective efficiency is the removal
efficiency based on the total amount of air entering the
building, not just the intake airflow through the filter.
Figure 13 depicts the dependence of the effective filter
efficiency on the rated or nominal efficiency for different
values of the ratio of infiltration to intake airflow for
an outdoor release. Therefore, if there is no infiltration
(QINF/QINT = 0), then the effective efficiency is the same
as the rated efficiency. As the infiltration rate increases
relative to the intake rate, the effective efficiency decreases
relative to the rated efficiency. For example, if infiltration
and intake are equal, which is a reasonable first order
assumption for a typically leaky commercial building, the
effective efficiency will be one-half of the rated efficiency.
Envelope infiltration can be thought of as a form of filter
bypass, i.e., air that flows around a filter instead of through
it and thereby is not exposed to the particle removal
processes of the filter. When a contaminant is released
directly at or into an air intake, entry via infiltration no
longer plays a role and the impact of the filter is
determined directly by the rated efficiency of the filter.
Depending on the quality of the filter installation and
maintenance over time, airflow bypass around the filter
can often be significant (Burroughs 2005a). As in the case
of infiltration, airflow that bypasses the filter will not have
any contaminant removed, again degrading the effective
efficiency of the filtration system. Figure 14 is similar to
Figure 13 but includes the impacts of bypass fractions of
5 percent and 10 percent to show the impacts on effective
efficiency. A bypass fraction of 5 percent means that
5 percent of the airstream intended to go through the
filter actually flows around it.
Figure 13 Impact of infiltration on effective filter efficiency
20
40 60
Rated or nominal filter efficiency (%)
100
-------
The figure shows that bypass has slightly more significant
impact when the infiltration-to-intake ratio is low, but clearly
shows the degradation performance due to filter bypass.
By considering a building airflow system as a single zone, the
relative exposure to an outdoor release given an upgrade in
filtration from an efficiency BI to a higher efficiency e2 can be
expressed as follows:
Equation 2 Q
1-e,, +
•HNF
Relative exposure =
Q
'INT
Q
•INF
Q
•INT
Therefore, if there is no infiltration, the relative exposure
is the ratio of 1 minus the "new" efficiency divided by
1 minus the "old" efficiency. For example, in the simulations
of the two-story office building presented in Section 4 with
no weather (QINF = 0), el = 16.4 percent and e2 = 89.6 percent.
Equation 1 therefore yields a relative exposure for the
higher efficiency relative to the lower efficiency of 12.4
percent, which is the same value as in Table 8. For nonzero
values of QINF, the relative exposure increases, reflecting
the degradation in performance for the higher efficiency
filtration. In that same example, with weather included, the
infiltration rate is 0.22 fr1, and the ratio of QINF to QINT is 0.58.
Equation 2 now yields a relative exposure of 48 percent,
which is very close to the value in Table 9.
Table 23 shows the relative exposure as defined by Equation
2, with lower values corresponding to less exposure with
the "new" filter relative to the "old" filter. The first column
shows the before and after MERV levels, while the second
shows the relative exposure assuming no infiltration. The
beneficial impacts are seen clearly, with the most significant
reductions seen for MERV values of 13 and higher. The third
column shows the relative exposure assuming an infiltration
rate equal to the intake rate for a general outdoor release,
which shows that without addressing infiltration, even the
highest filter efficiency retrofits are of limited effectiveness.
Relative exposure based on removal efficiency at roughly
1 ^imis as follows:
MERV 6 = 16.4 %, MERV 8 = 40 %, MERV 11 = 55.5 %,
MERV 13 = 89.6 % and MERV 16 = 99.5 %.
Figure 14 Impact of bypass on effective filter efficiency
20
40 60
Hated or nominal filter efficiency (%)
SO
JOO
-------
Table 23 Impact of enhanced filtration on exposure to outdoor release
Relative Exposure (%)
Filter Upgrade
No Infiltration Infiltration = Intake
MERV 6 to 8
MERV 6 to 11
MERV 6 to 13
MERV 6 to 16
MERV 8 to 13
MERV 8 to 16
71.8
53.2
12.4
0.6
17.3
0.8
87.1
78.7
60.1
54.7
69.0
62.8
The impacts of filtration in the mixed airstream, a common
location of particle filters in most air handling systems,
can also be quite significant. Generally, the airflow rate
that passes through a mixed air filter is roughly five times
higher than the outdoor air intake that passes through an
outdoor air filter (except under 100 percent outdoor air
operation). Therefore, mixed air filtration can remove more
contaminant from the building for a given level of filtration
once the contaminant has entered the building from an
outdoor or indoor release. As seen in the simulations, retrofit
effectiveness values (i.e., exposure with retrofit relative to
exposure without) on the order of 10 percent or even less can
be realized by filtration of the mixed airstream. But the actual
reduction is ultimately a function of the pre- and post-retrofit
filtration efficiency, the airflow through the system, and, of
course, the quality of the installation and maintenance.
When a contaminant is released within the building, the
location of that release relative to the occupants and the filter
location becomes critical. If the occupants are very close to
the release, filtration of the recirculation air may have little
or no impact on their exposure. If the release is located such
that the contaminant is drawn back via the return system to
the filter before being distributed to the rest of the building,
then recirculation filtration will be more effective overall.
However, occupants in the immediate vicinity of the release
may still be significantly exposed to the contaminant.
In addition to the rated efficiency of a filter, the air seal of
filter installations is critical to their installed performance
and must be addressed regardless of the current or retrofit
level of filtration (Burroughs 2005b). In fact, improving the
seal of existing filters may have a more significant benefit
than replacing the filters with higher efficiency filters without
addressing bypass. Filter seal is generally addressed in the
installation of higher-efficiency, e.g., HEPA, filters, but
maintenance of the seal over time is always an issue and
routine inspection of the filter seal should be part of normal
maintenance practice.
Costs
Like most building retrofits, the cost of enhanced filtration
is a combination of first costs and operating costs. Specific
examples of both are highlighted in the case study as
described in Section 3 and Appendix C, and the software
tool developed as part of this project provides the means for
properly accounting for all these costs in determining the
life-cycle costs of enhanced filtration and other retrofits.
These costs, specifically the interactions between first costs
and operating costs, are discussed in NIOSH (2003) and
Arnold et al. (2005).
First costs include the following:
• Filters
• Design work (in cases where system modifications are
required)
• Reconfiguration of filter racks (where required)
• Modification of air handling system fans, motors,
electrical (where required)
Operating costs include the following:
• Filter replacement and maintenance (incremental
above replacement costs of existing filters)
• Increased electrical consumption (when new filters
increase pressure drop and require more powerful fans)
Enhanced particle filtration has the potential for improving
indoor air quality, which has been associated with increased
occupant productivity (Fisk and Rosenfeld, 1997). While
difficult to quantify, increased productivity would correspond
to an economic benefit associated with better filtration. Better
filtration can also reduce dirt buildup on heat transfer surfaces
and result in better system efficiencies over time. These
benefits are also difficult to quantify but nonetheless can be
quite real. In addition, better filtration can improve overall
building cleanliness, potentially reducing housekeeping costs.
In the event that a release occurs, filtration can also reduce
the extent and cost of the follow-up decontamination effort.
Knowledge gaps
There are several areas where additional information would
increase our understanding of the impacts of enhanced
paniculate filtration. One is measurement of installed
performance as a function of system type and configuration,
filter type, and length of time since installation. As noted
earlier, there is very little field performance information,
and such measurements provide the only means of verifying
the actual impact of filtration in real buildings. In addition,
field measurements of filter bypass would also be useful and
could be related to different approaches to filter installation
-------
and sealing. Better understanding of the IAQ benefits of
improved filtration could also lead to better cost-benefit
decisions.
Summary
The addition or enhancement of particle filtration can
significantly reduce exposure to outdoor and indoor releases.
As revealed by the simulations discussed in Section 2 of this
report and in Table 23, upgrading from typically minimal
filtration levels of MERV 6 or 8 to MERV 13 or higher can
reduce the exposure to about 10 percent of the pre-retrofit
case, based on consideration of contaminant entry through
the intake alone. These simulations also show the advantages
of mixed air filtration over outdoor air filtration alone,
with the latter not having any impact on indoor releases.
Contaminant infiltration via envelope leakage can drastically
decrease the effectiveness of improved filtration, though the
reduction is difficult to predict without reliable estimates
of infiltration rates. The same degradation in the impacts of
improved filtration can also occur when filters are poorly
sealed in their frames, either initially or over time as seals
deteriorate. It is generally more important to first deal with
the integrity of these seals before upgrading the filters, and
the same may hold true for envelope airtightness as well.
The levels to which filtration can be enhanced are dependent
on the air handling system. Fan coil units, small rooftop
units, and other unitary systems often have limited space
for deeper filters and limited fan power to overcome the
increases in airflow resistance associated with better filters.
This situation was seen in the case study of the one-story
office building with rooftop units. When increased protection
is needed under such circumstances, it can be a challenge
to achieve it through filtration. Larger systems are generally
more adaptable to higher levels of filtration, though system
modifications to the filter racks and air handler housing, as
well as new fans and motors, may be required.
An advantage of enhanced filtration relative to some other
retrofits is that it is always working, as opposed to strategies
that rely on an operator-based response such as system
shutdown. The sensitivity of shutdown and other strategies
to timing was seen in the retrofit analysis, but no such timing
issues exist for filtration. Also, filtration is relatively simple
in that there are no moving parts and as long as air is brought
to the filter, it will remove contaminant. In addition, particle
filtration is part of current practice and the technology
is widely available. Therefore, there are no dramatically
new skills required of designers, installers, or operators as
there would be for some other retrofits. The same applies
to maintenance, as filter replacement is also part of current
practice. Finally, unlike some retrofit strategies such as
system shutdown in the event of an interior release, enhanced
filtration shouldn't increase exposure under any scenario.
4.2.2 Sorption-based Gaseous Air Cleaning
Objective
To remove gaseous contaminants from ventilation airstreams
through the use of adsorptive media that capture these
contaminants physically or chemically.
Description
Sorption-based gaseous air cleaning is currently employed
in a number of applications to control odorous, corrosive,
or otherwise undesirable gases generated within or outside
of buildings. A variety of sorbents are employed, including
activated carbon, alumina, and sorbents impregnated
with compounds to remove specific contaminants. The
effectiveness of these sorbents depends on the particular
sorbent-contaminant combination and the design of the
system that brings the air into contact with them. Gaseous air
cleaning devices are not typically employed in commercial
and institutional buildings, but they are seeing increasing use
in a number of applications such as manufacturing facilities
and museums and are receiving increased attention based
on concerns about building security. A significant amount of
information is available on gaseous air cleaning, including
general discussions of the technology and its application
(ASHRAE 2003, NAFA 2001), as well as its use in chembio
building protection (Kowalski 2002, NIOSH 2003).
Gas phase air cleaning systems remove contaminants through
either physical adsorption or chemisorption. Physical
adsorption is based on the attractive van der Waals forces
between the gas molecules and the sorbent surface, with
the removal capacity dependent on the surface area of the
sorbent. That dependency is the reason that porous materials
with high surface-to-volume ratios, such as activated carbon,
are so effective. Physical adsorption is a reversible process,
and therefore temperature has a strong effect on sorption
rates, resulting in lower removal efficiencies at higher
temperatures. In addition, other gas molecules will compete
for the available sorption sites. Water vapor acts as one such
competitor, and therefore elevated humidity has a significant
effect on the rate of adsorption, particularly for activated
carbon. Chemisorption involves chemical reactions between
the adsorbent surface and the gas molecule, resulting in better
retention of the contaminant than physical adsorption alone.
To induce chemisorption, adsorbents are impregnated with
various chemicals that target certain chemical classes such as
acid gases or specific chemicals such as chlorine.
The gaseous contaminants that are relevant to building
security cover a wide range, including nerve agents and
toxic industrial chemicals. No single sorbent or chemical
impregnant is able to remove all contaminants effectively,
and therefore a combination of sorbents is needed to
fully protect a building and its occupants. Some common
adsorbent materials include activated carbon, silica gel,
alumna, and zeolites, while chemical impregnants include
potassium permanganate, phosphoric acid, copper and silver
salts, and zinc oxide.
In addition to the specific adsorbent material and contaminant
of concern, the removal efficiency of a gas phase air cleaning
system depends on the surface area of the sorbent particles,
the residence time in the adsorbent bed, and the presence of
other airborne compounds that compete for adsorption sites.
The residence time depends on the media bed depth and the
airflow rate through the bed. A deeper bed, while increasing
residence time, also increases the pressure drop through the
-------
system. The adsorptive capacity of a system, which translates
to service life, depends on the mass of adsorbent employed
and the contaminant concentrations, including humidity, to
which the adsorbent is exposed. These contaminants include
both the contaminants the system is intended to remove and
others that compete for adsorption sites.
Available Performance Information
There are currently no standard test methods for determining
the contaminant removal efficiency of gaseous air cleaning
equipment for use in specifying and sizing these systems.
Manufacturers have performance data and experience in
a variety of forms that can be useful, but there is not yet
the equivalent of a MERV rating for gaseous air cleaning.
ASHRAE committee 145P is working on a method of test for
gas-phase air cleaning media, which should be available soon
for establishing the performance of different media, using a
consistent methodology. That committee is also working on
a method of testing full-scale air cleaning media beds, which
will also be very helpful in the application and specification
of such systems.
The performance of gas phase air cleaning is often
described in terms of breakthrough curves. These curves
are determined for an adsorbent/contaminant combination,
using a test apparatus in which an airstream containing a
known concentration of the contaminant flows through the
adsorbent bed. Breakthrough is generally defined as the
condition where the contaminant concentration downstream
of the air cleaning device reaches some specific fraction of
the upstream or challenge concentration, presumably because
the air cleaner sorptive capacity has been exceeded. The
breakthrough time is then the time between the initial
contact of the contaminant with the adsorbent and the
time when breakthrough has occurred at some fraction
of the challenge concentration, for example 50 percent.
Figure 15 is a representative breakthrough curve, which
plots the ratio of the downstream concentration to the
upstream or challenge concentration as a function of time.
Initially, very little contaminant gets past the air cleaner,
but after sufficient time, the media capacity is exhausted
and the contaminant "breaks through" to the downstream
side of the system. Breakthrough curves are often
determined at relatively high challenge concentrations
in order to complete the tests in a manageable amount of
time. Such breakthrough test results need to be related
to the performance at lower and perhaps more realistic
concentrations. Nevertheless, breakthrough curves can be
generated as a function of chemical properties, bed depth,
and other system design parameters.
Another key performance parameter is the service life of
the filter media, which depends on the mass of adsorbent
in the system, the exposure of the media over time to
temperature and humidity swings, and the exposure over
time to contaminants such as those normally found in air.
Service life can be determined analytically for a single
contaminant (NAFA 2001), but the influence of other
airborne contaminants makes the determination more
complicated in practice. Media manufacturers therefore
use other approaches, such as analyzing a media sample
from an installation to assess its remaining capacity,
in-place gas monitoring, or simply experience from
other installations, to estimate service life.
100
Figure 15 Representative breakthrough curve
S?
Nw'
E
«
I
ir>
C.
£ 50
'ft
o
0 *•
Time
-------
Protective Impacts
Gas phase air cleaning can reduce the exposure to chemical
contaminants, with the impact dependent on the removal
efficiency and the relative locations of the source, air cleaning
system, and occupants, as discussed for particle filtration.
Also, as in the case of particle filtration, gas phase air cleaning
systems must be properly installed and maintained to achieve
the intended performance.
The discussion of potential protective impacts in the previous
section on particle filtration is also relevant here. The major
difference is that the pre-retrofit removal efficiency is generally
zero for gaseous contaminants and the post-retrofit efficiency
is a function of the system employed (specifically the sorbent
medium and its mass) and the specific contaminant being
considered. Depending on the media, contaminant, system
design, and time and conditions since installation, the
removal efficiency can vary from 0 percent to 100 percent.
The issues of filter bypass and building envelope infiltration
are the same for gaseous air cleaning as they are for
paniculate filtration. Equation 1 describes the relative
exposure for an upgrade in particle filtration, given an
outdoor release, as a function of pre- and post-retrofit
removal efficiency and the infiltration-to-intake ratio. That
expression still applies here, with EJ = 0 percent and e2 set
equal to the gaseous removal efficiency e, as follows:
Equation 3
Relative exposure =
1-8 +
Q
INF
Q
INT
1 +
Q
INF
Q
INT
Table 24 shows the relative exposure for 100 percent and
95 percent efficient gaseous air cleaning. Again, envelope
infiltration significantly degrades the impact of air cleaning.
Table 24 Impact of gaseous air cleaning on exposure to outdoor release
Relative Exposure (%)
Removal Efficiency
No Infiltration Infiltration = Intake
100%
95%
0.0
5.0
50.0
52.5
When the contaminant is released within the building, the
location of that release relative to the occupants and the air
cleaner becomes critical. If the occupants are very close to
the release, air cleaning of the recirculation air may have
little or no impact on exposure. If the release is located such
that the contaminant is drawn back via the return system to
the air cleaning system before being distributed to the rest
of the building, then air cleaning will be more effective.
However, occupants in the immediate vicinity of the release
may still be seriously exposed to the release.
Costs
The cost of gas phase air cleaning includes the first and
operating costs listed below. Specific examples of both are
highlighted in the case study as described in Section 3 and
Appendix C.
First costs include the following:
• Air cleaning system
• Additional space for system (in some buildings, there
may be costs associated with floor space based on the
loss of rentable space)
• Design work (system modifications are generally
required for gas phase air cleaning)
• Modification of air handling system fans, motors,
electrical
Operating costs include the following:
• Media replacement
• Increased electrical consumption (associated
with increased pressure drop)
In general, gaseous air cleaning systems are associated
with a more significant pressure drop than particle filtration
devices. These larger pressure drops may in turn require
significant system modifications, including replacement of
fans and motors as well as associated electrical upgrades.
As was the case for enhanced particle filtration, gas phase
air cleaning also has the potential for improving indoor air
quality, which may increase occupant productivity.
Knowledge gaps
Test standards and associated rating systems are the primary
needs in the application of gas phase air cleaning. As noted
above, an ASHRAE committee is working on a method of
test for media, to be followed by a full-scale test method.
Additional information is also need to better predict and
determine media replacement schedules as a function of
system design parameters and exposure history of the media.
Summary
Gas phase air cleaning in outdoor air intakes can reduce
exposure to outdoor releases of gaseous contaminants based
on the removal efficiency for the particular contaminant of
concern. As seen in the simulations (Section 2) and Table 24,
air cleaning can reduce exposure on the order of 1 minus the
filter efficiency given contaminant entry through the intake
alone. Envelope infiltration can significantly decrease the
effectiveness, with the degradation dependent on the ratio
of the infiltration rate to the intake.
Due to the pressure drop and filter depth associated
with current gas phase technology, fan coil units, small
rooftop units, and other unitary systems are generally not
compatible with this retrofit technology. Larger systems are
-------
generally more easily adaptable to gaseous air cleaning, but
modifications may still be required. When designing a gas
phase air cleaning installation, it is important to consider the
interactions with other system components. For example,
locating particle filters upstream of the air cleaning system
will protect gas phase sorbent media from being "fouled"
by paniculate matter. In addition, many adsorption systems
are negatively impacted by humidity; therefore, it is often
preferable that cooling coils be located downstream from
the air cleaning system.
As was mentioned for particle filtration, gas phase air
cleaning has the advantage that it is always working, as
opposed to strategies that rely on an operator-based
response such as system shutdown. However, it is
important to remember that a gas phase air cleaning
system will generally achieve different levels of
effectiveness for different contaminants.
4.2.3 Ultraviolet Germicidal Irradiation (UVGI)
Objective
To kill or otherwise deactivate biological contaminants
through the use of ultraviolet irradiation of the airstream
passing through the device.
Description
UVGI systems have been used for many years to kill airborne
infectious contaminants (viruses, bacteria, and bacterial and
fungal spores) in healthcare facilities and other venues, with
many applications focused on controlling the transmission
of tuberculosis. These devices use ultraviolet irradiation in
the 250 nm to 260 nm wavelength range (the so-called "C"
band of the UV spectrum, sometimes referred to as UVC)
and are either installed in the upper portions of a room, with
shielding to protect the occupants, or in ductwork. The use
of these devices in healthcare facilities has been described
previously and application guidelines have been published by
the Centers for Disease Control and Prevention (CDC 1994,
1999a, and 1999b). More recently UVGI has been advocated
for more general application as an indoor air quality control
measure to keep ventilation system components, particularly
cooling coils, clean by reducing microbial growth in air
handling units (Dillard 2004). UVGI is also being proposed
for protecting buildings against bioagents in the event of an
intentional release (Kowalski and Bahnfleth 2003).
Available Performance Information
The effectiveness of these devices is typically expressed
in terms of deactivation rate, which is primarily a function
of device geometry, intensity of the light source, microbial
resistance of the bioagent of interest, and residence time of
the agent in the field of irradiation. Inactivation or "kill" rates
can be predicted with a fair level of reliability based on these
parameters (VanOsdell and Foarde 2002). However, there is
no standard test method for determining the effectiveness of
these devices and they are not generally supplied with the
performance data to determine kill rates. Kowalski (2003)
has proposed a UVGI Rating Value (URV) from 8 to 15 that
corresponds to an average light intensity expressed in units of
mW/cm2. Based on the exposure time and the susceptibility
of a particular organism, the URV value can then be
converted to a kill rate for that organism. However, the URV
concept has not yet been promulgated in an industry standard,
nor has any other rating system of effectiveness. At this
point, UVGI systems are described primarily in terms of the
lamp specifications, including the light intensity expressed in
[iW/m2. Efforts are currently under way by the International
Ultraviolet Association (www.iuva.org) to develop standards
to assess the effectiveness of UVGI devices and systems, as
well as installation guidelines. In addition, ASHRAE Task
Group TG2.UVAS Ultraviolet Air and Surface Disinfection
is another source of information, including a future ASHRAE
Handbook chapter, potential standards, and several planned
research projects. Also, a number of devices have been tested
as part of the U.S. EPA Technology Testing and Evaluation
Program, and reports of this testing are available at http://
www. epa. gov/nhsrc/.
Protective Impacts
The protection provided by UVGI against bioagents is
analogous to that provided by any other filtration system,
i.e., dependent on the deactivation efficiency for the agent or
agents of concern. However, as noted above, efficiency rating
systems have not yet been developed. Until they are, it is
difficult to assess the degree of protection offered. Kowalski
(2003) discusses kill rates as a function of exposure time and
light intensity for a number of bioagents and has proposed
the URV referred to above. If this concept becomes accepted
by the industry and is used to rate devices and installations,
it will provide a needed means of comparing products and
systems.
Even without a rating system, the impact depends on the
airflow through the device, the quality of maintenance, and
the device location relative to the source and the building
occupants. Lamp output can also degrade over time and
is dependent on lamp temperature, therefore both effects
need to be considered in designing systems and planning
maintenance. Kowalski (2003) and others suggest combining
UVGI with particle filtration since the latter is effective at
removing larger microbes such as spores that tend to be
more resistant to UVGI.
Costs
These devices consume electrical energy and require
maintenance to keep them operating effectively. They are
associated with a fairly low pressure drop, which reduces
the impacts on fan power and the need to reconfigure
ventilation systems. Like most building retrofits, their cost is
a combination of first and operating costs.
First costs include the following:
• UV lamps, fixtures, and associated electrical components
• Design work (in cases where system modifications are
required)
• Reconfiguration of ductwork (where required)
Operating costs include the following:
• Electrical energy consumed by lamps
• Lamp replacement
-------
As noted for enhanced particle filtration, UVGI has the
potential for improving indoor air quality, which has been
associated with increased occupant productivity (Fisk and
Rosenfeld, 1997). In particular, UVGI can help control
bioaerosols in buildings, which can also decrease infectious
disease transmission, healthcare costs, and sick leave. The
use of UVGI in the vicinity of cooling coils has the potential
additional benefit of improving heat transfer and more
efficient equipment operation. All of these potential benefits
can be difficult to quantify, but nevertheless they could be
quite important.
Knowledge gaps
The most important needs in the area of UVGI are industry
standards to rate devices and installations, as well as
guidance for installation and maintenance. Efforts are
under way to meet these needs. Field evaluation of installed
systems would also be helpful in better understanding
maintenance requirements, energy consumption, and other
parameters.
Summary
The use of UVGI in ventilation systems can likely reduce
exposure to bioagents, but until a rating system is developed
and employed by the industry, it will be challenging to design
and specify these systems. In the interim, there is experience
with UVGI application in healthcare facilities and elsewhere
that should be useful in other applications.
4.2.4 Photocatalytic Oxidation Air Cleaning
(PCO)
Objective
To remove organic chemicals, including bioaerosols, from
airstreams by flowing the air past a photocatalyst irradiated
by UV light.
Description
PCO is an air cleaning approach in which titanium dioxide
(TiO2) acts as a photocatalyst when irradiated by UV light,
removing organic chemicals, including both chemical
and biological contaminants. If the photocatalytic reaction is
100 percent complete, the by-products include only water
and carbon dioxide, but complete conversion is difficult to
achieve in practice. While PCO is not widely used for air
cleaning in buildings and there are only a small number
of products on the market, it is viewed as a potentially
promising technology. PCO devices are commercially
available, primarily in stand-alone recirculating units.
They consist of a UV light source configured such that
the airflow passing through the device is exposed to
both the light and surfaces coated with the catalyst. The
photocatalytic reaction oxidizes organic compounds in
chemical contaminants and presumably in biological
contaminants as well. The effectiveness of cleaners based
on UV-PCO technology depends on the photoactivity of
the catalyst, the UV light intensity on the catalyst surface,
contact time between the contaminated airstream and
catalyst surface, the properties of organic chemicals and
biological contaminants, and environmental conditions such
as relative humidity and temperature. There are concerns that
potentially harmful chemical by-products may form during
operation due to incomplete reaction of the contaminants
and that the catalyst can become "poisoned" by exposure to
various airborne substances and thereby rendered ineffective.
Nevertheless, PCO air cleaners may be expected to have low
maintenance requirements and a long service life due to the
continuous regeneration of the catalyst during operation.
Available Performance Information
While PCO devices are commercially available, there are no
test methods or rating systems for gas or biological removal,
and the performance data that are available are limited
primarily to the results of laboratory research studies (Blake
1994 and 1997, Jacoby et al. 1996, Tompkins and Anderson
2003). However, given a removal efficiency for a particular
contaminant, the exposure reductions for a PCO device are
analogous to those for other filtration or air cleaning systems.
Specifications for stand-alone devices vary but typically
include the rated airflow capacity, UV wavelength of the
light source, expected life of the light source, efficiency
of any particle filtration included in the device, and power
consumption. However, this information cannot be used to
predict contaminant removal efficiency.
Protective Impacts
The protection provided by PCO is analogous to that
provided by other filtration systems, but without removal
efficiencies for particular contaminants, the exposure
reduction offered by PCO systems cannot be determined.
Costs
PCO devices consume electrical energy and require
maintenance to keep them operating effectively. These
devices generally have low pressure drops compared to
particle filters and sorption-based gaseous air cleaning, which
would reduce their impact on fan power when installed in a
duct system. However, questions exist as to the useful life
of the catalysts in practice and the production of undesirable
by-products associated with incomplete photochemical
reactions.
Similar to UVGI, the cost of PCO is a combination of first
costs and operating costs.
First costs include the following:
• PCO components (light sources, catalyst, associated
housings, fans for stand-alone units)
• Design work (in cases where system modifications are
required)
• Reconfiguration of ductwork (where required)
Operating costs include the following:
• Electrical energy consumed by lamps
• Lamp and catalyst replacement
As discussed for the other filtration and air cleaning retrofits,
PCO has the potential for improving indoor air quality,
which has the potential for increased occupant productivity
and reduced healthcare costs. However, PCO technology
and application is not yet sufficiently developed and
demonstrated to evaluate the magnitude of such benefits.
-------
Knowledge gaps
Similar to UVGI, standards are needed to rate PCO
systems; guidance for installation and maintenance is
also needed. However, unlike UVGI, the technology
is still under development and no standardization efforts
are yet under way to meet these needs.
Summary
Photocatalytic oxidation appears to have the potential to
reduce exposure to chemical and biological contaminants, but
until rating standards are developed, it will be challenging
to design and specify these systems. In addition, more
experience with the application of PCO in buildings will
be needed to understand the factors impacting installed
performance.
4.2.5 Work-area Treatment
Objective
To capture contaminants at susceptible work areas, e.g., in
mail rooms, before they have an opportunity to spread to the
rest of the building.
Description
A variety of devices are available for capturing and removing
particulates from work areas, e.g., mail-opening stations,
which are generally considered relative to the removal of
bioaerosols. These devices are essentially air capture hoods
combined with high-efficiency particle filtration systems.
Some of these devices also incorporate antimicrobial
elements, gaseous air cleaning components, and UVGI. Some
exhaust to the outdoors while others recirculate the filtered
air back into the occupied space. These devices are similar
in many ways to biosafety cabinets that have long been
employed in research and medical laboratories to contain
potentially hazardous substances and have well-established
application and rating protocols. Biosafety cabinets could
conceivably be used for mail opening, but it may be hard to
justify the first cost and the training required in all but the
highest-risk situations. In such cases, a separate mail-opening
facility is often used instead.
Available Performance Information
The performance of these devices can be expressed in terms
of the airflow rate and contaminant removal efficiency,
which for particle filters is fairly straightforward as noted
earlier. Gaseous air cleaning or UVGI capabilities cannot be
similarly rated due to the lack of standard test methods but
can be tested to meet the needs of a particular application.
Another important parameter is the contaminant capture
effectiveness, but this parameter is not generally covered
in product specifications. Test methods for the capture
efficiency of laboratory fume hoods exist (ASHRAE 1995)
and could be applied to these devices as well, but the product
literature does not make reference to capture efficiency or
fume hood testing.
Protective Impacts
The protection provided by a work area treatment device
will depend on the capture efficiency and the filtration/air
cleaning removal efficiency for the contaminant of concern.
With good capture and filtration, such a device should be able
to capture essentially all of the contaminant. The exposure
from any contaminant that is not captured will impact the
personnel in the work area based on the airflow patterns in
the room, and then the rest of the building occupants based
on the quantity that isn't captured and the interzone airflows
within the building. It is good practice to maintain mail
rooms and other such spaces at a lower pressure than the rest
of the building, which should minimize transport to the rest
of the building and exposure of other building occupants.
Note that typical locations of mail rooms on the lower levels
of buildings make them particularly susceptible to stack-
driven airflows upward within the building.
Costs
The costs of these work area treatment devices include the
first cost of the device, the electrical energy consumed by the
fans, and the replacement costs of the filter elements. In the
event of a contaminated piece of mail entering a building,
these devices can prevent contamination of the building and
thereby save a great deal of money associated with building
decontamination.
Knowledge gaps
It would be helpful if these devices were rated for capture
efficiency of gases and particles so that devices could be
compared. Also, while paniculate removal efficiency can be
described, the performance of gaseous air cleaning and UVGI
cannot be quantified for these devices.
Summary
Work area treatment devices offer the possibility of capturing
contaminants released by a piece of mail or other package
entering a building. If effective, they can essentially eliminate
occupant exposure. Even if not 100 percent effective at
capturing the contaminant release, in combination with
depressurization of the impacted space, they can limit
exposure of other building occupants.
4.3 Retrofit Approaches
This section covers retrofit approaches to increase building
protection against airborne chembio releases. As described
earlier, these approaches do not consist of a single technology
but rather involve a change to a building or its systems or an
operational strategy intended to reduce exposure. As in the
previous section, the guidance includes a brief description
of the approach, a discussion of relevant performance data
and the protective impact that can be expected from its
application, the associated costs, and current information
gaps. As in the case of the retrofit technologies, it is expected
that more information on these approaches will be produced
in the future and that new ones may become available.
Therefore, it is important that building designers, owners,
operators, and others responsible for building protection stay
abreast of current developments.
-------
4.3.1 System Recommissioning
Objective
To improve building and system performance by evaluating
existing systems relative to their design and current building
conditions and then making modifications to equipment and
maintenance procedures deemed necessary by the evaluation.
Description
Relying on a building ventilation system to increase building
protection from a chembio release requires that the system
design be understood and that the system be operated and
maintained as intended. Ventilation system recommissioning
is a process by which a system's operation is evaluated
and then brought into line with its design. If the building
use has changed and the design needs updating, then
recommissioning would also involve design and system
modifications to meet the current building conditions.
Depending on the system, recommissioning can involve a
number of items, including testing and balancing airflow;
calibrating temperature, humidity, and other sensors used
to control system operation; checking dampers for proper
operation; reviewing system operating schedules; and
confirming system capacity relative to current loads. A
number of state utility programs and private firms offer
recommissioning services, and the role of commissioning
is identified in the EPA Energy Star program (EPA 2004).
ASHRAE (1996 and 2005) also has two guidelines that
address building and system commissioning.
Available Performance Information
While there have been a number of case studies in which
building ventilation systems were recommissioned, each
situation is unique in terms of the system, the degree to
which the system deviates from design, and the magnitude
and nature of the resulting modifications. Note that most of
these efforts have been motivated by energy efficiency goals
rather than building security, but the process is not very
different. While each situation is different, some of the key
performance parameters are listed below:
• System outdoor air intake rate
• Modulation of outdoor air as a function of outdoor
weather (including economizer operation)
• System supply airflow rate relative to return airflow rate
(which relates to building pressurization)
• Indoor-outdoor pressure differences across building
envelope (which is not always part of design specification,
but important in chembio applications)
• Airflow rates of exhaust fans (e.g., toilet, kitchen)
• System operation schedule
• Interzone pressures between selected spaces and occupied
portions of building (e.g., lobby, loading dock, mail room,
underground garage, bathrooms)
There is no comprehensive database of measured
versus design values of the above parameters based on
recommissioning or other field evaluation efforts. The EPA
BASE study did include supply airflow and outdoor air intake
measurements, which were compared to design values when
design documentation existed (Persily and Gorfain 2004).
These comparisons did show significant deviations from
design values in many cases, which presumably would have
been eliminated through recommissioning efforts.
Envelope tightness measurements, following by sealing
retrofits, can also be considered as part of recommissioning,
but these are covered separately in the following section.
Protective Impacts
The benefits of recommissioning in terms of building
protection depend on the extent of the deviation of
performance relative to design. The simulations presented
in Section 2 included several relevant cases, including no
outdoor air intake and an intake rate about half of design.
In these cases, the exposures to an indoor release were
significantly higher than the baseline condition of design
outdoor air intake. Other deviations from design that could
increase exposure are airflow imbalances that depressurize
the building, thereby increasing the rate of entry of an
outdoor contaminant via infiltration.
Costs
The costs of recommissioning depend on the size and
complexity of the building and its ventilation systems.
No rules of thumb exists that would allow an estimate
based on floor area. Similarly, the beneficial impacts of
recommissioning in terms of energy efficiency and improved
indoor air quality are also building and system specific but
nevertheless can be significant. A recent report evaluated
a number of commissioning case studies in terms of costs,
savings, and payback times in new and existing buildings
(Mills et al. 2004). While the studies in the report cover
all aspects of commissioning, the median results were as
follows: cost of $2.91/m2 ($0.27/ft2), whole-building energy
savings of 15 percent, and payback time of 0.7 years.
Knowledge gaps
While there is general acknowledgement that
recommissioning is a valuable and effective retrofit, there
is not much documentation of its effectiveness in terms
of system performance or economics. Case studies of
recommissioning would be valuable in providing quantitative
evidence of its value. In terms of building protection, it
would be very helpful if these studies considered inside-
outside and interzone pressure differences as well as building
infiltration rates in the pre- and post-evaluations.
Summary
Given the significant deviations between ventilation system
design and performance that have been shown to exist,
recommissioning is likely to have value in many buildings.
The specific problems that will be resolved and the extent
of the improvements will always depend on the building in
question. Most importantly, if the ventilation system is going
to be relied on for building protection, a recommissioning
effort is essentially required for the system to provide the
intended protection.
-------
4.3.2 Envelope Tightening
Objective
To increase building envelope airtightness, thereby reducing
the rate of outdoor contaminant entry associated with air
infiltration.
Description
Contaminants that are released outside a building enter the
interior through a combination of intentional outdoor air
intake through the ventilation system and unintentional air
infiltration through openings in the building envelope. The
latter mechanism is often more significant than generally
assumed, given typical levels of building leakage, potentially
resulting in significant contaminant quantities entering
buildings via envelope infiltration. The infiltration rate of
a building is determined by the airtightness of the exterior
envelope and the pressure differences acting across the
envelope. These pressure differences are determined by the
wind speed and direction in combination with the exposure
of the building to the wind environment, the indoor-outdoor
air temperature difference, and imbalances between the
ventilation systems airflows into and out of a building or
space. The dynamics of envelope leakage and infiltration are
described in ASHRAE (2005). This retrofit approach involves
increasing the level of building envelope airtightness by
sealing leaks in the envelope, thereby reducing air infiltration
and contaminant entry, given the pressure differences
imposed on the envelope.
Available Performance Information
The impact of this retrofit on exposure will be a function
of the pre- and post-retrofit airtightness levels, the
corresponding infiltration rates, and the relative fractions of
outdoor air entry via intentional intake (generally with some
particle filtration) and infiltration (unfiltered). The connection
between envelope airtightness and exposure can be complex
and is always situation specific. Whole-building envelope
airtightness is measured through fan pressurization testing
in which a fan is used to induce a specific indoor-outdoor
pressure difference across the building envelope and the
airflow rate required to maintain that pressure difference is
measured. Generally, a series of pressure differences in the
range of 10 Pa to 75 Pa is induced in such a test, and the
corresponding airflow rates are measured. The test procedure
has been standardized for many years and either employs a
fan brought to the building for the test or uses the building
air handling systems to induce the test pressures (ASTM
2003, CGSB 1996). The results are reported as the airflow
rate required to induce a certain reference pressure (e.g.,
50 Pa or 75 Pa), typically normalized by building volume,
floor area, or envelope surface area. These airflow rates are
often converted to an "effective leakage area," which is the
area of an orifice that would result in the same airflow as
that measured through the building envelope at a reference
pressure.
Envelope airtightness has been measured in a relatively
small number of commercial buildings. Figure 16 is a plot
25
20
Figure 16 U.S. commercial building airtightness data
_0_
_
a"
•Typically Leaky Home
•Tight U.S. Home
•Tight Swedish Home
*
•
!, * *
* *
*** *v
* »
**
*;»* *
(I
1920
1940
1960
Year of Construction
1980
2000
-------
of commercial building airtightness data as a function of
year of construction, where airtightness is expressed as the
effective leakage area (ELA) in cm2 at a reference pressure
of 4 Pa divided by the above-grade envelope surface area
in m2 (Emmerich and Persily 2005). The mean air leakage
value for the roughly 150 buildings in the figure is 4.3 cm2/m2
(0.06 inVft2). For reference, a typical U.S. home has a leakage
value on the order of about 3 cm2/m2 (0.04 inVft2), while tight
U.S. and tight Swedish homes correspond to roughly 1 cm2/
m2 (0.01 itf/ft2) and 0.3 cm2/m2 (0.004 irf/ft2), respectively.
The available data reveal that commercial buildings are not
particularly tight, relative to homes on a surface area basis,
and reveal no relationship between year of construction
and air leakage, dispelling the myth that new buildings are
"airtight."
The determination of envelope infiltration rates from
envelope airtightness values requires consideration of
weather-induced pressure differences and the impacts of
ventilation system airflows, and is best done using multizone
airflow analysis methods such as those embodied in the
CONTAM program (Walton and Dols 2005). While simpler
relationships between envelope airtightness and infiltration
have been developed for low-rise residential buildings
(ASHRAE 2005), they are not generally applicable to
commercial buildings of any complexity. Nevertheless,
all else being equal, a tighter building will have a lower
infiltration rate, and a lower infiltration rate will result in less
contaminant entry of an outdoor source.
The impacts of an envelope-tightening retrofit are
characterized by the change in envelope airtightness. There
have been only limited studies reporting before and after
envelope airtightness data (Shaw and Reardon 1995, Zhang
et al. 1995). While limited, these studies and other experience
show that reductions in whole-building air leakage as large as
50 percent can be achieved but not all sealing approaches will
necessarily be this effective. Commercial building leakage
measurements have shown that windows and doors generally
account for a small fraction of the total, in the range of
10 percent to 20 percent (Persily and Grot 1986). More often,
it appears that the dominant leakage sites are at interfaces
between different wall sections, wall-floor connections,
corners, and the interface between the roof and walls.
Depending on the wall construction, it can sometimes be
quite difficult to access some of these leakage sites for repair,
and additional experience and guidance is needed to guide
retrofit efforts.
Protective Impacts
Envelope tightening can reduce the exposure to outdoor
contaminant releases, with the amount of reduction
depending on the change in airtightness, the relative
magnitudes of the infiltration and intake rates, and the
level of filtration of the intake air. As noted above, a tighter
building has a lower infiltration rate and therefore less
outdoor contaminant entering a building. At the same time,
the lower building air change rate will cause the contaminant
that does enter the building to remain there longer, which will
1.2
1.0
•5 0.8
.2
Figure 17 Indoor concentration for different air change rates
^0.6
I
e
8 0.4
o
U
0.2
0.0
•Outside
-0,5 air changes per hour
• 1 air change per hour
•5 air changes per hour
0.5
1.5
2.5
Time (h)
3.5
4.5
-------
increase exposure. Ignoring any impact of filtration, these
two effects balance each other out and the exposure over an
extended period of time is independent of air change rate.
This effect is depicted in Figure 17, which shows the indoor
concentration at three air change rates corresponding to a
short-term increase in the outdoor concentration. While it
may not be obvious from this graph, the areas of the indoor
concentration curves, i.e., the integrated exposure over time,
are identical. Of course, if the occupants leave the building
soon after the release or the building is flushed with higher
levels of outdoor air intake, then the lower rates will indeed
result in less occupant exposure.
Therefore, tightening alone will not reduce long-term
exposure to an outdoor contaminant unless some action is
taken to evacuate the occupants or flush the building after
the contaminant episode has passed. However, if the outdoor
air intake is filtered, then reducing infiltration will reduce
exposure. The effects of filtration are generally most relevant
to paniculate contaminants, since gaseous air cleaning is
less common, but the dependency is the same. Equation 4
compares the exposure for two different levels of filtration
for a given ratio of infiltration to intake and can be applied
to this retrofit by considering the same level of filtration and
two different values of the infiltration to intake ratio.
Equation 4
Relative exposure =
1 B +
Q
INF-post
'/On
"OTAL - post
1-8 +
Q
INF-pre
' ^T
OTAL - pre
MNF-post
MNF-pre
where e is the filter efficiency of the outdoor air intake,
is the envelope infiltration rate after tightening,
is the infiltration rate before tightening,
is the total air change rate (intake plus infiltration)
after tightening,
-------
and Persily 1998), but again the reduction achieved will
depend on the individual building. Nonetheless, the potential
for energy reduction and, therefore, cost savings by envelope
tightening are very real.
In addition, envelope tightening should also improve indoor
air quality by decreasing contaminant entry via unfiltered
infiltration, which has the potential for productivity
increases as noted earlier for improved filtration. Increases
in productivity are, of course, difficult to quantify, but
are a potentially significant issue in areas with poor
outdoor air quality. Envelope tightening can also improve
moisture control in buildings, decreasing the likelihood of
condensation within exterior walls and other surfaces and
subsequent microbial growth.
Knowledge gaps
There is a need for more studies of the increases in
airtightness achievable through envelope sealing as a
function of sealing method and building construction, as well
as the costs associated with these efforts. Presumably more
envelope tightening efforts will occur in order to improve
energy efficiency of existing building, and it is important to
collect these data in conjunction with such efforts. Additional
information on the energy impacts of tightening would also
be useful to better assess and predict the cost effectiveness of
these sealing efforts.
Summary
Enveloping tightening can reduce the entry of outdoor
contaminants. However, exposure reduction requires that
the intake air be filtered or that the building be evacuated
or purged with outdoor air after the outdoor contaminant
episode has ended. In general, the exposure reduction will be
larger for more effective tightening and better filtration of the
outdoor air intake. However, tightening alone is not likely to
reduce exposure by more than 50 percent unless the intake air
filtration is on the order of 90 percent or better and the post-
tightening infiltration rate is reduced by at least one-half.
4.3.3 Building Pressurization
Objective
To eliminate or significantly reduce envelope infiltration and
the associated contaminant entry by bringing in sufficient
amounts of filtered outdoor air to maintain the building
at a higher pressure than outdoors. In this discussion, the
pressurization is intended to occur whenever the system is
operating rather than in response to an event.
Description
Building pressurization involves protecting a building against
outdoor contaminant releases through the overpressurization
of the building interior relative to outdoors and the removal
of the outdoor contaminant from the intake air via filtration
and/or air cleaning. To be effective, the amount of air intake
must be sufficient to overcome negative pressures that are
induced by weather and the operation of other systems, and
the level of filtration must be sufficient to remove significant
quantities of contaminant. As noted earlier, contaminants
that are released outside a building enter the interior through
a combination of intentional outdoor air intake through the
ventilation system and unintentional air infiltration through
openings in the building envelope. The latter mechanism
is often more significant than generally assumed, given
typical levels of building leakage. Building pressurization
is therefore intended to counter the latter mechanism
by eliminating, or at least reducing, the inward pressure
differences that drive infiltration.
Commercial buildings are generally designed with more
outdoor air intake than exhaust in order to control infiltration.
However, in reality, whether this design goal is achieved
or not depends on many factors, including the amount of
outdoor air intake, its distribution, the magnitude of the
pressures that induce infiltration, and the tightness of the
building envelope. Very few buildings have actually been
evaluated in terms of indoor-outdoor pressure differences,
but given the magnitude of weather-driven pressures and the
levels of building leakage, it is unlikely that this design goal
is being realized in very many circumstances. Cummings
et al. (1996a and 1996b) measured building pressures in a
number of small commercial buildings in Florida and found
many buildings under significant negative pressures relative
to outdoors due to combinations of duct leakage and poor
control of system airflows.
Available Performance Information
The parameters relevant to building pressurization include
the excess outdoor air intake (intake minus exhaust), building
envelope leakage, building surface-to-volume ratio, and
removal efficiency of the filtration and air cleaning systems
for the relevant contaminants. Excess outdoor air intake is a
ventilation system design parameter, but the values during
operation are the relevant parameter. Typical design values
for outdoor air intake as a fraction of supply airflow are
on the order of 10 percent to 20 percent in office buildings
(Persily and Gorfain 2004). This percentage is reduced
somewhat when toilet and other exhaust flows are included.
Given that commercial building supply airflow rates are on
the order of 5 L/s per m2 (1 cfm/ft2) of floor area, typical
excess outdoor air rates are roughly 0.5 L/s«m2 (0.1 cfm/ft2).
Building envelope leakage values, discussed in the previous
section, range from as low as 0.5 cm2 of leakage area per
m2 of envelope area (0.01 in2/ft2) to as high as 10 cm2/m2
(0.14 in2/ft2) and greater. Surface-to-volume ratios depend
on building size and floor plan. It is more straightforward
to instead consider the ratio of envelope surface area to
floor area. For a collection of 25 representative U.S. office
buildings (Emmerich and Persily 1998), the surface-to-floor-
area ratio ranged from 0.03 to 1.50, with a mean of 0.44.
Based on the surface-to-floor-area ratio and building
leakage, one can calculate the amount of outdoor air
required to pressurize a building. Figure 18 presents the
results of such a calculation, assuming that there are no
weather-driven pressures and no internal resistance to
airflow within the building. The values in the figure are
the airflow rates required to achieve a 5 Pa indoor-outdoor
pressure difference, and the lines correspond to different
values for the area ratio. There is nothing significant about
this particular pressure difference; it is used simply for
illustrative purposes. These results indicate that in leaky
-------
buildings, especially those with higher area ratios (smaller
buildings), relatively large quantities of outdoor air are
required to achieve 5 Pa of pressurization. In the leakiest
and smallest buildings, the quantities required are on the
order of total design supply air capacities. Performing these
calculations with weather-driven pressures would make the
required airflows higher by as much as an order of magnitude
under windy and cold conditions. Therefore, it is unlikely
that a leaky building can be pressurized at design minimum
outdoor air intake airflows. More importantly, the amount
of airflow required to pressurize a building needs to be
based on its geometry, the weather conditions to which it
is likely to be exposed, ventilation system design airflow
rates, and building envelope airtightness. If the latter value
has not been measured, then a high value should be used to
determine a conservative estimate. In an existing building,
these indoor-outdoor pressures can be measured under specific
conditions of weather and outdoor air intake to determine
whether the building is being pressurized. When making such
measurements, it is important to measure at multiple points on
the building facade, including different sides of the building
and multiple elevations.
It should be noted that in some buildings, the ventilation
system and controls might need to be modified to achieve
the desired levels of pressurization.
Protective Impacts
Building pressurization, when combined with high-efficiency
filtration and air cleaning, can be effective in protecting
against outdoor contaminant releases. The analysis discussed
in the previous section on envelope tightening can again be
used to estimate the change in exposure. However, the post-
retrofit intake rate QINT ost is higher than the pre-retrofit value
MNT-post-
and the relevant expression now becomes:
Equation 5
Relative exposure =
(Q«-Jl-e)+
- pos
t] ' ^
TOTAL - post
(Q.
|NT -
-pre
-pre
The reduction is now a function of the new infiltration rate
and the amount of intake air required to reduce it, as well as
of the filter efficiency e. This equation is used to calculate
the exposure reductions shown in Table 26 for three retrofit
cases. In the first case, the outdoor air intake is increased
by 50 percent and the infiltration rate is reduced by 90
percent. In the second, the intake is increased by 75 percent
and infiltration reduced by 95 percent. And in the final
case, intake is doubled and infiltration is eliminated. These
particular values do not reflect any particular expectations of
Figure 18 Airflow required for building pressurization to 5 Pa
*
H
Su rface area/Floor a ren
•^~Q.Q5 - Skyscraper
^^•0.5 - Average office
.25
1.0
1.5
2,0 - Small house
o
3
34567
Effective leakage area at 4 Pa (cmVm~)
If)
-------
the infiltration reduction due to these increases in air intake
but are employed simply to demonstrate the impacts of
pressurization. The relative exposure is presented for several
filter efficiencies, as well as for no filter at all. The latter case
shows that pressurization has no impact if there is no filter,
as expected. The other cases show the degree of protection
from reducing infiltration, with greater reductions for lower
infiltration rates and higher filter efficiencies. However, for
the two lowest filter efficiencies, pressurization has a limited
impact on exposure.
Before increasing outdoor air intake in an attempt to
pressurize the building, it is critical to assess the current
situation regarding building pressure relative to outdoors.
If the building is already under positive pressure, i.e., the
infiltration rate is already zero, then bringing in more outdoor
air increases space conditioning loads and makes the filter
"work harder" without any additional protective benefit. If
the filtration is less then 100 percent efficient, then the extra
outdoor air will actually result in more contaminant entering
the building and an increase in exposure.
Costs
The costs of building pressurization arise primarily from
the increased energy consumption associated with heating
and cooling the additional outdoor air required to pressurize
the building, which are a function of climate and outdoor
air quantities. Since it takes less outdoor air to pressurize
a building, these costs should serve as a motivation for
envelope tightening.
There may also be some first costs associated with modifying
the ventilation system and controls to bring in the extra
amounts of outdoor air. In some cases, the system may
require extra heating and cooling capacity, which would
also add to the first costs. Finally, the cost and maintenance
issues associated with filtration also apply to building
pressurization. Building pressurization has the potential
for positive economic impacts due to indoor air quality and
envelope durability improvements associated with reductions
in moist outdoor air entering the building envelope.
Knowledge gaps
While building pressurization is a fairly straightforward
concept, the key parameters are the air leakage value for the
building in question and the weather conditions for the site.
More measured airtightness data would make the design of
building pressurization strategies and controls more reliable,
but when considering a specific building, it is preferable to
measure the envelope airtightness of that building.
Summary
Building pressurization combined with effective filtration
can reduce exposure to outdoor releases. The reductions will
be higher for higher-efficiency filtration and air cleaning.
Therefore, good filtration installation and maintenance are
critical to the success of this approach. The infiltration rate
reduction with pressurization in place needs to be based
on weather conditions and building airtightness, such that
an appropriate amount of outdoor air is brought into the
building. Simply increasing outdoor air intake with the goal
of building pressurization may not be effective and could
make things worse in some situations.
4.3.4 Relocation of Outdoor Air Intakes
Objective
To move outdoor air intakes, usually to higher elevations,
such that they are less accessible to public right-of-ways,
therefore making it less likely that an individual can release a
contaminant into the intake.
Description
Outdoor air intakes are sometimes located where they are
easily accessed by pedestrians and are therefore vulnerable
to someone releasing a contaminant that will be pulled into
the building and distributed by the ventilation system. The
vulnerabilities created by accessible intake locations have
been identified as an issue of concern, and recommendations
have been made to move such intakes to higher elevations
(ASHRAE 2002, NIOSH 2002). The NIOSH document notes
that a height of 3.7 m (12 ft) above the ground will put an
intake out of reach "without some assistance." NIOSH also
Table 26 Example impacts of building pressurization on exposure to outdoor release
Relative Exposure (%)
Filtration Efficiency 50% intake increase; 75% intake increase; 100% intake increase;
infiltration 90% lower infiltration 95% lower no infiltration
25%
50%
95%
99%
99.9%
100%
No filter
87.5
70.8
20.8
14.2
12.7
12.5
100.0
86.5
68.5
14.6
7.4
5.7
5.6
100.0
85.7
66.7
9.5
2.0
0.2
0.0
100.0
-------
recommends a sloped and screened covering to the intake, so
that an item thrown on the intake will roll off. Figure 19 is a
schematic diagram of three potential intake locations, ranging
from "vulnerable" to "best." The second schematic clearly
shows a sloped intake, while the "best" option stresses
elevation instead of slope. Other recommendations noted in
these documents include providing distance from building
elements that could be used to access intakes, such as loading
dock or entryway roofs, and minimizing obstructions near
intakes that could make it difficult to observe someone in
their vicinity. In some buildings, it may be possible to run the
intake ductwork through the building interior to the roof, but
that approach consumes valuable interior space that may not
make it a realistic option.
Available Performance Information
There is no quantity that characterizes the degree of
accessibility of an air intake, but presumably a higher
intake is less likely to be subject to a release. The amount of
contaminant that will be drawn into a ventilation system from
a release near an intake is a complex function of the airflow
patterns around a building. Even without employing complex
analysis of airflow patterns and quantitative determinations
of accessibility, it is probably reasonable to assume that a
release at the intake will be unlikely to occur if it is relocated
sufficiently distant from publicly accessible locations.
Figure 19 Schematic of intake location options
(NIOSH 2002)
Protecting Outdoor Air Intakes
r* lAHU
AHU
VULNERABLE
BETTER
BEST
The EPA BASE study of 100 randomly selected U.S. office
buildings included the characterization of 141 ventilation
systems serving the 97 mechanically ventilated buildings in
the study (Persily and Gorfain 2004). Among many other
parameters, that study included the elevation of the air
intakes relative to ground level. The mean value of the intake
elevation for these systems is 5.4 m (18 ft), which may be
sufficient in many cases. However, the median value is 1.5 m
(5 ft) and the 25th percentile value is 0.3 m (1 ft), which could
indicate that many intakes are lower than perhaps they should
be. Of course, in addition to elevation, vulnerability of an
intake depends on the public access to the intake and on the
physical security around a building.
Protective Impacts
It seems reasonable to assume that all of a contaminant
released directly into an intake will be brought into a building
and that moving the intake to an inaccessible location will
eliminate any such contaminant entry. However, as noted
above, determining the amount of contaminant that enters
from a release near an intake is complex and requires
complex analysis approaches. In cases where an existing
intake is in an accessible location, the goal should be to move
it as far from such a location as practical. However, as noted
in the discussion of costs, it can be very expensive to move
intakes in some buildings and the degree of risk
to that building may not justify the cost. Closed-circuit
television cameras, security lighting, fences, and other
means of improving physical security have been suggested
as reasonable alternatives to moving intakes (NIOSH 2002).
Costs
There is clearly a cost associated with relocating air intakes,
which in some cases can be quite significant. In addition,
the relocation may modify the airflow resistance associated
with the intake, thereby requiring additional modifications
to the air handling system. These costs will be building and
system specific, and therefore cannot be generalized. The
case study described in this report includes an estimate for
a high-rise office building of roughly $250,000, but that is
only one estimate. Costs may be higher or lower in another
circumstance. Note, however, that in the case study building,
relocating the intakes would have blocked more than 100
windows and compromised the aesthetics of the building,
issues that are difficult if not impossible to translate into a
dollar value.
There can also be potential indoor air quality improvements
from raising outdoor air intakes when there is heavy motor
vehicle traffic and other ground level contaminant sources.
-------
Knowledge gaps
Given that this is a relatively effective retrofit, there is little
need for detailed analysis of its effectiveness. However,
additional case studies of the associated cost for given
building and system configurations would be useful to assist
building owners in the early stages of retrofit consideration.
Summary
Relocating accessible outdoor air intakes can dramatically
improve the level of building protection by essentially
removing that vulnerability. However, the practicality
and cost of this retrofit can vary among buildings, as can
its importance, based on the risks to which that particular
building is exposed. In cases where it is determined that
relocating the intakes is not an option or won't be pursued,
improving the physical security of the intakes and monitoring
activities in their vicinity will reduce the vulnerability.
4.3.5 Shelter-in-place
Objective
To reduce occupant exposure to an outdoor release by
moving building occupants to a designated space within
a building. This space, which may be equipped with
supplemental filtration and air cleaning, will experience
lower concentrations resulting from the outdoor release
and thereby provide protection to the building occupants
who have moved to this space.
Description
In the event of an exterior contaminant release, and in some
cases an interior release, building occupants can move to a
designated space that is relatively isolated from the rest of the
building and offers protection from the airborne contaminant.
During such sheltering, the building HVAC and exhaust
systems are all deactivated to eliminate intentional outdoor
air intake into the building, leaving only unintentional air
infiltration. The degree of protection will increase if the space
is well isolated in terms of airflow by having tight boundaries
and even moreso if the space is equipped with a filtration
and air cleaning system to remove contaminants that do enter
the space. This approach is also sometimes referred to as
"collective protection."
Shelter-in-place is a well-established concept and has been
implemented in a variety of settings and planning efforts.
For example, FEMA's Chemical Stockpile Emergency
Preparedness Program (CSEPP) has generated much
information, guidance, and training material for planning in
the event of a chemical release at a chemical storage site or
industrial facility (Blewett et al. 1996). As noted in this and
other publications, there are four basic approaches to shelter-
in-place:
• Normal: closing all windows and doors, and turning off all
mechanical equipment, such as HVAC systems
• Expedient: applying temporary air sealing measures to a
shelter space, such as taping over vents or placing plastic
sheeting over windows
• Enhanced: applying permanent air sealing measures to a
shelter space
• Pressurized: providing filtered/cleaned air to the shelter
to achieve an elevated air pressure relative to outside the
shelter, thereby greatly limiting air and contaminant entry
Much of the guidance that has been issued in the selection
and preparation of shelter-in-place spaces in buildings
focuses on size, location, and accessibility (NICS 1999
and 2001, Price et al. 2003). In many cases, sheltering is
envisioned as lasting for hours, until the outdoor contaminant
has cleared and it is safe to leave the building. In situations
where sheltering is expected to last longer, requirements for
food, water, and other basic needs become important. In fact,
as was discussed for envelope tightening, unless the shelter is
provided with filtration and air cleaning, the exposure in the
shelter will eventually approach that experienced outdoors.
Therefore, leaving the shelter and the building when it is safe
outdoors is an important aspect of this strategy. In addition,
carbon dioxide will build up in the shelter over time, which
is another reason for short-term use of this strategy unless
ventilation and air cleaning are employed.
A key aspect of shelter-in-place, as noted in the referenced
guidance material, is the training of the building occupants to
move quickly to the shelter when directed. Training drills are
noted as useful exercises, similar to evacuation training drills.
Available Performance Information
Key variables related to this approach include the airtightness
of interior partitions of the shelter and the airtightness
of the exterior envelope of the building itself. Existing
building airtightness data were discussed under the Envelope
Tightening approach. Even less information is available on
shelter airtightness, but studies are in progress that include
such measurements.
If filtration or air cleaning is employed, the airflow rate
through that system and the filter/air cleaner removal
efficiencies for the contaminant of concern are relevant.
Airflow rates are generally specified for commercial units
or can otherwise be determined for systems designed
for specific installation. As discussed earlier, paniculate
removal efficiencies are expressed in terms of MERV levels
but gaseous air cleaning efficiencies are more difficult to
determine.
Protective Impacts
Shelter-in-place can provide significant protection against
outdoor contaminant releases, as seen in the simulation
results in Section 2. Timing of occupant movement into the
shelter is critical, however, as is the timing of their leaving
the shelter after the outdoor contaminant has cleared.
The simulations discussed in Section 2 showed exposure
reductions on the order of 90 percent or more if the occupants
moved into the shelter before the release for a two-hour
sheltering period. Filtration and air cleaning reduce exposure
even more. But moving into the shelter after the release has
begun greatly reduces the effectiveness of the sheltering.
The parameters that will determine the effectiveness of
shelter-in-place are the exterior envelope and shelter
airtightness values, the outdoor weather driving infiltration
and contaminant into the building, interior zoning and
-------
temperatures as they affect internal airflow patterns, the
relative timing and duration of the release and the sheltering,
and the existence and effectiveness of any filtration and air
cleaning employed.
A significant amount of research has also been done on
shelter-in-place, but most of it focuses on the building itself
as the shelter as opposed to a designated space within the
building (Blewett and Area 1999, Fradella and Siegel 2005,
Sohn et al. 2005). letter and Whitfield (2005) examined the
protection provided by an interior bathroom of a residence,
in which tracer gas tests were used to estimate airflow rates
between the shelter, the rest of the house and the outdoors.
A later experimental study by letter and Proffitt (2006)
considered the protection offered by shelters in commercial
buildings. Swansiger et al. (2005) looked at the use of
interior stairwells, pressurized with filtered outdoor air as an
SIP option.
Costs
There is some cost involved in setting up a shelter-in-place,
particularly airtightening of the interior partitioning and
equipment costs for a filtration and air cleaning system if
employed. In general, these systems are only employed
if needed, and therefore they are not associated with any
significant operating costs. There are some maintenance costs
to ensure that the system will function properly in the event it
is needed.
Knowledge gaps
While shelter-in-place is fairly straightforward, the biggest
question regarding its implementation is knowing that a
release has taken place, or is about to take place, and that
sheltering is the appropriate action. A warning system based
on contaminant monitoring could answer these questions,
but this type of warning system is not typically available.
Therefore, better information is needed on how to determine
that sheltering is called for and when the occupants should
subsequently leave the shelter and go outdoors. There is also
a need for better information on shelter airtightness values
and how these values relate to the degree of protection
offered.
Summary
Shelter-in-place, especially when implemented in a timely
fashion, can reduce exposure to outdoor releases. The
reductions will be higher if filtration and air cleaning are
employed in the shelter. Effective sheltering depends on
proper selection of shelter spaces in a building, airtightening
of the partitions to adjacent spaces, and training of the
occupants to move quickly to the shelters when directed to
do so.
4.3.6 Isolation of Special-use Spaces
Objective
To limit contaminant releases in vulnerable spaces from
impacting the rest of the building, thereby reducing exposure
to the bulk of the building occupants.
Description
Some building spaces are more vulnerable to interior releases
due to public access (e.g., lobbies and parking garages) or
mail and delivery activities (e.g., mail rooms and loading
docks). Due to the increased vulnerability of such spaces,
keeping them at a lower pressure than adjacent portions
of the building can provide some protection in the event
of an incident. Such isolation can be achieved through
ventilation airflow control, i.e., exhausting more air than is
being supplied, and will generally be easier to achieve and
control if these spaces are served by a dedicated system. This
approach is more likely to be successful if attention is paid to
the airtightness of the boundaries between the space and the
rest of the building.
Available Performance Information
The effectiveness of this approach is determined by the
magnitude of the negative pressure achieved in the space
relative to adjoining spaces, which is a function of the system
airflows to and from the space and adjoining spaces, as well
as the airtightness of the space boundaries. Other important
variables include weather conditions as they impact building
pressures and the operation of other ventilation systems in
the building. The supply and exhaust airflow differential and
the airtightness of the space boundaries required for effective
isolation need to be considered on a case-by-case basis as
impacted by system airflow rates, weather conditions, and
location of the space in the building. For example, lower
level spaces, which include lobbies, loading docks, and many
mail rooms, are more subject to stack-driven flows upward
within a building. Multizone airflow modeling is useful in
assessing these situations and defining system airflows and
levels of partition airtightness required for effective isolation.
Protective Impacts
If effectively implemented, space isolation will limit
contaminant migration to other spaces within a building.
The occupants of the space where the release occurs will
be exposed, however, perhaps to significant quantities
of contaminant, and this approach will not protect them.
Examples of this approach were discussed in the case study
of the high-rise office building, where isolating the mail room
and the lobby was considered.
Costs
There may be some initial costs associated with airtightening
or modifications of system airflow rates to achieve the
desired pressure relationships. The latter will require some
maintenance in terms of periodically checking system
balancing to determine that these pressure relationships
still exist. In some cases, a new air handling system may be
required, which will also involve some operating costs. There
may also be some first and maintenance costs associated with
controls to modulate the system airflows in response to real-
time pressure monitoring between the space and an adjacent
space. The costs of isolating the mail room and the lobby of
the high-rise case study building are discussed in Section 3.
-------
Knowledge gaps
Additional information on interior partition airtightness,
as typically constructed and after airtightening, would be
helpful in the design of isolation strategies. These data would
also allow more specific guidance on the differential airflow
quantities required for effective isolation as a function of
building climate as well as floor plan and elevation.
Summary
Isolation of special-use spaces can contain indoor
contaminant releases, thereby protecting the rest of the
building from significant exposure. This approach requires
consideration of the pressures that need to be counteracted
and will be more effective if the partitions to adjacent spaces
are air sealed.
4.3.7 System Shutdown and Purging
Objective
To effectively implement a quick shutdown of all ventilation
systems or to induce a 100 percent outdoor air purge when
such actions will reduce occupant exposure to a contaminant
release.
Description
In some circumstances, shutting down a building ventilation
system or operating it with 100 percent outdoor air intake
may help protect building occupants from a chembio release.
Shutdown involves turning off all ventilation equipment,
including makeup air and exhaust fans. It is important to
include all equipment, since leaving on a toilet exhaust
system will contribute to building depressurization and
actually increase contaminant entry for an outdoor release.
Implementing a 100 percent purge can be effective in
removing a contaminant that has already been distributed
within a building. Ventilation systems equipped with
economizer cycles are already equipped with the necessary
controls to implement such an action. However, for both
shutdown and purging, the circumstances under which such
an action will be beneficial are very dependent on the release
location and timing, the amount of time that has passed since
the release occurred, and how much contaminant if any has
been distributed within the building and where.
Timing is critical to the effectiveness of a shutdown
response, and a single switch or "panic button" that
implements shutdown all at once instead of having to
individually deactivate each piece of equipment will
support more timely implementation. Such single-switch
control is generally much easier to set up in digital control
systems than in pneumatic systems, though the latter can
result in faster transmission of the action to the equipment.
The location of the switch and the protocols for who operates
it and under what circumstances are critical issues that need
to be considered in advance of any incident, and training
exercises are useful to increase the likelihood that such a
response will be implemented as intended.
Even with good controls and a single switch, it takes time
for a typical ventilation system to shut down due to delays
associated with fan spin-down and damper closing. These
delays can be countered by installing braking systems on
fans and quick-closing, tight dampers, but these items are not
standard in commercial building systems and will increase
costs.
Available Performance Information
Since both shutdown and purging are building specific
in their implementation and impact, there are no generic
performance data describing these approaches. In a given
building, key performance parameters include the building air
change rate, i.e., infiltration under shutdown and the intake
airflow under purging, and the time it takes to implement the
response.
In the case of shutdown, the system-off infiltration rate of a
building is a strong function of weather conditions. This rate
can be measured with tracer gas techniques or predicted with
multizone airflow modeling, but these approaches require a
certain level of sophistication. Perhaps more important is to
assess and understand the airflow patterns into and within a
building with the system off. These patterns can be assessed
through the use of smoke pencils and the measurement
of pressure differences at key locations in the building,
including entrances (including secondary entrances such
as loading docks), elevator and stairway doors at multiple
building levels, windows at multiple elevations, and roof
access doors. Such an effort can help to determine where air
enters and leaves the building with the system off and thereby
result in a better sense of where contaminants may enter the
building and how they might move through it. It is important
to conduct such an airflow assessment under different
weather conditions (wind and outdoor temperature) as
the airflow patterns will be impacted by weather.
Purging airflows are less likely to be impacted by
weather, but it is still important to verify that the
implementation of a purge cycle operates as intended.
Verification can involve measuring system airflows, in
particular the outdoor air intake rate. A less involved
assessment includes inspecting the intake, recirculation
and exhaust dampers, and the fan speeds to make sure
the system is, in fact, operating in a manner that will
bring in the maximum amount of outdoor air.
Protective Impacts
The degree of exposure reduction from either a shutdown
or purge is dependent on the timing of the response relative
to the release, the location of the release relative to the
occupants, and the building layout and system design. This
variability was seen in the simulation results presented
in Section 2, where timing was seen to be critical and the
exposure impacts were quite variable, based on the details of
the release.
Shutdown is likely to be most effective if an outdoor release
has occurred and there is sufficient warning to initiate the
shutdown before the contaminant is brought into the building
by the ventilation system. In some circumstances, a shutdown
may also be effective if a contaminant has entered a building
or has been released indoors and shutting down the system
prevents the contaminant from being distributed within the
-------
building. However, realizing the benefits of a shutdown in
such a situation requires a level of understanding of the release
timing and location and the building airflow patterns that is
not necessarily realistic. Also, system shutdown will lose the
ability to pressurize the building with the system, which will
increase contaminant entry if an outdoor release is still in
progress.
A purge cycle makes sense if a contaminant has already
been distributed within a building and the best course of
action is to remove it as quickly as possible. Such situations
include a release into a system return, or even an intake, or a
localized release that has mixed within the building. However,
realizing the benefits of a purge cycle requires knowledge
that such an event has occurred and that the contaminant has
migrated within the building to a degree that purging makes
sense. There is the associated issue of occupant awareness
during such an event. If there is sufficient awareness of the
circumstances of an event that purging is an appropriate
response, then it is likely that evacuation of the occupants is
also a reasonable response as well. One exception might be
if evacuation is not an option due to conditions outside the
building.
Costs
There are costs associated with the controls to quickly convert
system operation into a shutdown or purge mode, as well as
with the periodic maintenance to confirm that the controls
are operational. The costs will depend on the system type and
complexity, and the controls that already exist in the building.
A detailed design review will be required to determine what
work is needed to implement these controls and the costs
involved, as was done in the two case study buildings. If fan
braking systems and quick-acting dampers are required, they
will increase costs accordingly.
There are no economic benefits associated with shutdown and
purge capabilities, but having them in place does provide a
response that might be appropriate under other circumstances
such as less extreme indoor air quality incidents.
Knowledge gaps
As noted above, the most important information gaps are
how shutdown and purging will impact airflow patterns and
contaminant movement in a specific building under a specific
release scenario. More studies of their implementation in
individual buildings should improve our general understanding
of the impacts, as well as how and when to implement these
responses.
Summary
As noted above, the degree of exposure reduction from either
a shutdown or purge response depends on the timing of the
response, the nature of the release, and the building layout
and system design. It is unlikely to be entirely clear when
either response is advised, but having the capability is worth
considering in the event that it is needed. Even if the controls
and equipment are not modified to speed the implementation
of shutdown or purging, it makes sense to know how to
shut down all systems quickly, how to implement a purge
cycle using existing controls, and how either action will
impact air movement patterns in a building. Note that in
the absence of reliable information regarding a chembio
release, implementing a shutdown or purge cycle can actually
increase exposure in some circumstances.
4.3.8 Automated HVAC Response
Objective
To modify the operation of a building's ventilation system
in response to a contaminant sensor in a manner that reduces
occupant exposure.
Description
Given a timely and reliable signal from a contaminant
sensor, a building's automated control systems could modify
ventilation system operation to contain the contaminant in the
zone of an indoor release, or in the case of an outdoor release,
to prevent it from entering a building and to maintain the rest
of the building and egress paths at low and presumably safe
concentrations. These modifications could include stopping
and starting fans, repositioning dampers, or securely closing
doorways. These concepts have been used for many years in
smoke control systems to contain smoke in the fire zone and
provide a safe evacuation route for the building occupants
(Klote and Milke 2002). The manner in which a system's
configuration and operation would be modified depends
on the building and system design, and on the nature of
the contaminant release.
Available Performance Information
The speed, reliability, and ultimately cost of contaminant
sensors are key to the application of on automated HVAC
response and can be considered the weak link. Given the
speed at which air moves within buildings, a very fast sensor
is required to initiate a change in system operation before the
contaminant has spread within the building and defeated the
goals of the approach. Also, the sensor must be reliable to
avoid both false negatives and false positives. Sensors also
need to have a range of detection capabilities to cover the
various chemical and biological contaminants of interest. In
addition to fast sensors, the system changes also need to be
implemented more quickly than most ventilation systems
can change operating modes. This requirement means that
fast-acting and tight dampers will need to be installed in
place of typical dampers. Fan braking systems are also
needed to stop the airflows more quickly than is generally
possible in typical ventilation systems.
Protective Impacts
In theory, if the sensors and system capabilities are available,
and the building and system airflow dynamics are well
understood, this approach would be able to provide a high
level of protection. However, sensors that are fast and
inexpensive enough are not currently available for any
applications other than very high security buildings where the
costs are justified. Until sensor cost and reliability improves,
this approach is not a practical option in other buildings.
Costs
The cost of this approach includes the contaminant sensors,
which are very expensive at this time, and both the first and
-------
maintenance costs. In addition, the tight dampers and fan
braking systems noted above also involve first costs. Finally,
such a system will involve design costs related to the system
and control modifications.
Knowledge gaps
As noted, the biggest need to make this option more realistic
is the development of fast, reliable, and affordable sensors
covering a range of chembio contaminants. Much work is in
progress in sensor development, but it will still be some time
before the sensors are available to support application of this
approach at a reasonable cost.
Summary
While automated HVAC operational changes can in theory
reduce occupant exposures, the technology to implement this
approach does not currently exist. It is not clear when the
situation will change, but it is likely to be some years before
this option will be widely available.
4.4 Guidance Summary
This section has reviewed a number of retrofit technologies
and approaches for controlling exposure to chemical and
biological contaminant releases. The guidance provided is
summarized in Tables 27 and 28. Note the separate entry
in the fifth row of Table 27 for filtration and gaseous air
cleaning, which points out the key advantage that these
technologies are always in effect, assuming the systems
are properly installed and maintained, and therefore there
is no need for proper timing or implementation decisions.
Also, filtration and air cleaning will not increase exposure
if implemented at the "wrong" time, unlike some other
responses. The biggest problem with gaseous air cleaning
in particular is the lack of standards for testing and rating
these systems, but efforts are under way that should remedy
this situation.
Given the wide range of potential retrofit options, decisions
on which options to implement can be confusing. While
the appropriate actions in a given building are inherently
specific to that building, Table 29 presents a very simplified
framework for considering the various retrofit options
discussed in this report. The table contains four categories,
with the first being those retrofits that may reasonably be
implemented in any building. These include recommissioning
and enhanced particle filtration, based on the energy and
IAQ benefits. Shelter-in-place is also included in this
category because it is good to have such a contingency plan
in response to a wide range of events. Shelter-in-place may
range from simply designating such spaces in a building, and
perhaps some minimal air sealing, to a more comprehensive
effort to prepare a space that might include high levels of air
sealing, provisions for food and water, and filtration and air
cleaning capabilities. The second category includes options
that should be considered independent of the threats to a
given building. The first two are included based in part on
their energy and potential IAQ benefits, but since they can be
quite complex and costly in some facilities, they may not be
appropriate in all circumstances. Shutdown and purging are
also included in the category because they are good options
to have available, but may not be readily implemented in
some systems without costly modifications.
The third category includes several retrofits whose
implementation must be carefully considered based on
the threats and costs. This category is probably one of the
more challenging situations, where one must balance the
risk of the threats with potentially significant costs. The
fourth category includes two air purification technologies
that while commercially available are not associated with
a lot of performance data and design guidance. They may
be appropriate in some situations, but it can be difficult to
determine at the present time. Automated HVAC response
is also listed in the final category due primarily to the
limits of current sensor technology. Nevertheless, there are
some situations where the risks may be so significant that
this approach needs to be employed despite its cost and
challenges.
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Table 27 Summary of Retrofit Guidance for Retrofit Technologies
Retrofit Advantages Disadvantages Comments
System
Recommissioning
Envelope Tightening
Building
Pressurization
Relocation of Air
Intakes
Shelter-in-place
Isolation of Special
Spaces
Shutdown and
Purging
Automated HVAC
Response
Improves reliability of HVAC
systems for other protective
responses.
Improves IAQ and energy
efficiency.
Protects against outdoor
releases if effective filtration is
in place.
Improves IAQ and energy
efficiency.
Protects against outdoor
releases if effective filtration is
in place.
Protects against tampering with
accessible intakes.
Offers potential IAQ benefits
by avoiding ground level
contaminant sources.
Protects occupants against
outdoor, and some indoor,
releases.
Protects bulk of building from
releases in more vulnerable
spaces.
Can protect against outdoor
or indoor releases under some
circumstances.
Can contain release and
provide occupants with low
contaminant zones.
Provides no additional
protection beyond that inherent
in the design.
Requires effective filtration to
realize benefits.
Can be challenging to
implement and maintain
under all conditions in some
buildings.
Can be costly and impractical
in some circumstances.
Timing of occupant movement
critical to effectiveness.
Requires knowing that an
incident that merits sheltering
has taken place.
Does not protect those in space
of release.
Poor timing can increase
exposure.
Requires knowing that an
incident that merits action
has taken place.
Requires sensing beyond
current technology.
Proper response depends on
details of system and release;
not always clear.
Wrong timing or action can
increase exposure.
Benefits depend on
difference between
design intent and
existing performance.
More data needed on
cost and effectiveness
of sealing retrofits.
Amount of extra outdoor
air is based on climate
and airtightness.
Pressurization can lead
to envelope moisture
problems in cold
climates.
Occupant training and
communication are
important.
Design must be based
on driving pressures and
airtightness.
Lack of clear guidance
on design pressure
difference.
Even if proper action is
not always obvious, the
capability has value.
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Table 28 Summary of Retrofit Guidance for Retrofit Approaches
Retrofit Advantages Disadvantages Comments
Enhanced Particle
Filtration
Gaseous Air
Cleaning
UV Germicidal
Irradiation
Photocatalytic
Oxidation
All Filtration
and Air Cleaning
Technologies
Work-area
Treatment
Protection against bioagents.
Standard for removal efficiency,
MERV values.
Part of current practice.
General IAQ improvements.
Protection against gaseous
contaminants.
General IAQ improvements.
Protection against bioagents.
Low pressure drop.
General IAQ improvements.
Protection against bioagents
and gases.
Low pressure drop.
Always operating; no
timing issues.
Doesn't increase exposure
for any release scenarios.
Capture of contaminant releases
associated with localized
activities.
Pressure drop associated with
high-efficiency filters.
No standard test method.
Pressure drop associated with
high-efficiency filters.
More design guidance needed.
No standard test method.
Design guidance needed.
No standard test method.
No standard method to
determine whether catalyst
has become poisoned.
Design guidance needed.
Lack of test methods for
gaseous air cleaning,
UVGI, andPCO.
Current equipment not
rated for capture efficiency.
Lack of test methods for
gaseous removal.
Must control filter
bypass before upgrade.
Combination with
envelope tightening
provides maximum
protection against
outdoor releases.
Challenge of protecting
against range of gaseous
contaminants.
Challenge of protecting
against range of biological
contaminants.
Challenge of protecting
against range of biological
and gaseous contaminants.
Must address envelope
air leakage to realize
effectiveness.
Bypass will decrease
effectiveness.
Combination of methods
needed to protect against
range of chembio
contaminants.
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Table 29 Framework of Retrofit Options
Retrofits Comments
Implement in any building
System Recommissioning
Enhanced Particle Filtration
Shelter-in-place
Based on energy and IAQ benefits
Range of options depending on threats and building
Consider independent of threats
Envelope Tightening
Building Pressurization
Shutdown and Purging
Based on energy and potential IAQ benefits
As long as not cost-prohibitive for existing HVAC
system and controls
Consider if threats indicate and costs are commensurate
Isolation of Special Spaces
Relocation of Air Intakes
Work-area Treatment
Gaseous Air Cleaning
More performance data or technology development needed for general application
UV Germicidal Irradiation
Photocatalytic Oxidation
Automated HVAC Response
More likely to be appropriate in healthcare facilities
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5.0
Conclusions
This report has presented and discussed a number of
retrofit options for improving the protection of buildings
against chembio releases, including information about their
potential impact on occupant exposure and their cost. This
information is intended to help building owners and others
faced with decisions on how best to protect their buildings
from such releases. In order to make these decisions for a
particular building, the responsible parties must begin with an
assessment of the risk of the building and its vulnerabilities,
and as a result, determine the level of protection and the
associated expenditures that are appropriate. These decisions
are difficult, though some guidance has been developed to
assist in making them. But given that a decision has been
made to increase the protection of a building through the
application of such retrofits, the information in this report
should be useful in determining which retrofits make sense
for a given building and system and how they should be
implemented.
The retrofit options considered in this report focus on
commercially available options for engineering and
building system retrofits, as opposed to physical security
and other building management approaches. The options
include filtration and air-cleaning technologies, changes in
ventilation system operation, attempts to reduce the entry
of outdoor releases via envelope infiltration, and shelter-in-
place. However, before pursuing any of these retrofit options
in a particular building, it is essential to assess the current
condition of the building's HVAC systems and to bring their
operation in line with the design intent through a so-called
recommissioning effort. Such an effort should address system
airflow rates, control systems and the associated sensors,
filter fit and air seal, and other aspects of system operation
and maintenance. Without a properly operating ventilation
system and a maintenance program to keep it that way, no
retrofit should be expected to provide the level of protection
of which it may be capable.
In terms of the retrofits themselves, filtration and air cleaning
have the advantage of not relying on any advanced warning
of a release or on a human or automated response. Particle
filtration benefits from an established method of testing that
allows one to select filters based on MERV ratings, while
gaseous air cleaning and other air cleaning options do not yet
have such a method of testing. This lack of standards
makes it much more difficult to specify such systems
and to determine the anticipated benefits. For a filtration
or air-cleaning system to be effective, it must be properly
installed and maintained over time with a focus on
controlling bypass around the filters. When considering
outdoor contaminant sources, reducing envelope leakage
is critical to achieving the potential benefits of filtration.
If the building has typical levels of envelope airtightness,
the resulting infiltration can defeat the high levels of
protection that are possible with good filtration and air
cleaning. Similarly, while reducing infiltration through
airtightening and system airflow control can provide
protection against such outdoor releases, these approaches
are much more effective if there is good filtration of the
intake air.
Many of the other retrofit options require sound operational
decisions during a chembio release in order to provide
effective protection. Such decisions include whether and
when to shut down a system or use it to purge the building,
and whether and when to send occupants to a shelter-in-place
zone. Making and implementing these decisions depends on
knowledge about the event, training in advance of the event,
and communications both before and during the event.
While this effort has provided useful insight and tools for
considering chembio retrofits, additional work would be
valuable in increasing the understanding of retrofit impacts
for more building and system types, release scenarios, and
retrofit approaches. In particular, there are specific building
types, such as educational, healthcare, and retail facilities,
that are unique and merit more individual attention. In
addition, unitary systems and fan coil units are limited in
the filtration options that they can accommodate and need
to be examined more closely. Finally, there are an infinite
number of release and building occupancy scenarios that
may be considered. Further examination beyond the generic
cases studied here is likely to provide additional insights into
building protection. Other ideas for follow-up work include
field testing to "validate" the simulation results, tools to help
with the design and implementation of the retrofit options,
and research to document the indoor air quality and energy
efficiency benefits of some of the retrofits.
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-------
6.0
Acknowledgements
This effort was supported by the U.S. Environmental
Protection Agency under Interagency Agreement No. DW-
13-93010301-0 but was not subjected to EPA peer review.
The conclusions in this paper are therefore those of the
authors and are not necessarily those of the U.S. EPA. The
authors express their appreciation to John Chang and Jacky
Rosati at EPA, as well as Harold Marshall, Julie Wean, Doug
Thomas, and Jatin Patel at NIST. The assistance of Jose Reig
and Guillermo Ramsey of ESE Architects and Engineers
is also acknowledged. The authors greatly appreciate the
many helpful suggestions made by the following reviewers:
William Bahnneth, Barney Burroughs, Joan Bursey, Michael
Gressel, Patrick Spahn, and Steve Treado.
-------
-------
7.0
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Appendix A
Life-cycle Cost Analysis Tool
for Chem/Bio Protection of Buildings: Software Primer
(software available for download at http://www2.bfrl.nist.gov/software/LCCchembio/index.htm
Background
The National Institute of Standards and Technology (NIST)
is a nonregulatory federal agency within the U.S. Commerce
Department's Technology Administration. NIST develops
and promotes measurement, standards, and technology to
enhance productivity, facilitate trade, and improve quality
of life. In the aftermath of the attacks of September 11,
2001, NIST has taken on a key role in enhancing the
nation's homeland security.
NIST's Building and Fire Research Laboratory (BFRL) has
as its mission to meet the measurement and standards needs
of the building and fire safety communities. A key element
of that mission is BFRL's commitment to homeland security.
Specifically, the goal of BFRL's homeland security effort
is to develop and implement the standards, technology, and
practices needed for cost-effective improvements to the
safety and security of buildings and building occupants,
including evacuation, emergency response procedures, and
threat mitigation.
Due to concerns about potential airborne chemical and
biological releases in or near buildings, building owners
and managers and other decision makers are considering
retrofitting their buildings to provide better protection against
such events. A wide range of technologies and approaches are
being proposed with varying levels of efficacy and cost, as
well as with varying degrees of applicability to any particular
building or ventilation system.
Through support from the EPA Safe Buildings Program,
BFRL's Indoor Air Quality and Ventilation Group and
the Office of Applied Economics (OAE) are developing
guidance on building retrofit technologies and approaches
to promote increased building protection from chemical
and biological attack. This guidance will provide building
owners, managers, engineers, and other decision makers with
information about various retrofit strategies to improve the
safety of their buildings against airborne hazards and with
economic tools for use in selecting cost-effective approaches
to mitigating those hazards.
The Life-Cycle Cost Analysis Tool (LCAT) for chem/bio
protection of buildings incorporates and integrates research
being conducted by OAE under the EPA Safe Buildings
Program and under BFRL's homeland security effort. OAE's
research focuses on developing economic tools to aid facility
owners and managers in the selection of cost-effective
strategies that respond to natural and human-made hazards.
Economic tools include evaluation methods, standards that
support and guide the application of those methods, and
software for implementing the evaluation methods. OAE's
research has produced a three-step protocol for developing
a risk mitigation plan for cost-effective protection of
constructed facilities. This protocol has three essential
components: risk assessment, identification of potential
mitigation strategies, and economic evaluation. LCAT is
designed to help implement the third step in the protocol,
economic evaluation.
A brief synopsis of the three-step protocol is provided here.
Users interested in an in-depth description are referred
to NISTIR 7073. Risk assessment is used to identify the
risks confronting a facility and includes development of
possible damage scenarios, probability assessments for these
scenarios, and identification of the facility's vulnerabilities
and critical areas. Identification of mitigation strategies
provides performance and cost data for the possible
combinations of risk mitigation strategies. Combinations of
risk mitigation strategies are used to create a candidate set
of alternatives for in-depth economic evaluation. The third
component, economic evaluation, enables building owners
and managers to evaluate each alternative combination of
risk mitigation strategies and the sequence of cash flows
associated with their implementation. The alternative
combination that results in the lowest life-cycle cost is
designated the cost-effective risk mitigation plan.
Economic Evaluation Methods
Several methods of economic evaluation are available to
measure the economic performance of a new technology,
a building system, or like investment, over a specified
time period. Two of these methods—life-cycle cost and
present value of net savings—are especially well suited
to the economic evaluation of chem/bio hazard mitigation
retrofit strategies. OAE has extensive experience with both
methods. OAE's research on life-cycle cost analysis spans
more than 30 years. Early work by OAE economists led to
the development of an industry consensus standard, ASTM
E 917, for the life-cycle cost method. OAE's life-cycle
cost research was extended to the economics of protection
against natural disasters shortly thereafter. More recent
work has focused on specifying cost-effective responses to
terrorist risks. OAE's research on present value of net savings
paralleled its research on the life-cycle cost method and led
to the development of an industry consensus standard,
ASTM E 1074. OAE's ongoing research links the
standardized economic evaluation methods with a well-
defined cost-accounting framework and with software to
make implementation straightforward. The algorithms "sit"
behind the LCAT graphical user interface. OAE believes
most users prefer it that way so they can focus on only
those data elements required to perform the life-cycle cost
calculations. Users interested in mastering the calculation
procedures/algorithms employed in LCAT are referred to
NISTIR 7073.
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Life-Cycle Cost Method
The life-cycle cost (LCC) method measures, in present-value
or annual-value terms, the sum of all relevant costs associated
with owning and operating a building over a specified period
of time. The basic premise of the LCC method is that, to
an investor or decision maker, all costs arising from that
investment decision over time are potentially important
to that decision. Applied to chem/bio hazard mitigation,
the LCC method encompasses all relevant costs over a
designated study period, including the costs of designing,
retrofitting, constructing/installing, operating, maintaining,
repairing, replacing, and disposing of a particular design or
system. Pure benefits that result (e.g., increased rental income
due to improvements) are also included in the calculation of
the LCC.
The LCC method is particularly suitable for determining
whether the higher initial cost of a building or system
specification is economically justified by lower future costs
when compared to an alternative with a lower initial cost but
higher future costs. If a design or system specification has
both a lower initial cost and lower future costs relative to an
alternative, an LCC analysis is not needed to show that the
former is economically preferable.
The alternative with the lowest initial investment cost
(i.e., first cost) is typically referred to as the base case.
The LCC method compares alternative, mutually exclusive,
chem/bio retrofit strategies that satisfy a minimum level of
functionality to determine which is the least-cost means (i.e.,
which minimizes life-cycle cost) of satisfying that level over
a specified study period.
Present Value of Net Savings Method
Information used to compute LCC can also be used to
calculate the present value of net savings (PVNS). PVNS
measures the net savings from investing in a given alternative
instead of investing in the foregone opportunity (e.g., the
base case). PVNS equals the difference between the LCC
of the base case and the LCC of the mutually exclusive
alternative under consideration.
Any pure benefits that result (e.g., increased rental income
due to improvements) are included in the calculation of
PVNS since they are included in the LCC calculation. With
respect to the base case, if PVNS is positive, the alternative
is economic; if it is zero, the alternative is as good as the base
case; if it is negative, the alternative is uneconomical.
Getting Started
The software includes four case study applications: (1) a
high-rise office building, (2) an office building lobby, (3)
an office building mail room, and (4) a single-story office
building. Associated with each case study application are
two case study files. One file is a high-level summary of
the proposed retrofit alternatives. The second file contains
a detailed listing of cost items associated with each of the
proposed retrofit alternatives. The case study files provide a
convenient frame of reference through which one can learn
about the capabilities of the software and experiment with
the various means for editing, creating, and deleting data
elements. The case study files are designed to illustrate a
wide variety of software features through a set of simplified,
yet fairly realistic building-related examples.
Tips on Analysis Strategy
Developing a cost-effective risk mitigation plan is a
complicated process, entailing two distinct levels of analysis.
This "analysis strategy" systematically adds increased detail
to the decision problem. The first level is referred to as the
baseline analysis. Here we are working with our "best guess"
estimates. The baseline analysis provides a frame of reference
for the sensitivity analysis, which systematically varies
selected sets of data elements to measure their economic
impacts on project outcomes, such as the life-cycle costs
of competing alternatives.
The starting point for conducting an economic evaluation
is to do a baseline analysis. In the baseline analysis, all
data elements entering into the calculations are fixed. For
some data, the input values are considered to be known
with certainty. Other data are considered uncertain and their
values are based on some measure of central tendency, such
as the mean or the median, or input from subject matter
experts. Baseline data represent a fixed state of analysis.
For this reason, the analysis results are referred to as the
baseline analysis. The term baseline analysis is used to
denote a complete analysis in all respects but one; it does not
address the effects of uncertainty. When you open any of the
case study files, the data elements displayed on the various
software screens are the baseline values.
Sensitivity analysis measures the impact on project outcomes
of changing the values of one or more key data elements
about which there is uncertainty. Sensitivity analysis can be
performed for any measure of economic performance (e.g.,
life-cycle cost or present value of net savings). Therefore,
a sensitivity analysis complements the baseline analysis by
evaluating the changes in output measures when selected data
inputs are allowed to vary about their baseline values.
Overview of the Case Study Applications
The case study applications describe a variety of chem/bio
retrofit strategies for four prototypical building renovation
projects. Note that the cost estimates are for purposes of
illustration only—actual renovations of different building
types will face different costs and different risk profiles.
The cost data associated with the four prototypical building
renovation projects are presented in Appendix C of this
report, where they are presented at two levels of detail.
A "summary" format highlights the key cost items. The
summary listing records the type of cost information that
would be suitable for presentation to senior management or
other decision makers. The summary format provides the
basis for the four sets of summary case study files—one for
each prototypical building renovation project. A "detailed"
format covers the type of cost information that would be
provided as part of a building condition assessment. The
detailed listing of cost items "rolls up" into the cost items
-------
listed in the summary format. The detailed format provides
the basis for the four sets of detailed case study files.
Assumptions and Cost Data
Each of the four case study applications covers a 20-year
period beginning in 2005. Life-cycle costs are calculated
using a 7 percent real discount rate for the baseline analysis.
Information on cost items is needed in order to calculate
life-cycle costs. Cost items are classified under two broad
headings: (1) protection costs and (2) event-related losses.
Protection costs represent all costs tied to the building or
facility under analysis that are not associated with an event.
They include the initial capital investment outlays for
facilities and site work, future costs for filter replacements
and electricity for fan motors, future costs for space heating
and cooling, future renovations, and any salvage value for
plant and equipment remaining at the end of the study period.
Protection costs are classified as either investment costs or
noninvestment costs.
Event-related losses are based on annual outcomes, each
of which has a specified probability of occurrence. Each
outcome has a nonnegative number of cost items associated
with it (i.e., an outcome may have no cost items associated
with it if it results in zero losses). Note that although logic
is included within the software tool to handle event-related
losses, no estimates of these losses are included in the case
study applications.
High-Rise Office Building
The objective is to protect an 11-story high-rise office
building from external discharge of contaminants from a
single source near the outside air intakes and from a larger
cloud approaching the building. The floor area of the building
is 11,148 m2 (120,000 ft2). The building was erected in the
mid-1960s and has a rectangular configuration. It has been
well maintained and does not show significant signs of
aging. The outside air intake louvers are approximately 6.1
m (20 ft) above the ground. A variety of materials compose
the exterior envelope, including granite, marble, face brick,
glass, and extruded aluminum. The facades on the short axis
of the building are faced with grey face brick. The facades on
the long axis of the building are insulated porcelain spandrel
panels and fixed aluminum frame windows.
The building includes a lobby and a mail room.
Retrofit strategies to protect the lobby from a discharge
of contaminants carried by an individual and to protect
the mail room from introduction of contaminants in mail
packages are handled in separate analyses.
To protect the building from an external release of
contaminants, it is desirable to seal the building envelope
and retrofit filters in the air-handling units. The proposed
improvements are presented as three options. Each option has
a different filtration level.
Retrofit Alternatives for Protecting the
High-Rise Office Building
Option 1 (Filtration Level 1) provides a low level of particle
filtration capability and no gaseous capability. It involves
the following set of improvements:
• Sealing the exterior windows to make the building more
airtight
• Relocating the outside air intake to the roof
• Replacing existing Minimum Efficiency Reporting Value
(MERV) 6 filters with MERV 11 high capacity filters
• Modifying the electrical feeders to accommodate higher
motor horsepower
• Providing an electrical quick shut-off mechanism to stop t
he air handlers and return exhaust fans as needed during
an emergency
• Sealing and isolating six conference rooms to serve as
shelters-in-place during an emergency
Option 2 (Filtration Level 2) provides a high level of
protection against particles but no gaseous protection.
It involves the following set of improvements:
• Sealing the exterior windows to make the building
more airtight
• Relocating the outside air intake to the roof
• Replacing existing MERV 6 filters with a three-stage
filter consisting of MERV 8 pre-filter, 85 percent efficient
MERV 13 intermediate filter, and a 99.97 percent High
Efficiency Particulate Air (HEPA) filter
• Modifying the electrical feeders to accommodate
higher motor horsepower
• Providing an electrical quick shut-off mechanism to stop
the air handlers and return exhaust fans as needed during
an emergency
• Sealing and isolating six conference rooms to serve
as shelters-in-place during an emergency
Option 3 (Filtration Level 3) provides a high level of
protection against particle and gaseous contaminants. It
involves the following set of improvements:
• Sealing the exterior windows to make the building more
airtight
• Relocating the outside air intake to the roof
• Replacing existing MERV 6 filters with a five-stage filter
consisting of MERV 8 pre-filter, 85 percent efficient
MERV 13 intermediate filter, 99.97 percent HEPA filter,
99.9 percent gas phase filter, and MERV 11-post-filter
• Modifying the electrical feeders to accommodate higher
motor horsepower
• Providing an electrical quick shut-off mechanism to stop
the air handlers and return exhaust fans as needed during
an emergency
• Sealing and isolating six conference rooms to serve as
shelters-in-place during an emergency
-------
Office Building Main Lobby
The objective is to protect the main lobby from a discharge
of contaminants carried by an individual. The main lobby
is a 4.3 m (14 ft) high space that is approximately 325 m2
(3,500 ft2) in size. It is defined by exterior glass curtain walls
on two sides and marble finished walls on the other two sides.
It is accessed from the exterior through a 14 m2 (150 ft2) glass
enclosed vestibule with a series of two rows of four balanced
glass doors. The lobby is open to an elevator bank.
To protect the main lobby from a discharge of contaminants
carried by an individual, it is desirable to isolate the
lobby with airtight walls and doors and to provide an air
conditioning system dedicated to the lobby and capable of
maintaining it under negative pressure. The system must
also be capable of purging the lobby—one hundred percent
outside air and exhaust—and filtering the supply and exhaust
air. The proposed improvements are presented as two options.
Each option has a different filtration level. The two options
link to Filtration Levels 2 and 3 for the high-rise office
building. Filtration Level 1 was not considered because it
would not provide the level of protection desired for the
main lobby.
Retrofit Alternatives for Protecting the Main
Lobby
Option 1 (Filtration Level 2) provides a high level of
protection against particles but no gaseous protection.
It involves the following set of improvements:
• Isolating the open side of the lobby from the rest of the
building by installing tempered glass partitions with serf-
closing doors that allow building occupants continued
access to the lobby
• Installing a new air handling unit to serve the main
lobby only
• Relocating the outside air intake to the roof
• Equipping the air handling unit with a three-stage filter
consisting of MERV 8 pre-filter, 85 percent efficient
MERV 13 intermediate filter, and a 99.97 percent HEPA
filter
• Modifying electrical feeders to accommodate higher
motor horsepower
• Removing the existing exhaust fan and install two new
exhaust fans—one to serve as return/exhaust fan to the
existing air handling unit and the second to return/exhaust
the air to the new air handling unit—and running an
exhaust duct from the return duct to an existing louver
near the fan, and installing filters at the discharge side of
the new exhaust fan
• Installing a quick shut-off mechanism to stop the fans
• Maintaining the main lobby under negative pressure with
respect to the surrounding areas and the outdoors during
normal operations and during an emergency
Option 2 (Filtration Level 3) provides a high level of
protection against particle and gaseous contaminants. It
involves the following set of improvements:
• Isolating the open side of the lobby from the rest of the
building by installing tempered glass partitions with self-
closing doors that allow building occupants continued
access to the lobby
• Installing a new air handling unit to serve the main lobby
only
• Relocating the outside air intake to the roof
• Equipping the air handling unit with a five-stage filter
consisting of MERV 8 pre-filter, 85 percent efficient
MERV 13 intermediate filter, 99.97 percent HEPA filter,
99.9 percent gas phase filter, and MERV 11 post-filter
• Modifying electrical feeders to accommodate higher
motor horsepower
• Removing the existing exhaust fan and install two new
exhaust fans—one to serve as return/exhaust fan to the
existing air handling unit and the second to return/exhaust
the air to the new air handling unit—and running an
exhaust duct from the return duct to an existing louver
near the fan and installing filters at the discharge side of
the new exhaust fan
• Installing a quick shut off mechanism to stop the fans
• Maintaining the main lobby under negative pressure with
respect to the surrounding areas and the outdoors during
normal operations and during an emergency
Office Building Mail Room
The objective is to protect the mail room from
contaminants coming in via mailed packages. The mail
room is approximately 334 m2 (3,600 ft2) in size. It has a
2.3 m (7 ft 8 in) high suspended acoustical ceiling and is
enclosed with CMU walls and modular steel partitions.
The mail room has three interior walls and one exterior wall.
One wall and all interior partitions extend to the height of the
ceiling. On two walls, a total of three single and double doors
lead directly into interior corridors. There is a roll-up door
on the exterior wall, which serves as a receiving area for the
mail room.
To protect the mail room from contaminants coming in via
mailed packages, it is desirable to isolate the mail room with
airtight walls and doors and to provide a separate dedicated
air conditioning system capable of maintaining the mail room
under negative pressure. The system must also be capable
of purging the mail room—one hundred percent outside air
and exhaust—and filtering the supply and exhaust air. The
proposed improvements are presented as two options. Each
option has a different filtration level. The two options link
to Filtration Levels 2 and 3 for the high-rise office building.
Filtration Level 1 was not considered because it would not
provide the level of protection desired for the mail room.
-------
Retrofit Alternatives for Protecting the Mail
Room
Option 1 (Filtration Level 2) provides a high level of
protection against particles but no gaseous protection.
It involves the following set of improvements:
• Sealing mail room envelope: walls, ceiling, doors,
and slabs
• Providing upgraded filtration to the existing air
conditioning system and providing a new dedicated
return/exhaust fan
• Equipping the existing air handling unit with a three-stage
filter consisting of MERV 8 pre-filter, 85 percent efficient
MERV 13 intermediate filter, and a 99.97 percent HEPA
filter
• Modifying electrical feeders to accommodate higher
motor horsepower
• Equipping the existing exhaust fan with a MERV 8
pre-filter, an 85 percent efficient MERV 13 intermediate
filter, and a 99.97 percent HEPA filter
• Installing a quick shuting off mechanism to stop the fans
• Maintaining the mail room negative with respect to
the surrounding areas and the outdoors during normal
operations and during an emergency
Option 2 (Filtration Level 3) provides a high level of
protection against particle and gaseous contaminants. It
involves the following set of improvements:
• Sealing mail room envelope: walls, ceiling, doors, and
slabs
• Providing upgraded filtration to the existing air
conditioning system and providing a new dedicated return/
exhaust fan
• Equipping the existing air handling unit with a five-stage
filter consisting of MERV 8 pre-filter, 85 percent efficient
MERV 13 intermediate filter, 99.97 percent HEPA filter,
99.9 percent gas phase filter, and MERV 11 post-filter
• Modifying electrical feeders to accommodate higher
motor horsepower
• Equipping the existing exhaust fan with a MERV 8
pre-filter, an 85 percent efficient MERV 13 intermediate
filter, a 99.97 percent HEPA filter, a 99.9 percent gas phase
filter, and a MERV 11 post-filter
• Installing a quick shut-off mechanism to stop the fans
• Maintaining the mail room negative with respect to
the surrounding areas and the outdoors during normal
operations and during an emergency
Single-Story Office Building
The objective is to protect a single-story office building from
external discharge of contaminants from a single source near
the outside air intakes and from a larger cloud approaching
the building. The gross floor area of the office building is
1,612 m2 (17,350 ft2). The air conditioning system consists
of 28 rooftop heat pumps. Each heat pump controls its own
outdoor intake, making it necessary to protect 28 air intake
locations. The system does not have exhaust fans. The excess
air is relieved through barometric dampers. Therefore,
controlled purging is not possible. In addition, the rooftop
units cannot be retrofitted with the necessary filters due to the
low static pressure of the fans and lack of space to install the
filters.
The physical arrangement of this building makes it difficult
to retrofit the filters. The proposed improvements are
presented as three options. Each option has a different
filtration level. The three options link to Filtration Levels 1,
2, and 3 for the high-rise office building.
Retrofit Alternatives for Protecting the Single-
Story Office Building
Option 1 (Filtration Level 1) provides a low level of particle
filtration capability and no gaseous capability. It involves the
following set of improvements:
• Sealing the exterior envelope to make the building
more airtight.
• Replacing existing MERV 4 filters with MERV 11 filters
• Installing a quick shut-off mechanism to stop the
rooftop heat pumps.
Option 2 (Filtration Level 2) provides a high level of
protection against particles but no gaseous protection. It
involves the following set of improvements:
• Sealing the exterior envelope to make the building
more airtight
• Providing an outside fan with a three-stage filter
consisting of MERV 8 pre-filter, 85 percent efficient
MERV 13 intermediate filter, and a 99.97 percent
HEPA filter
• Ducting the filtered air to the intake of each rooftop unit
• Installing the fan and filter on a new platform at roof
level with the ductwork on the roof
• Installing a quick shut-off mechanism to stop the rooftop
heat pumps and outdoor air fans
Option 3 (Filtration Level 3) provides a high level of
protection against particle and gaseous contaminants. It
involves the following set of improvements:
• Sealing the exterior envelope to make the building more
airtight
• Providing an outside fan with a five-stage filter consisting
of MERV 8 pre-filter, 85 percent efficient MERV 13
intermediate filter, 99.97 percent HEPA filter, 99.9 percent
gas phase filter, and MERV 11 post-filter
• Ducting the filtered air to the intake of each rooftop unit
• Installing the fan and filter on a new platform at roof level
with the ductwork on the roof
• Installing a quick shut-off mechanism to stop the rooftop
heat pumps and outdoor air fans
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The Cost-Accounting Framework
The flexibility of the life-cycle cost method enables us to
classify and analyze costs in a variety of ways. The result
is a more focused representation of costs, referred to as the
cost-accounting framework. The cost-accounting framework
provides a convenient means for summarizing all costs
entering into the life-cycle cost calculations. The framework
is organized around a budget category classification. The
budget category classification uses cost types and cost items.
The cost types are used as placeholders for summarizing
and reporting aggregated cost information. Each cost type
is a collection of cost items. Each cost item has a unique
set of identifiers that places it within the cost-accounting
framework.
The budget category classification has three cost types,
based on which category of the budget the funds come from.
These cost types are: (1) capital investment, (2) operations
and maintenance (O&M), and (3) other. These cost types
correspond to widely used budget categories for private and
public sector cost accounting. // is important to note that the
dollar amounts accruing to all three cost types are inclusive
of any expected event-related losses. In the context of the
previous section, capital investment costs accrue to the
investment cost category and O&M and other costs accrue
to the noninvestment cost category. All acquisition costs,
including costs related to planning, design, purchase, and
construction, are investment-related costs and fall under
the capital investment cost type. Residual values (resale,
salvage, or disposal costs) and capital replacement costs
are also investment-related costs. Capital replacement
costs are usually incurred when replacing major systems or
components (e.g., exhaust fans) and are paid from capital
funds. Cost items falling under the O&M cost type include
energy and water costs, maintenance and repair costs, and
minor replacements (e.g., replacing belts and seals) related to
maintenance and repair. O&M costs are usually paid from an
annual operating budget, not from capital funds. Other costs
are noncapital costs that cannot be attributed to the O&M
cost type.
Navigating Within the Software
This section gives you a guided tour of Version 1.0 of the
Life-Cycle Cost Analysis Tool (LCAT 1.0). The goal of
the guided tour is for you to work systematically through
the hierarchy of screens used to input, analyze, and display
project-related data.
Opening/Creating a Project File
Launch the software by clicking on LCAT 1.0 icon found on
your desktop or by clicking LCAT 1.0 in the Start menu in
Programs/Life-Cycle Cost Analysis Tool. The first screen to
appear prompts you to open an existing project file, create a
new project file, or open an example project. Figure Al is a
reproduction of the Prompt window. Recall that the software
comes with a set of case study files. Thus, even when you
launch the software for the first time, there are already
several example project files, any of which you may choose
to open. If you select Open an Existing Project or Open an
Example Project and click the Start button, then you will be
taken to the Open Project window. The Prompt window also
includes a View Tips checkbox. If you select View Tips and
click the Start button, you will be taken to the Software Tips
window. (Throughout this section, software features [e.g.,
buttons] are highlighted through the use of italics font.)
Figure A2 displays the Software Tips window. The Software
Tips window is designed as a handy reference for first-time
users. It highlights material contained in this Primer as well
as several basic concepts for navigating within the software
and for saving results.
As a first step, open one of the case study files and use the
File Save As feature to make additional copies with Ice
extensions. Suggested file names are testOl.lcc and test02.lcc.
Use the test files to gain familiarity with the software. This
way, if you inadvertently change or delete a data element, or
create a new data element, you can go back to the case study
file for the reference solution. When you use the File Save
As feature with one of the case study files, the new file (e.g.,
testOl.lcc) will be saved in the "existing projects" directory.
Figure Al Life-Cycle Cost Analysis Tool
Prompt Window
Life-Cycle Cost Analysis Tool
for Chem/Bio Protection
Of Buildings
'*" Open an Existing Project
<~ Open a New Project
•""" Open an &:ample Project
i/iew Tips
Start
NtST
Motional Institute »»
-------
Figure A2 Software Tip Window
Welcome!
This software enables you to define hazard scenarios, identify possible consequences
of those scenarios and compare costs associated with different strategies for protecting
your facilities from Chern/Bio hazards.
The following are a few tips for using the software.
View the software primer, case study examples, and a glossary of terms, by clicking on the Help
menu.
Use the _x| in the upper right hand corner to exit a window.
Save your data while working by clicking Save from the File menu.
Enter data following the tree hierarchy in the Cost Summary Window starting with the Description
section then add data for Alternatives and finally enter the Cost/Loss information.
Evaluate how changes in a single variable impact the calculated values of life-cycle costs in the
Sensitivity Analysis section.
Use the Data report to verify data inputs. Use the Results report to rewiewthe results.
Figure A3 Open Project Window
Look in: | C3 example ' | IS CJ' il
§ High-Rise Office (Detailed), Ice H Office Mail Room (Detailed), Ice
§ High-Rise Office (Summary), Ice |s3| Office Mail Room {Summary}. Ice
Blow -Rise Office (Detailed), Ice
8| Low-Rise Office (Summary), lee
Q Office Lobby (Detailed). Ice
IS| Office Lobby (Summary). Ice
Filename: Op
Files of type: |'.lcc j*j Car
alal
en |
eel
If you exit the software and later wish to open a user-created
"test" file, you will need to select Open an Existing Project
from the Prompt window.
Figure A3 is a sample Open Project window that lists the
various case study files provided with the software. The
Open Project window shown in Figure A3 was opened by
selecting the Open an Example Project option in the Prompt
window and clicking the Start button. Note that the high-rise
office building has two case study files—High-Rise Office
(Summary).lcc and High-Rise Office (Detailed).Ice. The
"summary" file is an abbreviated version of the high-rise
office building case study. It provides a convenient means for
highlighting key features of the software. It is used within the
Primer to illustrate these software features. The "detailed"
file demonstrates how to handle a fairly complicated retrofit
project. It focuses on breaking out the various cost items
presented in the summary file into their constituent parts.
Highlighting the desired file and clicking the Open button
opens that file. Double clicking on the highlighted file opens
the file as well. The Open Project window includes a Cancel
button. If you click on the Cancel button, you will return to
the Prompt window.
-------
Figure A4 Cost Summary Window When Starting a New Project
Cost Summary Window -
- Project
Description
Alternatives
Cost/Loss
- Uncertainty
Sensitivity
- Reports
Data
Results
Alternatives
r
r
r
r
Evaluation Method:
Cost Types by Budget Category:
I*' Capital Investment
I? OSM
I* Other
Measure of Economic Performance
Base Case
Aft. 1
Aft.2
Alt. 3
Cost Summary Window and Main Menu
The Cost Summary window is displayed whenever a new
project is started, an existing project file is opened, or a
case study file is opened. When a project is created, the
Cost Summary window is blank. Figure A4 is an example
of the Cost Summary window displayed when starting a
new project. As you enter data into the software, the Cost
Summary window displays the current value of life-cycle
costs for each cost type and alternative being analyzed. It
is recommended that you keep the Cost Summary window
open while working in the software. If you wish to close the
window, it can be reopened at any time by selecting Project
from the tool bar and then selecting Cost Summary.
The software is designed to analyze up to four alternatives
(see Figure A4). The Cost Summary window allows you to
select both the cost types and the alternatives to be included
in the economic evaluation. These "choices" are represented
in Figure A4 by the "cost type" check boxes and the
"alternative" check boxes within the Alternatives group box
in the lower left-hand corner.
A tree on the left-hand side of the Cost Summary window
serves as the Main Menu to the software. The tree contains
three top-level nodes: Project, Uncertainty, and Reports.
Recall that software features are highlighted through the use
of italics font. The tool bar at the top of the Cost Summary
window provides another means for accessing the three top-
level nodes. The tool bar also includes File and Help options.
File options include Save, Save As, Close Project, and Exit.
Help options include Tips, which opens the Software Tips
window, and Help, which opens an on-line version of the
Primer and a Glossary of Terms. If you wish to print the on-
line Primer from the Help menu, click Print the selected topic
option from the Print Topics pop-up window and then select a
printer from the pop-up Print window.
Project Information
The options listed under the Project node allow you to enter
project information, define alternatives, and manage cost-
related information.
Clicking the Description option on the Main Menu opens
the Project Description window. Here you can enter project
information such as the project's name, a brief description
of the project, the base year selected for all present value
calculations, the length of the study period, whether a
constant dollar or current dollar analysis is to be performed,
and the discount rate. Note that when a constant dollar
analysis is selected, you must use a real discount rate. When
a current dollar analysis is selected, you must use a nominal
discount rate. Within LCAT 1.0, the nominal discount rate
and the real discount rate are linked via a formula that
includes a term for general inflation. Figure A5 displays
the Project Description window for the high-rise office
building case study. The descriptive material is designed to
help decision makers differentiate among multiple projects
competing for limited investment funds.
Clicking the Alternatives option opens the Project
Alternatives window, which allows you to add and delete
project alternatives as well as enter information about the
alternatives. Figure A6 displays the Project Alternatives
window for the high-rise office building case study. The Base
Case tab is selected. The window is constructed so you can
switch from one alternative to another. The text box in the
middle of the window allows you to enter a brief description
of the alternative, which serves to differentiate one alternative
from another.
Cost-related input screens for the software product are of two
basic types: (1) protection costs and (2) event-related losses.
You access these screens by selecting the Cost/Loss option on
the Main Menu.
Protection Costs
Clicking the Cost/Loss option opens the Protection Costs/
Event-Related Losses window. This screen manages the
creation, deletion, and editing of protection costs and event-
related losses. Upon entering the Protection Costs/Event-
Related Losses window, you must select the alternative for
which information is to be reviewed or input. Both the costs
and events portions of the window are active for the selected
-------
Figure A5 Project Description Window for the
High-Rise Office Building Case Study
Project Description - High-Rise Office Building
Project Name:
Project Description:
The objective is to protect an 11-story high-rise office building from
external discharge of contaminants from a single source near the
intakes and from a larger cloud approaching the building. To
protect the building from an external release, it is desirable to seal
the building envelope and retrofit filters in the air-handling units.
The proposed improvements are presented as three options. Each
option has a different filtration level. NOTE: The high-rise office
Base Year:
[2CC5Vj
Analysis Information
<* Constant Dollar Analysis
Real Discount Rate:
f" Current Dollar Analysis
Length of Study Period f/ears):
I af
Figure A6 Project Alternatives Windows for the
High-Rise Office Building Case Study
HI Project Alternatives -
Base
Case
%ema
Alternative 1
live Name:
High-Rise Office Building
Alternative 2 ] Alternative 3
Level 1 Protection
description:
Option 1 provides a low level of particle filtration capability
and no gaseous capability. Option 1 involves the following
set of mprovements. Sealing the exterior windows to make
:he bulding more airtight. Replacing existing MERVSfters
with MERV11 high capacity filters. Modifying the electrical
:eeders to accommodate higher motor horsepower.
Provid ng an electrical quick shut off mechanism to stop the
air handlers and return exhaust fans as needed during an
emergency.
Delete Alternative
-------
alternative. Since our focus is on protection costs, however,
we will address only the cost portion of the window here. The
following subsection deals with event-related losses. Once
the alternative is selected, the Protection Costs/Event-Related
Losses window displays all cost items associated with that
alternative. Figure A7 is an example of the Protection Costs/
Event-Related Losses window for the Base Case. Notice that
the protection costs are listed in alphabetical order according
to their Budget Category—Investment, O&M, and Other. If
a large number of cost items have been entered, some costs
will be hidden but can be viewed by scrolling down the list.
In this case, no costs are hidden.
Highlighting and clicking the selected cost item opens the
appropriate Cost Information window. This "edit" feature
allows you to review and, if desired, modify any previously
recorded information for the cost item of interest. Figure A8
is an example of the Capital Investment Cost Information
window for the high-rise office building case study. Figure
A8 displays information on the HVAC Upgrade cost item for
Alternative 1 (Option 2, enhanced protection from biological
contaminants). Figure A9 is an example of the O&M Cost
Information window for the Replacing HEPA Filters cost
item for Alternative 1. Figure A10 is an example of the Other
Cost Information window for the Change in Traffic Pattern
cost item for Alternative 2 (Option 3, enhanced protection
from chemical and biological contaminants).
Figure A7 Protection Costs/Event-Related Losses
Window for the High-Rise Office Building Case
Study: Protection Costs for the Base Case
Alternative: BC: Level 1 Protection
Costs
Investment: Electrical Modifications
Investment: HVAC Upgrade
Investment: Relocate .Air Intakes to Roof
Investment: Sealing the Envelope
Investment: Shefter-ln-Place
O&M: Electricity (Heat, Cool, Ltg, 04S Equip)
OSM: MERV 6 Replacement Cost Avoided
OSM: Replacing Filters {MERV 11}
Add Investment Cost
Add O&M Cost
Add Other Cost
Delete All
Events
Add Event
The Protection Costs/Event-Related Losses window is
the means through which new cost items are created. The
creation of a new cost item is accomplished by selecting
the appropriate Budget Category cost type button—Add
Investment Cost, Add O&M Cost, or Add Other Cost—from
the list on the right. The software then opens the Cost
Information window associated with the selected cost type.
The Cost Information windows allow you to name the cost
item, generate a cost estimate via separate entries for quantity
and unit cost, and specify the timing of cash flows and any
escalation rates that need to be applied (see Figures A8, A9,
andAlO).
Reference to Figures A8, A9, and A10 record the cost choices
that map individual cost items into the cost types reported
in the Cost Summary window. The Capital Investment Cost
Information window offers three choices for classifying a
cost item: (1) Initial (2) Replacement, and (3) Salvage. An
initial investment cost, as its name implies, occurs at the
beginning of the Base Year (i.e., Year 1 or, in this case, 2005).
A capital replacement cost occurs in some future year. Use
the drop-down menu to specify the year in which the capital
replacement is to take place, recalling that Year 1 is the Base
Year. A salvage value is a negative capital cost (i.e., a receipt)
occurring at the end of the study period. The salvage value is
the value of the asset, assigned for tax computation purposes,
that is expected to remain at the end of the depreciation
period. The choices for classifying a cost item for O&M and
Other costs (see Figures A9 and A10) are the same:
-------
Figure A8 Capital Investment Cost Information Window for the High-Rise Office Building
Case Study: HVAC Upgrade for Alternative 1
~ High-Ms^ Office Building
Alternative: Aft. 1: Level 2 Protection (Biological Agents)
Cost ltem:
Quantity:
Unit Cost:
Capital Investment
<• Initial
<~ Replacement
^ Salvage
Figure A9 O&M Cost Information Window for the High-Rise Office Building Case Study:
Replacing HEPA Filters for Alternative 1
,0aM Cost Infprpwtim - High-Rise '-QjFpce Building,
tertative: AH. 1: Level 2 Protection (Biological Agents)
Cost Item:
Quantity:
Unit Cost:
O&M
6.00
f~ Annually Recurring
(* Periodic (other than annual)
(~ Aperiodic
Escalation Rate:
First Occurrence:
Last Occurrence:
Occurs Every (in years):
J
_» fTear = 2CB5)
20
_»J [Year = 2024}
Figure A10 Other Cost Information Window for the High-Rise Office Building Case Study:
Change in Traffic Pattern for Alternative 2
.Other.Cost Infopnatjon.- High-Rise .dffieg. Building
Alternative: AH. 2: Level 3 Protection (Chemical & Biological Agents)
Other
Cost Item
Quantity-:
Unit Cost:
1.00
5.000.00
f*~ Annually Recurring
<~ Periodic {other than annual)
C Aperiodic
Escalation Rate:
(1) Annually Recurring, (2) Periodic (other than annual),
and (3) Aperiodic. Periodic costs, such as HEPA filter
replacements, occur less frequently than annually—say
every three years. Aperiodic costs are one-time costs that
occur at some point in the future. If feasible, when preparing
estimates for a cost item, include allowances for design/
engineering services, taxes, overhead, and other indirects.
Event-Related Losses
Treatment of event-related losses is an important part of a
"balanced" life-cycle cost analysis whenever chem/bio or
other human-made or natural hazards are involved. LCAT
1.0 treats events as a hierarchy. Associated with an event
are outcomes and outcome probabilities. Associated with
outcomes are outcome costs. The combination of outcome
probabilities and outcome costs are the "losses" associated
with a given event.
As noted earlier, clicking the Cost/Loss option opens the
Protection Costs/Event-Related Losses window. This screen
manages the creation, deletion, and editing of protection
costs and event-related costs. Upon entering the Protection
Costs/Event-Related Losses window, you must select the
alternative for which information is to be reviewed or input.
Both the costs and events portions of the window are active
for the selected alternative. However, we will address only
the event-related costs portion of the window here. Once
the alternative is selected, the screen displays all events
associated with that alternative.
Highlighting and clicking the selected event opens the Event
Information window. This feature allows you to review and,
if desired, modify any previously recorded information for
the event of interest. The Protection Costs/Event-Related
Losses window is the means through which new events are
created. The creation of a new event is accomplished by
-------
selecting Add Event from the list on the right. The software
then opens the Event Information window. The Event
Information window allows you to name the event, provide a
brief description of the event, enter the dates of first and last
occurrence, and edit event-related outcomes. First occurrence
and last occurrence specify the period of time over which
a specific set of event-related losses occur. The rationale
behind "breaking" events up into segments over the study
period is that some mitigation measures may affect outcome
probabilities. Such mitigation measures, if implemented in
the future, might significantly reduce outcome probabilities
and hence event-related losses. Figure All is an example of
the Event Information window.
Associated with each event is a set of outcomes. Information
on event-related outcomes is accessed via the Outcomes/
Outcome Costs window. This screen is reached by clicking
the Edit Outcomes option in the Event Information window
(see Figure All). Clicking the Edit Outcomes option opens
Figure All Event Information Window
Alternative: BC: Level 1 Protection
Evert:
Description:
Classification Information
First Occurrence: |1
Last Occurrence: |1
(Year = 2005)
] (Year = 2COE
Edit Outcomes
-------
the outcomes portion of the Outcomes/Outcome Costs
window. Figure A12 is an example of the Outcomes/Outcome
Costs window. This screen manages the creation, deletion,
and editing of outcomes. The Outcomes/Outcome Costs
window displays all outcomes associated with the event of
interest. The event/outcome costs portion of the Outcomes/
Outcome Costs window is initially grayed out, indicating that
it is inactive. However, once an outcome is selected, the costs
associated with that outcome become active.
Highlighting and clicking the selected outcome opens the
appropriate Outcome Information window. This feature
allows you to review and, if desired, modify any previously
recorded information for the outcome of interest. The
Outcomes/Outcome Costs window is the means through
which new outcomes are created. The creation of a new
outcome is accomplished by selecting Add Outcome from
the list on the right. The software then opens the Outcome
Information window. The Outcome Information window
allows you to name the outcome, provide a brief description
of it, assign a probability of occurrence for it (outcome
probabilities are a by-product of the risk assessment), update
the sum of all outcome probabilities for the event of interest,
and edit outcome-related cost items. Figure A13 is an
example of the Outcome Information window.
Figure A12 Outcomes/Outcome Cost Window
Outcomes/Outcome Costs - High-Rise Office Building
^^^^^^^^^^^^^^^^^^^^^^^^^^^f^'^^'*^^'^^'^S^^^^^^'^^'^^^*'^^fa^^O!!la
•Alternative: BC: Level 1 Protection
Event:
Event Outcome
Add Outcome
Delete .All
-------
Outcomes are characterized by their severity and their
occurrence probabilities. An event includes the full range of
outcomes from no damage to extreme damage. For a given
event, the sum of all outcome probabilities equals 1.0. Thus,
the no damage outcome would usually have a very high
probability, corresponding to maintenance of the status quo,
whereas an extreme damage outcome would have a very low
probability. Outcome probabilities are the "key" driver of
event-related losses since these losses are "expected" values.
Outcome probabilities are expressed as annual values. Thus,
the "chance" an event-outcome combination occurs in a
given year equals its outcome probability.
Because event-related losses are expected to have a major
influence on which alternative is the most cost effective,
the sum of all outcome probabilities is required to equal 1.0
in order for either the Data Report or the Results Report to
be output. OAE's objective was to avoid situations where
losses were either ignored (i.e., a sum less than 1.0) or double
counted (i.e., a sum greater than 1.0). Once an event has
been created and one or more outcomes assigned to it, it
is possible to edit the outcome probabilities. Once the sum
of all outcome probabilities equals 1.0 (100 percent in the
Probability Information group box), it is possible to generate
both the Data Report and the Results Report. The Data
Report is designed as a check on user-supplied inputs so it
includes the outcome probabilities.
Figure A13 Outcome Information Window
Memative: BC: Level 1 Protection
Event:
Outcome:
Description:
Probability Information
Outcome Probability:
Sum of all Outcome Probabilites for this Event:
O.QOWK
Update Total
-------
Associated with each outcome is a set of event-related
cost items. Typical event-related cost items are damage to
the facility, loss of use of the facility (e.g., function and
contents), and medical expenses. For example, if an event-
outcome combination produced damage to the facility,
equipment replacements might result. Information on
event-related cost items is accessed by closing the Outcome
Information window (see Figure A13), which reveals the
event/outcome cost portion of the Outcomes/Outcome Costs
window. This screen manages the creation, deletion, and
editing of event-related cost items. The Outcomes/Outcome
Costs window displays all event-related cost items associated
with the outcome of interest.
Highlighting and clicking the selected event-related cost
item opens the appropriate Event/Outcome Cost Information
window. This feature allows you to review and, if desired,
modify any previously recorded information for the event-
related cost item of interest. The Outcomes/Outcome Costs
window is the means through which new event-related cost
items are created. The creation of a new event-related cost
item is accomplished by selecting the appropriate Budget
Category cost type button—Add Investment Cost, Add O&M
Cost, or Add Other Cost—from the list on the right. The
software then opens the Event/Outcome Cost Information
window, which allows you to name the event-related cost
item, generate a cost estimate via separate entries for quantity
and unit cost, and specify any escalation rates that need to
be applied. Figure A14 is an example of the Event/Outcome
Cost Information window.
Figure A14 Event/Outcome Cost Information
Window
Event:
Outcome:
Alternative: BC: Level 1 Protection
Cost Type: Capital Investment
Event/Outcome Cost Item:
Quantity:
Unit Cost (3):
Escalation Rate {%):
1.00
-------
Cost Summary Window
Once all data have been input, the Cost Summary window
displays the life-cycle costs for each alternative. Costs
are reported for each cost type and in total. Figure A15
reproduces the Cost Summary window for the completed
baseline analysis for the high-rise office building case study.
The Cost Summary window provides the option for you
to view calculated values for a measure of economic
performance other than life-cycle costs. The drop-down
menu in the Evaluation Method box lets you select the
PVNS (present value net savings) as an alternative measure
of economic performance. The PVNS values reported on
the Cost Summary window are calculated vis-a-vis the Base
Case. PVNS measures net savings of investing in the given
alternative instead of investing in the Base Case. Thus, when
the PVNS method is selected, the only meaningful values are
the ones listed under the column headings Alt. 1, Alt. 2, and
Alt. 3.
Figure A15 Cost Summary Window for the High-Rise Office Building Case Study:
Baseline Analysis
lllll^p™-™
- Project
Description
Alternatives
Cost/Loss ,- , ,. .. ., ,
Evaluation Method:
- Uncertainty
Sensitivfty
- Reports
Data C031 Types by
Results
I* Capital Inv
Alternatives
^ I^.C??!S W 08M
17 .Alt. 1
17 A"- 2 W Other
r
Measure of Economic Performance
Base Case Alt. 1 AIL 2 Alt. 3
LCC j-J $3.485.148 $3.042.030 $4.579.809
Budget Category:
ssbnent S982.703 S1. 207.213 S2.028.125
S2.502.445 S3.152.657 S5.134.405
SO -51.317.840 -S2.582.721
-------
Sensitivity Analysis
Recall that in the baseline analysis all data elements entering
into the calculations are fixed. Thus, the baseline analysis is a
complete analysis in all respects but one: it does not address
the effects of uncertainty. Note that the baseline analysis
for the four case study applications includes only protection
costs.
Sensitivity analysis, as implemented inLCAT 1.0, lets
you evaluate how changes in a single variable impact the
calculated values of life-cycle costs. The sensitivity analysis
feature in LCAT 1.0 is based on techniques presented in
ASTM Standard Guide E 1369. Depending on the variable
selected, it may impact a single alternative or it may impact
all alternatives.
The Sensitivity Analysis window is entered by clicking the
Sensitivity option under the Uncertainty node. The window,
as configured in Version 1.0, has a single tab, Change in a
Single Factor.
The left-hand side of the Change in a Single Factor tab lists
the hierarchy of factors that can be evaluated. Each factor
is associated with a node in the hierarchy. Upon entering
the tab, the Project and Alternatives nodes appear at the
left. All alternatives evaluated in the baseline analysis are
listed immediately below the Alternatives node. The squares
immediately to the left of each node in the hierarchy are
marked with a + (plus sign) or a - (minus sign). A plus sign
means that additional nodes and/or factors reside beneath that
node. A minus sign means that a node has been opened. Since
each project has alternatives associated with it, upon entering
the Change in a Single Factor tab, you will note that the
Alternatives node has a minus sign in its square on the left.
Nodes can be opened or closed. For example, clicking the
square by the Project node opens the node and the single
factor Discount Rate (7.00 percent) appears beneath it.
Note that there is no square to the left of Discount Rate.
This means that Discount Rate is a factor that can be
selected for evaluation. Note that the factor line in the
hierarchy includes both the factor name (Discount Rate)
and its value (7.00 percent). Highlighting the factor Discount
Rate (7.00 percent) selects that factor. The right-hand side
of the screen includes the Results group box, a drop-down
menu for percent changes about the baseline value of the
selected factor, and a Compute button. Clicking on the
Compute button causes three sets of values to be computed.
Figure A16 shows the results of a 10 percent deviation about
the baseline value of the discount rate. Note that the name of
the factor appears at the upper left-hand corner of the Results
group box. Since the Discount Rate is the same for each
alternative, results for the Base Case, Alternative 1,
and Alternative 2 are reported. Note that the Minimum,
Baseline, and Maximum values for the factor, Discount Rate,
are displayed. Figure A16 shows that the discount rate has a
fairly strong impact on the computed value of life-cycle
costs for the Base Case, Alternative 1, and Alternative 2.
Figure A16 Sensitivity Analysis Window: Using the Change in a Single Factor Tab
to Evaluate the Impact of the Discount Rate on Life-Cycle Costs
•ipensitivift.AnalyBis-.High-Rise.Offl^.Building
c
lange in a Single Factor
- Project
Discount Rate {7.00%}
- Alternatives
* BC Level 1 Protection
+ Alt 1 Level 2 Protection (Biological Agents)
* Alt 2 Level 3 Protection (Chemical S Biological
< >
Range: |v-10:> _^j \ Compute jj
Results
Discount Rate
Base Case Alternative 1 Alternative 2
Minimum (6.30%) S3.626.725 S3.143.056 54.700.555
Baseline (7.00%) S3.485.148 S3.042.030 54.579.809
Maximum (7.70%) 53.355.070 52.949.131 S4.4S8.277
Save Results for Reports
Clear Saved Results | Discount Rate
Clear Saved Resute | A*- 1: Level 2 Protection (Biological Agents): Replacing Filters (HEPA):
Clear Saved Results I Alt- 2: Level 3 Protection {Chemical _Biological Agents}: Replacing
-------
Figure A17 uses Alternative 2 to illustrate how to open
up the hierarchy within a given alternative. The nodes
immediately beneath the Alt. 2: Level 3 Protection (Chemical
& Biological Agents) node are labeled Costs and Events.
Additional nodes are listed beneath the Costs node. Opening
the Costs node, we see that 11 nodes are listed beneath it.
These nodes correspond to the cost items entered via the
Capital Investment, O&M, and Other Cost Information
windows. Note that each of the 11 nodes indicates the
budget category it falls under. One of the 11 nodes has
been opened—O&M: Replacing Gas Phase Filters—to
reveal factors. The factor selected for analysis is the Unit
Cost of Replacing Gas Phase Filters. Under the Range
drop-down menu, we have selected a 10 percent deviation
about the baseline value of the annually recurring Unit Cost
of $108,000 (i.e., $648,000 for all six units). Clicking the
Compute button causes three sets of values to be computed.
Because this factor affects only Alternative 2, only values
for Alternative 2 are displayed. Reference to the Results
group box reveals that this factor has a strong impact on
life-cycle costs.
Event-related costs are evaluated by opening the Events node
for the alternative of interest. If events have been entered,
the nodes listed beneath the Events node are the individual
events defined by the user. Beneath each individual event
node are the outcomes. If an outcome had costs associated
with it, then the event/outcome cost items are listed as nodes
beneath it. The factors—unit cost and escalation rate—appear
beneath each event/outcome cost item.
The bottom right-hand portion of the window contains the
Save Results for Reports group box. As its name suggests, the
Save Results buttons may be used to save up to three sets of
computed results. For example, the discount rate had a strong
impact on life-cycle costs for the Base Case, Alternative 1,
and Alternative 2. Thus, saving these results might prove
useful in supporting a recommendation for one alternative
over another. Any results that you choose to save will appear
in the Results Report. Note that more than one range can be
used and saved for a single factor.
Figure A17 Sensitivity Analysis Window: Using the Change in a Single Factor
Tab to Evaluate the Impact of the Unit Cost of Replacing Gas Phase Filters on
Life-Cycle Costs for Alternative 2
™==^
Change in a Single Factor
- Project
Discount Rate !7.£KK)
~ Alternatives
+ BC: Level 1 Protection
t All 1 Level 2 Protection (Biological Agents)
- AH. 2: Level 3 Protection (Chemical S Biological
- Costs
Other: Change in Traffic Pattern
investment: Electrical Modifications
O&M: Electricity {Heat, Cool, Ltg, 043 Equip)
investment: HVA£ Upgrade
O&M: MERV 6 Replacement Cost Avoided
Other: Productive/ Improvement (1.{]>;)
Investment: Relocate Air Intakes to Roof
- O&M: Replacing Fibers {Gas Phase)
UnS Cost ($108.000)
Escalation Rate (0.50';)
O&M: Replacing Filters (HEPA)
O&M; Replacing Piters {MERV 11)
O&M: Replacing Filers (MERV 13)
O&M: Replacing Piters (MERV 8)
investment: Sealing the Envelope
Investment: SheteMn-Place
Events
Range:
Compute
Results
Ait. 2: Level 3 Protection {Chemical Biological Agents] Replacing Filters (Gas Phase): Unit Cost
(1108,000) (+/-10X)
Aiemative 2
Minimum (597,200)
Baseline (5108,008)
Maximum (5118,800)
Save Results for Reports
dear Saved Results
54.418,153
S4,573.303
S4.741.453
Discount Rate
dear Saved Results Aft. 1: Level 2 Protection (Biological Agents): Replacing Filters fHEPA):
: " Unit Cost (S7.20§)!V-1fl*i)
Dear Saved Results ^ ^: Level 3 Protection (Chemical Biological Agents): Replacing
•' Rttera {Gss Phase): Unit Cost (S108"OQG) (*A10%)
-------
Reports
The Life-Cycle Cost Analysis Tool produces two types of
reports. Although the reports share a number of similarities in
terms of their content, their functions are very different. Each
report is accessed via the Reports node on the main menu.
Clicking the Data or Results option under the Reports node
takes you to the selected report type.
The Data Report is intended as a means for checking the
accuracy of the information that you entered into the Life-
Cycle Cost Analysis Tool. The Results Report is designed
to help you "drill down" on how individual cost items are
distributed across Budget Category cost types. This approach
gives you a snapshot of all of the costs entering the analysis,
expressed in present value terms, which "roll up" into the
life-cycle costs recorded in the Cost Summary window. The
Results Report also includes any sensitivity analyses you
decide to save. The Results Report is intended for submission
to senior management as part of the documentation supporting
the specific project being considered for funding. The Results
Report is sufficiently detailed to provide a concise
snapshot of the underlying data, including the candidate
set of alternatives evaluated, the types of analyses
performed, and the results of those analyses.
Clicking on the Data option under the Reports node
opens the Data Report. The Data Report consists of
(1) a Cover Sheet, (2) Background Information on the
project (e.g., Project Name, Project Description, Study
Period, and Analysis Information), (3) Alternative
Information - Descriptive Summary (e.g., Alternative
Name, Alternative Description, Event Name, Event
Description, Outcome Name, Outcome Description, and
Key Parameters), (4) Alternative Information - Protection
Cost Data Summary (e.g., Cost Item and Dollar Amount),
and (5) Alternative Information - Event/Outcome Cost Data
Summary (e.g., Event, Outcome, Event/Outcome Cost Item,
and Dollar Amount). Figure A18 reproduces the Cover
Page of the Data Report for the high-rise office building
case study.
Figure A18 Cover Page of the Data Report for the High-Rise
OfNceJB^
High-Rise Office Building
Data Report
UM-CycIt Con Anilyth Tort for
ChtmfBle Pfaiiteilan of Bu 1 dings
NBT
-------
Figure A19 Protection Costs Data Summary Page of the Data Report for Alternative 1
Alternative Information - Protection Cosls Data Summary
Preitcitan Ceia Sumnury: l.t¥*l I ntttetitn ilisluflieal Ag*rm1
Coif Htm
Yrai t-xii c:
angary
*m«
Verifying the accuracy of input data is essential to ensure that
the results of the economic evaluation are consistent with the
underlying data. The Data Report is specifically designed to
verify the accuracy of the input data. Figure A19 provides
information on the protection costs for Alternative 1.
Clicking on the Results option under the Reports node opens
the Results Report. The Results Report consists of (1) a
Cover Sheet, (2) Background Information on the project
(e.g., Project Name, Project Description, Study Period,
and Analysis Information), (3) Alternative Information
- Descriptive Summary (e.g., Alternative Name, Alternative
Description, Event Name, Event Description, Outcome
Name, Outcome Description, and Key Parameters),
(4) Summary of Life-cycle Costs, (5) Summary of Costs
by Alternative sorted by Budget Category (e.g., Cost Item
and Present Value Dollar Amount), (6) Summary of Annual
Costs by Alternative and Budget Category (e.g., Present
Value Dollar Amounts for each Year for Capital Investment,
O&M, Other, and in Total), (7) Summary of Annual Costs by
Alternative (e.g., Present Value Dollar Amounts for each Year
for each Alternative), and (8) any saved sensitivity analyses.
-------
Figure A20 Summary of Life-Cycle Costs Page of the Results Report for the
High-Rise Office Building Case Study
Tow L*"€s-d«
OiM
fthnr
Summary of Life-Cysle Costs
Rmm Cmsm f$| &Kmmm]y(* 1
3 4651J3 3 MI
1» 7SJ I »!
250244S
Figure A20 reproduces the Summary of Life-Cycle Costs
Page of the Results Report for the high-rise office building
case study. When you examine Figure A20, you will note
that it is a reproduction of the Cost Summary window for
the baseline analysis. Figure A20 includes the check boxes
to indicate clearly whether any data elements have been
excluded from the life-cycle cost totals. Figure A20 is the
starting point for the "drill down" analysis of the computed
values for life-cycle costs.
-------
Figure A21 is the second page of the three-page Summary
of Costs by Alternative portion of the Results Report. Figure
A21 covers Alternative 1. All costs are expressed in present
value dollar amounts and include designations for the cost
types, which map them into the cost-accounting framework.
If you wish to examine how a particular cost item contributes
to the amounts shown on the Summary of Life-Cycle Costs
page, choose the cost item, see where it fits in the cost-
accounting framework, and then trace it back to Summary of
Life-Cycle Costs page.
Because event-related cost items are very similar across
alternatives (e.g., damage to the facility and loss of use of
the facility) but differ in their magnitude, it is sometimes
desirable to use the Summary of Costs by Alternative to
calculate a "loss differential" between the Base Case and
one of more of the alternatives. This can be done for either a
single event-related cost item, a combination of event-related
cost items, or all event-related losses. For example, if damage
to the facility were the event-related cost item of interest,
subtract its value for the alternative of interest from its value
for the Base Case. To do this, you will need to pull values
from at least two Summary of Costs by Alternative sections
of the Results Report—one for the Base Case and one for
each alternative of interest.
Figure A21 Summary of Costs by Alternative Page of the Results Report
for Alternative 1
Alternafve 1:
Bud get Category
Capital Investment
Summary of Costs by Alternative
Level 2 Protection (Biological Agents)
O&M
Other
Cost Item
Electrical M edifications
HVAC Upgrade
Relocate Air Intakes to Roof
Sealing the Envelope
Sherfter-ln-Place
Electricity (Heat, Cool, Ltg, OSS Equip)
MERV 6 Replacement Cost Avoided
Replacing Filters (HEPA;
Replacing Filters (MEW 13)
Replacing Filters (MERV' 8)
Productivity Improvement (0.5%)
Total
Present Value ($)
107.365
209,445
225,261
625.326
39,316
2,931,084
-31,815
173.248
72,187
7.954
-1,317,840
3,042.030
12/01/2006
Page 8
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In developing a cost-effective risk mitigation plan, it is useful
to see how costs are distributed over time. The Results Report
provides two separate means for examining and assessing
annual costs. The Summary of Annual Costs by Alternative
and Budget Category provides a detailed disaggregated
synopsis of annual costs. Thus, if you want to examine how
major equipment replacements affect annual costs, examine
the entries under the Capital Investment heading and look
for years in which significant increases in costs occur.
The Summary of Annual Costs by Alternative provides
aggregated side-by-side comparisons of the alternatives being
evaluated. Figure A22 reproduces the Summary of Annual
Costs by Alternative page for the high-rise office building
case study. These side-by-side comparisons are useful in
determining when a particular alternative has a "bulge" in
costs—say at the beginning of the study period or associated
with a major replacement—or when one alternative's annual
costs begin to escalate at a significantly higher rate. Both
pieces of information are useful in understanding the pros
and cons of each alternative being evaluated. It is important
to recognize that the goal of the analysis is to gain insights
into the decision problem.
Figure A22 Summary of Annual Costs by Alternative Page of the Results
Report for the High-Rise Office Building Case Study
Summary of Annual Costs by Alternative
Year
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
12/01/2006
Base Case
1,205,155
207.682
193,893
181,019
169.000
157,779
147,303
137.522
128,391
119,866
111.907
104,477
97,539
91.063
85,016
79,371
74.101
69.181
64,587
60,298
Present Value ($]
Alternative 1
1.411,918
136,715
126,948
165,502
109,436
101,597
133,779
87,544
81,255
108,115
69,984
64,942
87,355
55,907
51,866
70,565
44,627
41,391
56,990
35,595
Alternative 2
2.767,280
66,741
60,949
103,253
50,727
491,134
81,561
38,300
34,817
64,323
353,913
26,004
50,639
21,288
19,225
277,525
15,612
14,036
31,200
11,282
Page 13
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Next Steps
Now that you have completed the guided tour, use the
test files to gain familiarity with the software. Experiment
with the various means for editing, creating, and deleting
data elements. Create simple applications using your own
data to master the full capabilities of the Life-Cycle Cost
Analysis Tool. Build more complex applications and use
the sensitivity analysis feature to evaluate how changing the
values of key inputs affects economic performance. Use the
Results Report to learn how to drill down on key cost drivers
and use that information to help guide you in conducting
and saving additional sensitivity analyses. Have as a goal
to use the software as a decision support tool. It is largely
self documenting, it lays out the information going into the
analysis, and it provides guidance in choosing a cost-effective
risk mitigation plan.
Visit the OAE Web site (http://www.bfrl.nist.gov/oae/oae.
html) to learn about future updates and pending software
releases.
References
ASTM. 2002. ASTM Standard E 1369, Standard Guide for
Selecting Techniques for Treating Uncertainty and Risk in
the Economic Evaluation of Buildings and Building Systems,
American Society for Testing and Materials.
ASTM. 2005. ASTM Standard E 917, Standard Practice
for Measuring Life-Cycle Costs of Buildings and Building
Systems, American Society for Testing and Materials.
ASTM. 2006. ASTM Standard E 1074, Standard Practice
for Measuring Net Benefits and Net Savings for Investments
in Buildings and Building Systems, American Society for
Testing and Materials.
Chapman, R.E., Leng, C.J. 2004. Cost-Effective Responses
to Terrorist Risks in Constructed Facilities, NISTIR 7073,
National Institute of Standards and Technology.
-------
Appendix B
Case Study Retrofit Design Documentation
Disclaimer
The retrofits presented in this appendix are specific to the
buildings examined in terms of the available options and
the details of implementation. They are based on the efforts
of a single architectural and engineering (A&E) firm and
are not necessarily optimal for these or any other buildings.
While the recommendations and designs are of interest to
the general question of building protection, they cannot
necessarily be generalized to other buildings. Determining
retrofit options and designs for a specific building always
requires consideration of the unique features of that building.
Background
Section 3 of this report described a case study investigating
the application of building protection retrofits in two actual
buildings, specifically to identify and design potential
retrofits to these buildings, given their particular floor
plans and HVAC system designs. Two office buildings,
with very different floor plans and ventilation system
designs, were selected for the case study. One is a high-rise
office building with central air-handling systems serving
most of the building, in addition to several other features of
interest, including intakes near ground level, a loading dock,
a mail room, and a public-access lobby. The other building is
a one-story office building with multiple rooftop air handling
units and no spaces other than offices.
The retrofit design and cost estimation was performed by
an A&E firm and was based on a list of candidate retrofits
identified by NIST. The A&E firm then proceeded with the
design work, producing detailed designs for implementing
the retrofits. As part of this effort, the A&E firm reviewed the
existing mechanical and control systems in the two buildings,
including all original architectural, structural, mechanical,
and electrical plans and any modifications of these plans. The
firm also conducted field inspections of the buildings and
systems and then performed the design work and prepared
detailed descriptions, drawings, and cost estimates of the
proposed retrofits.
This appendix contains more detailed descriptions of the
buildings and retrofit designs excerpted from the A&E report.
A&E Description of Existing Condition
This case study includes two buildings located in an office/
lab complex in a suburban area. The first building is a
high-rise office building with an office tower referred to as
Wing A. The scope of this study covers the tower served
by Mechanical Room #4 in the mezzanine level, the main
lobby of the high-rise office building, and the mailroom in
the basement of Wing B of the high-rise office building.
Additionally, the scope includes the rooftop heat pumps on
the roof of a second building—a one-story office building.
High-rise Office Building Tower
The high-rise office building, built in the mid-1960s, is an
eleven-story tower with an elevator penthouse, basement, and
subbasement covering an area of 130,500 ft2. At its base, the
structure is flanked by adjoining one- and-two story wings,
which includes Wing B, with a central open courtyard.
A variety of materials compose the exterior walls, including
granite, marble, face brick, glass, and extruded aluminum.
The east and west facades of the tower are faced with grey
face brick with insulated porcelain spandrel panels and fixed
aluminum frame windows enclosing the north and south
elevations.
There are six air conditioning units (ACU-A1, ACU-A2,
ACU-A3, ACU-A4, ACU-A5, and ACU-A6) installed in
Mechanical Room #4 located in the mezzanine floor of
Wing A. The units are field-assembled panel construction.
They are generally in good condition and some of the coils
have been replaced, while others appear to be the original
design. Each unit has a mixing box with outside air louvers,
outside air dampers, minimum outside air dampers, and
return air. Each unit has a filter rack holding 20 in x 20
in x 4 in 30 percent pleated filters. There were several
manufacturer's filters represented, but it is fair to assume
these are nominal ASHRAE 30 percent filters (per ASHRAE
Standard 52.1) or MERV 6 filters (per ASHRAE Standard
52.2). The filters are upstream accessible through an access
door located in the mixing section of each unit. There is
also a downstream access door that serves the access
section between the filter bank and the heating coil section.
With the exception of air conditioning units ACU-3 and
ACU-4, the supply fans are original installation. All the
motors were recently replaced with high-efficiency motors.
Exhaust/return fans designated E-A-1, E-A-2, E-A-3, E-A-4,
E-A-5 and E-A-6 return the air to their corresponding air
handling unit or exhaust the air, depending on whether the
units are operating with the minimum outside air or under
the economizer cycle.
The air handling units are all fed from the Motor Control
Centers MCC-A1 and MCC-A2 located in the same
mechanical room. Combination starters and disconnect
switches for supply and exhaust fans for ACU-A1, ACU-A3,
ACU-A4, and ACU-A5 are installed in Motor Control Center
MCC-A1 and starter/disconnects for supply and exhaust fans
are installed in MCC-A2.
Mechanical Room #4 is in the mezzanine level and
the bottom of the outside air intake louvers are around
20 ft above the ground. The building has a rectangular
configuration, with the north and south sides full of windows
at the floors above the mezzanine and outside air intake
louvers at the mechanical room.
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The temperature controls are pneumatic and each ACU is
started and stopped manually or by means of time clocks
installed in each unit's control panel. The ACUs operate
24 h/d all year round.
High-rise Office Building, Main Lobby
The main lobby is a 14 ft high space that is approximately
3,500 ft2 in floor area. It is defined by exterior glass curtain
walls on the north and east sides and marble finished walls
on the south and west sides. It is accessed from the exterior
through a 150 ft2 glass enclosed airlock with a series of two
rows of four balanced glass doors located on the east wall.
On the southern perimeter, the lobby is open to the elevator
bank of Wing A and an exhibition space located in Wing B.
The lobby is also open to Wing E west of Wing A.
The main lobby does not have a dedicated air-conditioning
unit, but is served by Air Handling Unit ACU-A2 and return/
exhaust fan E-A-2. Air Handling Unit ACU-A2 located in the
mezzanine mechanical room serves the main lobby and the
adjacent corridors. Four supply air branches with hot water
reheat coils are each connected to the main supply air duct
from ACU-A2. Two of the ducts run down to the main lobby
(adjacent to the elevators) and supply air to linear diffuser
located at the north and east perimeter walls of the main
lobby. The other two supply ducts supply air to Corridor #13,
Corridor #14, and the exhibit area.
The return/relief exhaust air fan E-A-2 returns the air to
ACU-A2 or exhausts it, depending on the outdoor conditions.
A 50 in x 30 in return duct connected to E-A-2 returns the air
from the main lobby, the adjacent corridors, and the exhibit
area. The duct is connected to an 84 in x 48 in x 24 in sheet
metal plenum in the lobby's ceiling plenum. A 48 in x 13 in
duct returns the air from the main lobby and is connected to
the same plenum. Ducts that are 33 in x 20 in, 33 in x 27 in,
and 40 in x 7 in return the air from Corridor #13, Corridor
#14, and the exhibit area and are connected to the same
plenum.
Exhaust fan E-A-2 is located in a space between the two
elevator shafts behind exhaust fan E-A-8.
The temperature controls are pneumatic and air handling unit
ACU A2 and the exhaust/return fan E-A-2 are started and
stopped manually or by means of time clocks installed in the
unit's control panel. The ACU and the fan operate 24 h/d all
year round.
The main lobby air handling unit ACU-A2 supply and return/
exhaust fans E-A-2 are fed from the Motor Control Center
MCC-A2 located in Mechanical Room #4 on the mezzanine
floor.
High-rise Office Building, Mail Room
The mail room is approximately 3,600 ft2 and has a 7 ft 8 in
high suspended acoustical ceiling system. It is enclosed by
CMU walls and modular metal partitions. With the exception
of the east, west, and south walls, the north wall and all other
interior partitions extend to the height of the ceiling. On the
east and west walls, a total of three single and double doors
lead directly into an interior corridor. There is a roll-up door
on the exterior south wall in the receiving area and the mail
room.
The mail room does not have a dedicated air-conditioning
unit. Air handling unit ACU-BI and return fan E-A-2a
operate at minimum outside air and have the capability to
modulate to 100 percent outdoor air (economizer cycle). Air
handling unit ACU-BI is located in the mechanical room
on the basement of Wing B. ACU-BI is of field assembled
panel construction. The unit is in good condition and serves
the mail room and other surrounding rooms. The mechanical
room is crowded with six ACUs, several exhaust fans,
domestic hot water storage tanks, pumps, overhead ductwork,
piping, electrical conduits, etc. The ceiling plenum in the
mail room is also fairly congested with ductwork, piping,
electrical conduits, etc.
The return/relief exhaust air fan E-B-la returns the air from
the areas surrounding the mail room to ACU-BI or exhausts
the air, depending on whether the ACU is operating with
minimum outside air or under the economizer mode. The
exhaust air fan E-B-lb exhausts the air from the mail room
without returning any air to ACU-BI. Both fans are located in
Mechanical Equipment room #2 in the basement of Wing B.
The temperature controls are pneumatic and air handling
unit ACU B-I, return fan E-A-la, and exhaust fan E-B-lb
are started and stopped manually or by means of time clocks
installed in the unit's control panel The ACU and the fan
operates 24 h/d all year round.
The mail room air handling unit supply and return/exhaust
fans are fed from Motor Control Center MCC-B1 located in
Mechanical Room #2.
One-story office building
The one-story office building is a contiguous group of large
one-story trailers that have been joined to form a single
building of 17,040 ft2. The building is approximately 15 ft
high with 6 exterior single and double doors and 67 fixed
double glazed windows. Additionally, the floor is penetrated
by a number of plumbing pipes and electrical conduits
coming from the crawl space.
Twenty-seven rooftop heat pump units provide heating,
ventilation, and air-conditioning to the one-story office
building. Each unit is controlled by a single room thermostat.
These units are built to have 1 in thick throw-away air filters.
The rooftop heat pumps are currently fed from two panels
located in the electrical equipment room.
A & E Findings and Recommendations
High-rise Office Building Tower
General Findings
Without the benefit of a detailed inspection of the exterior
glazed areas of the building, it is believed that decades of
aging and weathering will necessitate substantial reseating
around the glazed surfaces and exterior penetrations.
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To extend the six outside air intakes from the mezzanine
mechanical room to the roof will require running ductwork
up the exterior walls, blocking around 130 windows and
compromising the aesthetics of the building. Extending
the outside air intakes through the inside the building with
ductwork will require valuable space at each floor.
The installed air filters are MERV 6 with an efficiency of
25 percent to 30 percent.
The existing motor control centers MCC-A1 and MCC-A2
have adequate capacity and available spare/space modules to
accommodate the proposed modifications.
Protection needed against an outdoor or indoor biological
or chemical release will require the installation of a quick
shut-off switch and quick purge switch to be centrally located
in the guard control office that is manned 24 h/d. Currently,
there are no areas designated as shelters-in-place to protect
the occupants of the building.
Recommended Retrofits
Sealing Building Envelope
Seal and reseal, as required, around the interior and exterior
of windows, doors, and penetrations of the building envelope.
Elevate Outdoor Air Intake
Extend the six outside air intakes, from the mezzanine
mechanical room to the roof by installing ductwork on the
exterior.
Implement Shelter-In-Place
To augment the ability of building occupants to shelter-in-
place, areas of refuge should be distributed throughout the
building. These "shelters-in-place" will be sealed rooms in
which the building occupants will assemble for a defined
period of time.
Install Shut-Off and Purge Switches
Protection against an outdoor or indoor biological or
chemical release requires the installation of a quick shut-off
switch and a quick purge switch to be centrally located in
continuously manned guard control office. The electrical
system that will provide an immediate shutdown of the
AHU's supply fans consists of a shut-off switch to be located
in the guard control office in the basement and will control a
multipole relay to be installed in an available spare bucket in
the existing Motor Control Center MCC-A1 in Mechanical
Room #4. Each relay contact is then connected to the
corresponding starters of the supply fans inMCC-Al
and MCC-A2.
The electrical system that will provide an immediate start-up
of the AHU's exhaust fans consists of a purge switch to be
located in the guard control office in the basement and will
control a multipole relay to be installed in an available spare
bucket in the existing Motor Control Center MCC-A1 located
in the Mechanical Room #4. Each relay contact is then
connected to the corresponding starters of the exhaust fans
inMCC-Al andMCC-A2.
Upgrade to Filtration Level 1
Upgrade all filters from the current MERV 6 filters to 4 in
MERV 11 high-capacity filters. This change will result in
increased efficiency and longer life relative to the standard
capacity filter. Use the existing 20 in x 20 in frames so major
changes to the structure will not be required. Changes to the
fan and motor are not required.
Upgrade to Filtration Level 2
Upgrade each AHU with a three-stage filter system
consisting of 4 in pre-filter, 85 percent intermediate filter,
and 99.97 percent HEPA filter. Remove the existing filter
bank assembly to achieve this level of filtration. Install a
new field fabricated, build-up bank of HEPA-rated frames
within the existing AHUs with new safing on all four sides.
The frames will have HEPA clamping mechanism to
achieve 99.97 percent seal. Safings will consist of 18/20
gauge galvanized steel. Screw in place and seal with an
appropriate sealant the frames and safing. To achieve the
maximum amount of filter area, the nominal frame size
will be 24 in x 24 in and 12 in x 24 in, as required.
Replace the following fans and motors because of the
increase in pressure requirements to meet the requirements
of additional static pressure drop:
a. ACU-A1: Replace the existing 15 hp fan motor with a
new 25 hp motor.
b. ACU-A2: Replace the 15 hp motor with a new 25 hp
motor.
c. ACU-A3: Replace the 30 hp motor with a new 40 hp
motor.
d. ACU-A4: Replace the 25 hp motor with a new 40 hp
motor.
e. ACU-A5: Replace the 40 hp motor with a new 50 hp
motor.
f. ACU-A6: Replace the supply fan S-A-6(B) with a new
fan and the 20 hp motor with a new 40 hp motor.
The pre-filter should be changed four times per year, one final
filter change per year, and one HEPA filter change per year.
Modify the Motor Control Centers MCC-A1 and MCC-A2
by removing existing ACU-A1 thru ACU-A6 combination
starters/disconnect switches and associated feeders. Provide
for new motors:
a. ACU-A1: Install in MCC-A1 combination starter size 2
and 60 A disconnect switch, and connect new 25 hp motor
with 3 #6 and 1 #10 ground in 1 in conduit.
b. ACU-A2: Install in MCC-A2 combination starter size 2
and 60 A disconnect switch, and connect new 25 hp motor
with 3 #6 and 1 #10 ground in 1 in conduit.
c. ACU-A3: Install inMCC-Al combination starter size
3 and 100 A disconnect switch, and connect new 40 hp
motor with 3 #3 and 1 #8 ground in 1 1/4 in conduit.
d. ACU-A4: Install in MCC-A1 a combination starter size
3 and 100 A disconnect switch, and connect new 40 hp
motor with 3 #3 and 1 #8 ground in 1 1/4 in conduit.
e. ACU-A5: Install in MCC-A1 a combination starter size
3 and 125 A disconnect switch, and connect new 50 hp
motor with 3 #2 and 1 #6 ground in 1 1/4 in conduit.
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f. ACU-A6: Install in MCC-A2 a combination starter size
3 and 100 A disconnect switch, and connect new 40 hp
motor with 3 #3 and 1 #8 ground in 1 1/4 in conduit.
The modifications to the Motor Control Centers MCC-
Al and MCC-A2 will result in a considerable increase
in the load. Replace the existing main circuit breaker in
switchboard 101-A1 with new 3-pole, 600 A, and connect
to the MCC-A1 and MCC-A2 with new 600 A feeder.
Upgrade to Filtration Level 3
Upgrade each AHU with a five-stage filter system consisting
of 4 in pre-filter, 85 percent intermediate filter, 99.97 percent
HEPA filter, 99.99 percent gas phase filter, and 2 in post filter.
Remove the existing filter bank assembly to accommodate
this level of filtration. Include ASZM-TED A military grade
carbon (per US Army standard EA-C-1704) designed for
chemical contaminants as the gas phase filter bank designed
to provide approximately 0.10 s of residence time. Remove
the existing filter bank assembly to achieve this level of
filtration. Install two new field-fabricated, build-up banks
of HEPA- rated frames within the existing AHUs with
new safing on all four sides. The frames will be 14-gauge
stainless steel with welded corners and ground filter seal
surface. The frames will have HEPA clamping mechanism
to achieve 99.97 percent seal. Safings will consist of 18/16
gauge stainless steel. Weld in place the frames and safing,
mechanically fasten, and seal them to the plenum with
appropriate sealant. To achieve the maximum amount of filter
area the nominal frame size will be 24 in x 24 in and 12 in x
24 in, as required to achieve the maximum of filter area.
Replace the following fans and motors because of the
increase in pressure requirements to meet the requirements of
additional static pressure drop:
a. ACU-A1: Replace the supply fan S-A-l(C) with a new
supply fan and the 15 hp motor with a 40 hp motor.
b. ACU-A2: Replace the 15 hp motor with a 30 hp motor.
c. ACU-A3: Replace the 30 hp motor with a new 50 hp
motor.
d. ACU-A4: Replace the supply fan S-A-4(B) with a new
fan and the 25 hp motor with a new 50 hp motor.
e. ACU-A5: Replace the 40 hp motor with a new 75 hp
motor.
f. ACU-A6: Replace the supply fan S-A-6(B) with a new
fan and the 20 hp motor with a new 50 hp motor.
Modify the Motor Control Centers MCC-A1 and MCC-A2
by removing existing ACU-A1 thru ACU-A6 combination
starter/disconnect switches and associated feeders. Provide
for new motors:
a. ACU-A1: Install in MCC-A1 combination starter
size 3 and 100 A disconnect switch, and connect new
40 hp motor with 3 #3 and 1 #8 ground in 1 1/4 in
conduit.
b. ACU-A2: Install in MCC-A2 combination starter size
3 and 70 A disconnect switch, and connect new 30 hp
motor with 3 #4 and 1 #8 ground in 1 in conduit.
c. ACU-A3: Install in MCC-A1 combination starter
size 3 and 125 A disconnect switch, and connect new
50 hp motor with 3 #2 and 1 #6 ground in 1 1/4 in
conduit.
d. ACU-A4: Install inMCC-Al combination starter
size 3 and 125 A disconnect switch, and connect new
50 hp motor with 3 #2 and 1 #6 ground in 1 1/4 in
conduit.
e. ACU-A5: Install in MCC-A1 combination starter size
4 and 175 A disconnect switch, and connect new 75
hp motor with 3 #2 and 1 #6 ground in 2 in conduit.
f. ACU-A6: Install in MCC-A2 combination starter
size 3 and 125 A disconnect switch, and connect new
50 hp motor with 3 #2 and 1 #6 ground in 1 1/4 in
conduit.
The modification to the Motor Control Centers MCC-A1
and MCC-A2 results in a considerable increase in the load.
Replace the existing main circuit breaker in switchboard 101-
Al with new 3 pole, 600 A, and connect to the MCC-A1 and
MCC-A2 with new 600 A feeder.
High-rise Office Building, Main Lobby
General Findings
Given the present configuration, it is not possible to contain a
release that occurs within the lobby. However, it is important
to install airtight physical barriers to limit contaminant spread
into the rest of the building.
To maintain the air conditioning of the main lobby
independent from the surrounding areas, a new AHU
(ACU-A-2a) and exhaust fan (E-A-2a) will be required.
Currently, ACU-A2 supplies air to the main lobby, Corridor
#13, Corridor #14, and the exhibit area, and return/exhaust
fan E-A-2 returns air to the unit or exhausts it during the
air economizer cycle from these areas. The amount of air
circulated through the lobby should be removed from ACU-
A2 and E-A-2 to maintain the lobby independent from the
other areas.
To isolate the main lobby from the surrounding areas, fan
E-A-2 should be replaced by two fans: 1) new fan E-A-2
should replace the existing fan and return the air from the
nonlobby spaces to air handling unit ACU-A-2, and 2) new
fan E-A-2a should be dedicated to return/exhaust the air from
the lobby to the new ACU 2a. The new air exhaust fan should
be fitted with Filtration Level 2 or 3 to prevent spreading
hazardous materials from the lobby to the outdoors during an
emergency.
There are two options for the new exhaust fan E-A-2a. It
should be equipped with Filtration Level 2 or 3. Installation
of Filtration Level 1 is not recommended because it will not
provide the level of protection required when discharging
contaminated air to the outside.
The space available to install a new air handling unit, an
exhaust fan, filters, and ductwork is very tight and will
require removal and relocation of existing ductwork, piping,
control and electrical panels, and electrical conduits. Some of
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the headroom could be reduced by installing new ductwork
under existing ductwork, piping, and electrical conduits. Due
to existing conditions, the installation of Filtration Level 3
will be considerably more difficult than the installation of
Level 2.
Recommended Retrofits
Elevate Outdoor Air Intakes
Relocate the outside air intakes to the roof.
Physical Separation
Isolate the east lobby of Wing A from the rest of the building
by providing tempered glass partitions with serf-closing glass
doors that will allow the building occupants continued access
to the lobby and exhibition spaces. The isolating partitions
will also include a matching marble finish above the glazed
areas.
The building has a sprinkler system, therefore isolating the
lobby in the manner proposed will not compromise egress
requirements, impair visibility, or prohibit the transmittance
of natural light.
Accessory door hardware will take into account the style and
character of the existing building, will seal potential points
of air infiltration, and will enable the mechanical system
to maintain the designed air pressure differentials between
adjacent spaces.
HVAC Isolation
Install a new air handling unit (ACU-A2a) in Mechanical
Equipment Room #4 to serve the main lobby only. Provide
ACU-A2a with air economizer cycle, air filters, a hot water
preheat coil, cooling coil, and supply fan. Install the unit
in the southeast corner of the room in front of ACU-A-2.
Connect the supply duct from the unit to the existing supply
duct with hot water reheat coils serving the lobby. Install
chilled water branches from the nearby mains to the cooling
coil and hot water branches from the nearby hot water mains
to the heating coil. Bring outside air to the unit from an
existing louver in the northeast corner of the room.
Remove the existing exhaust fan E-A-2, and install two new
exhaust fans, one fan (E-A-2) to serve as return/exhaust fan
to the existing ACU-A2 from the areas surrounding the lobby
and the other (E-A-2a) to return/exhaust the air to the new
ACU-A2a, and run an exhaust duct from the return duct to
an existing louver near the fan. Install filters on the discharge
side of the new exhaust fan E-A-2a.
Select and balance ACU-A2a and E-A-2a to maintain the
main lobby approximately 10 percent negative with respect
to the surrounding areas and the outdoors during normal
operation and during an emergency.
Upgrade to Filtration Level 2
Equip the AHU with a Level 2 filter system consisting of a
4 in pre-filter, 85 percent intermediate filter, and 99.97
percent HEPA filter in a filter section and a 7.5 hp motor.
Install in Motor Control Center MCC-A2 a combination
starter size 1 and 20 A disconnect switch and connect new
7.5 hp motor with 3 #12 and 1 #12 ground in 3/4 in conduit.
Provide fan E-A-2a with Filtration Level 2 system.
Equip the fan with a 5 hp motor to meet the additional
requirements of the filter's static pressure drop. Remove in
MCC-A2 combination starter/disconnect switch for fan E-A2
and associated feeder. Install in its place a combination starter
size 0 and 15 A disconnect switch, and connect a new 5-hp
motor with 3 #12 and 1 #12 ground in 3/4 in conduit. Install
in MCC-A2 a combination starter size 1 and 20 A disconnect
switch and connect a new 7.5 hp motor with 3 #12 and 1 #12
ground in 3/4 in conduit.
Upgrade to Filtration Level 3
Equip the AHU with Filtration Level 3 consisting of a 4-in
pre-filter, 85 percent intermediate filter, 99.97 percent HEPA
filter, 99.99 percent gas phase filter, and a 2-in post-filter in a
filter section, and install a 7.5 hp motor.
Install in Motor Control Center MCC-A2 a combination
starter size 1 and 20A disconnect switch, and connect a new
7.5 hp motor with 3 #12 and 1 #12 ground in 3/4 in conduit.
Provide fan E-A-2a with a Level 3 filter system consisting of
a 4 in pre-filter, 85 percent intermediate filter, 99.97 percent
HEPA filter, 99.99 percent gas phase filter, and 2 in post-filter
in a filter section.
Equip fan E-A-2a with a 7.5 hp motor to meet the additional
requirements of the filter's static pressure drop. Remove in
MCC-A2 the combination starter/disconnect switch for fan
E-A2 and associated feeder. Install in its place a combination
starter size 0 and 15 A disconnect switch, and connect a new
7.5 hp motor with 3 #12 and 1 #12 ground in 3/4 in conduit.
Install in MCC-A2 a combination starter size 1 and 20 A
disconnect switch and connect new E-A-2 7.5 hp motor with
3 #12 and 1 #12 ground in 3/4 in conduit.
High-rise Office Building, Mail Room
General Findings
The walls, ceilings, and doors are not airtight and cannot
contain a release within the room.
It will not be possible to install a dedicated new air
handling unit in Mechanical Room #2 due to congestion in
the mechanical room and ceiling space above the mail room.
In addition, a new outside air duct would need to be installed
from the present unit's outside air intake to the top of the
existing architectural louver located above a Wing D entrance
door. This duct modification will raise the outside air intake
to around 30 ft (roof level) from the ground. Therefore, since
a new dedicated unit cannot be installed, the fallback position
is to upgrade the filtering system of the existing AHU.
The existing exhaust fan E-B-2b dedicated to the mail room
will need to be fitted with a new filter bank with one of the
two filter options (2 or 3) to prevent spreading hazardous
materials from the mail room to the outdoors during an
emergency.
Installation of Filtration Level I filters, as described above, is
not recommended because it will not provide the quality of
protection required for the mail room.
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During a previous expansion and renovation of the mail
room, a corridor between the room and the loading dock
became part of the mail room, the air registers connected
to the exhaust duct from the exhaust fan E-13-1A were
removed, and the duct was abandoned in place. Presently,
the air supplied to the mail room is exfiltrated through two
transfer grilles to the adjacent corridors at the east and west
side of the room.
Recommended Retrofits
Physical Separation
Seal room envelope: walls, ceilings, doors and slabs.
HVAC Isolation
Maintain the mail room at negative pressure all the time
during normal and emergency operation by adjusting the
supply and return airflows.
Upgrade to Filtration Level 2
Upgrade ACU-B1 with Filtration Level 2 system,
consisting of a 4-in pre-filter, 85 percent intermediate filter,
and 99.97 percent HEPA filter. Remove the existing filter
bank assembly to achieve this level of filtration. Install a
new field-fabricated, build-up bank of HEPA-rated frames
within the existing AHU with new safing on all four sides.
The frames will have HEPA clamping mechanisms to
achieve 99.97 percent seal. Safings will consist of 18/20
gauge galvanized steel. Screw in place and seal with an
appropriate sealant the frame and safing. To achieve the
maximum amount of filter area, the nominal frame size
will be 24 in x 24 in and 12 in x 24 in, as required.
Replace the existing 25-hp fan motor with a new 40-hp
motor to overcome the additional static pressure. Remove
from MCC-B1 the combination starter/disconnect switch
for fan S-B-1 and associated feeder. Install in its place a
combination starter size 3 and 100 A disconnect switch,
and connect a new 40 hp motor with 3 #3 and I #8 ground
in 1 1/4-in conduit.
Equip existing exhaust fan E-B-2b with Filtration Level 2
system, consisting of a 4-in pre-filter, 85 percent intermediate
filter, and 99.97 percent HEPA filter in a filter section.
Remove the MCC-B 1 combination starter/disconnect switch
for fan E-B-1 b and associated feeder. Install in its place a
combination starter size 0 and 15 A disconnect switch, and
connect a new 2 hp motor with 3 #12 and 1 # 12 grounds in
3/4-in conduit.
Replace the existing 1-hp fan motor with a 2-hp motor to
meet the additional static pressure drop associated with the
filter.
The pre-filter should be changed four times per year, one final
filter change per year, and one HEPA filter change per year.
Upgrade to Filtration Level 3
Upgrade ACU-B 1 with Filtration Level 3 system,
consisting of a 4-in pre-filter, 85 percent intermediate filter,
99.97 percent HEPA filter, 99.99 percent gas phase filter, and
a 2-in post filter. Remove the existing filter bank assembly
to achieve this level of filtration. The filter bank for the gas
phase will include ASZM-TEDA military grade carbon
designed for chemical contaminants and be designed to
provide approximately 0.10 s of residence time. Remove
the existing filter bank assembly to achieve this level of
filtration. Install two new field-fabricated, build-up banks
of HEPA-rated frames within the existing AHU with new
safing on all four sides. The frames will be 14-gauge stainless
steel with welded corners, welded, and ground filter seal
surface. The frames will have HEPA clamping mechanisms
to achieve a 99.97 percent seal. Safings will consist of 18/16
gauge stainless steel. Weld in place the frames and safing,
mechanically fasten, and seal them to the plenum with
appropriate sealant. To achieve the maximum amount of
filter area, the nominal frame size will be 24 in x 24 in and
12 in x 24 in, as required.
Replace the existing 25-hp fan motor with a new 40-hp motor
to overcome the additional static pressure. Remove inMCC-
B1 the combination starter/disconnect switch for fan S-B-1
and associated feeder. Install in its place combination starter
size 3 and 100A disconnect switch, and connect a new 40-hp
motor with 3 #3 and 1 #8 ground 1 1/4-in conduit.
Equip the fan with Filtration Level 3 system, consisting of
a 4 in pre-filter, 85 percent intermediate filter, 99.97 percent
HEPA filter, 99.9 9 percent gas phase filter, and a 2-in post-
filter.
Replace the existing fan and the 1-hp motor with a new fan
and a 2-hp motor to meet the additional static pressure drop.
Remove in MCC-B 1 the combination starter/disconnect
switch for fan E-B-lb and associated feeder. Install in its
place a combination starter size 0 and 15 A disconnect
switch, and connect new 2-hp motor with 3 #12 and 1 #12
in 3/4-in conduit.
The pre-filter should be changed four times per year, one final
filter change per year, and one HEPA filter change per year
for more efficient and energy saving operation.
One-story office building
General Findings
The one-story office building is a modular type building
composed of 24 trailers attached together. The building is
heated, ventilated, and air conditioned by 28 rooftop heat
pumps. The space where the supply fan and the motor are
located in the heat pumps is tight and will not permit the
replacement of the installed fan with a larger supply fan and
motor to handle additional static pressure that will be able to
support more efficient particle and gaseous removal filters.
Nor is there enough space to install additional filters inside
the heat pumps. In addition, the units have air economizer
systems that supply 100 percent outside air while in this
mode of operation and will require the selection of the
filters to handle the larger airflow.
Recommended Retrofits
The provision of better outside air filtration to the heat pumps
will require the installation of one or two outside air supply
fans on the roof with filter banks for each of the three filter
options indicated above for the high-rise office building
and running a supply duct from the fan to each unit. The
-------
28 rooftop heat pump units on the roof (approximately one
per trailer) supply 1600 cfm each with approximately 160
cfm minimum outside air each during normal operation and
1600 cfm during air economizer operation. The outside air
introduced by each unit, which is not exhausted through toilet
exhaust or exfiltration, is exhausted by means of a barometric
damper in each unit. During an emergency, each unit's fan
should supply 1600 cfm outside air each for a total of
44,800 cfm. About 35,840 cfm should be exhausted and
8,900 cfm should remain in the building to maintain around
20 percent positive pressure during emergencies. The outside
air intake filters will require a casing of 10 ft H x 10 ft W and
24 in D (or similar dimensions) for Option No. 2 and 10 ft H
x 10 ft W and 52 D (or similar dimensions) for Option No. 3.
To achieve the maximum amount of filter area, the nominal
frame size will be 24 in x 24 in and 12 in x 24 in, as required.
The supply fan alone will weigh approximately 3,400 Ibs
plus the weight of the filter banks and the ductwork. The
building's roof will not be able to support all this weight
unless additional structural reinforcement is provided.
Another option is to install two fans with the filters and
ductwork, but this still will require additional structural
reinforcement.
Instead of installing the fan(s) and filter bank(s) on the
roof, they can be installed on an elevated platform at the
same height as the roof and adjacent to the east side of the
building. From there the ductwork runs to each heat pump.
Variable frequency drive(s) should be provided to modulate
the outside air fan(s) in order to supply the minimum outside
air during normal operation and 100 percent air during
emergency operation.
The 28 rooftop heat pumps are powered from HVAC panels
PA-7 and PA-8 and both panels are full, with each containing
circuits for 14 heat pumps. The proposed installation of two
outside air fans shall instead be powered each from the main
panels PA-1 and PA-2.
Upgraded filtration should be provided as indicated below.
The protection needed against a biological or chemical
release will require the installation of a quick shut-off
switch at the reception desk.
Seal Building Envelope
To enhance the airtightness of the structure, it is
recommended to patch roof leaks, seal around exterior
windows, provide exterior doors with gasket hardware
to close gaps between door leaves, replace exterior door
thresholds with others designed to form a seal at the base of
doors, and seal around pipe and conduit floor penetrations
within the building's crawl space.
Install Shut-Off Switch
The protection needed against outdoor releases requires the
installation of quick shut-off switches to stop the rooftop heat
pumps. This switch is to be located at the reception desk.
Upgrade to Filtration Level 1
Installation of Filtration Level 1 filters is not recommended
because it will not provide the quality of protection required.
However, the existing filtration could be improved by
replacing the existing MERV 4 filters with 1-in thick MERV
11 filters. The MERV 11 filters will not affect the system
static pressure.
Upgrade to Filtration Level 2
Provide two outside air supply fans on two steel platforms,
supported by steel legs on footings and with metal grating,
adjacent to the east side of the building and at the same
height of the roof. Provide with each fan a7ftHx8ftW
filter bank, with Filtration Level 2 as described for the high-
rise office building. Connect the new fans to the filter banks
and to their respective heat pump units with ductwork to each
unit's air intake. Provide variable frequency drives for each
fan to modulate the outside air to each unit during normal
operation and during emergency operation. Provide automatic
controls with a static pressure sensor in each fan supply
duct to control the respective fan. Interlock the exhaust fans
controls with the existing heat pumps controls.
Provide a 20-hp motor with each outside air supply fan.
Install in main panels PA-1 and PA-2 each a 3-pole, 50 A
circuit breaker for each of the proposed supply fans. Install a
combination variable frequency drive, disconnect the switch
at each supply fan location, and connect the 20-hp motors
with 3 # 8 and 1 # 10 ground in 1-in conduit.
UPGRADE TO FILTRATION LEVEL 3
Provide two outside air supply fans on two platforms
adjacent to the east side of the building at roof height.
Provide each fan with a 3.5 ft x 4 ft filter bank with Filtration
Level 3 as described above. Connect the new fans to the filter
banks and to their respective heat pump units with ductwork
to each unit's air intake. Provide a variable frequency drive
for each fan to modulate the outside air to each unit during
normal operation and during emergency operation. Provide
automatic controls with a static pressure sensor in each
fan supply duct to control the respective fan. Interlock the
exhaust fans controls with the existing heat pumps controls.
Provide a 25-hp motor with each of the two outside air
supply fans. Install in main panels PA-1 and PA-2 each a
3-pole, 70 A circuit breaker for each of the proposed
supply fans. Install a combination variable frequency drive,
disconnect the switch at each supply fan location, and
connect the 25-hp motors with 3 # 6 and 1 # 8 ground in
1 1/4 in conduit.
-------
-------
Appendix C
Case Study Retrofit Cost per Unit of Floor Area
The cost data presented in this appendix are based on a
critical analysis of the contractor-provided estimates for
initial capital costs (i.e., first costs) and annually recurring
costs for filter replacement for a variety of chembio retrofit
strategies in the two case study buildings.1 This appendix
presents a fairly detailed classification of cost data, in which
major cost items (e.g., HVAC upgrade) are broken down into
their constituent cost items (e.g., remove existing filter bank).
The cost data are presented as a series of tables organized
around four retrofit categories in the two case study
buildings: (1) high-rise office building, (2) lobby in the
high-rise office building, (3) mail room in the high-rise
office building, and (4) low-rise office building. Within each
category, the tables are organized around the three levels of
filtration considered as well as by the non-filtration retrofits.
The three filtration levels are as follows: Level 1, minimal
protection from biological contaminants and no protection
from chemical contaminants; Level 2, enhanced protection
from biological contaminants and no protection from
chemical contaminants; and, Level 3, enhanced protection
from biological contaminants and enhanced protection from
chemical contaminants. Tables C.I through C.3 present initial
capital costs in the high-rise
office building for Filtration Levels 1 through 3,
respectively. Table C.4 covers annually recurring costs
for the filter replacements for the high-rise office building.
Table C.5 covers initial capital costs for the high-rise office
building for five nonfiltration retrofits, i.e., envelope sealing,
moving the outdoor air intake, installing quick shut-off/
purge switches, sheltering-in-place, and system testing and
balancing. Tables C.6 and C.7 cover initial capital costs
for the lobby in the high-rise office building for Filtration
Levels 2 and 3. Table C.8 covers initial capital costs for the
two nonfiltration retrofits of the lobby, i.e., installing interior
partitions between the lobby and the rest of the first floor and
raising the outdoor air intake serving the lobby. Tables C.9
and C. 10 cover initial capital costs for Filtration Levels 2
and 3 in the mail room in the high-rise office building. Table
C.ll covers initial capital costs for sealing the mail room
partitions from the rest of the basement. Tables C. 12 through
C. 14 cover initial capital costs for Filtration Levels 1 through
3, respectively, in the low-rise office building. Table C.I5
covers initial capital costs for sealing the envelope of the
low-rise office building. Note that the sums of the constituent
cost items in the tables may not add to the dollar amount for
the major cost items due to independent rounding.
'Note that the cost estimates are for purposes of illustration
only—actual renovations of different buildings will face
different costs and different risk profiles.
With the exception of Table C.4, which deals with annually
recurring costs for filter replacement rather than initial capital
costs, each table has four columns: (1) Cost Item, (2) Total
Cost, (3) Cost per Square Foot ($/ft2), and (4) Cost per Square
Meter ($/m2). The entries under the Cost Item column record
the major cost items in boldface font (e.g., HVAC Upgrade);
each constituent cost item is indented and printed in regular
font. The values under the Total Cost column record the
overall cost for the major cost item in boldface font. The
constituent cost items are printed in regular font; their sum is
equal to the dollar amount for the major cost item. Columns
3 and 4 are patterned after Column 2. The per unit cost for
each major cost item is shown in boldface font and the per
unit costs for each constituent cost item are shown in regular
font. Note that the sums of per unit costs of the constituent
cost items may not add to the dollar amount for the major cost
item due to independent rounding.
Table C.4, which covers annual filter replacement costs
for the high-rise office building, is broken into two parts.
Part A reports annual costs per air-handling unit (AHU).
There are six AHUs in the high-rise office building. Part B
reports annual costs per unit of floor area. Part A of Table
C.4 has nine columns. The first two columns designate the
system and type of filter. Table C.4 makes reference to four
systems: (1) As Is, (2) Filtration Level 1, (3) Filtration Level
2, and (4) Filtration Level 3. Filters are designated by their
MERV (Minimum Efficiency Reporting Value) rating, as
HEPA (High Efficiency Paniculate Air) or Gas Phase ACS
(Air-Cleaning System). Columns 3 through 7 record the
information needed to calculate the cost per change per AHU.
Column 8 records the number of changes per year for each
type of filter. Column 9 records the annual cost per AHU for
each system and type of filter. Part B of Table C.4 has four
columns: (1) Cost Item, (2) Total Annual Cost, (3) Cost per
Square Foot ($/ft2), and (4) Cost per Square Meter ($/m2).
The entries under the Cost Item column record the system in
boldface font; each constituent cost item (i.e., type of filter)
is indented and printed in regular font. The values under the
Total Annual Cost column record the overall cost for the
system in boldface font. The constituent cost items are printed
in regular font; their sum is equal to the dollar amount for the
system. Columns 3 and 4 are patterned after Column 2. The
annual cost per unit for each system is shown in boldface font
and the annual cost per unit for each constituent cost item
is shown in regular font. Note that the sums of the annual
costs per unit of the constituent cost items may not add to
the annual cost per unit for the system due to independent
rounding.
-------
Table C.I Cost for Level 1 Filtration for the High-Rise Office Building
Cost per Unit Floor Area
Cost Item Total Cost ($)
$/ft2 $/m2
HVAC Upgrade
Remove Existing Filter Bank
Upgrade Air Handling Unit w/ One Bank MERV 1 1
Frames, Clips, and Filters
Sating, Stiffener Bars, and Welding
Electric Motor 25 hp w/ Belts and Pulley
Electric Motor 40 hp w/ Belts and Pulley
Electric Motor 50 hp w/ Belts and Pulley
Centrifugal Fan 40 hp
Miscellaneous
Balance Air Handling Unit
Mobilization and Demobilization
Clean-Up
71,354
3,640
1,843
2,070
8,467
11,773
6,643
21,303
8,504
3,848
1,600
1,664
0.59
0.03
0.02
0.02
0.07
0.10
0.06
0.18
0.07
0.03
0.01
0.01
6.40
0.33
0.17
0.19
0.76
1.06
0.60
1.91
0.76
0.35
0.14
0.15
-------
Table C.2 Cost for Level 2 Filtration for the High-Rise Office Building
Cost per Unit Floor Area
Cost Item Total Cost ($)
$/ft2 $/m2
HVAC Upgrade
Remove Existing Filter Bank
Remove Electric Motor and Assembly Wiring
Remove Centrifugal Fan
Upgrade the Air Handling Unit w/ One Bank of HEPA-
Rated Galvanized Steel, Frames, Clips, and Filters
Safmg, Stiffener Bars, and Welding
Electric Motor 25 hp w/ Belts and Pulley
Electric Motor 40 hp w/ Belts and Pulley
Electric Motor 50 hp w/ Belts and Pulley
Centrifugal Fan 40 hp
Miscellaneous
Balance Air Handling Unit
Clean-Up
Mobilization and Demobilization
Electrical Modifications
Remove Miscellaneous (Wire, Conduit, and Switches)
SWBD C/B - 600 A, 3P
Wire Miscellaneous
Conduit: 3 in EMT
Combination Starter Size 2/Switch
Combination Starter Size 3/Switch
Conduit: 1 in EMT
Conduit: 1 1/4 in EMT
Disc. Switch 60 A, 3P
Disc. Switch 100 A, 3P
Disc. Switch 200 A, 3P
209,445
3,640
3,952
520
135,465
2,070
8,467
11,773
6,643
21,303
8,501
3,848
1,600
1,664
86,415
3,921
5,883
24,246
22,271
6,864
15,692
978
2,182
1,055
2,217
1,107
1.75
0.03
0.03
0.00*
1.13
0.02
0.07
0.10
0.06
0.18
0.07
0.03
0.01
0.01
0.72
0.03
0.05
0.20
0.19
0.06
0.13
0.01
0.02
0.01
0.02
0.01
18.79
0.33
0.35
0.05
12.15
0.19
0.76
1.06
0.60
1.91
0.76
0.35
0.14
0.15
7.75
0.35
0.53
2.17
2.00
0.62
1.41
0.09
0.20
0.09
0.20
0.10
: Entries recorded as 0.00 indicate values less than $0.01.
-------
Table C.3 Cost for Level 3 Filtration for the High-Rise Office Building
Cost per Unit Floor Area
Cost Item Total Cost ($)
$/ft2 $/m2
HVAC Upgrade
Remove Existing Filter Bank
Remove Electric Motor and Assembly Wiring
Remove Centrifugal Fan
Upgrade the Air Handling Unit w/ One Bank of HEPA-
Rated Galvanized Steel, Frames, Clips, and Filters
Safing, Stiffener Bars, and Welding
Electric Motor 30 hp w/ Belts and Pulley
Electric Motor 50 hp w/ Belts and Pulley
Electric Motor 75 hp w/ Belts and Pulley
Centrifugal Fan 40 hp
Centrifugal Fan 50 hp
Miscellaneous
Balance Air Handling Unit
Clean-Up
Mobilization and Demobilization
Electrical Modifications
Remove Miscellaneous (Wire, Conduit, and Switches)
SWBD C/B - 600 A, 3P
Wire Miscellaneous
Conduit: 3 in EMT
Combination Starter Size 3/Switch
Combination Starter Size 4/Switch
Conduit: 1 in EMT
Conduit: 1 1/4 in EMT
Conduit: 2 in EMT
Disc. Switch 100 A, 3P
Disc. Switch 20 OA, 3P
1,025,156
3,640
3,952
1,560
843,564
6,493
6,351
8,868
13,286
21,303
68,933
39,215
3,848
1,600
2,544
91,617
3,957
5,883
24,996
22,271
19,615
5,435
414
2,327
813
1,478
4,428
8.54
0.03
0.03
0.01
7.03
0.05
0.05
0.07
0.11
0.18
0.57
0.33
0.03
0.01
0.02
0.76
0.03
0.05
0.21
0.19
0.16
0.05
0.00*
0.02
0.01
0.01
0.04
91.96
0.33
0.35
0.14
75.67
0.58
0.57
0.80
1.19
1.91
6.18
3.52
0.35
0.14
0.23
8.22
0.35
0.53
2.24
2.00
1.76
0.49
0.04
0.21
0.07
0.13
0.40
: Entries recorded as 0.00 indicate values less than $0.01.
-------
Table C.4 Summary of Annual Filter Replacement Costs for the High-Rise Office Building
Part A Annual Costs per Air-Handling Unit
Cost Per Change per AHU (costs in $) Annual Cost
System Material Changes/Year AMM^CM
Unit Cost Units Material Cost Labor Cost Total perAHU($)
As Is
MERV6
5
20
100
20
120
4
480
TOTAL 480
Level 1
MERV11
8
20
160
32
192
1
192
TOTAL 192
Level 2
MERV8
MERV13
HEPA
5
125
300
20
20
20
100
2,500
6,000
20
500
1200
120
3,000
7,200
1
0.33
0.33
120
1,000
2,400
TOTAL 3,520
Level 3
MERV8
MERV13
HEPA
GPAC
MERV11
5
125
300
4,500
8
20
20
20
20
20
100
2,500
6,000
90,000
160
20
500
1,200
18,000
32
120
3,000
7,200
108,000
192
1
0.33
0.33
0.2
2
120
1,000
2,400
21,600
384
TOTAL 25,504
NOTE: Costs are per AHU and there are six AHUs in the building.
Table C.4 Summary of Annual Filter Replacement Costs for the High-Rise Office Building
Part B Annual Costs per Unit of Floor Area
Cost Item
System As Is
MERV6
System Level 1
MERV11
System Level 2
MERV8
MERV13
HEPA
System Level 3
MERV8
MERV13
HEPA
GPAC
MERV11
Total Annual Cost
($)
2,880
2,880
1,152
1,152
21,120
720
6,000
14,400
153,024
720
6,000
14,400
129,600
2,304
Cost per Unit Floor Area
$/ft2 $/m2
0.02
0.02
0.01
0.01
0.18
0.01
0.05
0.12
1.28
0.01
0.05
0.12
1.08
0.02
0.26
0.26
0.10
0.10
1.89
0.06
0.54
1.29
13.12
0.06
0.54
1.29
11.63
0.21
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Table C.5 Cost for Non-filtration Retrofits for the High-Rise Office Buildings
Cost per Unit Floor Area
Cost Item Total Cost ($)
$/ft2 $/m2
Sealing the Envelope
Seal Exterior Windows and Openings
Swing Staging Equipment
Scaffolding
Seal Doors and Thresholds
Move Outside Air Intake to Roof
Swing Staging Equipment
Scaffolding
Duct Support
Painting
Remove Louver - 8 ft x 4 ft
Bird Screen
Ductwork
Clamps, Anchors
Shelter-In-Place (covers six shelters in building)
Seal Doors and Thresholds
Miscellaneous sealing (Registers, Windows, Fixtures,
Plates)
Seal Ceiling Slab Openings
Supply Damper Incl. Elect. Motor - 10 in Dia
Return Damper Incl. Elect. Motor - 16 in x 8 in
Stand Alone Filtration/Air Cleaning Units
Quick Shut-Off and Purge
System Testing, Adjusting, and Balancing
625,326
352,285
214,611
54,858
3,573
225,261
7,495
10,363
11,899
11,258
208
2,804
178,256
2,978
93,812
5,359
4,990
22,318
3,706
3,438
54,000
20,949
75,000
5.21
2.94
1.79
0.46
0.03
1.88
0.06
0.09
0.10
0.09
0.00*
0.02
1.49
0.02
0.78
0.04
0.04
0.19
0.03
0.03
0.45
0.17
0.63
56.09
31.60
19.25
4.92
0.32
20.21
0.67
0.93
1.07
1.01
0.02
0.25
15.99
0.27
8.42
0.48
0.45
2.00
0.33
0.31
4.84
1.88
6.73
* Entries recorded as 0.00 indicate values less than $0.01.
-------
Table C.6 Cost for Level 2 Filtration for the Office Building Lobby
Cost per Unit Floor Area
Cost Item Total Cost ($) ;
$/ft2 $/m2
HVAC Upgrade
Ductwork
Caps
Air Handling Unit - ACU-A2 w/ Coils
Ductwork
Duct Insulation - Fiberglass Board Type 3 Lb Density -
1 1/2 in Thick
Louver 48 in x 48 in with Wall Opening
Duct - Flex. Connector
2 in Dia. Piping - Sch. 40
Reducer 6 in x 2 in
2 in Dia. Piping Hook-up
2 in Dia. Elbow
2 in Dia. Piping Fiberglass Insulation -1 1/2 in Thick
2 in Dia. Piping - Sch. 40
Demobilization
Reducer 3 in x 2 in
2 in Dia. Piping Hook-up
2 in Dia. Elbow
2 in Dia. Piping Fiberglass Insulation - 1 1/2 in Thick
Concrete Pad
Louver 0/A Air
Balancing Air Handling Unit
Controls
Piping
Valve Tag (Brass - 2 in Dia.)
Upgrade the Air Handling Unit w/ One (1) Bank of HEPA
Rated Galvanized Steel, Frames, Clips and Filters
Clean-Up
Housing
Exhaust Fan E-A2
Exhaust Fan E-A2B
HEPA Solution Budget Double Wall Insulated
Remove and Relocate Existing Piping, Ductwork, Electrical
Conduit, Wire, and Additional Material
Mobilization and Demobilization
Electrical Modifications
Remove Miscellaneous (Wire, Conduit, Switches)
Combination Starter Size I/Switch
Wire: #12 THHN
Conduit: 3/4 in EMT
Disc. Switch, 30 A, 3P
$14,112
1,407
139
8,529
23,225
15,693
279
235
1,409
464
5,168
786
382
1,409
800
317
5,168
786
382
394
595
494
16,698
1,409
464
13,631
624
1,932
5,819
4,266
2,645
24,998
1,567
9,432
254
5,354
1,349
1,050
1,425
40.60
0.40
0.04
2.44
6.64
4.48
0.08
0.07
0.40
0.13
1.48
0.22
0.11
0.40
0.23
0.09
1.48
0.22
0.11
0.11
0.17
0.14
4.77
0.40
0.13
3.89
0.18
0.55
1.66
1.22
0.76
7.14
0.45
2.69
0.07
1.53
0.39
0.30
0.41
437.27
4.33
0.43
26.24
71.46
48.29
0.86
0.72
4.34
1.43
15.90
2.42
1.18
4.34
2.46
0.97
15.90
2.42
1.18
1.21
1.83
1.52
51.38
4.34
1.43
41.94
1.92
5.94
17.90
13.12
8.14
76.92
4.82
29.02
0.78
16.47
4.15
3.23
4.38
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Table C.7 Cost for Level 3 Filtration for the Office Building Lobby
Cost per Unit Floor Area
Cost Item Total Cost ($)
$/ft2 $/m2
HVAC Upgrade
Ductwork
Caps
Air Handling Unit - ACU-A2 w/ Coils
Ductwork
Duct Insulation - Fiberglass Board Type, 3 Lb Density -
1 1/2 in Thick
Louver 48 in x 48 in with Wall Opening
Duct - Flex. Connector
2 in Dia. Piping - Sch. 40
Reducer 6 in x 2 in
2 in Dia. Piping Hook-up
2 in Dia. Elbow
2 in Dia. Piping Fiberglass Insulation -1 1/2 in Thick
2 in Dia. Piping - Sch. 40
Reducer 3 in x 2 in
2 in Dia. Piping Hook-up
2 in Dia. Elbow
2 in Dia. Piping Fiberglass Insulation - 1 1/2 in Thick
Concrete Pad
Louver 0/A Air
Balancing Air Handling Unit
Controls
Piping
Valve Tag (Brass - 2 in Dia.)
Clean-Up
Housing
Exhaust Fan E-A2
Exhaust Fan E-A2C
HEPA and Gas Filter Equipment
Remove and Relocate Existing Piping, Ductwork, Electrical
Conduit, Wire, and Additional Material
Mobilization and Demobilization
Electrical Modifications
Remove Miscellaneous (Wire, Conduit, Switches)
Combination Starter Size I/Switch
Wire: #12 THHN
Conduit: 3/4 in EMT
Disc. Switch, 30 A, 3P
199,609
1,407
139
8,529
27,194
19,653
279
235
1,409
464
5,168
786
382
1,409
317
5,168
786
382
394
595
494
16,698
1,409
464
624
1,932
5,819
4,266
65,843
24,998
2,366
9,432
254
5,354
1,349
1,050
1,425
57.03
0.40
0.04
2.44
7.77
5.62
0.08
0.07
0.40
0.13
1.48
0.22
0.11
0.40
0.09
1.48
0.22
0.11
0.11
0.17
0.14
4.77
0.40
0.13
0.18
0.55
1.66
1.22
18.81
7.14
0.68
2.69
0.07
1.53
0.39
0.30
0.41
614.18
4.33
0.43
26.24
83.67
60.47
0.86
0.72
4.34
1.43
15.90
2.42
1.18
4.34
0.97
15.90
2.42
1.18
1.21
1.83
1.52
51.38
4.34
1.43
1.92
5.94
17.90
13.12
202.59
76.92
7.28
29.02
0.78
16.47
4.15
3.23
4.38
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Table C.8 Cost for Non-filtration Retrofits for the Office Building Lobby
Total Cost Cost Per Unit Floor Area
Cost Item ,,...
($) $/ft2 $/m2
Isolating the Lobby
Marble
Concrete Lintel
1/2 Tempered Glass
Metal Doors (Frames) Hdw
Seal Doors and Thresholds
CMU
Extend Outside Air Intake to Roof
Opening Wall
Bird Screen
Ductwork
Clamps, Anchors
Swing Staging Equipment
Scaffolding
Duct Support
Painting
64,067
23,508
475
10,473
23,424
3,873
2,314
23,773
400
140
11,842
496
1,458
5,073
2,400
1,964
18.30
6.72
0.14
2.99
6.69
1.11
0.66
6.79
0.11
0.04
3.38
0.14
0.42
1.45
0.69
0.56
197.13
72.33
1.46
32.22
72.07
11.92
7.12
73.15
1.23
0.43
36.44
1.53
4.49
15.61
7.38
6.04
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Table C.9 Cost for Level 2 Filtration for the Office Building Mail Room
Cost per Unit Floor Area
Cost Item Total Cost ($)
$/ft2 $/m2
HVAC Upgrade
Remove Existing Filter Bank
Remove Electric Motor and Assembly Wiring
Upgrade the Air Handling Unit w/ One (1) Bank of HEPA-
Rated Galvanized Steel, Frames, Clips, and Filters
Sating, Stiffener Bars, and Welding
Housing Filters
Ductwork
Duct Insul. - Fiberglass Board Type - Thick 1 1/2 in
Electric Motor 2 hp
Electric Motor 40 hp w/ Belts and Pulley
Exhaust Fan E-A2
Exhaust Fan E-A2B
Exhaust Fan Filters (3 Stage)
Handling and Shipping 5% on Material
Clean-Up
Sealant
Balancing Air Handling Unit
Exhaust Register 24 in x 12 in
Exhaust Registers 24 in x 12 in
Mobilization and Demobilization
Electrical Modifications
Remove Miscellaneous (Wire, Conduit, Switches)
Combination Starter Size 3/Switch
Miscellaneous Wire
Conduit: 1 1/4 in EMT
Disc. Switch, 100 A, 3P
Combination Starter Size 0/S witch
Conduit: 3/4 in EMT
Disc. Switch, 30 A, 3P
63,350
607
693
16,940
345
2,400
6,773
5,818
688
5,887
4,267
4,267
8,907
1,708
277
223
641
654
654
1,600
8,897
667
3,923
483
388
739
1,785
438
475
17.60
0.17
0.19
4.71
0.10
0.67
1.88
1.62
0.19
1.64
1.19
1.19
2.47
0.47
0.08
0.06
0.18
0.18
0.18
0.44
2.47
0.19
1.09
0.13
0.11
0.21
0.50
0.12
0.13
189.67
1.82
2.08
50.72
1.03
7.19
20.28
17.42
2.06
17.62
12.78
12.78
26.67
5.11
0.83
0.67
1.92
1.96
1.96
4.79
26.64
2.00
11.75
1.45
1.16
2.21
5.34
1.31
1.42
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Table C.10 Cost for Level 3 Filtration for the Office Building Mail Room
Cost per Unit Floor Area
Cost Item Total Cost ($)
$/ft2 $/m2
HVAC Upgrade
Remove Existing Filter Bank
Remove Electric Motor and Assembly Wiring
Remove Exhaust Fan
Upgrade the Air Handling Unit w/ One (1) Bank of HEPA-
Rated Galvanized Steel, Frames, Clips and Filters
Sating, Stiffener Bars, and Welding
Housing Filters
Ductwork
Duct Insul. - Fiberglass Board Type - Thick 1 1/2 in
Electric Motor 2 hp
Electric Motor 40 hp w/ Belts and Pulley
Exhaust Fan E-A2
Exhaust Fan E-A2C
Exhaust Fan 2 hp
Exhaust Fan Filters (5 Stage)
Handling and Shipping 5 % on Material
Clean-Up
Sealant
Balancing Air Handling Unit
Exhaust Registers 24 in x 12 in
Mobilization and Demobilization
Electrical Modifications
Remove Miscellaneous (Wire, Conduit, Switches)
Combination Starter Size 3/Switch
Wire Miscellaneous
Conduit: 1 1/4 in EMT
Disc. Switch, 100 A, 3P
Combination Starter Size 0/Switch
Conduit: 3/4 in EMT
Disc. Switch, 30 A, 3P
156,118
607
693
260
81,592
345
3,310
6,773
5,818
688
5,887
4,267
4,983
1,852
30,389
5,081
424
254
641
654
1,600
8,897
667
3,923
483
388
739
1,785
438
475
42.85
0.17
0.19
0.07
22.66
0.10
0.92
1.88
1.62
0.19
1.64
1.19
1.38
0.51
8.44
1.41
0.12
0.07
0.18
0.18
0.44
2.47
0.19
1.09
0.13
0.11
0.21
0.50
0.12
0.13
461.87
1.82
2.08
0.78
244.29
1.03
9.91
20.28
17.42
2.06
17.62
12.78
14.92
5.54
90.98
15.21
1.27
0.76
1.92
1.96
4.79
26.64
2.00
11.75
1.45
1.16
2.21
5.34
1.31
1.42
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Table C.ll Cost Per Unit of Floor Area for the Air Sealing Retrofit of the Mail Room
Cost per Unit Floor Area
Cost Item Total Cost ($)
$/ft2 $/m2
Sealing the Envelope
Seal/Patch Corridor Walls
Replace/Install Thresholds
Seal Doors
Seal/Patch Ceiling Slab
29,086
15,798
952
1,570
10,766
8.08
4.39
0.26
0.44
2.99
87.08
47.30
2.85
4.70
32.23
Table C.12 Cost for Level 1 Filtration for the Low-Rise Office Building
Cost per Unit Floor Area
Cost Item Total Cost ($)
$/ft2 $/m2
HVAC Upgrade
Remove Filters
New Filters
Clean-Up
Mobilization
Electrical Modifications
Remove Panel CB - 400 A
MCB - 400 A w/ Shunt Trip, 480 V
Emergency Mushroom Push Button
Wire: #12 THHN
Conduit: 3/4 in EMT
2,099
170
956
173
800
11,792
213
9,806
223
346
1,203
0.12
0.01
0.06
0.01
0.05
0.68
0.01
0.57
0.01
0.02
0.07
1.30
0.11
0.59
0.11
0.50
7.31
0.13
6.08
0.14
0.21
0.75
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Table C.13 Cost for Level 2 Filtration for the Low-Rise Office Building
Cost per Unit Floor Area
Cost Item Total Cost ($)
$/ft2 $/m2
HVAC Upgrade
One (1) Bank of HEPA-Rated Casing and Filters,
Clips and Filters
Steel Platform for Fans and Filters
Ductwork
Centrifugal Fan
Clean-Up
Sealant
Balancing Air Handling Unit
Mobilization
Electrical Modifications
Panel C/B: 70 A - 3P - 480 V W/S Hunt Trip
VFD/Switch, 25 hp, 4 BOV, NEMA 3R
Wire: #6 THHN
Wire: #8 THHN
Conduit: 1 l/4inRGS
Remove Panel CB - 400A
MCB - 400 A w/ Shunt Trip, 480 V
Emergency Mushroom Push Button
Wire: #12 THHN
Conduit: 3/4 in EMT
284,132
172,189
26,877
42,071
34,475
624
856
6,239
800
69,550
1,696
46,370
1,634
412
7,495
213
9,806
223
365
1,337
16.38
9.92
1.55
2.42
1.99
0.04
0.05
0.36
0.05
4.01
0.10
2.67
0.09
0.02
0.43
0.01
0.57
0.01
0.02
0.08
176.26
106.82
16.67
26.10
21.39
0.39
0.53
3.87
0.50
43.15
1.05
28.77
1.01
0.26
4.65
0.13
6.08
0.14
0.23
0.83
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Table C.14 Cost for Level 3 Filtration for the Low-Rise Office Building
Cost per Unit Floor Area
Cost Item Total Cost ($)
$/ft2 $/m2
HVAC Upgrade
One (1) Bank of HEPA-Rated Casing and Filters,
Clips and Filters
Steel Platform for Fans and Filters
Centrifugal Fan 20 hp
Ductwork
Clean-Up
Sealant
Balancing Air Handling Unit
Mobilization
Electrical Modifications
Panel C/B: 70 A - 3P - 480 V W/S Hunt Trip
VFD/Switch, 25 hp, 4 BOV, NEMA 3R
Wire: #6 THHN
Wire: #8 THHN
Conduit: 1 l/4inRGS
Remove Panel CB - 400 A
MCB - 400 A w/ Shunt Trip, 480 V
Emergency Mushroom Push Button
Wire: #12 THHN
Conduit: 3/4 in EMT
193,734
90,031
26,877
26,235
42,071
624
856
6,239
800
69,550
1,696
46,370
1,634
412
7,495
213
9,806
223
365
1,337
11.17
5.19
1.55
1.51
2.42
0.04
0.05
0.36
0.05
4.01
0.10
2.67
0.09
0.02
0.43
0.01
0.57
0.01
0.02
0.08
120.18
55.85
16.67
16.28
26.10
0.39
0.53
3.87
0.50
43.15
1.05
28.77
1.01
0.26
4.65
0.13
6.08
0.14
0.23
0.83
Table C.15 Cost for Envelope Air Sealing of the Low-Rise Office Building
Cost per Unit Floor Area
Cost Item Total Cost ($)
$/ft2 $/m2
Seal Envelope
Seal Exterior Windows
Seal Crawl Space Openings
Seal Doors and Thresholds
Sheet Metal
Patch Roof
32,356
7,046
17,332
2,680
2,866
2,433
1.86
0.41
1.00
0.15
0.17
0.14
20.07
4.37
10.75
1.66
1.78
1.51
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-------
&EPA
United States
Environmental Protection
Agency
PRESORTED STANDARD
POSTAGES FEES PAID
EPA
PERMIT NO. G-35
Office of Research and Development
National Homeland Security Research Center
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
Recycled/Recyclable
Printed with vegetable-based ink on
paper that contains a minimum of
50% post-consumer fiber content
processed chlorine free
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