United States
Environmental Protection
Agency
E PA-600/R-99-053
June 1999
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\/cnr\ riesearcn cinu
Development
A PRELIMINARY METHODOLOGY FOR
EVALUATING THE COST-EFFECTIVENESS
OF ALTERNATIVE INDOOR AIR
QUALITY CONTROL APPROACHES
Prepared for
Office of Radiation and Indoor Air
Prepared by
National Risk Management
Research Laboratory
Research Triangle Park, NC 27711
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TECHNICAL REPORT DATA
NRMRL-RTP-161 (Ptease read Iivwuetiom on th€ reverse before complete ||| |||| || |||||||l(| |||||||| III
1. REPORT NO. 2.
EPA-60O/R-99-O53
s.i III Illl II IIIlll
P PBS 9
-156184
4. TITLE AND SUBTITLE
A Preliminary Methodology for Evaluating the Cost-
effectiveness of .Alternative Indoor Air Quality
Approaches
5. REPORT DATE
June 1999
6. PERFORMING ORGANIZATION CODE
7. AUTHOFUS)
D. Bruce Henschel
S. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
See Block 12
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
NA (Inhouse)
12. SPONSORING AGENCY NAME ANO ADDRESS
EPA, Office of Research and Development
Air Pollution Prevention and Control Division
Research Triangle Park, NC 277E
13. TYPE OF REPORT AND PERIOD COVERED
Final; 3/98 - 2/99
14. SPONSORING AGENCY CODE
EPA/600/13
ts. supplementary notes ^uthor Henschel's Mail Drop is 54; Ms phone is 919/541-4112.
is.AesTRACTXhe report defines a simplified methodology that can be used by indoor air
quality (LAQ) diagnosticians, architects/engineers, building owners/operators, and
the scientific community, for preliminary comparison of the cost-effectiveness of
alternative IAQ control measures for any given commercial or institutional building.
Such a preliminary analysis could aid the user in initial decision-making prior to
retaining experts (such as heating, ventilation, and air-conditioning engineers and
building modelers) who could conduct a rigorous evaluation. The preliminary method-
ology consists of text, logic diagrams, and worksheets that are intended to aid the
user in: (1) assessing which IAQ control option(s) might apply to the specific building
being addressed; (2) designing alternative control measures (involving increased out-
door air ventilation, air cleaning, or source management), and developing rough in-
stalled and operating costs for these measures; (3) estimating the approximate effec-
tiveness of the alternative control measures in reducing occupant exposure to con-
taminants of concern; and (4) comparing the cost-effectivness of the alternative con-
trol measures under consideration, to aid in selecting the optimal control approach.
17, KEY WORDS AND DOCUMENT ANALYSIS
a, DESCRIPTORS
b.lDENTIFIERS/OFEN ENDED TERMS
e. cosati Field/Group
Air Pollution
Quality Control
Cost Effectiveness
Public Buildings
Air Pollution Control
Stationary Sources
Indoor Air
13 B
13H, 14D
14A •
13 M
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report}
Unclassified
21. NO. OF PAGES
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 <9-73}
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FOREWORD
The U.S. Environmental Protection Agency is charged by Congress with pro-
tecting the Nation's land, air, and water resources. Under a mandate of national
environmental laws, the Agency strives to formulate and implement actions lead-
ing to a compatible balance between human activities and the ability of natural
systems to support and nurture life. To meet this mandate, EPA's research
program is providing data and technical support for solving environmental pro-
blems today and building a science knowledge base necessary to manage our eco-
logical resources wisely, understand how pollutants affect our health, and pre-
vent or reduce environmental risks in the future.
The National Risk Management Research Laboratory is the Agency's center for
investigation of technological and management approaches for reducing risks
from threats to human health and the environment. The focus of the Laboratory's
research program is on methods for the prevention and control of pollution to air,
land, water, and subsurface resources; protection of water quality in public water
systems; remediation of contaminated sites and groundwater; and prevention and
control of indoor air pollution. The goal of this research effort is to catalyze
development and implementation of innovative, cost-effective environmental
technologies; develop scientific and engineering information needed by EPA to
support regulatory and policy decisions; and provide technical support and infor-
mation transfer to ensure effective implementation of environmental regulations
and strategies.
This publication has been produced as part of the Laboratory's strategic long-
term research plan. It is published and made available by EPA's Office of Re-
search and Development to assist the user community and to link researchers
with their clients.
E. Timothy Oppclt, Director
National Risk Management Research Laboratory
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EPA-600/R-99-053
June 1999
A PRELIMINARY METHODOLOGY
FOR EVALUATING THE COST-EFFECTIVENESS OF
ALTERNATIVE INDOOR AIR QUALITY CONTROL APPROACHES
by
D. Bruce Henschel
Air Pollution Prevention and Control Division
National Risk Management Research Laboratory
U. S. Environmental Protection Agency
Research Triangle Park, NC 27711
PROTECTED UNDER INTERNATIONAL COPYRIGHT
ALL RIGHTS RESERVED.
NATIONAL TECHNICAL INFORMATION SERVICE
U.S. DEPARTMENT OF COMMERCE
Reproduced from
best available copy.
Prepared for
U. S. Environmental Protection Agency
Office of Research and Development
Washington, D. C. 20460
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NOTICE"
This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
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ABSTRACT
A simplified methodology is defined that can be used by indoor air quality (IAQ)
diagnosticians, architects/engineers, building owners/operators, and the scientific
community, for preliminary comparison of the cost-effectiveness of alternative IAQ
control measures for any given commercial or institutional building. Such a
preliminary analysis could aid the user in initial decision-making prior to retaining
experts (such as HVAC engineers and building modelers) who could conduct a
rigorous evaluation.
This preliminary methodology consists of text, logic diagrams, and worksheets
that are intended to aid the user in;
1) assessing which IAQ control option(s) might be applicable in the specific
building being addressed;
2) designing alternative control measure [involving increased outdoor air (OA)
ventilation, air cleaning, or source management steps], and developing rough
installed and operating costs for these measures;
3} estimating the approximate effectiveness of the alternative control measures
in reducing occupant exposure to contaminants of concern; and
4) comparing the cost-effectiveness of the alternative control measures under
consideration, to aid in selection of the optimal control approach.
In this report, the term "cost-effectiveness" refers to the incremental increase
in annualized cost per unit reduction in exposure by the building occupants.
"Exposure" is the number of person-hours per year during which the occupants are
exposed to a unit concentration of the contaminant of concern; in this report, the
units of exposure are (mg/m3)-person-hr/yr. The most cost-effective control approach
is the one offering the lowest annualized cost per unit reduction in exposure.
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TABLE OF CONTENTS
Page
Abstract ii
List of Figures vii
List of Tables viii
Metric Conversion Factors ix
Section 1. Objectives and Approach 1-1
1.1 Introduction 1-1
1.2 Objective 1-3
1.3 Approach 1-4
1.4 Considerations Regarding "Effectiveness" 1-5
Section 2. Identification of Candidate I AO Control Options 2-1
2.1 Selecting Between Improved Ventilation, Air Cleaning,
and Source Management 2-1
2.1.1 Source(s) Located Outdoors 2-2
2.1.2 Localized Problem Resulting from Indoor Sources 2-3
2.1.3 Building-Wide Problem Resulting from Indoor Sources 2-4
2.2 Considerations Regarding Air Cleaning 2-6
2.2.1 Central In-Duct Air Cleaners 2-6
2.2.2 Self-Contained Air Cleaners 2-7
2.3 Considerations Regarding Source Management 2-8
Section 3. Estimating the Costs of lAQ Control Options:
Improved Ventilation 3-1
3.1 Introduction 3-1
3.2 Estimating the Required Increase in Ventilation Rate 3-2
3.3 Estimating Installed Costs for Increases in Ventilation Rate 3-4
3.3.1 HVAC Components that Will or Will Not
Require Modification 3-4
3.3.2 Approaches for Increasing Cooling/Heating Capacity 3-6
3.3.3 Installed Costs in Existing Buildings (Retrofit Case) 3-7
3.3.4 Installed Costs in the New Construction Case 3-10
iii
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TABLE OF CONTENTS (continued)
Page
3.4 Estimating Operating and Maintenance Costs for Increases in
Ventilation Rate 3-12
3.4.1 Annual Operating Costs 3-12
3.4.2 Annual Maintenance Costs 3-14
3.5 Estimating Total Annualized Costs for Increases in
Ventilation Rate 3-14
Section 4, Estimating the Costs of IAQ Control Options:
Air Cleaning 4-1
4.1 Introduction 4-1
4.2 Estimating the Required Air Cleaner Performance 4-2
4.3 Estimating installed Costs for Centra! Air Cleaners 4-4
4.3.1 Installed Costs for Central Particulate Air Cleaners 4-4
4.3.2 Installed Costs for Central Air Cleaners for
Gaseous Contaminants 4-5
4.4 Estimating Operating and Maintenance Costs for
Central Air Cleaners 4-6
4.4.1 Annual Operating Costs 4-6
4.4.2 Annual Maintenance Costs 4-7
4.5 Estimating Total Annualized Costs for Central Air Cleaners 4-9
4.6 Estimating Costs for Self-Contained Air Cleaners 4-9
Section 5. Estimating the Costs of IAQ Control Options:
Source Management 5-1
5.1 Introduction 5-1
5.2 Estimating the Required Extent of Source Management 5-1
5.2.1 Constant Sources 5-1
5.2.2 Decaying Sources 5-3
5.3 Source Removal 5 5
5.3.1 Remove High-Emitting Furnishings, Solvents,
or Equipment 5-5
5.3.2 Improve Maintenance to Remove Contamination 5-6
5.3.3 Red uce Activity Generating Emissions 5-7
5.4 Source Replacement 5-7
5.4.1 Use of Low Emitting Materials (LEMs) 5 7
5.4.2 Allowing Source to Decay Before Use 5-9
5.4.3 Use of Contamination-Resistant Materials 5-10
5.5 Source Treatment 5-11
5.6 Source Relocation 5-12
5.7 Source Rescheduling 5-12
5.8 Adjustment of Occupancy Patterns 5-13
iv
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TABLE OF CONTENTS (continued)
Page
Section 6. Estimating the Effectiveness of IAQ Control Options 6-1
6.1 Absolute Exposure Values 6-1
6.1.1 Rigorous (Computer-Assisted) Calculations 6-1
6.1.2 Simplified Calculations 6-3
6.2 Relative Exposure Values 6-4
Section 7. Assessing the Cost-Effectiveness of IAQ Control Options 7-1
7.1 Absolute Values for Cost-Effectiveness 7-1
7.2 Relative Values for Cost-Effectiveness 7-2
7.3 Interpretation of Cost-Effectiveness Results 7-2
7.3.1 Required Effectiveness Is Known 7-3
7.3.2 Effectiveness to Be Achieved is Open to Judgement 7-3
7.3.3 Effectiveness Is Not Subject to Adjustment • 7-6
Section 8. References 8-1
APPENDIX A. Worksheets A-1
Worksheet 1. Estimation of Outdoor Air Increase Required to
Achieve Desired Reduction in Contaminant Concentration Using
Increased Ventilation. A-3
Worksheet 2A. Estimation of Installed Costs for Increased OA:
Enlarged Central Units - Retrofit Case. A-4
Worksheet 2B. Estimation of Installed Costs for Increased OA:
Dedicated-OA Unit - Retrofit Case. A-13
Worksheet 3A. Estimation of Installed Costs for Increased OA:
Enlarged Central Units - New Construction Case. A-20
Worksheet 3B. Estimation of installed Costs for increased OA:
Dedicated-OA Unit - New Construction Case. A-30
Worksheet 4. Estimation of Annual Operating Costs for
Increased OA, A-40
v
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TABLE OF CONTENTS (continued)
Page
Worksheet 5. Estimation of Annual Maintenance Costs for
Increased OA. A-48
Worksheet 6. Estimation of Total Annualized Costs for
Increased OA. A-50
Worksheet 7. Estimation of Air Cleaner Efficiency Required
to Achieve Desired Reduction in Contaminant Concentration
Using a Central Indoor Air Cleaner. A-53
Worksheet 8. Estimation of Installed Costs for Central
Indoor Air Cleaners. A-57
Worksheet 9. Estimation of Annual Operating Costs for
Central Indoor Air Cleaners. A-63
Worksheet 10. Estimation of Annual Maintenance Costs for
Central Indoor Air Cleaners. A-68
Worksheet 11. Estimation of Total Annualized Costs for
Central Indoor Air Cleaners. A-75
Worksheet 12. Estimation of Costs for Soif Contained
Indoor Air Cleaners. A-77
Worksheet 13. Estimation of Costs for Source Management:
Source Replacement by Low-Emitting Materials (LEMs). A 82
Worksheet 14. Absolute Reduction in Exposure Resulting from
Implementation of an IAQ Control Measure; Simplified
Calculation. A 89
Worksheet 15. Relative Reductions in Exposure Achieved by One
IAQ Control Measure Compared Against Alternative Measures. A-92
vi
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LIST OF FIGURES
Page
Figure 1A. Logic diagram for selecting an IAQ control approach:
Part A (sources outside building). 2-9
Figure 1B. Logic diagram for selecting an IAQ control approach:
Part B (localized problem resulting from sources
inside building). 2-10
Figure 1C. Logic diagram for selecting an IAQ control approach:
Part C (building-wide problem resulting from sources
inside building). 2-11
Figure 2. Logic diagram for assessing particulate or gaseous air
cleaners as an IAQ control approach where air cleaning
is an option. 2-12
Figure 3. Logic diagram for assessing source management as an IAQ
control approach where source management is an option. 2-13
Figure 4. Illustrative plot of cost-effectiveness vs. effectiveness
for one particular building. 7-4
Figure A-1. Alternative locations for central indoor air cleaners
within the HVAC system. A-55
Figure A-2. Schematic diagram and mass balance equation for a zone
being treated using a self-contained air cleaner. A-81
VII
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LIST OF TABLES
Page
Table A-1, Incremental Increases in Cooling and Heating Capacities
Necessitated by Increases in Outdoor Air Ventilation
Rates (by Geographical Location). A-11
Table A-2. Approximate Installed Costs of Air Handlers and Retrofit
Ducting. A-12
Table A-3. Approximate Total and Incremental Installed Costs for a
New Rooftop Cooling System. A-18
Table A-4. Approximate Total and Incremental Installed Costs for
Heating Capacity in a New Rooftop HVAC System. A-19
Table A-5. Incremental Installed Costs of Air Handlers and Ducting
in a New Building. A-29
Table A-6. Incremental Annual Cooling and Heating Energy Require-
ments per Unit Increase in OA Ventilation Rate
(by Geographical Location). A-47
Table A-7. Capital Recovery Factors. A-52
Table A-8. Equations to Compute Air Cleaner Efficiency, rj> Required
to Achieve Desired Indoor Concentration, ClN. A-56
Table A-9. Approximate Fractional Efficiency of Various In-Duct
Particulate Indoor Air Cleaners. A-60
Table A-10. Approximate installed Costs of Various In-Duct
Particulate Indoor Air Cleaners. A-62
Table A-11. Approximate Replacement Costs of Media Cartridges
for Particulate Media Air Cleaners. A-73
Table A-12. Sorption Capacity of Granular Activated Carbon Air
Cleaners for Various Organic Compounds. A-74
VIII
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METRIC CONVERSION FACTORS
Although it is EPA's policy to use metric units in its documents, non-metric
units have been used in this report consistent with common practice in the heating,
ventilating, and air-conditioning industry. Readers more accustomed to the metric
system may use the following factors to convert to that system.
Non Metric
inch (in.)
foot (ft)
square foot (ft2)
cubic foot (ft3)
cubic foot per minute
(cfm)
pound (lb)
pound per cubic foot*
(lb/ft3)
gallon (gal.)
inch of water (in. WG)
degrees Fahrenheit (°F)
British thermal unit
(Btu)
therm (100,000 Btu)
British thermal unit per hour
(Btu/h)
ton (of refrigeration)
(12,000 Btu/h)
horsepower (hp)
Times
0.0254
0.305
0.0929
0.0283
37
0.454
1.60 x 107
3.78 x 10 3
249
5/9 (°F - 32)
0.293
29.3
0.293
3,520
0.746
Yields Metric
meter (m)
meter (m)
square meter (m2)
cubic meter (m3)
liters per second (L/s)
kilogram (kg)
milligrams per cubic meter*
(mg/m3)
cubic meter (m3)
pascals (Pa)
degrees Celsius (°C)
watt-hour (W-hr)
kilowatt-hours (kW-hr)
watt (W)
watts (W) of cooling
capacity
kilowatt (kW)
* Note: By convention, indoor concentrations are expressed in metric units (mg/m3)
throughout this report.
IX
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[This page intentionally blank.]
x
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SECTION 1
OBJECTIVES AND APPROACH
1.1 INTRODUCTION
The control techniques for reducing the concentrations of indoor air pollutants
can be viewed as falling into three broad categories:
1} improved ventilation - including increases in the quantity of outdoor air (OA)
supplied to a building, and/or improvement in the distribution and mixing of the
supply air {OA plus recirculated air) throughout the various zones in the
building;
2) air cleaning - typically involving devices mounted in the central HVAC ducting,
or self-contained devices (having their own fans) mounted in the occupied
zones, capable of removing particulate or gaseous contaminants from the
circulating air; and
3) source management - which can include removal of all or part of the source,
replacement of the source by a lower-emitting alternative, treatment of the
source to reduce emissions, re-location of the source, re-scheduling of the
timing when the source is allowed to be active {to avoid occupied periods), or
re-location of the building occupants in order to reduce occupant exposure.
There are different conditions under which each of these approaches is most
likely to be included - or excluded -- as a candidate for IAQ control in a particular
building. In some cases, one of the approaches might be the only logical candidate.
Improved ventilation will be an obvious selection in cases where diagnostics in
an existing building show that an IAQ problem in one zone of the building results from
inadequate distribution of supply air to that zone. Increases in OA to the building as
a whole are a logical choice when the indoor pollutants are being generated through-
out the building (so that source management is potentially a less attractive option),
when only moderate reductions in indoor concentrations are needed (since practical
increases in OA rates will likely be capable of only moderate degrees of contaminant
dilution), and when there is excess capacity in existing HVAC heating and cooling
coils (so that modifications to the existing mechanical system will not be required to
accommodate the increased OA). When the pollutant source is isolated in a localized
area, localized exhaust of that area - considered here to fall into the category of
"improved ventilation" — can be a logical selection, serving both to increase the
1-1
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ventilation rate in that area (by drawing increased supply air from adjoining zones
inside the building) and to prevent the contaminants in that area from being dispersed
throughout the building. But improved ventilation/increased OA will clearly not be a
logical choice when the outdoor air is the pollutant source, unless that problem can
be addressed by re-locating the OA intake.
Air cleaning will be an obvious candidate whenever the outdoor air is the
pollutant source, and this problem cannot be addressed by re-locating the OA intake
or the source that is creating the outdoor concentrations. In such cases, increased
ventilation is not an option. Air cleaning would also be a clear candidate in those
cases where the pollutants are being generated throughout the building (complicating
the application of source management), when the pollutant of concern is amenable
to air cleaning, and when the required reduction in pollutant concentration is greater
than the moderate levels practically achievable by increased ventilation. (In concept,
a 100% efficient air cleaner mounted in the central HVAC ducting -- through which
the building air is recirculated at a typical rate of 7 air changes per hour - might be
expected to reduce indoor concentrations by about 85% to 90%. By comparison,
increasing the OA ventilation rate from 20 cfm/person to, say, 40 or 60 cfm/person
would reduce concentrations by only about 50% to 65%.) Where an air cleaner
would have to be retrofitted into the ducting of an existing HVAC system, air cleaning
will more likely be a candidate when the existing air handler has sufficient excess
capacity to handle the increased pressure drop created by the air cleaner.
Source management will be the logical selection whenever the source can be
conveniently removed or otherwise managed. This is most likely to occur in cases
where the source is in a localized area and is readily accessible, or when the source
is an activity that can be easily modified. When a significant portion of the source is
amenable to source management, this approach can be the most effective of the three
approaches in reducing occupant exposure.
Consideration of the control costs, and of the effectiveness of the controls in
reducing occupant exposure to indoor pollutants, can be valuable when selecting and
designing the IAQ control approach (or combination of approaches) for a particular
building. In cases where the logical control approach appears obvious a priori, a cost-
effectiveness analysis might reveal that modifications in the design or implementation
of this approach - impacting its effectiveness -- could result in a lower cost per unit
reduction in exposure. In cases where the preferred control approach is not apparent
beforehand, a cost-effectiveness analysis could indicate which of the alternative
approaches would provide the lowest cost per unit reduction, and the specific design
for that approach that would minimize the cost.
1-2
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1.2 OBJECTIVE
The objective of this study was to develop a preliminary methodology for
utilizing cost-effectiveness considerations in selecting and designing the IAQ control
approach (or combination of approaches) for any given commercial or institutional
building, This methodology was to be applicable for the variety of different
commercial and institutional building types (e.g., offices, retail establishments,
schools, hospitals), and for both existing buildings (retrofit) and new construction.
This preliminary methodology guides the user through:
1) an assessment of which IAQ control option(s) might be applicable in the
specific building that the user is addressing;
2) a rough estimation of the installed costs, and the operating and maintenance
(O&M) costs, associated with the identified control technique(s) in that
building, where possible;
3) a rough estimation of the effectiveness of the control technique(s) in that
building, where possible; and
4) a comparison of the cost-effectiveness of the control techniques, based on the
estimated costs and effectiveness, to enable a preliminary screening of the
alternatives.
The potential users of such a methodology were envisioned as including IAQ
diagnosticians, architects/engineers, building owners/operators, and the scientific
community. From a practical standpoint, this preliminary methodology might assist
a building operator or an IAQ diagnostician in assessing the potential cost-effective-
ness of, say, increased ventilation before hiring an HVAC engineer to consider
modifications to the mechanical system. Or it could aid the scientific community in
assessing, e.g., what performance will have to be achieved with air cleaners (in terms
of, say, the required carbon lifetime in granular activated carbon units) in order for air
cleaning to be more cost-effective than increased ventilation in particular types of
applications. It could suggest to an architect how great a premium might be paid for
low-emitting materials in constructing and furnishing a new building, before this
source management approach becomes less cost-effective than other alternatives.
Only a preliminary methodology was attempted here, involving rough estimates.
Many site-specific variables will impact the performance and cost of each control
technique (and hence the technique's cost-effectiveness) in any given building. These
include variables associated with the building, the HVAC system, the nature and
location of the IAQ pollutant source(s), the building occupancy pattern, and the design
and operation of the IAQ control system. Moreover, a rigorous estimation of the
1-3
-------
control system costs, and the system's effectiveness in reducing occupant exposure,
would require the expertise of, e.g., HVAC engineers and computer modelers, applied
specifically to the building under consideration. A methodology that could guide the
user through a rigorous assessment of each of the several classes of variables for any
selected building utilizing the required expertise -- and that, based on this assessment,
could then provide definitive site-specific guidance regarding control selection and
design — would require a comprehensive compilation of charts and nomographs,
and/or a computer-based expert system. Such a rigorous methodology was beyond
the scope of this effort.
Given the large number of site-specific variables that determine the cost and
effectiveness of IAQ controls in a specific building, it was recognized a priori that the
preliminary methodology developed here would necessarily be fairly general if it were
to be broadly applicable to many different buildings. Accordingly, the preliminary
methodology serves as a general framework for site-specific cost-effectiveness
analysis by the user, assisting in the thought process but not serving as a "cook-
book".
1.3 APPROACH
To assist the user in identifying which IAQ control approaches might be
considered in a specific building (Item 1 in Section 1.2 above), a series of logic
diagrams has been prepared indicating the conditions under which improved
ventilation, air cleaning, and source management are most likely to be candidates.
These logic diagrams are presented and discussed in Section 2 of this report.
To aid in estimating the installed, the O&M, and the annualized costs associated
with the control techniques (Item 2 in Section 1.2 above), Worksheets 1 through 13
in Appendix A have been prepared, illustrating approaches for;
a) making key design decisions to enable the costing of specific approaches
(including, e.g., determination of the amount of additional ventilation air
required, or the required per-pass removal efficiency of an air cleaner); and
b) roughly estimating the installed, the operating, and the maintenance costs of
specific controls, generally utilizing simplifying "rules of thumb" and default
values (for, e.g., equipment and utilities costs).
For more rigorous designs and cost estimates, the user is referred to HVAC engineers
and equipment vendors, and to computer modelers familiar with building energy and
cost modeling. The simplified cost estimation approach is described in Sections 3
through 5.
1-4
-------
To aid in estimating the effectiveness of the techniques in reducing occupant
exposure (Item 3 in Section 1.2 above), Worksheets 14 and 15 (in Appendix A) are
introduced in Section 6, for approximating these reductions for each of the control
approaches. These worksheets assist in the estimate of; absolute reductions in
exposure, where such an estimate is possible; or relative reductions in exposure
achieved by one control approach compared to another, where absolute estimates are
not feasible. For more rigorous estimates, the user is referred to computer modelers
capable of more rigorously computing pollutant concentrations and occupant
exposures throughout the building considering building air flows, source decay, etc.
To aid in a preliminary comparison of the cost-effectiveness of the alternative
IAQ control measures that are being evaluated (Item 4 in Section 1.2 above),
procedures are presented in Section 7 for estimating the absolute or relative cost-
effectiveness of the alternatives (depending upon whether absolute or relative
exposure reductions were estimated in Section 6). Methods for presenting and
interpreting these cost-effectiveness results are described, to aid in the selection of
an optimal IAQ control approach.
In this report, it is assumed that — prior to the implementation of this
methodology — the necessary diagnostic testing has already been completed to define
the nature and source of the IAQ problem that is to be addressed (EPA, 1991). Thus,
such "problem-definition" diagnostic testing is not included in this methodology.
However, the methodology in some cases suggests additional information gathering
to aid in evaluating alternative control approaches.
1.4 CONSIDERATIONS REGARDING "EFFECTIVENESS"
In this methodology, the "effectiveness" of an IAQ control measure refers to
the degree to which the control measure reduces occupant exposure to the pollutant
of concern. "Exposure" in a given building would take the general form:
the pollutant concentration to which each individual occupant is exposed during
any given hour of occupancy in the building
times
the number of hours of occupancy in the building by that occupant over the
total period of interest (e.g., over a year)
times
the total number of occupants.
1-5
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Exposure would thus have units of (concentration) x (persons) x (time). If the period
of interest were one year, typical units of cumulative exposure would be
(mg/m3) • person • hr per year.
[Note: By convention, indoor concentrations are shown in metric units throughout
this report.]
The effectiveness of a control measure would be the change in exposure
achieved by that control, i.e.,
effectiveness = - A(exposure).
The minus sign indicates that a negative change (a reduction) in exposure represents
a positive effectiveness.
Correspondingly, the "cost-effectiveness" of the measure would be expressed
as:
cost-effectiveness = - A(cost)/'A(exposure),
i.e., the unit increase in control cost per unit reduction in occupant exposure. A
control measure having good cost-effectiveness would charge a (relatively) low cost
for a (relatively) large reduction in exposure. Where the effectiveness is expressed as
the exposure reduction per year, cost is commonly expressed as an average
annualized amount, including average annual O&M costs plus an annual capital
recovery figure accounting for the installed costs.
As used here, the term "effectiveness" addresses only the reduction in the
concentrations to which occupants are exposed over time. It does not address the
reductions in actual contaminant uptake by the occupants (the "absorbed dose"), nor
any resulting health benefits.
Since both the cost and the effectiveness of a given IAQ control category (e.g.,
improved ventilation! will depend upon the degree of control that the control was
designed to achieve, it is clear a priori that the cost-effectiveness will vary as a
function of effectiveness. Also, more effective control approaches (such as source
management) will sometimes have a highercost than other, less effective approaches,
but could turn out to be more cost-effective at their greater level of effectiveness.
Thus, it is apparent that - in a rigorous analysis -- the cost-effectiveness of a control
approach would have to be plotted as a function of effectiveness, in order to enable
a fair comparison among alternative approaches at a given level of effectiveness.
1-6
-------
It should be noted that the absolute value for occupant exposure in a given
building, with and without control measures, will involve a fairly sophisticated
computation. This computation would require a mass balance -- addressing source/
sink characteristics and building/HVAC flow dynamics -- to determine indoor
concentrations as a function of time and as a function of location within the building.
The detailed occupancy pattern of the building would then be superimposed on these
mass balance results. The concentration at a given location in the building will vary
hourly, depending upon, e.g., HVAC operation and pollutant source decay rates. The
exposure experienced by any individual occupant will depend upon which hours that
occupant spends in which locations within the building, a pattern that will vary from
occupant to occupant. A fairly sophisticated computer model will be required to
compute and sum the hourly exposures of each individual occupant over the course
of a year, if rigorous, absolute exposures are to be determined in computing control
effectiveness.
Even where a computer model is used to compute an absolute control
effectiveness, one might commonly choose to assess the effectiveness for selected,
representative occupants, rather than the total for all occupants in the building. In
such cases, the effectiveness might be expressed as the reduction in [(mg/m3) * hr]
per representative person per year.
Where the user wishes to make preliminary estimates of effectiveness (and
cost-effectiveness) without a computer model, Worksheets 14 and 15 (Appendix A)
are introduced in Section 6 for developing either:
a) rough estimates of the absolute reductions in exposure with a given control
approach, which - using the procedures in Section 7 - permit estimation of the
approximate cost-effectiveness of that approach; or
b) the relative reduction in exposure, permitting estimation of the relative cost-
effectiveness of one control approach vs. another - e.g., the cost-effectiveness
of Control Option 1 divided by that of Control Option 2.
This latter procedure avoids the need to calculate absolute values of exposure.
1-7
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[This page intentionally blank.]
1-8
-------
SECTION 2
IDENTIFICATION OF CANDIDATE IAQ CONTROL OPTIONS
As indicated by Item 1 in Section 1.2, the first step in this preliminary
methodology is the identification of those IAQ control options that might be
considered as candidates in any particular building that the user might be addressing.
2.1 SELECTING BETWEEN IMPROVED VENTILATION, AIR CLEANING, AND
SOURCE MANAGEMENT
Figures 1 A, 1B, and 1C are logic diagrams illustrating the thought process that
can be used in deciding which control approaches will be applicable, given any set of
circumstances that the user is encountering.
The user begins with Figure 1 A, which addresses the case where the source
creating the indoor air problem is located outdoors. If the source is not outdoors, the
user proceeds to Figure 1B, which addresses the case where the source is indoors but
the IAQ problem is localized within the building. If the source is indoors and the IAQ
problem is distributed throughout the building, the user proceeds to Figure 1C.
The logic sequence begins in the upper left in each figure. "Yes" responses to
questions in the logic sequence lead the user toward the right, and "No" responses
lead the user downward, until a suggestion is ultimately reached regarding whether
ventilation, air cleaning, or source management appears to be the more logical
approach.
Where the logical approach appears to be improved ventilation, the figures walk
the user through additional logic steps intended to better define the specific nature of
the appropriate improved ventilation step. These additional steps sometimes refer the
user to Appendix A worksheets that are introduced in Section 3, to assist in designing
and costing the improved ventilation method. Where the logical approach appears to
be air cleaning or source management, Figures 1A-1C refer the user to other figures,
presented later in Section 2, that assist in the design and costing of these approaches,
to the extent possible.
These logic diagrams ask a series of questions. In some cases, the answers to
the questions might be readily apparent, or might have been obtained during problem-
definition diagnostic testing conducted prior to the application of this methodology.
In other cases, where the answers are not known, the questions are suggesting
additional information-gathering or diagnostic testing that might be needed to aid in
control selection.
2-1
-------
2.1.1 Source(s) Located Outdoors
Figure 1A illustrates the logic in cases where the source(s) creating the indoor
problem is (are) located outside the building.
The outdoor pollutants will be entering the building either via the outdoor air,
or via soil gas. When soil gas is the source, one can consider additional OA supply
into the building, either to adjust the indoor pressure on the ground floors of the
building (to reduce or prevent soil gas entry), or to dilute the entering soil gas
contaminants. In either case, such an increase in OA is considered an "improved
ventilation" control approach for the purposes of this methodology.
If neither of these OA-related steps would adequately control the soil gas
contaminants, then soil depressurization (and/or perhaps foundation sealing) would be
the only alternatives. These are considered to be "source management" approaches.
If the outdoor air is the source of the indoor pollutants, the first question is
whether this problem results because the OA intake for the building's mechanical
system is located too near to a localized outdoor source (such as a loading dock or a
dumpster). If this is the case, the user should explore the possibility of moving the
OA intake ("improved ventilation") or re-locating the outdoor source ("source
management").
If re-location of the intake or the source is not an option, the primary alternative
would seem to be installation of an air cleaner on the incoming OA. For complete-
ness, Figure 1A suggests that one might also consider reducing the OA intake; this
will probably not commonly be a practical approach.
Mechanically supplied OA is generally the predominant route by which the
contaminated outdoor air will enter the commercial and institutional buildings being
addressed in this document. Thus, Figure 1A and the preceding discussion focus on
the OA that is being introduced by the mechanical system. In some cases,
unacceptable amounts of the outdoor contaminants might also enter the building via
uncontrolled infiltration through the building shell. Re-location of the mechanical
system's OA intakes, or installation of an air cleaner to treat the incoming OA, will not
address this uncontrolled OA entry. If the contaminants in infiltrating air cannot be
reduced by re-locating the outdoor source ("source management"), other options to
consider would include: a) supplying increased OA through the mechanical system
(with an air cleaner treating the intake air), to pressurize the building and thus prevent
the infiltration ("improved ventilation" combined with "air cleaning"); or b) an
appropriate air cleaning approach. Possible air cleaning approaches could include:
installation of a central air cleaner in the mechanical system, treating all of the
recirculating building air; or, if the infiltration is occurring only in certain zones,
installation of self-contained air cleaners treating those zones.
2-2
-------
2.1.2 Localized Problem Resulting from Indoor Sources
Figure 1B illustrates the logic in cases where the pollutant source is indoors, but
the IAQ problem is localized within the building (e.g., appears to be limited to a
particular zone or room).
In many such cases, the localized problem results from a localized source --
e.g., an improperly vented storage area for chemicals, occupant activities, water
damage (and hence biological contamination}, or new carpeting or furniture in that
zone or room. The first question to ask in such cases is whether in fact there is such
a localized source creating the problem, and whether this source can reasonably be
removed or reduced, If a local source is responsible, such a source management
approach will generally be the most effective at reducing (or eliminating) contaminant
concentrations. And, since the source is confined to a fairly limited area, this
approach might well be the most conveniently implemented as well.
If a localized source is not responsible for the IAQ problem, some localized
problem with the ventilation system must be responsible. For such cases, Figure 1B
inquires whether: a) the localized area is receiving proper supply air flow from the
HVAC system; and b) whether this supply air is being adequately mixed within the
localized area. If inadequate localized ventilation is the cause of the problem,
appropriate modifications to the air distribution system ("improved ventilation") would
appear to be the logical solution.
In some cases, the source of the localized IAQ problem will be a localized
source that is not amenable to being removed or reduced, or that cannot bo reduced
to a sufficient extent to adequately reduce contaminant levels. For example, the
source might be some occupant activity that cannot be curtailed, such as food
processing, graphics, or laboratory activities. In cases where source management is
not a practical (or cost-effective) complete solution with a localized source, improved
ventilation approaches should be considered, increasing air supply to the area. A
common method for increasing supply air to a localized area containing a source is to
exhaust air from that area to outdoors. This method provides the combined benefit
of increasing local ventilation by drawing air from adjoining areas of the building
(diluting the contaminant), while also depressurizing the area (preventing the
contaminant from dispersing to other zones in the building). Figure 1B also shows the
option of modifying the HVAC system to provide more air to the area directly via the
supply ducting, an option that might be accompanied by local exhaust (to ensure
increased local ventilation). Where source management and/or improved ventilation
are not cost-effective, one can also consider the option of air cleaning, perhaps using
a self-contained air cleaner (incorporating its own circulating fan, independent of the
HVAC system) treating only the localized area.
2-3
-------
The logic diagrams necessarily require "yes" or "no" answers, and their layout
might thus imply that only one possible ultimate end-point. In practice, the user might
find that an answer to certain logic questions is "maybe". For example, source
removal might be one possible solution, or partial solution, but must be compared
against localized exhaust ventilation as another, possibly more cost-effective
alternative.
2.1.3 Building-Wide Problem Resulting from Indoor Sources
Figure 1C illustrates the logic when the pollutant source is indoors, and the IAQ
problem is distributed throughout the building.
The first question asked in the figure is whether the building-wide problem
results from localized emissions indoors that are being distributed throughout the
building by the HVAC system. Where this is the case, source management addressing
that localized source, or isolation of the source (including exhaust ventilation of the
area where the source is located), would appear to be logical approaches to be
considered first.
If the indoor source is not localized, but is building-wide, the next question is
whether an approach other than improved ventilation should be considered at the
outset. While source management can sometimes be more difficult to implement
when the sources are distributed throughout the building, there will be cases when
it will be a strong candidate on a building-wide scale. For example, low-emitting
building materials and furnishings can be considered when a new building is being
planned.
A central question determining whether air cleaning should be considered
initially is whether the pollutant of concern is reliably removed by commercially
available air cleaners. The pollutant most reliably removed by indoor air cleaners is
particulates (ASHRAE, 1996). Technically, some gaseous contaminants can also be
removed by indoor air cleaners (ASHRAE, 1995), although gaseous indoor air cleaners
have not found such wide application in practice. Where the pollutant emission
source is building-wide, it will probably often be most cost-effective to mount the air
cleaner in the central HVAC ducting, rather than using self-contained units (discussed
previously as an option for localized sources).
If building-wide source management and air cleaning are not clear-cut
alternatives at the outset, the next question posed in Figure 1C is whether the HVAC
system itself might be the source of the IAQ problem. Most commonly, HVAC-
created contaminants will include microbiologicals (growing on moist components in
the system) and dust (when the particulate air filters in the system are not functioning
properly). The most common control approach in these cases will be to clean the
system, or to design and operate the system to avoid biological growth ("source
2-4
-------
management"). In some cases, maintenance of the particulate filters ("air cleaning")
will be the appropriate approach.
The next question in Figure 1C is whether the indoor source is intermittent
(e.g., chemical spills in the building or periodic use of chemical cleaners). In general,
intermittent sources that occur at widely spaced (and possibly irregular) time intervals
would seem to be less amenable to treatment with improved ventilation, since it
appears intuitively unattractive to consistently ventilate the building at an increased
rate in order to handle the occasional spike in concentration that will occur when the
intermittent source becomes active. For completeness, the figure suggests that
increased ventilation might be considered in cases where the spikes can be detected
by a sensor in the HVAC control system, and the ventilation rate can be designed to
automatically increase whenever these spikes are detected. But in practice, such a
sensor controlled approach would not seem to be commonly applicable. In practice,
improved ventilation will likely be a candidate for intermittent sources only when; a)
the intermittent sources are so frequent that they may be treated as essentially
continuous sources; or b) the increased ventilation can be activated manually (e.g.,
with an exhaust fan in the area where the source occurs) whenever the source
becomes active.
If the answers are "no" to all of the questions up to this point in Figure 1C --
i.e., if there is a fairly steady building-wide source for which source management and
air cleaning are not obvious solutions at the outset, and which is not being created
within the HVAC system -- then improved ventilation (increasing OA to the entire
building) would appear to be a logical control approach. The major deterrent to using
increased ventilation under these circumstances would be if the contaminant
concentrations in the building were so great that OA rates could not cost-effectively
be increased sufficiently to provide the needed reductions.
Given that increased OA appears to be a leading candidate at this point in the
logic, the next question is whether the HVAC system is in fact supplying the amount
of OA for which it was designed, and the amount of OA specified in applicable
standards such as ASHRAE 62-1989 (ASHRAE, 1989). If the mechanical system is
not providing the proper amount of OA, the appropriate first step would be to make
any necessary system modifications to correct this problem. If pollutant concentra-
tions remain too high even after such modifications, then further OA increases might
be considered, as discussed in the following paragraphs.
If the HVAC system is providing the proper amount of OA, Figure 1C directs
the user to Worksheet 1 in Appendix A, which can be used to estimate the increase
in OA that would be required to achieve the desired reduction. The next question is
whether the existing HVAC system (in the case of existing buildings) - or the
mechanical system that has been specified for a new building -- has sufficient cooling
2-5
-------
arid heating capacity to accommodate this increase in OA without modifications to the
equipment.
If the mechanical system has sufficient heating/cooling coil capacity to handle
the required increase in OA, the primary cost impact will be the energy cost for
conditioning the increased OA flows and for operating the fans at increased capacity.
For this case, Figure 1C refers the user to additional worksheets to aid in a rough
estimation of these energy costs. If the existing (or specified) cooling or heating
capacity would have to be increased to condition the increased OA, the figure refers
to further worksheets that will also assist in rough estimations of installed costs for
the enlarged equipment.
2.2 CONSIDERATIONS REGARDING AIR CLEANING
In a number of cases, Figures 1A through 1C suggest that the user consider air
cleaning as a candidate control option. Figure 2 is a supplementary logic diagram to
assist the user in assessing air cleaning options in these cases.
As indicated previously, a primary consideration when identifying air cleaning
as an option is that the pollutant of interest must be amenable to reliable removal by
commercially-available air cleaners.
As with Figure 1B, Figure 2 begins by asking if the pollutant source is
localized - i.e., if it impacts only one zone, or a portion of a zone, among a number
of zones being treated by a given HVAC unit within the building. Where the problem
is localized in this manner, it would commonly be treated by local exhaust ventilation
or source management rather than by air cleaning. Accordingly, the discussion of air
cleaning in this document focuses on central air cleaners, mounted in the ductwork
of the HVAC unit and thus generally treating all of the zones conditioned by that unit.
However, there are individual cases -- including, e.g., clean rooms and smoking
lounges - where users might sometimes wish to consider self-contained air cleaners,
independent of the HVAC system, as an option for localized treatment (Flanders
Filters, 1994; Pierce et al., 1996). Thus, for completeness, Figure 2 includes this
option.
2.2.1 Central In-Duct Air Cleaners
If the pollutant source cannot reasonably be addressed by localized self-
contained units, Figure 2 refers the user to Worksheet 7 in Appendix A, for estimating
the required per-pass removal efficiency of a central, duct-mounted air cleaner for
removing particulate or gaseous contaminants. The results from this worksheet --
which will depend upon whether the air cleaner will be treating the recirculating
building air or the incoming outdoor air -- will aid in selecting and sizing the air cleaner.
2-6
-------
The next questions address whether — in the case of existing buildings — there is
sufficient space in the existing mechanical room to physically accommodate the air
cleaner that would be required, and sufficient excess static pressure capability in the
existing central air handler to handle the added pressure drop that the air cleaner will
create. In the case of new buildings in the design phase, the analogous questions
would be whether the mechanical room or the air handler would have to be enlarged.
The issues of space and pressure drop can be important. A typical particulate
filter module capable of treating 2,000 cfm (i.e., about 2,000 ft2 of floor area at
1 cfm/ft2} will commonly have dimensions of perhaps 2 by 2 by 1 ft. Many of the
granular activated carbon (GAC) modules that are offered commercially to remove
gaseous organics are of similar dimensions. A central air handler treating, say,
8,000 ft2 would require four of these modules combined into a filter bank of a
configuration best suited to the available space (e.g., four modules aligned side by-
side, or four modules stacked two by two). These banks, plus the associated ducting,
might require more space than will sometimes be available in small mechanical rooms,
especially when the additional space required for maintenance is considered.
The pressure drops associated with particulate filters commonly range from
perhaps 0.1 to over 1.0 inch of water (in. WG), depending upon air velocity, dust
loading on the filter, and design removal efficiency. The pressure drops associated
with GAC filters of the common V-bank configuration might range from below 0.5 to
above 1.0 in. WG, depending on velocity, carbon particle size, and bed depth. These
added pressure drops could impact the performance of an air handler that might have
been selected to provide at maximum static pressure of, say, 6 to 8 in. WG.
If the existing mechanical room and air handler (or the new building as
designed) can accommodate the required central air cleaner, then Figure 2 directs the
user to worksheets that can aid in the rough estimation of installed, O&M, and
annualized costs. If the mechanical room and/or the air handler are inadequate, the
user must assess the feasibility and costs of installing the air cleaner remote from the
air handler, or of enlarging the mechanical room and air handler as necessary.
2.2.2 Self-Contained Air Cleaners
Self-contained air cleaners are independent of the central HVAC system. These
air cleaners incorporate their own fan to circulate the air from the occupied space
through the unit, and might be mounted, e.g., in the overhead plenum.
Where the source is localized, and where self-contained units appear to be an
option, Figure 2 refers the user to Worksheet 1 2, which will assist in estimating the
air cleaner flow capacity required to provide the needed reduction in contaminant
concentration. Vendor information on the performance and characteristics of available
units can also assist in this assessment.
2-7
-------
With this rough estimation of the hardware requirements, the user must then
assess whether there is sufficient space, electrical power, etc., in the localized area
to accommodate the self-contained air cleaner, if there is, Figure 2 refers the user to
the worksheet that can assist in a rough estimation of the installed, O&M, and
annualized costs for this approach. If the localized area is not readily amenable to
accommodating a self-contained air cleaner, the user must assess the feasibility and
costs associated with modifying the space to accommodate the unit(s).
2.3 CONSIDERATIONS REGARDING SOURCE MANAGEMENT
In a number of cases, Figures 1A through 1C suggest that the user consider
source management as a candidate control option. Figure 3 is a supplementary logic
diagram to assist the user in assessing source management options in these cases.
Figure 3 walks the user through the various classes of activities that are
considered "source management", and provides some practical examples of each.
Clearly, those source management activities that are applicable in any given building --
and their costs and effectiveness — will depend heavily on the characteristics of that
particular site.
2-8
-------
YES
Design HVAC mods,
estimate costs to provide
the increased OA. See Figure 1C,
Worksheets 1 through 6.
ho
I
to
Consider soil
depressurization,
foundation sealing.
See, e.g.,
Henschel, 1993;
Leovic and Craig,
1993
Can
increases in
OA ventilation rate
provide adequate
reductions?
START
Can
increases in
indoor pressure
adequately
reduce soil gas
entry?
Design HVAC mods,
estimate costs to implement
the increase in indoor pressure
See, e.g., Fowler etal., 1997;
Leovic and Craig, 1993
Is
the location
of the OA intake
(HVAC mechanical
vent) creating the
problem?
Can
the OA intake
(or the sources
impacting the intake)
be relocated?
Is
the source
outside the building
(outdoor air or
soil gas)?
Is
outdoor
air the
source?
Assess feasibility,
estimate costs of
relocating intake
Assess feasibility,
costs of relocating
the pertinent sources
(See Fig. 3.)
Consider
sir cleaner
for incoming
OA 'See Fig 2)
Can
A volume be
reduced sufficiently
to adequately
reduce indoor
concentrations?
Is
OA intake
volume greater
than required by
applicable
standards?
Design HVAC mods
estimate costs for
reducing OA
Go to
Figure 1 B
Consider
air cleaner
for incoming
OA (See Fig 2)
Improved
ventilation/HVAC
modifications
Air
Cleaners
i Source
i Management
Figure 1A. Logic diagram for selecting an IAQ control approach: Part A (sources outside building).
-------
START
. YES
Go to
Figure 1 A
KEY:
Air Cleaning
^Source Management i
ro
I
o
Is
there an
important source
in that area that can
can be removed/
reduced?
Are
highconcenNy YES
trations limited to
a localized
area?
j Consider source
i management
i (See Fig. 3.)
Do
HVAC mods
appear possible to
supply sufficient
additional air to
that area?
Design required
HVAC mods,
estimate costs.
Is
that area
receiving supply
air flow consistent
with HVAC
design?
Does
diffuser/return -v yes
intake configuration
provide adequate
air mixing in tha
area?
There must be an
important (continuous
or Intermittent) source
in that area that cannot
be removed/reduced.
Go to
Figure 1 C
NO
Is
localized
exhaust an
option?
NO
Consider sir Cleaning
(perhaps alocal self
contained unit)
{See Fig. 2.)
Will
re-design to
improve mixing
help address
the problem?
Design required
diffuser/return
mods, estimate costs.
Modify HVAC operation
to provide design supply
flow. Consider further
HVAC mods (as above)
if further reduction needed
Figure 1B. Logic diagram for selecting an IAQ control approach:
inside building).
Part B (localized
problem resulting from sources
-------
START
s
the sourc
outside the
building?
| Improved
ventilation
Goto
Figure 1A
A.r
Source Management
Are
igh concen
tratons limited
to localized
areas?
Gotc
Figure 1B
Are
pollutant
from localize
araa(s) being distri-
buted through
building by,
HVAC?, '
Can
sources in
ocalized area(s
be removed/
reduced'
Consider source
management.
(See Fig. 3
Consider local exhaust of
source area(s), sealing of
returns drawing air from source
arsa(s) into central HVAC system
If
source
is distributed
throughout building,
is it potentially
amenable to source
management?
Examples: Replacement of sources
by low-emitting materials
scheduling of emitting activities
(e.g., painting) when building is
unoccupied.
Consider source
management.
(See Fig. 3}
Is
pollutant
amenable to re
moval by com
mercial air
•cleaners
Consider
air 6e?nmg
(See Fig 2.1
Conduct HVAC maintenance as appropriate
cleaning to remove microbials; cleaning to
remove dust and other contaminants; filter
maintenance. Modify HVAC design/operation
to reduce sites for biological arowth
Is
the HVA
system the
source?
Can
a sensor b
sed to vary vent
ation rate in respons
to fluctuations in
the source?.
Consider source
management,
(See Fig. 3.)
s
the sour
intermittent
€enstiM|
aiftkiapsng,
i'$e-e ' 3. a.)
Is
the HVAC
system supplying
OA to the building at a
rate consistent with design
(and with applicable
standards)?
Is
the design
capacity of the
existing heating/cooling
coils sufficient to
provide this addi
tionai OA?
Estimate the additional OA
required to reduce indoor
concentrations to acceptable
levels (Worksheet 1).
Estimate operating & maintenance costs
associated with increased OA flow in
existing system. (Worksheets 4 through 8).
Assess feasibility, estimate installed and
Q&M costs, for: a) increasing capacity of
existing equipment; or b) adding a dedicated
OA unit. (Worksheets 2 through 6).
Modify HVAC operation to provide design OA
flow. Consider further OA increases
(as above) If further reduction is necessary,
Figure 1C. Logic diagram for selecting an I AO control approach: Part C (building-
wide problem resulting from sources inside building).
2-11
-------
YES
YES
YES
NO
NO
NO
YES
YES
NO
NO
the source"
localized?
/there space,,
^electrical capacity ,
to acommodate the
self-contained air
cleaner(s) in the
X. occupied /
x. space? ./
/ existing
/ air handler
capable of handling
the added a P
, created by the /
\ air cleaner?/
Is there
/sufficient space in\
/ the mechanical room
to accommodate the central
air cleaner(s) near
\the air handler? /
Will a
/self-containea\
air cleaner treating
the localized area
\ address the
\ problem? /
START
Assess feasibility,
estimate costs of
modifying the space
and installing/operating
air cleaner
Estimate the installed
and operating costs
for the central air
cleaner {Worksheets
8 through 11).
Estimate the installed
and operating costs
for the self-contained
air cleaner
(Worksheet 12).
Estimate flows needed
to achieve required mass
removal (Worksheet 12).
Size the self-contained
unit(s) based on vendor
information.
Pollutant is amenable to
removal by commercial
air cleaners, and air cleaning
is an option suggested by
Figure 1.
Estimated per-pass removal
efficiency required from a
central air cleaner (Worksheet 7).
Size the central unit(s) based
on vendor information.
Assess feasibility,
estimate costs of
installing air cleaner
' remote from air handler,
of incieasing air handler
. static pressuie capability,
and/or of installing/
opeiating air cleaner
^adapted from Worksheets
8 through 11)
Figure 2. Logic diagram for assessing particulate or gaseous air cleaners as an IAQ control approach where
air cleaning is an option.
-------
START
Source management
is an option
suggested by Figure 1
Can^
" source be^
partially or
completely
.removed?/
YES
Examples:
1. Remove the high-emitting building furnishings, solvents
(office supples, janitorial, etc.), or equipment.
2. Improve maintenance to remove microbials from HVAC
or contaminated furnishings, dust from carpeting or
HVAC, etc.
. Reduce activity that creates emissions,
Can
source be
replaced by a
lower-emitting
alternative?
Estimate cost of implementing
the appropriate
source management approach.
Examples:
1. Use low-emitting materials in constructing and
furnishing the building.
2. Allow source emissions to decay (e.g., "air out"
new carpeting) before placing source inside the
building.
3. Use microbiakesistant duct liners.
Can
source be
treated to reduce
emissions''
Ca
source b£
relocated to
an isolated or
exhausted
area?.
Example: Encapsulate the source; e.g., with a coating
or sealant.
Examples:
1. Move solvents to an exhausted janitorial closet.
2. Move outdoor sources away from OA intake.
3. Locate photocopiers in exhausted room.
Can
source be
escheduled to
reduce occupan
exposure?
Can
occupanc
patterns be modi\^§§
fied to reduce
exposure?
Example: Schedule cleaning, painting, building
renovation activities during periods when building is
unoccupied
Example: Delay moving occupants into a new building
until sources (e.g., construction materials and
furnishings) have had an opportunity to decay.
Consider options
other than
source management.
Figure 3. Logic diagram for assessing source management as an IAQ control
approach where source management is an option.
2 13
-------
[This page intentionally blank.]
2-14
-------
SECTION 3
ESTIMATING THE COSTS OF IAQ CONTROL OPTIONS;
IMPROVED VENTILATION
As indicated by Item 2 in Section 1.2, the second step in this preliminary
methodology is the development of rough cost estimates for the candidate IAQ control
options that have been identified in Section 2.
In this preliminary methodology, these rough estimates are viewed as an initial
screening tool to assist the user in making a first cut among the candidates. Of
course, better cost estimates could be developed for all of the control options if the
required expertise (e.g., in HVAC engineering) were available in house or on a
consulting basis, and if the time and resources were available. The objective of this
methodology is to facilitate a fairly quick, inexpensive comparison -- by users who
might not possess ali of the specialized expertise required for a rigorous cost analysis
of each option -- before more substantial efforts are undertaken to develop better
estimates.
This section and the two that follow include worksheets to assist the user in
making key design decisions (e.g., regarding required ventilation increases or air
cleaner effectiveness), and -- where possible — in roughly estimating installed, O&M,
and total annualized costs for the control options. To derive the rough estimates, the
worksheets utilize broad assumptions, "rules of thumb", and other shortcuts that
sacrifice accuracy but enable a reasonable number to be developed fairly simply for
comparative purposes.
The cost number that will be used in the subsequent computation of "cost-
effectiveness" is the total annualized cost. This includes the average annual O&M
cost plus an annual capital recovery factor applied to the installed cost.
This section addresses cost estimation for control options involving improved
ventilation. Sections 4 and 5 address the costs for control options involving air
cleaning and source management, respectively.
3.1 INTRODUCTION
Four types of control steps are suggested in Figures 1A through 1C that fall
under the category of "improved ventilation".
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15 Re-location of the OA intake, in cases where outdoor contaminants are being
drawn into the building because the OA intake is located near an outdoor
pollutant source. The cost of implementing this HVAC modification will be so
site-specific that meaningful assistance in the general costing of this step
cannot be provided here.
2) A djustments to the supply air distribution system, and/or the diffuser and return
grille configurations, to improve supply air distribution and mixing. Such
modifications can sometimes be fairly simple, for example, adjusting the
position of a damper; in other cases, the required modifications could be more
complicated. Because the required activities will be so site-specific, and might
require specialized diagnostics, meaningful assistance in the general costing of
this step cannot be provided here.
3} Localized exhaust ventilation, to increase the ventilation rate in a given area and
to depressurize the area. The amount of exhaust that is required in a particular
building — and the ease with which that area can be, e.g., manifolded into the
central exhaust ducting for the building — will be very site-specific. Thus,
again, it is not felt that meaningful assistance in the general costing of this step
can be provided here.
4) increased outdoor air, to dilute the indoor contaminants (or possibly to
pressurize the ground floor of the building to prevent soil gas entryj. For this
improved ventilation step, generalized worksheets appear to be possible that
might be of assistance to a user in assessing a site-specific case.
Accordingly, the worksheets that follow focus on the case of increased OA.
For ease of reference, all of the worksheets in this report are presented in
Appendix A.
3.2 ESTIMATING THE REQUIRED INCREASE IN VENTILATION RATE
The first step in assessing the costs associated with increasing the OA
ventilation rate, is to estimate the OA increase that will be required. Worksheet 1 in
Appendix A presents the step-wise procedure for estimating the needed increase,
assuming that dilution is the sole mechanism by which the contaminant concentration
is reduced.
The standard dilution calculation reflected in Worksheet 1 shows that if one
wants to reduce the indoor concentration to, say, one-half of the current concentra-
tion, then the OA flow rate must be increased by a factor of 2 above its current value.
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This calculation assumes that the concentration of the contaminant of concern is zero
in the outdoor air, and that the indoor air is well mixed.
To conduct this calculation, one must know: a) the current pollutant
concentration in the indoor air; b) the concentration to which the pollutant must be
reduced; and c) the current flow of OA into the building {or into the area of interest).
In some cases, these parameters will be known; the indoor concentration of a
contaminant, and the OA intake rate, can certainly be measured. However, in
practice, there will be occasions where the user will have to make some judgements
in making the requested entries into Worksheet 1. For example, exactly which
contaminant(s) should drive the calculation? Where the current concentration is not
steady, is the time-averaged concentration the best value to enter on Line 1 of the
worksheet? On what basis does one select the concentration to which the current
levels are to be reduced? Clearly, the simple format of the worksheet has some
potentially non-trivial questions embedded within it. This underscores the point made
in Section 1.2, that this preliminary methodology functions more to outline a thought
process rather than to provide cookbook answers.
The worksheet addresses the case where the contaminant of concern is a
consistent problem throughout the entire portion of the building served by a given air
handler. The OA being provided by that air handler is correspondingly being increased
to treat that entire portion of the building in a uniform manner. Figure 1B suggests
that — when there is a localized source - one option could be to modify the air handler
to provide more total direct supply air (OA plus recirculated air) to the area where the
source is located. In this case, as a first approximation, one might use Worksheet 1
to estimate the additional "clean" supply air that would have to be provided to
adequately reduce the concentration in the local area. The inaccuracy in using the
worksheet in that manner is that the added supply air will increase the mixing of the
local contaminant throughout the area served by the air handler in question, and the
supply air (which is largely recirculated air) will thus increasingly deviate from the
assumption that there is zero concentration of contaminant in the ventilating air. If
a localized source were indeed to be addressed by an increase in direct supply air, the
user would really have to consider the entire portion of the building treated by that air
handler, possibly moderately increasing OA flows to that entire portion (as well as
increasing supply to the localized problem area). The required mass balance in such
a case is more complicated than the simple procedure shown in Worksheet 1.
Figure 1A suggests pressurization of the ground floor of a building (through
increased OA to that area) as a means for preventing soil gas entry into the building.
The pressurization mechanism is very different from that of dilution, on which
Worksheet 1 is based. The amount of additional OA to achieve sufficient pressuriza-
tion of a building is very site-specific, and cannot be addressed here.
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3.3 ESTIMATING INSTALLED COSTS FOR INCREASES IN VENTILATION RATE
Often, the existing HVAC equipment will have to be modified to accommodate
an increase in the OA ventilation rate. An installed cost will be incurred for making
these modifications.
Where increased OA is to be retrofit into an existing building, the term "existing
equipment" will refer to the pre-existing hardware in that existing building. For new
buildings yet to be constructed, that term, as used here, refers to the current
specifications for the HVAC equipment originally designed to be installed into that
new building — equipment that must now be modified before construction to
accommodate increased OA. For the new-building case, the "installed costs" for
increased ventilation are in fact the incremental increase in the installed cost of the
mechanical system resulting from the adjustments that are made in the specifications
to increase the OA rate.
3.3.1 HVAC Components That Will or Will Not Require Modification
Among the equipment components in the HVAC system, only the central supply
fan, the return fan (if present), and the supply and return ducting will consistently not
be impacted by an increase in outdoor air. All of the other components are subject
to potential modification, depending upon the design of the HVAC system.
Cooling and heating capacity. The cooling and heating capacity of the existing
HVAC units will generally have to be increased to handle the sensible and latent load
added by the increased OA, unless the original system was designed with sufficient
excess capacity. An increase in capacity will require increases, for example, in: the
cooling and heating coil surfaces; the capabilities of the condenser, compressor, and
chiller associated with the cooling system; and, depending upon the source of heating,
the capacity of the furnace or the electrical service to the resistance heaters.
Central supply fans. It is unlikely that an increase in OA will require
modifications to the existing central air handlers that circulate the conditioned air
throughout the building. Central air handlers are commonly designed to supply about
1 cfm per ft2 of floor area (OA plus recirculating air). In office buildings that have
been designed according to ASHRAE 62-1989 - supplying 20 cfm OA per person
with 7 persons per 1,000 ft2 (i.e., 0.14 cfm/ft2 of OA) — OA will constitute about
14% of the total supply air being circulated. This OA rate could be increased 7-fold
(to 140 cfm/person) before the total supply air reached 100% OA with the existing
air handlers. Only if the OA rate had to exceed about 140 cfm/person would it be
necessary to increase the flow capacity of the existing central air handlers. Such
substantial OA increases will not commonly be considered.
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Return fans (if present). Consistent with the supply fans, the return fans will
be designed to return about 1 cfm/ft2 from the zones to the central heating/cooling
unit, regardless of the volume of OA being provided to the space. Thus, an increase
in OA supply to the zones will not increase the required flow capacities of the return
fans, except in the unlikely event that the increased OA rate being considered were
greater than 100% OA for the existing system, as discussed above.
Supply and return ducting. An increase in OA rate will not impact the required
dimensions of the ducting that delivers supply air from the central units to the zones,
and that returns zone air to the central units. As discussed above, the total volume
of air moving through this ducting will remain unchanged as the OA rate is increased.
OA intake fans (if present). Many HVAC systems do not include OA intake
fans. In systems having economizers - i.e., in systems dampered to draw in up to
100% OA ~ there is commonly no OA fan, In such cases, adjustments to the OA
intake dampers will enable the existing central air handler to draw additional OA
without modifications to the hardware. However, some HVAC systems -- including
some with economizers - do include OA intake fans. In particular, an intake fan is
one option for ensuring a constant minimum OA intake rate in variable volume
systems where the rate might otherwise drop below the minimum as system flows
vary with load (Kettler, 1998). In these cases, an increase in the minimum OA
requirement would necessitate an increase in the capacity of the intake fan. Also, in
systems without economizers - i.e., in systems designed to provide a fixed OA intake
rate -- an OA intake fan would have to be added, or the existing intake fan enlarged,
if that OA rate were to be increased.
OA intake ducting. In systems having economizers, the existing OA intake
ducting will be sized to accommodate up to 100% OA. Thus, no increase in the
dimensions of the intake ducting will be needed when OA is increased (from, say,
14% OA to anything less than 100% OA). But in systems without economizers, the
OA intake ducting will be sized for the lesser, fixed amount of OA that had been
provided previously. In such systems, the duct dimensions would have to be
increased (or new ducting added in parallel with the existing ductwork) to provide the
required additional OA volume without excessive pressure loss or noise in the ducting.
Some OA intake ducting might be added when a dedicated-OA unit is used to
retrofit increased OA into an existing building, as discussed later, even if the central
system has an economizer.
Pressure relief (exhaust) fans and ducting. When OA is increased, the amount
of air removed from the building must likewise be increased to prevent unacceptable
levels of building pressurization. Pressure relief is provided by; a) localized exhausts
(from bathrooms and janitorial closets), which would commonly remain unchanged as
OA rate is increased; and b) exhaust of some fraction of the recirculating air from the
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central return ducting, referred to here as "central exhaust". It is the central exhaust
that would be increased to accommodate the increased OA intake.
In systems having economizers, the existing central pressure relief component —
the exhaust ducting leading off of the return ducting, and any central exhaust fan, if
present -- has been designed to handle up to 100% OA. Thus, an increase in OA rate
will necessitate no increase in the existing pressure relief hardware (except in the
unlikely event that the increased OA rate exceeds 100% OA on the original system).
However, in systems without economizers, the pressure relief component has been
sized to handle only the lesser, fixed amount of OA provided by the original system.
In these cases, the capacity of any central exhaust fan would have to be increased,
and the dimensions of the exhaust/relief ducting would have to be increased to
accommodate the greater exhaust flow.
3.3.2 Approaches for Increasing Cooling/Heating Capacity
Two alternative approaches will commonly be considered for increasing HVAC
system cooling and heating capacity to handle the loads associated with an increase
in OA.
The first approach is to enlarge the central HVAC units - e.g., adding additional
cooling coil surface, installing larger condenser/compressor units and chillers, adding
heating elements and electrical (or furnace) capacity. This approach will be most
easily applied in new construction, where the capacity increases can be accomplished
simply by specifying higher-capacity components at the outset. However, even in
retrofit cases, it could be possible to, e.g., replace an existing bank of direct
expansion evaporator coils in the central unit and the corresponding compressor/
condenser unit with components having a greater refrigeration capacity.
The second approach is to install a separate HVAC unit, independent of the
central units, that would serve solely to treat the incoming OA and to supply it to the
OA intake ducting of the central system. Such separate units are referred to here as
"dedicated-OA" units. While a dedicated-OA unit could be considered in either an
existing building or in new construction, it offers particular attraction in the retrofit
case. In retrofit situations, the new dedicated-OA unit would make it possible for the
pre-existing HVAC units to handle the increased OA flow without modifications to the
existing equipment.
Dedicated OA units will generally involve direct-expansion cooling and electric
heating elements, making them independent of central system chillers and furnaces.
There is no return air to the dedicated-OA unit; the unit might be viewed as an "OA
intake fan" with conditioning capability incorporated.
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In the discussion that follows, each of these two approaches will be considered
under each of two circumstances: a) the OA increase is to be implemented in an
existing building (the retrofit case); and b) the OA increase is being considered for a
new building not yet constructed.
3.3.3 installed Costs in Existing Buildings (Retrofit Case)
Enlarged Centra! Units
Worksheet 2A in Appendix A presents a procedure for estimating the installed
costs associated with increasing the capacity of the existing central HVAC units in the
retrofit case. This worksheet assumes that the pre-existing HVAC systems do not
have sufficient cooling and heating capacity to handle the OA increase without
modification.
Worksheet 2A is based on the following scenario (presented in terms of the
equipment components discussed in Section 3.3.1).
Cooling and heating capacity. The existing cooling coils, and the associated
condenser/compressor units, are removed from each of the HVAC units
in the building, and replaced with coils and condenser/compressor units
having the required greater refrigeration capacity. Likewise, the heating
elements are removed and replaced with higher-capacity elements.
Since this simplified worksheet assumes direct-expansion cooling units
having electric heat, it will be less accurate for systems involving chillers
and furnaces.
OA intake fan (if present). In cases where an OA intake fan is required, the
worksheet assumes that the pre-existing fan is retained and is supple-
mented with a single new fan designed to provide the incremental
additional OA that is required by all of the HVAC units in the building.
{Where the OA flows are sufficiently great, the user might need to
consider multiple new supplemental OA fans, each fan serving some
number of the HVAC units in the building.)
OA intake ducting. In systems without economizers - where the OA increase
would require that the pre-existing intake ductwork be supplemented in
some manner to handle the increased OA flow — the worksheet assumes
that new ducting is retrofit specifically for the new OA fan discussed
above, directing the supplemental OA from that fan to the individual
HVAC units.
In systems with economizers, no modifications to the existing OA
intake ductwork are needed. In systems with an economizer but having
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an OA intake fan -- e.g., a modern VAV unit having an OA fan to assure
constant OA supply — it is assumed that the new supplemental OA fan
delivers its OA into the pre-existing intake ducting.
Central exhaust fan (if present). Systems that have a central exhaust fan but
do not have an economizer may require an increase in the capacity of the
exhaust fan. The worksheet assumes that, in these cases, the capacity
increase is accomplished by installing a new, supplemental exhaust fan
designed to exhaust an air volume equal to the incremental increase in
the OA supply rate.
Central exhaust ducting. In systems without economizers, the required
increase in exhaust flow would necessitate that the pre-existing exhaust
ductwork be supplemented in some manner. In these cases, the
worksheet assumes that new ducting is retrofit specifically for the new
exhaust fan discussed above, drawing the supplemental exhaust air from
the zones served by the individual HVAC units.
The size of the required increase in cooling capacity is estimated in the
worksheet by computing the sensible and latent energy required to cool the
incremental volume of increased OA from the 1 % value of outdoor enthalpy for
cooling design for the local climate [as defined by the American Society of Heating,
Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE, 1997a)], to an indoor
enthalpy corresponding to 75 °F and 50% relative humidity. Similarly, the required
increase in heating capacity is estimated from the sensible energy required to heat the
incremental OA volume from the 99% value of outdoortemperature for heating design
for the local climate, as defined by ASHRAE, to an indoor temperature of 70 °F. The
worksheet includes a table presenting the tons of additional refrigeration capacity and
the kW of additional heating capacity per 1,000 cfm of incremental OA, for a variety
of geographical locations based on these ASHRAE data.
The installed cost associated with replacement of the existing cooling coils and
the condenser/compressor unit — $830 per ton of refrigeration capacity — was derived
from Means Mechanical Cost Data (Means, 1996), based upon the costs for new coils
and new condenser/compressor units assuming a direct-expansion system, as defined
in the worksheet. To account for the retrofit costs (removing the original coils and
condenser), the $830/ton figure includes a doubling of the labor costs for installing
new units. Likewise, the installed cost associated with replacement of the heating
elements ($35/kW) was derived in a similar manner, assuming electric duct heaters.
The installed costs of new supplemental OA and exhaust fans and ducting, if
required, were likewise obtained from Means, as defined in the footnotes to Table
A-2. To account for retrofit costs, the installed cost of ducting was increased by $40
per linear foot, based on prior experience.
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New Dedicated-OA Unit
Worksheet 2B in Appendix A presents a procedure for estimating the installed
costs associated with the addition of a new dedicated-OA unit in the retrofit case.
Worksheet 2B is based on the following scenario.
Cooling and heating capacity. A new rooftop direct-expansion system with
electric heat is installed having the capacity required to condition the
incremental additional OA that is to be supplied to the building. The
capacities of the pre-existing HVAC units in the building remain
unchanged; the existing units continue to be responsible for conditioning
the original OA volume. The one new dedicated-OA unit is assumed to
provide the conditioned incremental OA for all of the original HVAC units
in the building. However, if the incremental OA flows are sufficiently
great, the user might need to consider multiple new dedicated-OA units,
each serving some number of the original HVAC units.
OA intake fan (if present!. The air handler associated with the new dedicated-
OA unit is, in effect, the OA intake fan for the incremental OA flow. In
systems that require an OA intake fan, the air handler in the new unit
fulfills this requirement for the additional flow, and no additional costs
are encountered for increased OA intake fan capacity. The pre-existing
intake fan is retained, and continues to supply the original OA volume to
the original HVAC units.
OA intake ducting. In systems with economizers, it is assumed that the
incremental additional OA being supplied by the dedicated-OA unit can
be delivered into the pre-existing OA intake ducting; no modifications to
the ducting are required, since it was designed to handle up to 100%
OA. In systems without economizers, it is assumed that new intake
ducting is retrofit into the building to deliver the incremental OA from the
new dedicated-OA unit to the inlets of each of the original HVAC units.
This new intake ducting is assumed to consist of a main trunk line from
the dedicated-OA unit, splitting into branches leading to each HVAC unit.
The original intake ducting remains in place, supplying the original OA
volume to the units.
Central exhaust fan (if present). Systems that have a central exhaust fan but
do not have an economizer may require an increase in the capacity of the
exhaust fan. As in Worksheet 2A above, Worksheet 2B assumes that,
in these cases, the capacity increase is accomplished by installing a new,
supplemental exhaust fan designed to exhaust an air volume equal to the
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incremental increase in the OA supply rate. Any pre-existing exhaust fan
remains in place, and continues to function as before.
Central exhaust ducting. In systems without economizers, Worksheet 2B (like
Worksheet 2A) assumes that new ducting is retrofit specifically for the
new exhaust fan, drawing the supplemental exhaust air from the zones
served by the individual HVAC units. The original exhaust ducting
continues to function as before.
The installed costs of the new dedicated-OA unit as a function of cooling
capacity were derived from Means (Means, 1996}, considering single-zone rooftop
direct-expansion units having cooling capability only, as described in the footnotes to
Table A-3. The cost of adding heating capacity to these new units was likewise
derived from Means based on electric duct heaters, as discussed in Table A-4.
The required cooling and heating capacity for the new dedicated-OA unit, and
the costs of new supplemental intake and exhaust fans and of retrofit exhaust ducting
(if needed), are estimated in the same manner as described previously in connection
with Worksheet 2A.
3.3.4 Installed Costs in the New Construction Case
Enlarged Central Units
Worksheet 3A in Appendix A presents a procedure tor estimating the installed
costs associated with increasing the capacity of the central HVAC units to handle
increased OA in the new construction case. In this case, it is assumed that a system
capable of handling and conditioning the increased OA flow is now to be installed in
lieu of the system that had originally been designed for the as yet unconstructed
building.
Worksheet 3A is based on the following scenario.
Cooling and heating capacity. The originally designed cooling and heating
capacities are increased for each of individual HVAC units in the building,
to handle the increased OA flow to each. The air handler, cooling coils,
condenser, compressor, heating elements, and controls of each unit are
re-designed as required before construction. Since this simplified
worksheet assumes direct-expansion cooling units having electric heat,
it will be less accurate for systems involving chillers and furnaces.
OA intake fan (if present). In cases where one or more OA intake fans are
required in the new building, the worksheet assumes that intake fans of
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greater capacity are installed in lieu of the lower-capacity, originally
designed fans.
OA intake ducting. In systems without economizers -- where the OA increase
would require that the intake ductwork be supplemented in some manner
to handle the increased OA flow - the worksheet assumes that intake
ducting of larger dimensions is installed in lieu of the original intake
ducting. The basic configuration of the original intake ducting is
otherwise retained. In systems with economizers, no modifications to
the originally designed OA intake ductwork are needed.
Central exhaust fan (if present). In systems that have one or more central
exhaust fans but do not have economizers, Worksheet 3A assumes that
exhaust fans of greater capacity are installed in lieu of the originally
designed, lower-capacity fans.
Central exhaust ducting. In systems without economizers, the worksheet
assumes that exhaust ducting of larger dimensions is installed in lieu of
the original exhaust ducting. The basic configuration of the original
exhaust ducting is otherwise retained. In systems with economizers, no
modifications to the originally designed exhaust ductwork are needed.
The incremental installed cost of the enlarged HVAC units, fans, and ductwork
are estimated in this worksheet in a manner similar to that discussed previously for
Worksheets 2A and 2B (based upon the cost data in Means), with one significant
difference. In the two retrofit worksheets, the costs are the total costs of new
dedicated-OA HVAC units, new fans, and new ducting. In Worksheet 3A, by
comparison, the costs are the incremental costs associated with installing a larger unit
in lieu of the originally designed unit.
In addition, in Worksheet 3A, the ductwork costs do not reflect the additional
$40 per linear foot installation cost associated with retrofitting ducting into an existing
building.
New Dedicated-OA Unit
Worksheet 3B in Appendix A presents a procedure for estimating the installed
costs associated with the use of a dedicated-OA unit in the new construction case.
In this case, it is assumed that -- since a dedicated OA unit is to be installed in a new
building -- it will be designed to condition all of the OA entering the building, rather
than just the incremental increase in OA.
Worksheet 3B is based on the following scenario.
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Cooling and heating capacity. One or more rooftop direct-expansion systems
with electric heat, dedicated to treating the incoming OA, are added to
the original design. These added units have the capacity required to
condition all of the OA that is now to be supplied to the building. The
dedicated-OA units provide conditioned OA to the inlets of the originally
designed HVAC units. The cooling and heating capacities of all of the
originally designed HVAC units in the building are reduced, since the
original units will no longer be required to condition OA, providing a cost
savings that partially offsets the cost of the dedicated-OA units.
OA intake fan (if present). The air handlers associated with the dedicated-OA
units become, in effect, the intake fans for the entire OA flow into the
building. In systems that included OA intake fans in the original design,
these intake fans can now be eliminated, resulting in a cost savings.
OA intake ducting. In systems with economizers, it is assumed that the
increased total volume of OA being supplied by the dedicated-OA units
is delivered into the originally designed OA intake ducting with no
modifications to the original ducting design. In systems without
economizers, the worksheet assumes that intake ducting of larger
dimensions -- but otherwise of the same configuration as the original -
is installed in lieu of the original intake ducting.
Central exhaust fan {if present). For systems that have central exhaust fans
but do not have economizers, Worksheet 3B assumes that exhaust fans
of greater capacity are installed in lieu of the originally designed fans.
Central exhaust ducting, in systems without economizers, the worksheet
assumes that exhaust ducting of larger dimensions is installed in lieu of
the original exhaust ducting.
3.4 ESTIMATING OPERATING AND MAINTENANCE COSTS FOR INCREASES IN
VENTILATION RATE
3.4.1 Annual Operating Costs
The annual operating cost associated with an increase in ventilation rate will be
the incremental energy cost resulting from: 1) cooling and heating the increased flow
of outdoor air; and 2} where applicable, operating the enlarged or new intake or
exhaust fans.
Worksheet 4 in Appendix A presents a method for estimating these energy
costs, when rigorous modeling of building energy consumption and costs is not
possible.
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Cooling and heating energy. The incremental energy consumption associated
with increased ventilation will depend not only on the local climate, but on the times
of day when this OA is being supplied and conditioned. For example, a calculation of
heating energy consumption that is based solely on the total heating degree-days in
a given climate, could be misleading; the mechanical system may in fact not be
supplying OA to the building during the middle of the night, when the coldest hours
(that significantly impact the heating degree-day figure) occur. In addition, the nature
of the mechanical system can impact the actual energy that is required to provide the
needed heating and cooling of the incremental OA.
Accordingly, the DOE-2 building energy computer model has been used to
compute the required energy output from the mechanical system per incremental cfm
of OA in a variety of climates with alternative mechanical systems, assuming that OA
is being supplied 13 hours per day, 5 days per week. The results -- in the form of the
average Btu of cooling energy output and Btu of heating energy output per
incremental cfm for the different cities - are tabulated for the user to draw upon. The
details are summarized in the footnotes to Table A-6 in Worksheet 4. Where the
user's system is supplying OA for a different period than that assumed in the DOE-2
modeling, the worksheet makes a correction in the tabulated energy requirements,
assuming that consumption will change proportionally with the change in the number
of hours per day, or the number of days per week. It is felt that this approach will be
more accurate than would be calculations based on cooling and heating degree-days -
which would assume that the OA is being supplied 24 hours per day, 365 days per
year -- followed by a correction downward to the reduced number of hours per year
during which the user's system is actually supplying OA.
Using the required energy output from the mechanical system, obtained as
discussed in the preceding paragraph, the annual incremental cost of energy is then
computed accounting for the system efficiency and the unit cost of fuel or electricity.
Energy for new or enlarged fans. Worksheet 4 assumes that the incremental
additional OA or exhaust air being handled by the fan is being supplied into ductwork
sized such that — at the total flow that will exist in the ducting — the pressure loss will
be 0.1 in. WG per linear foot. If the fan is new, the new ductwork is sized to provide
this duct loss. If the fan is enlarged, the ducting is likewise assumed to be enlarged,
such that the enlarged fan, like the original fan it replaces, would have this same duct
loss.
From the average length of ductwork and the average number of fittings and
other flow obstructions in the ducting (including the coils and filters, in the case of the
dedicated-OA air handlers), the total required pressure differential across the fan can
be determined. The total incremental fan output power is then computed as being
equal to the incremental flow rate times the pressure differential. The required annual
input energy requirements are determined from the output power, accounting for the
fan efficiency and the hours per year of fan operation.
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3.4.2 Annual Maintenance Costs
A procedure for estimating annual maintenance costs for increased ventilation
is presented in Worksheet 5 in Appendix A.
For the purposes of this rough estimate, it is assumed that increases in
ventilation cause an increase in maintenance costs only when: a) a new intake or
exhaust fan is added; or b) a new dedicated-OA HVAC unit is added. No increase in
maintenance is assumed to result from enlargements of existing equipment.
Worksheet 5 prompts the user to enter an estimate for the number of additional
maintenance labor hours per year that is expected per fan or per dedicated-OA unit
added to the building. As a default, the worksheet suggests arbitrary but reasonable
figures of 5 hr/yr for each fan, and 20 hr/yr for each dedicated-OA unit. A labor rate
of S35/hr (including overhead) is suggested, based upon the hourly rate data in Means
(Means, 1996).
3.5 ESTIMATING TOTAL ANNUALIZED COSTS FOR INCREASES IN VENTILATION
RATE
The total annualized cost can be determined using Worksheet 6 in Appendix A.
The total annualized cost consists of two components:
1) an annualized amount that amortizes the total installed cost derived in Section
3.3; plus
2) the total annual operating and maintenance cost derived in Section 3.4.
The annualized amount to be charged for the installed costs is determined using
the Capital Recovery Factor (CRF), a standard approach in costing calculations. The
user selects the number of years, n, over which the installed cost is to be amortized,
and the interest rate, i, that is to be charged. The value of n will commonly be the
estimated lifetime of the equipment. The value of i may be the rate that is being paid
on money borrowed to install the equipment, or the interest rate that could have been
obtained on the money had it been invested rather than used for the installation.
Based on the selected values of n and i, the CRF is calculated using an equation
derived from standard compound interest considerations (Humphreys and Wellman,
1996):
CRF = [i(1 +i)n] / [(1 + i)n - 13.
The CRF is the fraction of the initial installed cost that must be amortized each
year if - after n years, i.e., after n equal "payments" - the initial cost is to be
recovered with an i percent annual interest rate being charged on the unpaid balance.
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Accordingly, the total annualized cost computed in Worksheet 6 for the
increase in OA ventilation rate is the sum of:
1) the CRF multiplied by the incremental total installed cost derived from
Worksheet 2A, 2B, 3A, or 3B, as appropriate; plus
2) the incremental annual operating cost, derived in Worksheet 4; plus
3) the incremental annual maintenance cost, derived in Worksheet 5.
To assist the user, a table of values for the CRF (as a function of the selected values
of n and i) is included in the worksheet.
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3-16
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SECTION 4
ESTIMATING THE COSTS OF IAQ CONTROL OPTIONS:
AIR CLEANING
4.1 INTRODUCTION
As indicated in Figures 1 and 2, and as discussed in Section 2.2, it will
sometimes be appropriate to consider the use of air cleaners to remove the contamin-
ants) of concern. From a practical standpoint, air cleaners are most likely to be
considered in cases where ventilation or source management are not clear options
(e.g., when the outdoor air is the contaminant source), and where indoor air cleaning
technology is well demonstrated for the contaminant(s) of concern (such as particu-
late matter and perhaps VOC molecules of sufficiently high molecular weight).
Two classes of indoor particulate air cleaners are considered: "media" air
cleaners; and electronic air cleaners (ASHRAE, 1996). For the purposes here, media
air cleaners include; pleated filter panels, commonly enclosed in cartridges; bag filters;
and variations of these types (e.g., pocket filters). Electronic air cleaners are
electrostatic precipitators. Only particulate air cleaners having an average removal
efficiency of 65% or greater, as measured using ASHRAE Standard 52.1-1992
(ASHRAE, 1992), are considered here for IAQ purposes; it is assumed that lower-
efficiency filters are already present on the HVAC system, to protect the fan and coils.
High-efficiency particulate air (HEPA) filters — offering 99.97% or greater removal
efficiencies on 0.3 //m particles — are included here in the event that the user wishes
to consider maximum particulate control. HEPA filters, generally high-efficiency media
cartridge filters, are commonly used in clean-room applications.
The air cleaners considered here for gaseous contaminants involve the use of
beds of dry, granular material acting by physical adsorption (e.g., granular activated
carbon), chemical absorption (e.g., activated alumina impregnated with potassium
permanganate), or catalysis. Such air cleaners can be considered for the control of
a variety of gaseous contaminants (ASHRAE, 1995), although the focus here is on the
removal of VOCs.
The discussion here focuses on the case where the air cleaners are centrally
mounted, in the ducting of one (or more) of the HVAC units serving the building. In
this situation, the air cleaners will be treating all of the building air being recirculated
by the HVAC unit (or all of the intake OA, depending on where the cleaners are
mounted within the ducting); all of the zones being conditioned by that HVAC unit will
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be impacted proportionally. Central, in-duct mounting is the configuration most
commonly considered when treatment of a significant source is required.
In some cases, there may be a source which impacts only one zone (or a
portion of one zone) among the multiple zones being conditioned by a given HVAC
unit. Often in such cases, it will be preferable to consider local exhaust ventilation or
source management for such sources, rather than air cleaning. However, in some
cases, the user might wish to consider localized air cleaning, using self-contained air
cleaners within the affected zone {Flanders Filters, 1994; Pierce et al., 1996). Self-
contained units include their own fan to circulate air through the unit, and operate
independently of the HVAC system. Accordingly, Section 4.6 provides a costing
approach for the case of self-contained air cleaners.
As illustrated in Figure 2 and discussed in Section 2.2, the addition of a central,
in-duct air cleaner will result in an increased pressure drop, necessitating a more
powerful motor on the central air handler. This will in turn result in increased fan
heat, which will have to be removed by the cooling system when the system is
operating in the cooling mode. Further, there is the issue regarding the availability of
space for the central air cleaners within the mechanical room (or at a location remote
from the mechanical room). The costing worksheets provided in this section address,
to the extent possible, the first two of these issues; the incremental costs of a larger
fan motor and of removing the heat generated by the larger motor. The worksheets
do not attempt to address any extraordinary costs associated with, e.g., modifying
the mechanical room or the HVAC hardware to accommodate the air cleaner, since
these costs will be so site-specific.
Accordingly, the installed costs for the air cleaners computed in the worksheets
here assume that there are no particular complications in the installation which would
significantly increase installation labor hours and materials. In addition, the installed
costs for the larger fan motor address only the incremental cost for the larger motor,
beyond the cost of the smaller motor that would otherwise be sufficient; these costs
do not include any costs associated with the replacement of a smaller, pre-existing
motor with a new, larger one. No installation cost impact is included for any required
increase in the cooling capacity of the HVAC unit, to remove the increased fan heat.
Thus, the approximate installed costs estimated here will be more representative of
a new installation, rather than a retrofit installation with complications,
4.2 ESTIMATING THE REQUIRED AIR CLEANER PERFORMANCE
To enable estimation of the installed and O&M costs of the air cleaner, it is first
necessary to determine the required contaminant removal performance of the unit.
Worksheet 7 in Appendix A presents a method for estimating the required fractional
removal efficiency, n, of central, in-duct air cleaners. (A method for estimating the
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required performance of self-contained air cleaners is presented in a later worksheet
addressing such units.)
The calculations in Worksheet 7 are based on a simple mass balance around the
zone(s) being conditioned by the HVAC unit into which the air cleaner is being
mounted. The exact nature of the mass balance equation is determined by where in
the ducting the air cleaner is mounted: in the incoming outdoor air (for cases where
the OA is the pollutant source); or in the recirculating building air, either prior to or
following mixing with OA (for cases where the source is in the zones). See Figure A-1
in Worksheet 7.
For each of these locations, the worksheet determines the air cleaner efficiency
that is required if the average concentration in the zone(s) is to be reduced to the
desired value. For particulate air cleaners, this efficiency will dictate the nature of the
air cleaner that is selected, potentially impacting the installed cost -- especially if the
requirements lead to the selection of an electronic air cleaner or a HEPA filter rather
than a media filter of lesser efficiency. Efficiency requirements can also impact
operating costs - increasing power consumption if media filters creating greater
pressure drops are needed, reducing consumption if electronic air cleaners are used
having modest pressure drops and moderate power consumption by the corona wires
and collection plates [ ~ 30 W/1,000 cfm (ASHRAE, 1996)]. And high efficiency
requirements will increase maintenance costs by increasing the required replacement
frequencies for media filters or cleaning frequencies for electrostatic precipitators.
For air cleaners that remove gaseous contaminants using granular sorbents --
where removal efficiency is essentially 100% when the sorbent is fresh, but
progressively deteriorates once breakthrough begins — increased efficiency
requirements can be met either through an increase in sorbent mass, or an increase
in sorbent replacement frequency, or some combination of the two. Higher efficiency
requirements for gaseous air cleaners would increase the installed cost, if the designer
elects to increase sorbent mass. Increased sorbent mass would also increase
operating costs (power consumption), by increasing the pressure drop through the
deeper sorbent beds. But in the worksheets that follow here, it is assumed that
increased efficiency is achieved solely by increasing sorbent replacement frequency.
With this approach, only maintenance costs are increased (though potentially
significantly); installed and operating costs remain unchanged.
To conduct the calculation in Worksheet 7, one must know a number of
things - the target contaminant concentration (CIPJ) to which the indoor levels should
be reduced, the concentration (C0A) of this contaminant in the outdoor air, the flows
of outdoor air (Q0A) and total supply air (Qs) into the space, and the rate (S) at which
the contaminant is being generated indoors. These parameters would require some
measurements, and will sometimes be difficult to determine. Adding to the
complexity of this assessment are issues such as: which contaminant(s) should drive
4-3
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the calculation (determining C,N); the basis on which C,N should be selected; and the
likely variation with time of some of the key parameters (COA, S). So the relatively
simple worksheet format incorporates some non-trivial questions on which the user
will have to make some judgements. But the worksheet does illustrate the theory that
must be considered in making this analysis.
4.3 ESTIMATING INSTALLED COSTS FOR CENTRAL AIR CLEANERS
Installation of a central air cleaner in the HVAC ducting will require: 1) the
procurement and installation of the air cleaner itself; 2) potentially, for media
particulate filters and for gaseous air cleaners, a larger motor for the central air-
handling fan, to compensate for the pressure drop across the cleaner; and 3)
potentially, increased cooling coil capacity, to remove, at peak load, the additional
heat produced by the power being supplied to the larger fan or to the electronic air
cleaner. There will be an installed cost associated with this equipment.
For convenience in the worksheets here, the installed cost of increasing the
cooling system capacity is neglected. [According to one estimate (Henschel, 1998),
this component could be perhaps 10% of the total installed cost for the air cleaner.]
Accordingly, only the installed costs of the air cleaner itself and of the enlarged fan
motor are considered.
As discussed in Section 4.1, the installed costs for air cleaners computed in the
worksheet here assume that there are no particular complications in the installation.
Thus, the estimates here will be more representative of a new installation, rather than
a retrofit installation with complications.
4.3.1 Installed Costs for Central Particulate Air Cleaners
A procedure for estimating the installed costs for either media or electronic
particulate air cleaners is presented in the first sections of Worksheet 8 in Appendix
A.
In this procedure, Worksheet 8 first assists the user in selecting the appropriate
air cleaner, based upon the performance requirements computed in Worksheet 7. To
aid in this selection, available data are tabulated giving the fractional efficiencies that
might be expected for various media and electronic air cleaners in removing particles
of several sizes (0.01, 0.1, and 1 //m).
With this selection made, the user may then either obtain an estimate from a
vendor for this type of air cleaner, or may use a simplified table (Table A-10) included
with the worksheet. The table presents rough installed costs per 1,000 cfm air
throughput for each of the several types of air cleaners. These installed costs include
4.4
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the cost of the air cleaner and of the increase in fan motor horsepower, but exclude
any costs for increased cooling capacity, as indicated above.
As indicated in the footnotes to Table A-10, the uninstalled costs for the media
air cleaners themselves - including pleated panel cartridges and the frame to support
the cartridge bank -- were derived for vendor quotes. Installation labor was estimated
assuming no complications in the installation, and was costed using labor rates from
Means (1996} for sheet metal workers.
The incremental installed cost for the increase in fan motor capacity per 1,000
cfm throughput were obtained from data in Means, assuming that the average
pressure drop across the media filter over its lifetime is 1 in. WG. (In practice, the
pressure drop across the filter will generally increase from a fraction of an inch when
the filter cartridges are new, depending on filter efficiency, to something greater than
1 in. WG at the time the cartridges are replaced, based upon vendor literature.) These
incremental fan motor costs address only the incremental increase in horsepower
required to overcome the added 1 in. WG pressure drop. In retrofit cases, it might
sometimes be necessary to replace a smaller, pre-existing motor with a larger one,
requiring that an entire new motor be purchased; this situation is not addressed in the
Table A-10 numbers.
As shown in the table, there is little variation in the installed cost of cartridge
fitters as the efficiency is increased from ASHRAE 65 to ASHRAE 95.
The installed costs for electronic air cleaners were obtained from Means.
4.3.2 Installed Costs for Central Air Cleaners for Gaseous Contaminants
A procedure for estimating the installed costs for air cleaners for gaseous
contaminants is presented in the last section of Worksheet 8.
The worksheet directs the user either to obtain an installed cost estimate for
the air cleaner from a vendor, based upon the expected air throughput, or to compute
the installed cost directly assuming a unit cost of $680 per 1,000 cfm throughput.
Since variations in required removal efficiency are addressed entirely through
adjustment of the sorbent replacement frequency, as discussed earlier, the efficiency
results from Worksheet 7 do not impact the installed cost estimated here.
The $680 per 1,000 cfm unit installed cost includes the cost of the air cleaner
itself, plus the incremental cost of an enlarged fan drive motor to handle the increased
pressure drop. The cost of the air cleaner - $660 per 1,000 cfm - is obtained from
a rigorous cost estimate for a granular activated carbon unit, derived from vendor
quotes (Henschel, 1998). The air cleaner costed in that study was of a typical design,
with the granular carbon being contained within 1-inch-deep panel beds mounted in
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a V-bank configuration, marketed in modules having a capacity of 2,000 cfm each.
The same unit air cleaner cost is obtained from Means (1996) for full-flow activated
charcoal air cleaners,
The incremental installed cost of the enlarged motor for the air handler — $20
per 1,000 cfm — was derived in the same manner as described in Section 4.3.1 for
the case of particulate air cleaners. A pressure drop of 1 in. WG was assumed across
the 1-inch-thick carbon panel beds (Henschel, 1998S -- the same as the average
pressure drop expected across the media particulate filters -- dictating the incremental
additional fan horsepower that is needed. This is the approximate pressure drop that
would be calculated for 1-in.-thick beds of 8 x 16 mesh granular material, at the face
velocity of 80 ft/min representative of some commercial V-bank panel reactors.
Thinner beds, coarser carbon particles, or lower face velocities would reduce the
pressure drop.
4.4 ESTIMATING OPERATING AND MAINTENANCE COSTS FOR CENTRAL AIR
CLEANERS
4.4.1 Annual Operating Costs
The annual operating cost associated with central air cleaners will consist of the
incremental energy cost for: 1) the increase in power consumption by the fan motor
to accommodate the added pressure drop, in the case of media particulate filters and
gaseous air cleaners; 2) power consumption by the corona wires and plates, in the
case of electronic air cleaners; and 3! added power consumption by the cooling
system in removing the incremental heat added to the air stream by the enlarged fan
motor or the electronic air cleaner, when the HVAC system is operating in the cooling
mode.
Worksheet 9 in Appendix A presents a method for estimating these energy
costs, for each of the types of central air cleaners.
Increased fan horsepower. Worksheet 9 estimates the incremental additional
fan horsepower requirements by multiplying the total airflow through the air cleaner
times the average pressure drop across it, accounting for fan/motor efficiency, and
applying the appropriate conversion factors. The annual energy consumption (kWh/yr)
is then computed by multiplying this power requirement times the number of hours
per year that the fan will be operating. The annual operating cost for the larger fan
motor is determined from this energy consumption, based on the unit cost of
electricity.
Default values are provided for all of the parameters - pressure drop, fan
efficiency, hours of fan operation, and unit energy costs — if the user does not have
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values readily available. As discussed in Sections 4,3.1 and 4.3.2, the default
pressure drop across media particulate filters and gaseous air cleaners is 1 in. WG.
The pressure drop across the electronic air cleaners is assumed to be small.
Electronic air cleaner power consumption. The power to the corona wires and
plates of electrostatic precipitators is computed by defining a power consumption per
unit air throughput. The default value for this parameter, suggested in the worksheet,
is 30 W per 1,000 cfm throughput. This figure is the mean of the typical range (20
to 40 W per 1,000 cfm) cited in the literature (ASHRAE, 1996).
Increased cooling costs. The incremental increase in power input to the fan
motor, and the power input to the electronic air cleaner, will appear in the building as
heat. Some fraction of this incremental heat will have to be removed by the cooling
coils, when the system is operating in the cooling mode. Likewise, when the system
is in the heating mode, one might expect the heating load to be correspondingly
reduced.
Calculations were made using the DOE-2 computer model, to assess the
building energy impacts resulting from the installation of air cleaners in a variety of
climates. These calculations suggest that, on average, a high percentage of the
incremental heat introduced by the enlarged fan motor or the electronic air cleaner will
have to be removed by the cooling system. Only a few percent of the added heat
seems to contribute to a reduction in building heating energy requirements, even in
cold climates.
Thus, Worksheet 9 assumes that -- for the purposes of this rough estimate --
all of the energy input to each of the air cleaners will appear as heat that has to be
removed by the cooling coils. This added energy is multiplied by the electric input
ratio (EIR) for the cooling system - the default value of which is 0.34 kW of electric
input to the system per kW of cooling provided to the air stream - to determine the
incremental additional electric input required to the compressor/condenser. This result
is then multiplied by the unit cost of electricity to give estimated annual energy costs
for increased cooling.
4.4.2 Annual Maintenance Costs
Worksheet 10 in Appendix A presents a method for estimating the annual
maintenance costs for each of the types of central air cleaners.
Maintenance costs are assumed to include:
a) the materials and labor costs associated with periodic replacement of the filter
media, in the case of media particulate air cleaners;
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b) the labor costs associated with periodic cleaning of the corona wires and
plates, in the case of electronic air cleaners; and
c) the materials and labor costs associated with periodic replacement of the
granular sorbent, in the case of air cleaners for gaseous contaminants.
For each type of air cleaner, Worksheet 10 first computes the mass of
contaminant per year that the air cleaner will be removing, based upon the volumetric
flow through the unit, the average contaminant concentration in the air stream, and
the removal efficiency. The worksheet then computes the mass of contaminant that
can be accumulated on the air cleaner before maintenance is required, and, from this,
derives the number of times per year that maintenance is necessary. Multiplying this
frequency times the cost per maintenance event yields the annual maintenance cost.
The mass of contaminant that can be accumulated before maintenance is
required must be obtained from the vendor for media air filters; the filter must be
replaced before the pressure drop created by the increasing dust cake becomes
unacceptably high. Likewise, the allowable mass of particulate that can be collected
by electronic air cleaners must be obtained from the vendor; cleaning is required
before the depth of the dust layer impacts the electrostatic properties sufficiently to
degrade precipitator performance below specifications.
For gaseous air cleaners, the user may obtain an estimate from the vendor
regarding the mass of the particular organic compound(s) of concern that can be
accumulated per unit mass of sorbent, before the organics will break through the
sorbent bed in unacceptable amounts. Alternatively, the user is provided with a table
(based upon independent data on sorption capacities on granular activated carbon)
that presents the mass of organic compound per unit mass of carbon. These values
depend heavily on the nature of the specific organic compounds of interest, and on
their inlet concentrations into the air cleaner. Once the mass of organics per unit
mass of sorbent is thus estimated, the replacement frequency will be determined by
the mass of sorbent present in the air cleaner per unit air throughput.
The cost per maintenance event in Worksheet 10 for particulate media filters
is based on vendor quotes for replacement filter cartridges; the labor cost associated
with replacing the cartridges is assumed to be small. The cost per event for electronic
air cleaners is based on the labor hours required for the cleaning operation, a number
that the user must estimate. For gaseous air cleaners, the cost per event is computed
from: the unit cost of replacement sorbent (default $3/lb for carbon, based on vendor
quotes); the mass of sorbent in the air cleaner (commonly about 45 lb per 1,000 cfm
air throughput for carbon); the labor required to replace the carbon (default 1 labor
hour per 1,000 cfm); and the cost for disposal of the spent sorbent (default $0.05/lo,
assuming the waste material can be sent to a standard landfill).
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Irs all cases, the default labor rate in the worksheet is the rate obtained from
Means (1996) for building laborers.
4.5 ESTIMATING TOTAL ANNUALIZED COSTS FOR CENTRAL AIR CLEANERS
The total annualized cost for central air cleaners can be determined using
Worksheet 7 7 in Appendix A.
Worksheet 11 uses the costs derived in Worksheets 8, 9, and 10 to compute
the total annualized cost for air cleaners, following the same format used in
Worksheet 5 for increases in ventilation rate (see Section 3.5),
4.6 ESTIMATING COSTS FOR SELF-CONTAINED AIR CLEANERS
Sections 4.2 through 4.5 -- and Worksheets 7 through 11 - address central,
in-duct air cleaners. This section addresses the case of self-contained air cleaners.
The procedure for estimating the costs of self-contained units is presented in
Worksheet 12 in Appendix A. Figure A-2 at the end of that worksheet provides a
generic schematic diagram for the self-contained case.
Worksheet 12 begins by estimating the value for the key parameter that will be
used in sizing and costing the self-contained unit, analogous to the computation in
Section 4.2 for central air cleaners. For the central units, the flow through the air
cleaner is dictated by the total flows around the HVAC unit, and depends only on
where the air cleaner is located within the HVAC system. Thus, in Section 4.2, the
key parameter being computed is the required air cleaner efficiency, given the flow
rate. But with self-contained units, the key parameter is the flow rate of air from the
affected space, Qc, that must be circulated through the air cleaner; this will dictate
the size and number of self-contained units that must be installed in the space.
Accordingly, in Worksheet 12, the user is asked to estimate a priori what the
efficiency of the self-contained units will be — e.g., based on vendor literature — and
the focus is then on computing the necessary flows.
The analysis shown for self-contained units in Figure A-2 is similar to that in
Figure A-1 and Table A-8 for central units (see Worksheet 7). Of course, the mass
balance equation for self-contained units is somewhat different, and, as discussed
above, is solved for Qc rather than for rj. For simplicity, the mass balance equation
in Figure A-2 ignores the effect of the other zones being conditioned by the HVAC
system, either as sources of the contaminant of concern, or as sources of dilution air,
to the zone of interest.
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The computed flow Gc is then used in Worksheet 12 to determine the number
of self-contained units that will be required in the zone, considering the flow capacity
of the individual units available from the vendor. Depending upon the size of the
affected zone and the contaminant reductions that are necessary, it might be
expected that multiple self-contained units will commonly be required in the zone to
provide the desired performance. The installed cost for each air cleaner is determined
from the vendor's quote for the uninstalled unit plus the user's estimate of the cost
of installation in the occupied space (e.g., mounting and wiring), which will be highly
site-specific. The total installed cost for the set of air cleaners will then be obtained
by multiplying the installed cost per air cleaner times the number of air cleaners
needed.
The annual operating (electricity) costs for self-contained air cieaners arise from
the same sources as in the case of the central unit, namely, power consumption by:
a) the fan; b) the electronic air cleaner, if applicable; and c) the cooling system, in
removing the heat introduced by a) and b). The only difference is that, with the self-
contained units, the fan power consumption arises from the separate fan contained
within each unit, rather than from the incremental increase in consumption by the
central HVAC air handler. With that difference, the computational approach in
Worksheet 12 for the annual operating costs of self-contained units is essentially the
same as that for central units in Worksheet 9, discussed in Section 4.4.1.
Likewise, the estimation of annual maintenance costs in Worksheet 12 follows
exactly the procedure used in Worksheet 10 for central air cleaners (discussed in
Section 4.4.2). And the estimation of the total annualized costs follows the same
procedure used in Worksheet 11 for central units.
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SECTION 5
ESTIMATING THE COSTS OF IAQ CONTROL OPTIONS:
SOURCE MANAGEMENT
5.1 INTRODUCTION
As illustrated in Figure 3, the IAQ control methods that fall into the category
of "source management" cover a wide array of different procedures: use of low-
emitting materials, removal or relocation of sources, maintenance activities, source
treatment, and adjustments to occupancy patterns. Furthermore, the difficulty and
costs involved in implementing any one of these methods — in fact, the determination
if and exactly how the method can be implemented -- will be highly site-specific.
Thus, for source management, it is generally difficult to define rigorous worksheets
similar to those presented in Sections 3 and 4 for the ventilation and air cleaning
cases.
Accordingly, this section is not subdivided in the same manner as the preceding
two (installed costs, operating costs, etc.), but rather, is subdivided according to the
types of source management options as defined by the diamonds on the left side of
Figure 3. Within each subsection, the specific control methods that represent that
type of source management option are discussed in terms of the types of issues that
the user will need to address in assessing installed and annualized costs. But often,
no attempt will be made to provide a rigorous worksheet, except in cases where such
a worksheet is feasible and potentially helpful.
5.2 ESTIMATING THE REQUIRED EXTENT OF SOURCE MANAGEMENT
5,2.1 Constant Sources
Some sources might be viewed as having an essentially steady emission rate,
for the purposes of this analysis. The best example of a truly constant source would
be a continuous occupant activity — e.g., constant operation of a photocopier or a
printer — that releases contaminants at a steady rate during occupied hours. Even
where the activity is not continuous, but is frequent and consistent -- e.g., repetitive
use of solvent-containing office supplies during occupied hours, causing periodic
concentration spikes — the resulting average concentration over the duration of the
work day might be represented as relatively constant within the uncertainties of this
analysis. Sources which are not continuous, where the emission rate irreversibly
5-1
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decays over time -- typical, e.g., of building materials arid furnishings — might simulate
a constant source over moderate time intervals in cases where the particular source
decays at a slow rate. (For example, composite wood office furniture have such a
slow decay rate in some cases.) Microbiological contamination on building or HVAC
surfaces may release airborne biologicals and VOCs at a relatively constant rate.
In cases where the source is essentially constant, the effect of a source
management step might be approximated using a simple mass balance. Such a mass
balance around a zone containing the source (using the flow diagram illustrated in
Figure A-1, Worksheet 7, in the Appendix) yields the relationship
Csm/C0 = [QaCaK + SsJ/[GaCaK + SJ (Equation 5-1)
where
Csm = the concentration of the contaminant of concern in the zone after
source management is applied (mg/m3);
C0 = the concentration in the zone before source management (mg/m3);
Qa = the outdoor air flow rate into the zone (cfm);
CA = the concentration of that contaminant in the outdoor air (mg/m3);
K = concentration conversion factor, 6.2 x 10"8 (lb/ft3)/(mg/m3);
Ssm = the emission rate from all sources of that contaminant in the zone after
source management (Ib/min); and
SD = the emission rate from all sources before source management (Ib/min).
In cases where the outdoor concentration of the contaminant of concern is zero, the
above equation naturally reduces to one of direct proportionality:
Csm/C0 = Ssm/S0. (Equation 5-2)
Where there are multiple types of constant sources emitting the same contaminant,
then SQ in the above equations would be represented by
SD = SOB + S0.h + Son + . . . (Equation 5-3)
where the subscripts a, b, and c represent the different sources. Ssm would be
represented similarly.
For any generic source, the emission rate S would be defined by the expression
S = suA (Equation 5-4)
where
5 2
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su = unit emission rate, i.e., the rate per some unit measure of the amount
of source present {e.g., Ib/min per ft2 of source surface, or Ib/min per
photocopier or other device); and
A = amount of source present {e.g., ft2 of source area, or number of
emitting devices).
Source management involves reduction of the values of su and/or A during periods
when the building is occupied. This could be achieved by some combination of:
reducing the inherent value of su in one of several ways; eliminating some of the
source (i.e., reducing A); or modifying the time at which the source is active, or the
occupancy pattern of the building, so that su has decayed to a reduced level by the
time the space is occupied.
Estimation of the extent of source management required for constant sources
would involve the following steps.
1) Estimate or determine: the required reduction in the indoor concentration
(yielding the required value of Csm/C0); and, if CA ^ 0, the values of S0, QA, and
CA-
2) Using Equation 5-1 or 5-2, compute Ssm/S0.
3) Depending upon the nature of the source and the source management step
being considered, use Equation 5-4 to assess how su and/or A will be reduced
to achieve the desired value of Ssm/S0 computed in Step 2, i.e., so that
(su.smAsm)/(su.oA0) = Ssm/S0 (Equation 5-5)
where susm and su.Q are the values of su with and without source management,
respectively. If, for example, the source management were to consist solely
of reducing the amount A of source while su remains unchanged, then Asm
would have to equal A0 x (Ssm/S0). If A were to remain unchanged, then su_sm
would have to equal su.0 x (Ssm/S0). Where there are multiple sources (a, b, and
c) emitting the same contaminant, then differing adjustments could be made to
So a, S^, and Soc in Equation 5-3 to achieve the desired overall value of Ssm.
The reasoning illustrated in the above steps will be cited in Sections 5.3
through 5.8, indicating how this analysis might be applied under the various source
management scenarios to assess the extent of source management required in cases
where the source is constant.
5.2.2 Decaying Sources
Many sources decay over time, at rates dependent on the nature of the source.
For example, the emissions from newly applied latex paints - after a substantial spike
immediately following application — may decay to near zero within days, or perhaps
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a week or two. Emissions from new carpeting might be expected to decay to near
zero within a few months. Liquid products used in the building -- e.g., floor wax,
janitorial cleaner, personal hygiene products -- decay very rapidly, within hours; in
fact, the contaminants may be released into the air almost instantaneously after
application, with the "decay" period being more a measure of how long it takes for
the ventilation system to flush the spike of contaminants out of the space.
Estimating the required extent of source management for these sources -- to
achieve some desired reduction in average indoor concentrations or annual occupant
exposure — cannot be computed as simply as is possible in Section 5.2.1 for constant
sources. Because emissions vary with time, computer modeling would be required,
incorporating appropriate mathematical expressions for the source's emission and
decay characteristics, including the required experimentally determined constants. A
number of models are available that enable such modeling (Sparks, 1991; FSEC,
1992; Walton, 1994; Guo, 1999). However, such modeling is beyond the scope of
this simple methodology.
The inability to estimate simply the total or time-averaged effects of modifying
decaying sources will not necessarily prevent some consideration of source
management with such sources. It is known that such sources often decay to near-
zero emissions in days, weeks, or, in the case of carpeting, months. Sources, such
as paint or carpeting, that are introduced into the building on a one-time basis and that
decay relatively quickly will probably have a minimal effect on the long-term exposure
of the occupants (although peak short-term exposures could be significant). Thus,
computer modeling to assess long-term, chronic occupant exposures from these
sources -- and the effects of source management steps to reduce these long-term
exposures - is probably unnecessary. If the objective is to reduce short-term, acute
exposures - one of the most likely objectives of managing quickly decaying sources -
then one might roughly estimate the relative reduction in peak exposure as being
proportional to the relative reduction in emission factors expected to be achieved by
implementing the source management step.
Where the source management step is to involve some delay in the exposure
of occupant to the source - by delaying occupancy of a new building while sources
decay, or by "airing out" a product before introducing it into the building — general
knowledge of the decay periods for the different types of sources would be sufficient,
without any modeling, to define what an appropriate deiay period might be. Of
course, modeling would still be required if one wished to rigorously compute the
reduction of occupant exposure achieved by this step, for the purposes of quantifying
cost-effectiveness.
Some decaying sources may simulate a constant source. For example, the
decay period for composite wood furniture -- at least for some contaminants -- may
be a couple years. Thus, as indicated in Section 5.2.1, it may be reasonable to treat
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the furniture during its first couple years as a constant source emitting at its average
rate during the year. Likewise, liquid supplies that are used frequently and consis-
tently during occupied periods might be assumed to be a constant source having an
average emission factor, even though they are in reality a sequence of spikes that
occur during each use. However, liquid supplies that are used infrequently during
periods of low occupancy -- e.g., floor wax — could not be analyzed in this manner.
5.3 SOURCE REMOVAL
5.3,1 Remove High-Emitting Furnishings, Solvents, or Equipment
This step involves the permanent removal of part or all of the source. This is
distinguished from replacement of the source (Section 5.4) or relocation of the source
(Section 5.6), and suggests that at least some of the materials/equipment that are
generating the emissions are not really necessary on-site.
Referring to Equation 5-5 in Section 5.2.1, this source management step would
involve making Asm sufficiently small relative to Aa,
Some of the issues that the user will need to address in costing these source
management options are listed below.
The source is a furnishing
1) Exactly where, and in what quantity, are these furnishings located throughout
the building?
2) Which portion of these furnishings are to be removed? Can a sufficient amount
of the furnishings be removed, so that Asm becomes sufficiently small to
provide the desired reduction in exposure?
3) In existing buildings (retrofit cases), what will be involved in removing the
portion of the furnishings that are to be removed? For example, if the
furnishing is carpeting, is it covered with extensive furniture that will have to
be moved? Is there molding that will have to be removed/re-installed? How is
the carpeting attached to the floor? Will any refinishing of the underlying
flooring be required before the space can be re-occupied?
4) Estimate the cost of removing the furnishing. In existing buildings, this will
involve an estimation of the one-time renovation costs for the type of efforts
suggested in 3) above. For new construction, this cost may in fact be an
installed cost savings, since it will translate into a reduction in the originally
planned furnishings in the new building (e.g., fewer square yards of carpeting).
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The source is a solvent (janitorialproducts, etc.)
5) Can a sufficient amount of this source in fact be removed to provide the
required reductions in exposure?
6) How will the removal of this source impact day-to-day activities in the building?
For example, will contract janitorial service personnel who used to store
cleaning products in the building now have to transport them into the building
daily?
7) Estimate the annual maintenance (or operating) costs for implementing these
changes.
The source is equipment (reproduction equipment, photo-finishing equipment,
etc.)
8) Can a sufficient amount of this equipment in fact be removed from the site, to
provide the required reductions in exposure?
9) How will the removal of this equipment impact day-to-day activities in the
building? For example, will some task which was previously performed in the
building now have to contracted out to an off-site supplier?
10) Estimate the cost of removing the equipment (in existing buildings) and, as
necessary, the net annual costs for conducting the tasks with this equipment
off-site. For new construction, there may be some savings in installed or
annual costs from not having to purchase or lease the equipment in the first
place.
5.3.2 Improve Maintenance to Remove Contamination
This step includes maintenance/cleaning activities designed to remove
contamination (such as biocontaminants) that is present, e.g., in the HVAC system
or on other surfaces within the building, and that is acting as an emission source.
Again, the objective of this step is to reduce the value of Asm in Equation 5-5.
Some of the issues that the user will need to address in costing these source
management option are;
1) Exactly where in the building is the emitting contamination located?
2) How extensive is the contamination in these locations? Can the contaminated
surface reasonably be cleaned, or does it have to be replaced (Section 5.4)?
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3) Estimate the cost of the maintenance/cleaning effort, perhaps with the aid of
vendor quotes. Will this cost be a one-time renovation cost, resulting from,
e.g., water damage that is not expected to recur? Or will it be have to be
repeated periodically {e.g., periodic cleaning of the HVAC system), representing
a continuing, annual cost?
5.3.3 Reduce Activity Generating Emissions
Some emissions result from occupant activities - e.g., smoking, the use of
personal care products, or the use of office supplies and equipment.
Reductions in the on-site use of office supplies or equipment were addressed
in Section 5.3.1 above. Elimination, e.g., of smoking on-site is a policy issue that
cannot be addressed in this economic analysis.
5.4 SOURCE REPLACEMENT
5.4.1 Use of Low-Emitting Materials (LEMs)
One approach commonly considered for source management is the replacement
of an existing or planned "high-emitting" source — carpeting, furniture, paint,
photocopier, etc. -- with a comparable material or equipment item having lower
emissions.
Referring to Equation 5-5, this source management step would involve making
the unit emission rate after source management, su.sm, sufficiently small relative to the
rate prior to source management, su,0.
Because this approach is commonly considered -- and because it is somewhat
more amenable to a worksheet format than are many other source management
methods — Worksheet 13 in Appendix A has been prepared for this LEM replacement
case. While this worksheet is not as rigorous as those addressing ventilation and air
cleaning — requiring more effort by the user in deriving some of the entries — it
illustrates the thought process that would be used in comparing the costs of LEM
replacement against the costs of the competing alternatives of ventilation or air
cleaning.
Worksheet 13 is subdivided into sections for the retrofit and the new
construction cases, since the calculational process is somewhat different between the
two. In both cases, the user is first asked to estimate the unit cost for the low-
emitting material or product versus the originally planned, higher emitting material.
As estimate is also requested for the differences, if any, in the useful lifetime of the
low- vs. higher-emitting materials. While this analysis seems to imply that the low-
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emitting material may be more expensive or shorter-lived, this will not necessarily be
the case.
For the retrofit case, the installed cost of the LEM is derived in the worksheet
from: a) the installed cost that would be incurred if the LEM were being installed in
a new building without complications; plus b) the additional installation costs resulting
from the complications of retrofit, i.e., clearing the work area, removing and disposing
of the old material, any required surface preparation, and restoration of the space after
installation. Due to the highly site-specific nature of this effort, it is left to the user
to define the costs of the LEM (e.g., based on vendor quotes) and to define the
additional costs for retrofit for the particular building under consideration. The
annualized costs for this LEM replacement effort are computed from this total installed
cost utilizing a Capital Recovery Factor (CRF) that is based on the number of years,
nL, representing the expected lifetime of the LEM,
For the new construction case, the cost of the LEM replacement approach will
be the incremental cost of installing the LEM in lieu of the originally planned material
in the first place. In this case, the appropriate cost is the incremental difference
between; the annualized cost of installing the LEM (i.e., the total installed cost for the
LEM times the CRF based on the expected lifetime, nL, of the LEM); and the
annualized cost of installing the original material (i.e., the total installed cost for the
original material times the CRF based on its expected lifetime, n0).
The above calculational approach assumes that the user knows the cost of the
LEM beforehand, and wishes to compute the resulting annualized cost. From that
annualized cost, and from the reductions in exposure (i.e., the "effectiveness")
resulting from the LEM replacement (see Section 6), the user could then proceed to
compute the cost-effectiveness of this approach (see Section 7).
As an alternative, Worksheet 13 also addresses the reverse of this calculation:
the user is assumed to know what reduction in exposure is needed, and the cost-
effectiveness with which this required exposure reduction can be achieved using
alternative, competing approaches involving increased ventilation or air cleaning. The
question then becomes, What is the maximum premium that could be paid for a LEM
(compared to the original material) before LEM replacement becomes less cost-
effective than ventilation or air cleaning? From the required effectiveness and cost-
effectiveness, the maximum allowable annualized cost for LEM replacement is
determined, and the worksheet then helps the user back-calculate what the cost of
the LEM can be. The user would then have to determine whether a suitable low-
emitting material is available at this price that can provide the required exposure
reductions.
As discussed in Section 5.2.2, it can be difficult to quantify the long-term
reductions in occupant exposures that can be achieved through source management
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steps (such as the use of LEMs) unless: a) the source is a constant source; or b) the
source is a decaying source, but it recurs frequently and consistently during occupied
hours, or it decays very slowly (over a period greater than a year), in which case it
may simulate a constant source. The exposure effects from managing constant
sources can be estimated using a simple mass balance (Section 5.2.1), But if the
source does not recur frequently and if it decays completely over a relatively short
period (days, weeks, or a few months), quantification of long-term exposure effects
requires computer modeling of the building, plus sufficient information on the emission
and decay characteristics of the material to serve as input to this computer model
(Section 5.2.2). Such computer models will not be available to many users of this
document; and, in many cases, the necessary data on LEM emission characteristics
will not be available.
Thus, it will often not be straightforward for the user to perform the reverse
calculations discussed in the preceding paragraph, if the source is non-recurring and
decays in a period shorter than a few months (as will commonly be the case). It will
not be easy for the average user to determine what reduction in annual occupant
exposure a given LEM product on the market will provide, or to quantitatively compare
this reduction against that achievable with ventilation or air cleaning.
From modeling that has been performed, it appears that - with non-recurring
emission sources that decay to become non-sources within a few months or less,
such as carpeting or paints - the primary benefit of substituting LEMs is a reduction
in acute exposures when the sources are new. The reduction in chronic, annual
exposures — of the type used in computing cost-effectiveness in this document — will
often be modest with this type of source, The greatest impact on chronic exposure
using LEM replacement is likely to be achieved with constant sources (or sources
which simulate constant sources), such as slow-decaying materials (perhaps such as
composite wood furniture), or such as products that are in continual use in the
building -- e.g., photocopiers, office supplies, or janitorial cleaning products.
5.4.2 Allowing Source to Decay Before Use
For non-recurring emission sources that decay relatively quickly, one option that
is sometimes considered is to allow the source to decay before being introduced into
the building. This could be done with furnishings that are brought into the building,
e.g., with carpeting or furniture. This approach is being considered "source
replacement" here, in that a higher-emitting source (the new product) is being
replaced by a lower-emitting (aged) product. (One might also consider this procedure
to be a variation of "Source Treatment", Section 5.5.)
Referring to Equation 5-5, this source management step would involve leaving
the source outside the building until such time as the unit emission rate of the new
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product {without source management), su.c, decays to a suitably lower value (after
source management), susm.
Issues that can be considered in costing this approach are:
1} How long should the product be thus "aired out", in order to provide the
needed reduction in acute (or chronic) exposure? Computer modeling, with
data input on the decay characteristics of this source, would enable this
calculation.
2) Will the supplier air out the product for this time period? Will the supplier
estimate an incremental cost for this procedure?
3) If building owner/operators are going to perform this procedure themselves, is
the labor and off-site space available? Can a cost be associated with this labor
and space?
4) Will any costs be incurred as a result of the delay in introducing the product
into the building? For example, will furniture have to be rented to address an
on-going need during the time that the new, purchased furniture is being aired
out?
5.4.3 Use of Contamination-Resistant Materials
Where the emission source is not an emission source at the time of installa-
tion - but may develop into a source (e.g., by contamination) following installation -
then one possible source management option would be to install a material which is
resistant to such contamination. The classic example of this scenario is the bio-
contamination of building or mechanical system surfaces. The use of microbial-
resistant duct liners for the mechanical system would be a specific example of this
source management approach.
This is the same LEM concept discussed in Section 5.4.1, with the exception
that, in Section 5.4.1, the source was assumed to be an emitter at the time of
installation. In the current section, the material is assumed to develop into a source
after installation, and the objective is to install a material less prone to do so.
Some of the issues to be addressed in costing this source management
approach are listed below.
1) What quantity of material in the current or designed building is subject to
replacement by the contamination-resistant material? For example, what
lengths and diameters of ducting are being considered for modification with
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microbial-resistant duct liners? In retrofit cases, what portion of the existing
material is reasonably accessible for replacement or modification?
2} To what extent is the contamination-resistant material expected to reduce
emissions relative to the original material (i.e., what is su.sm relative to suJ?
Given the amount of resistant material to be installed, will that provide the
desired reductions in occupant exposures?
3) In a new building, what are the uninstalled cost and installation cost of this
resistant material, relative to the original material?
4) In retrofit cases, what will be the uninstalled cost of the resistant material and
what will be the cost associated with: clearing space as necessary to gain
access to the materials to be replaced; removing, modifying, and/or disposing
of the original materials that are to be replaced; and restoring the space?
5.5 SOURCE TREATMENT
One source management approach that could be considered would be to treat
an emission source in some manner so that it would no longer be a source. One
example would be encapsulation of existing contaminated duct liners, to prevent the
release of emissions from biocontaminants in the liners. One might also postulate
coatings on certain product or building surfaces, to trap contaminants that would
otherwise be released.
There are other specific source management activities that might be considered
"source treatment", depending on the user's semantics, For example, improved
maintenance to remove contaminants (considered as source removal, Section 5.3.2)
or allowing materials to decay before use (considered as source replacement, Section
5.4.2) might be considered to be source treatment. In this document, a step is
termed "source treatment" only when the original contaminants are allowed to remain
in the source, but the source is treated in some manner to prevent their release.
Some of the issues that would impact the costing this generic source manage-
ment approach are suggested below.
1) What material or product is being considered for treatment, and what is the
nature of the treatment? Must the treatment be performed on site, or can the
treatment of the materials/products be performed off-site by a supplier?
2) What quantity of material in the current or designed building is subject to
treatment? In retrofit cases, what portion of the existing material is reasonably
accessible for treatment?
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3) To what extent is treatment expected to reduce emissions relative to the
original material (i.e., what is su.sm relative to s^.J? Given the amount of
material that can be treated, will that provide the desired reductions in
occupant exposures?
4) For treated materials/products to be obtained from an off-site supplier for a new
building, what are the uninstalled cost and installation cost of this treated
material, relative to untreated material? For treatment to be performed on-site
in a new building, how will this add to installation costs?
5) In retrofit cases, what will be the costs associated with; clearing space as
necessary to gain access to the materials to be treated; removing (if necessary)
and treating the original materials; and restoring the space?
5.6 SOURCE RELOCATION
In some cases, it might be possible to retain the emitting source on-site -
avoiding the need for removal, replacement, or treatment — if the source can be
relocated such that the emissions no longer contribute to occupant exposure (or
contribute only to a reduced extent). Examples include relocation of indoor sources
to an exhausted space within the building (such as a janitorial closet); or relocation of
outdoor sources such that their emissions no longer appear in the outdoor air intake
into the building.
The costs of source relocation will be very site-specific. Among the general
issues that the user would consider in costing this option would be:
1) To what location(s) might the source be relocated?
2) What would be the costs of preparing the new location to accommodate the
source?
3) What would be the cost of moving the source to the new location, in the case
of existing buildings? For new buildings, what would be the incremental cost
of installing the source in the new location in lieu of the previously planned
location?
5.7 SOURCE RESCHEDULING
With non-recurring sources that decay fairly quickly, it will sometimes be
possible to reschedule the time during which the source is active, such that occupant
exposure is reduced. A classic example is scheduling of interior painting to occur over
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weekends, when the building has a much lower occupancy. Depending on the
emission and decay characteristics of the paint, the high contaminant peaks seen
during the painting activity might have decayed by perhaps 90% by the time
occupants re-enter the building, if the painting is completed 48 hours before the
occupants return.
Among the general issues impacting the cost of this option would be:
1) What are the complications of rescheduling? Is the source expected to decay
sufficiently quickly -- and does the indoor space remain unoccupied for
sufficiently long intervals -- to warrant the effort involved in rescheduling?
2} What cost items will increase by virtue of rescheduling, and by how much?
(For example, what overtime premium will have to be paid for the painters to
work overnight and on weekends?)
5.8 ADJUSTMENT OF OCCUPANCY PATTERNS
Another option for reducing exposure to non-recurring, decaying sources is to
keep the occupants out of the affected portion of the building during the time that the
source is active. Examples of the option are: a} to delay moving occupants into a
newly constructed building until the new sources in the building have had an
opportunity to decay; and b) to keep occupants of an existing building out of a wing
of the building during the time that renovations are underway.
Issues to be considered in costing this approach are:
1) Is it practical to keep the occupants out of the space — e.g., by renting
alternative space, or preventing access to the renovated portion of the
building - for the duration required to permit sufficient decay of the source(s)?
For the concentration spikes from freshly applied paints, this period could
involve several days for significant (e.g., 90%) reductions, and a week or two
for essentially complete decay. For carpeting, this period could involve a month
or two for moderate (e.g., 50%) reductions, and a number of months for
essentially complete decay.
2} If alternative, temporary space is to be used while the sources in the main
space decay, what will be the costs of leasing and furnishing this temporary
space, and of providing utilities and maintenance, as applicable? Will these
costs for the temporary space be offset in any way by a reduction in utilities,
maintenance, etc., for the main space while it is unoccupied?
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In an existing building under renovation, will costs be incurred in installing
temporary alternative routes for pedestrian traffic, resulting from the need to
avoid the area under renovation?
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SECTION 6
ESTIMATING THE EFFECTIVENESS OF IAQ CONTROL OPTIONS
In Sections 3 through 5, simplified methods were presented for estimating the
incremental increase in cost resulting from implementation of each of the three IAQ
control approaches. This number represents the term "A(cost)" in the expression
defining "cost effectiveness" (see Section 1.4), i.e.,
cost-effectiveness = - A(cost)/A(exposure). (Equation 6-1)
In the current section, a procedure is discussed for estimating the other term in the
equation, A(exposure), i.e., the effectiveness of the control step in reducing occupant
exposure.
As discussed in Section 1,4, "exposure" is expressed as the number of person-
hours of exposure to a unit concentration of contaminant per year. The units are thus
of the form (mg/m3) • person • hr per year. If one wishes instead to consider the
exposure of an average building occupant, the total occupant exposure can be divided
by the number of occupants, and unit exposure will then be expressed in units of
(mg/m3) * hr per average person per year. Alternatively, the exposure calculation may
be performed for a selected typical person, in which case the units would be
(mg/m3) • hr per typical person per year. The user may employ any of the above
definitions of exposure (total exposure of all occupants, or exposure per average or
typical occupant), as long as the same definition is used consistently in comparing the
effectiveness (and cost-effectiveness) of alternative IAQ control approaches.
Section 6 is subdivided into two subsections. The first subsection addresses
methods for estimating the absolute reductions in exposures that will be achieved
with a given control approach [A(exposure)]. The second addresses a simpler
procedure for estimating the relative reduction in exposure that can be achieved by
one control approach compared to another [i.e., A(exposure).,/A(exposure)2].
6.1 ABSOLUTE EXPOSURE VALUES
6.1.1 Rigorous (Computer-Assisted) Calculations
From a practical standpoint, only users who have access to a suitable computer
model will be in a position to rigorously estimate absolute reductions in occupant
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exposure resulting from IAG control measures. It is anticipated that many users of
this document will not be readily able to utilize such a model. In fact, this document
is intended for use by persons who are not in a position to perform such modeling, to
enable rough estimates of cost-effectiveness before someone is retained who can
conduct this modeling. Section 6.1.1 is included here for the purpose of illustrating
the logic behind such rigorous calculations.
Consider the case where one of the building occupants spends one hour in a
zone within the building, and where, during that particular hour, the concentration of
the contaminant of concern within that zone is 1 mg/m3. The total exposure during
that hour is
(1 mg/m3) • (1 person) • (1 hr) = 1 (mg/m3)-person-hr.
If one tracked this person throughout a year -- recording the zone occupied by this
person and the average concentration in that zone during each hour of occupancy --
the above calculation could be repeated for each hour that this person was in the
building during the year. The sum of all of these hourly exposures would be the total
exposure experienced by this person during the year. Repeating this annual calcula-
tion for every occupant of the building, and summing over every person, would yield
the total (mg/m3)-person-hours of exposure in the building per year.
The concentrations that a given occupant might see could vary from hour to
hour. For one thing, the person might move from one zone within the building to
another having a different concentration, or might leave the building altogether. Thus,
occupancy pattern plays a role. In addition, the concentration within a given zone can
vary from hour to hour: an existing source can be decaying; a new source might be
introduced (e.g., use of some office supply or cleaning product); or the cycling of the
HVAC system might be creating fluctuations in concentration. An example of this
latter effect is overnight or weekend shutdown of the HVAC system, which can result
in higher-than average zone concentrations during the first hour or two after startup
at the beginning of the work day.
To rigorously perform this tedious hour-by-hour computation of exposures with
changing concentrations, one needs a suitable computer model. There are several
types of models available for estimating these exposures, varying in complexity.
The simplest type of model is referred to here as a "mass balance" model, and
is represented by the models of Sparks (1991) and Guo (1999). This type of model
uses a simple mass balance approach for computing hour-by-hour concentrations in
each zone of the building — assuming that each zone is separate and internally well-
mixed — based on the following input from the user.
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1} The distribution of sources and sinks among the zones, and the exact
characteristics of each source and sink. The model includes various equations
that define the emission/decay characteristics for various types of sources
{first-order decay, second-order decay, etc.); the user must select the type of
equation to be used to represent each source, and values of the specific
constants to be used in each equation (determining, e.g., initial emission rate,
the decay rate, and the sink sorption/desorption characteristics).
2) Flows of air from one zone to another, and from the outdoors to each zone.
This would include building air recirculation and OA supply by the HVAC
system, OA infiltration directly into the zone, and interzonal air movement
independent of any HVAC system. These flows must all be specified as input
to the model; the model is not able to calculate these flows independently.
The mass balance models then use the hour-by-hour concentrations in each zone of
the building, and the occupancy patterns of each zone, to compute the total exposure
in the building for the period of interest, e.g., over the course of a year.
A somewhat more complicated type of model is referred to here as a "building
simulation" model, represented by the models of FSEC (1992) and Walton (1994).
This type of model is similar to mass balance models, with one important exception:
the air flows between zones, and between the outdoors and each zone, do not have
to be specified as model inputs. These models compute building energy requirements
and HVAC system performance, and, in doing so, compute the mechanically induced
flows to the different zones and the flows induced by pressure differences between
zones.
A third type of model, referred to here as a "computational fluid dynamics"
(CFD) model, is the most sophisticated of the alternative model types. Both the mass
balance and the building simulation model types assume the zones to be internally
well-mixed units; CFD models avoid this need, allowing consideration of gradients
within zones. However, this level of sophistication and computational effort is beyond
what is necessary for the exposure calculations used in IAQ cost-effectiveness
analysis, even in those cases where building modeling experts become involved.
6.1.2 Simplified Calculations
From a practical standpoint, a computer model is necessary to compute
absolute exposure if the user is to rigorously account for the variations in indoor
concentrations with time, as discussed in Section 6.1.1. Accordingly, if absolute
exposure is to be estimated without such a model, it will be necessary to simplify the
calculation by assuming that the occupants are exposed to a steady, average indoor
concentration over the course of the year, and that the occupancy pattern is simple
and consistent.
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Worksheet 14 in Appendix A presents a simplified method for estimating the
effectiveness (the change in exposure) that will result from applying an lAQ control
measure, considering the reduction achieved in the annual average concentration.
Worksheet 14 first asks the user to estimate the average annua! concentrations
of the contaminant of concern in each of the zones of interest, with and without
implementation of the IAQ control measure. The difference between these two
represents the reduction in concentration achieved by the control step. This
difference is then multiplied by the average number of occupants and the average
hours of occupancy per year in each zone, to provide the reduction in the annual
exposure in each zone. Summing these reductions over all of the zones of interest
yields the total reduction in exposure for all of these zones (e.g., for the entire
building).
It will generally not be straightforward to estimate the annual average
concentrations with and without the control measure, which the worksheet requires
as a surrogate for the time-varying concentrations that will exist in reality. In cases
where such average concentrations cannot reasonably be estimated, the user may
wish to consider the approach used in Section 6.2 below, which avoids the need to
compute absolute concentrations, either with or without the control measure.
Instead, the approach in the next section uses simply the fractional reduction
expected from a control measure, and compares it against the fractional reductions
achieved by other measures.
Even if the uncertainties in estimating absolute concentrations might make
Worksheet 14 difficult to use in some cases, the worksheet still useful in illustrating
the concept of the exposure/effectiveness calculation.
As discussed in Section 1.4, the "effectiveness" of a control measure is
described by the equation
effectiveness = - A(exposure).
Worksheet 14 computes the value of A(exposure) created by implementation of the
control step. Because the control step presumably will reduce the concentration and
hence reduce the exposure, the change in exposure will be negative. According to the
equation above, a negative change in exposure translates into a positive effectiveness
for the control measure.
6.2 RELATIVE EXPOSURE VALUES
The difficulties involved in estimating the average contaminant concentrations,
discussed in Section 6.1.2 above, can be avoided in cases where it is sufficient for
the user to estimate only the relative reductions in exposure achieved by one control
measure compared to another. In this situation, where only the relative performance
6-4
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of alternative techniques is of interest, it is not necessary to know the actual before-
and-after concentrations with either technique. Nor is it necessary to estimate the
occupancy pattern of the building, as Worksheet 14 requires.
The estimation of relative reductions in exposure still requires the user to
estimate the fractional (or percentage) reduction achieved by each of the control
measures being considered. But such an estimation of reduction will commonly be
much more reliable than will be an estimation of the absolute concentrations involved.
For example, the estimate that a doubling of OA ventilation rate will provide a 50%
reduction in exposure will generally be more reliable than will be estimates of the
actual indoor concentrations before and after that estimated 50% reduction.
Of course, if one computes only the relative effectiveness of one measure
versus another in this section, that will permit the calculation in Section 7 only of
relative cost-effectiveness values for the measures being compared. But that may
often be sufficient, given that the user's objective will commonly be to select the
most cost-effective of the alternative measures under consideration.
Worksheet 15 in Appendix A presents a method for estimating the relative
reductions in exposure that can be achieved with one IAQ control measure in
comparison against other measures under consideration.
Worksheet 15 simply asks the user to estimate the fractional change in the
annual average exposure for each of the control measures under consideration. For
example, doubling the OA ventilation rate would likely provide a 50% reduction in
indoor concentrations (resulting in a fractional change of -0.5 in total occupant
exposure), according to the approach in Worksheet 1. Perhaps an air cleaner might
be designed that can reduce concentrations by 75%, using the mass balance
considerations in Worksheet 7 (providing a fractional change in exposure of -0.75).
Removing 80% of a source might be expected to reduce indoor concentrations by
about 80% (a fractional change of -0.8). Based on Equation 6-2 above, the
effectiveness of these three measures would thus be +0,5, +0.75, and +0.8,
respectively.
The relative effectiveness of these control measures in this hypothetical case
is readily computed. The doubling of the ventilation rate is 0.5/0.75 = 0.67, or 67%
as effective as the postulated air cleaner; and it is 0.5/0.8 - 0.62, or 62% as
effective as the postulated source management step. These ratios can be estimated
without any knowledge of absolute indoor concentrations or occupancy patterns.
For the purposes of the discussion of relative cost-effectiveness in Section 7.2,
it is useful here to express mathematically the intuitive ratio that is being computed
in the preceding paragraph. Assume that:
6-5
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E0 = total annual occupant exposure in the building prior to implementing
any IAQ control measure l(mg/m3}-person-hr);
E, = total annual exposure if Measure #1 is implemented;
Ez = total annual exposure if Measure #2 is implemented;
= fractional reduction in annual average indoor air concentration if
Measure #1 is implemented; and
X2 = fractional reduction in annual average indoor air concentration if
Measure #2 is implemented.
The total annual exposures with the two control measures, E, and E?, are related to
the uncontrolled exposure E0 by the expressions
E, = (1-X1)E0 = Ec- X,E0
and
E2 = (1-X2)E0 = E0 - X2E0,
Thus, the change in exposure being achieved by the two measures are
A(exposu re), = E., - E0 = X,E0
and
A(exposure(? = E2 - E0 = -X2E0.
The effectiveness of the two measures is
(effectiveness^ = -A(exposure), = X1E0
and
(effectiveness)2 = -A(exposure)2 = X2E0.
Accordingly, the relative effectiveness of the two measures is
(effectiveness)1/{effectiveness)2 = X1E0/X2Et> = X1/X2. (Equation 6-1}
Thus, E0 — the absolute parameter that is difficult to estimate ~ cancels out, The
relative effectiveness is simply the ratio of the fractional reductions of the two
measures.
6-6
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SECTION 7
ASSESSING THE COST-EFFECTIVENESS OF IAQ CONTROL OPTIONS
With the annualized cost estimates from Sections 3 through 5, and the
effectiveness estimates from Section 6, it is now relatively straightforward to
compute the cost-effectiveness of the IAQ control options that are being considered.
An issue to be considered when making decisions based upon the cost-
effectiveness results, is that cost-effectiveness will be a function of the effectiveness
of the control measure. A given control measure designed to provide, say, a 50%
reduction in exposure may be more or less cost-effective than the same measure
designed to provide a 75% reduction. Accordingly, when alternative control measures
are compared, the comparison will be fairest when the alternatives are compared at
a consistent level of effectiveness. This issue is discussed in Section 7.3.
7.1 ABSOLUTE VALUES FOR COST-EFFECTIVENESS
If absolute values for A(exposure) are estimated from Section 6.1 (Line 8 of
Worksheet 14), then these values can be used in the expression
cost-effectiveness = - A(cost)/A(exposure)
to compute the absolute cost-effectiveness for the particular control measure being
considered. The value for A(cost) in the expression would be the total annualized cost
for the measure, obtained from; Line 9 of Worksheet 6, for ventilation measures; Line
9 of Worksheet 11, or Line 29 or Worksheet 12, for air cleaning measures; or Line 11
or Line 23 of Worksheet 13, for source management measures.
The units of cost-effectiveness would be $ per (mg/nr)-person-hr/yr, based on
the units that have been used throughout this document.
This simple calculation would be performed for each of the control measures
being considered. Since this computation normalizes the total annualized cost for
each measure to account for the measure's effectiveness, these results permit the
alternative measures to be directly compared even when the measures have different
levels of effectiveness.
7-1
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The interpretation of these results — to compare (and select between)
alternative control measures - is further discussed in Section 7,3,
7.2 RELATIVE VALUES FOR COST-EFFECTIVENESS
As discussed in Section 6.2, it will often be more convenient to estimate the
relative effectiveness of one control measure versus another, rather than the absolute
effectiveness of either measure. This approach avoids the difficulties and uncertain-
ties involved in estimating the average annual concentrations and the occupancy
patterns in the building. But if the user estimates only relative effectiveness, the cost-
effectiveness calculations here are likewise limited to relative values.
As discussed at the end of Section 6.2, the relative effectiveness of two
control measures is the ratio of the fractional reductions that they can achieve in
indoor concentrations:
(effectiveness)^'(effectiveness^ = X,/X2. (Equation 6-1)
If C, is defined as the total annualized cost of Measure #1 in dollars (from Worksheet
6, 11, 12, or 13), and C2 as the annualized cost of Measure #2, then the relative cost-
effectiveness of the two measures will be:
(cost-effectiveness),/(cost-effective ness)^ =
{C1/[-A(exposure)1]}/{C2/[-ii(exposure)2]} =
[C-,/(effectiveness)., ]/[C2/(effectiveness)2] =
(C-,/C2) x [(effectiveness)2/(effectiveness),] =
C^/Cp^ = (C1/X1)/(C2/X2). (Equation 7 1)
Where multiple IAQ control measures were being considered, pairs of alternative
measures would be compared in this manner to identify the one offering the best
relative cost-effectiveness (i.e., the lowest cost per unit reduction in exposure, or the
lowest value of Cx/Xx in the above equation).
7.3 INTERPRETATION OF COST EFFECTIVENESS RESULTS
As indicated previously, the cost-effectiveness of any given IAQ control
measure will generally depend on the effectiveness that the measure has been
7-2
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designed to achieve. This needs to be considered when evaluating the results from
the cost-effectiveness analysis, and when making decisions based on these results.
Many of the IAQ control measures can be designed or operated to achieve
alternative degrees of reduction in occupant exposure. Where the measure involves
an increase in OA ventilation rate, the system can be designed for greater increased
in the OA rate, to provide increased effectiveness. Where the measure involves, e.g.,
activated carbon air cleaners to reduce VOC exposure, system operation can be
modified to reduce the frequency of carbon replacement, a step that would reduce
effectiveness but also reduce annualized costs. The costs (and the cost-effectiveness)
of these measures will vary if these design or operating changes are implemented.
7.3.1 Required Effectiveness Is Known
Where the user has defined the level of effectiveness that must be achieved --
and where there is this flexibility in designing/operating each of the various control
options to achieve this desired reduction in indoor concentrations and exposure -- the
approach for comparing the options may be relatively straightforward. The cost
analysis in Sections 3, 4, and/or 5 would be conducted for the various control
measures, each designed/operated to achieve the defined level of effectiveness. In
such cases, (effectiveness), = (effectiveness);, (and X-, = X2) in Equation 6-1, and
Equation 7-1 above reduces to
(cost-effectiveness),/(cost-effectiveness)2 = C^/C2. (Equation 7-2)
That is, the user is seeking the control measure that will provide that desired
effectiveness at the least annualized cost.
7.3.2 Effectiveness to Be Achieved Is Open to Judgement
In other cases, the precise level of exposure reduction that is to be achieved
may be more of a judgement call. In those cases, the cost-effectiveness analysis here
may aid the user in deciding what level of exposure reduction to pay for.
In such cases, it can be useful to plot cost-effectiveness as a function of
effectiveness for the various control measures under consideration, to aid in this
decision process. Figure 4 is an illustrative example of how such a plot might appear,
for the case where the contaminant of concern is VOCs.
Note that Figure 4 is largely qualitative, and is for a hypothetical building. The
exact positions and slopes of the curves could vary significantly from building to
building. "Effectiveness" on the abscissa is expressed, not as an absolute change in
VOC exposure [in (mg/m3) person hr/yr], but as the dimensionless fractional reduction
in exposure, X, relative to the uncontrolled case.
7 3
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\/nC a\r c\eaner
•yo6 removed
6°i°
te»se ^
-------
Four curves are shown in the figure. The solid curve is for increased OA
ventilation, in the case where this increase is accomplished utilizing a dedicated-OA
unit. (The option of using a dedicated-OA unit to condition the increased OA, versus
enlargement of the central HVAC unit, is discussed in Section 3.) The dashed curves
are for VOC air cleaners utilizing granular activated carbon.
The bottom-most dashed curve in Figure 4 is for the case where the specific
VOC compound of concern is decane, which is effectively sorbed on carbon; for this
building, the estimated carbon replacement frequency is once every 24 months to
maintain full air cleaner removal performance for decane. The middle dashed curve
represents hexane (estimated carbon lifetime of 4 months); and the upper curve
represents methyl ethyl ketone (MEK) (estimated carbon lifetime of 2 months). Some
individual VOCs (e.g., formaldehyde) are sorbed more weakly than MEK, in which case
carbon lifetime would be even shorter and the cost higher per unit reduction in
exposure. (See Table A-12 in Worksheet 10.) The left-hand (lesser-reduction) points
on each of the air cleaner curves represent the case where the carbon replacement
frequencies estimated above have been reduced by half for each of the organic
compounds, such that breakthrough through the carbon bed is allowed to occur for
some period before the carbon is replaced, reducing the average efficiency.
A plot such as Figure 4 could enable the user to draw several conclusions,
assisting in the selection of the more cost-effective IAQ control approach for this
particular (hypothetical) building.
For one thing, the relative cost-effectiveness of air cleaning vs. increased
ventilation will depend heavily on the specific organic compounds of concern. If the
compounds are strongly sorbed on carbon - such as decane - then a GAG air cleaner
would appear to be more cost-effective than increased ventilation (i.e., to involve a
lower cost per unit reduction in exposure), at all levels of effectiveness. If the
compounds have a moderate affinity for carbon - such as hexane - carbon sorption
and increased ventilation will be of roughly comparable cost-effectiveness. And if the
compound is more weakly sorbed than hexane, GAC air cleaning will be less cost-
effective than ventilation.
This result illustrates the importance of defining the specific organic compounds
of concern before evaluating the cost-effectiveness of GAC air cleaning. From Table
A-12 (Worksheet 10), it should be noted that inlet concentration, as well as the
identity of the specific compound, can also impact GAC sorption capacity (and hence
carbon replacement frequency and costs). Thus, where the nature and/or concentra-
tions of the specific VOCs may vary with time in a given building, it may be useful to
plot a family of air cleaner curves as in Figure 4, reflecting these varying compounds
and/or inlet concentrations, to provide the perspective required for assessing the cost-
effectiveness.
7-5
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Another conclusion that can be drawn from Figure 4 is that, for most of the
control measures in this hypothetical building, the cost per unit reduction in exposure
becomes modestly higher at greater levels of effectiveness, as might intuitively be
expected. That is, the control measures become modestly less cost-effective at
greater levels of contaminant removal. The user would have to make a judgement
regarding whether to pay the additional price to achieve the greater reduction in
exposure.
Again, it is re-emphasized that the cost curve relationships in Figure 4 are for
one particular, hypothetical building, and would be different for different buildings.
7.3.3 Effectiveness Is Not Subject to Adjustment
In Sections 7.3.1 and 7.3.2, it is assumed that the user has some flexibility in
designing and operating the IAQ control measures, to achieve alternative levels of
performance from any given control measure. There may be some situations where
this flexibility will not exist, or will be limited.
For example, the pre-existing HVAC system in a particular building may
accommodate a certain maximum incremental increase in the OA ventilation rate
(which will provide a fractional exposure reduction X.). In this same building, there
may be a certain amount of a given pollutant source that can practically be considered
for removal (which will provide a fractional reduction X2), and logic dictates that this
entire amount be removed, if in fact source removal is to be implemented. In this
building, the user does not have much practical flexibility of increasing or decreasing
the incremental additional OA or the amount of source to be removed, in an effort to
compare both of these measures at the same level of effectiveness. Rather, the user
is constrained to compare two fixed approaches having inherently different levels of
effectiveness (X- ^ X2).
in such cases, the cost-effectiveness of the alternative measures would be
computed according to Section 7.1 or 7.2. If the measure which is the least
expensive also happens to be the one providing the greatest reduction in exposure —
and is thus necessarily the most cost-effective - then the selection between the
options is obvious. Where the less effective measure happens to be the least
expensive ~ and perhaps the most cost-effective as well - then the user is required
to make the judgement regarding whether to pay additional for the greater reduction
in exposure.
7-6
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SECTION 8
REFERENCES
ASHRAE (1989! Ventilation for Acceptable Indoor Air Quality, Atlanta, GA, American
Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. (ANSI/
ASHRAE Standard 62-1989).
ASHRAE (1992) Gravimetric and Dust-Spot Procedures for Testing Air-Cleaning
Devices Used in General Ventilation for Removing Particulate Matter, Atlanta,
GA, American Society of Heating, Refrigerating, and Air-Conditioning Engineers,
Inc. (ASHRAE Standard 52.1-1992).
ASHRAE (1995) ASHRAE Handbook: Heating, Ventilating, and Air-Conditioning
Applications, Chapter 41 (Control of Gaseous indoor Air Contaminants),
Atlanta, GA, American Society of Heating, Refrigerating, and Air-Conditioning
Engineers, Inc.
ASHRAE (1996) ASHRAE Handbook: Heating, Ventilating, and Air-Conditioning
Systems and Equipment, Chapter 24 (Air Cleaners for Particulate Contam-
inants), Atlanta, GA, American Society of Heating, Refrigerating, and Air-
Conditioning Engineers, Inc.
ASHRAE (1997a) ASHRAE Handbook: Fundamentals, Chapter 26 (Climatic Design
Information), Atlanta, GA, American Society of Heating, Refrigerating, and Air-
Conditioning Engineers, Inc.
ASHRAE (1997b) ASHRAE Handbook: Fundamentals, Chapter 32 (Duct Design),
Atlanta, GA, American Society of Heating, Refrigerating, and Air-Conditioning
Engineers, Inc.
Elder, Mark (1998) Personal communication, Norfolk, VA, Mark Elder and Associates.
EPA (1991) Building Air Quality: A Guide for Building Owners and Facility Managers,
Washington, DC, U. S. Environmental Protection Agency and National Institute
for Occupational Safety and Health (Report No. EPA/400/1-91/033, GPO
Accession No. 055-000-00390-4).
Flanders Filters (1994) The AIRVELOPE 57, Washington, NC, Flanders Filters, Inc.
8-1
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Fowler, C. S., A. D. Williamson, B. E. Pyle, and S. E. McDonough (1997! Large
Building Radon Manual, Research Triangle Park, NC, U. S, Environmental
Protection Agency (Report No. EPA-600/R-97-124, ISITIS Accession No, PB98-
123995).
FSEC (1992) Florida Software for Enervironment Computation, Version 3.0, Cocoa,
FL, Florida Solar Energy Center (Report No. FSEC-GP-47-92).
Guo, Zhishi (1999) Personal communication, Research Triangle Park, NC, National
Risk Management Research Laboratory, U. S. Environmental Protection Agency.
Hanley, J. T., D. S. Ensor, D. D. Smith, and L. E. Sparks (1994) "Fractional Aerosol
Filtration Efficiency of In-Duct Ventilation Air Cleaners," Indoor Air, 4 (3), 169-
178.
Henschel, D. B. (1993) Radon Reduction Techniques for Existing Detached Houses:
Technical Guidance (Third Edition) for Active Soil Depressurization Systems,
Research Triangle Park, NC, U. S. Environmental Protection Agency (Report No.
EPA/625/R-93/011).
Henschel, D. B. (1997) Energy Costs of IAQ Control Through Increased Ventilation
in a Small Office in a Warm, Humid Climate: Parametric Analysis Using the
DOE-2 Computer Model, Research Triangle Park, NC, U. S. Environmental
Protection Agency (Report No. EPA-600/R-97-1 31, NTIS Accession No. PB98-
113368).
Henschel, D. B. (1998) "Cost Analysis of Activated Carbon Versus Photocatalytic
Oxidation for Removing Organic Compounds from Indoor Air," J. Air & Waste
Manage. Assoc., 48 (10), 985-994.
Humphreys, K. K., and P. Wellman (1996) Basic Cost Engineering, 3rd ed., New
York, NY, Marcel Dekker, Inc., pp. 219-225.
Kettler, J. P. (1998) "Controlling Minimum Ventilation Volume in VAV Systems,"
ASHRAE Journal, 40 (5), 45-50.
Leovic, K. W., and A. B. Craig (1993) Radon Prevention in the Design and Construc-
tion of Schools and Other Large Buildings, Research Triangle Park, NC, U. S.
Environmental Protection Agency (Report No. EPA/625/R-92/016).
Means (1996) Means Mechanical Cost Data, 19th ed., M. J. Mossman, ed.,
Kingston, MA, R. S. Means Co.
8-2
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Pierce, W. M., J. N. Janczewski, B. Roethlisberger, M. Pelton, and K. Kunstel (1996)
"Effectiveness of Auxiliary Air Cleaners in Reducing ETS Components in
Offices," ASHRAE Journal, 38 (11), 51-57.
Sparks, L. E. (1991) EXPOSURE Version 2: A Computer Mode! for Analyzing the
Effects of Indoor Air Pollutant Sources on Individual Exposure, Research
Triangle Park, NC, U. S. Environmental Protection Agency (Report No. EPA-
600/8-91-013, NTIS Accession No. PB91 201095).
U. S. Department of Defense (1956) DOP-Smoke Penetration and Air Resistance of
Filters, Philadelphia, PA, Department of the Navy - Defense Printing Service
(MIL-STD-282).
VanOsdetl, D. W., M. K. Owen, L. B. Jaffe, and L. E. Sparks (1996) "VOC Removal
at Low Contaminant Concentrations Using Granular Activated Carbon," J. Air
& Waste Manage. Assoc., 46 (9), 883-890.
Walton, G. N. (1994) CONTAM93 User Manual, Gaithersburg, MD, National Institute
of Standards and Technology, U. S. Department of Commerce (Report NISTIR
5385).
York, D. A., E. F. Tucker, and C. C. Cappiello (eds.) (1981) DOE-2 Reference Manual
{Version 2,1A) - Part /, Los Alamos, NM, U. S. Department of Energy (Report
No. LBL-8706 Rev.2, NTIS Accession No. LBL-8706 Rev. 2).
8-3
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[This page intentionally blank,]
8-4
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APPENDIX A
Worksheets
A-1
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[This page intentionally blank,]
A-2
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WORKSHEET 1
Estimation of Outdoor Air Increase Required
to Achieve Desired Reduction in Contaminant Concentration
Using Increased Ventilation
1. Enter the current average concentration of the
contaminant of concern in the building (or
in that portion of the building served by a
given air handler) -- in suitable units (e.g.,
ppmv) ppmv
2. Enter the average concentration to which the
level in Line 1 above should be reduced --
in the same concentration units as above ppmv
3. Calculate the desired concentration as a
fraction of the current concentration (Line 2
divided by Line 1)
4. Enter the current flow of OA into the building
(or into the portion served by the air handler
in question) -- in suitable units (e.g., cfm) cfm
5. Compute the total OA flow that is required if
the desired concentration (Line 2) is to be
achieved (Line 4 divided by Line 3) -- in
the same units as Line 4 cfm
6. Compute the incremental increase in outdoor
air flow rate required to achieve the desired
reduction in concentration (Line 5 minus
Line 4) cfm
A-
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WORKSHEET 2A
Estimation of Installed Costs for Increased OA:
Enlarged Central Units - Retrofit Case
Enter Basic Data
1. Enter the incremental increase in OA intake rate
that is required for the entire building, in
cfm {from Line 6 of Worksheet 1). cfm
2. Enter the incremental increase in OA to each of
the HVAC units serving the building:
2(1). Increase in OA to Unit #1
2(2). Increase in OA to Unit #2
2(3). Increase in OA to Unit #3
etc.
[Note: The sum of Lines 2(1} through 2{x)
should sum to the total on Line 1.]
3. Enter the original cooling capacity for each of
the HVAC units serving the building:
3(1). Cooling capacity of Unit #1
3(2). Cooling capacity of Unit #2
3(3). Cooling capacity of Unit #3
etc.
4. Enter the original heating capacity for each of
the HVAC units serving the building:
4(1). Heating capacity of Unit #1
4(2). Heating capacity of Unit #2
4(3). Heating capacity of Unit #3
etc.
(continued)
cfm
cfm
cfm
tons
tons
tons
kW
kW
kW
A-4
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Worksheet 2A (continued)
Estimate Cost of Increased Cooling/Heating Capacity
5. Refer to Table A-1 at the end of this worksheet.
Locate in Column A the city having the climate
most closely representing the user's.
6. From Columns B and C of Table A-1, enter the
required cooling and heating capacity per
1,000 cfm OA for the climate of this city.
6a. Cooling capacity: _
6b. Heating capacity:
7. Compute the incremental additional cooling
capacity for each of the HVAC units in the
building, to treat the increased OA.
7(1). Unit #1 [Line 2(1) x Line 6a -*• 1,000]
7(2). Unit #2 [Line 2(2) x Line 6a + 1,000]
7(3). Unit #3 [Line 2(3) x Line 6a + 1,000]
etc.
8. Compute the incremental additional heating
capacity for each of the HVAC units in the
building, to treat the increased OA.
8(1). Unit #1 [Line 2(1) x Line 6b 1,000]
8(2). Unit #2 [Line 2(2} x Line 6b + 1,0001
8(3). Unit #3 [Line 2(3) x Line 6b - 1,0001
etc.
9. Compute the revised total cooling capacity required
for each of the HVAC units in the building,
increased to handle the increased OA load.
9(1). Unit #1 I Line 3(1) + Line 7(1)1
9(2). Unit #2 [Line 3(2) + Line 7(2)]
9(3). Unit #3 [Line 3(3) + Line 7(3)]
etc.
A-5
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Worksheet 2A (continued)
10. Compute the cost of replacing the pre-existing
cooling coils and cooling equipment in each
HVAC unit, with enlarged components having
the capacity determined in Item 9 above.
10{1). Unit #1 [Line 9(1) x $830/ton] $
10{2), Unit #2 [Line 9(2) x $830/ton] $
10(3). Unit #3 [Line 9(3) x $830/ton] $
etc.
[Note: The cost of $830/ton, derived from Means (1996), includes: a) removal of
the old coils and the old condenser/compressor ($130/ton, assumed to equal the
labor charges in Section 157-230 of the citation for installation of new coils and
condensers); b) installation of new coils in the central unit (including more rows
and/or more fins/inch), to increase capacity ($100/ton, from Section 157-201-0470
to -0640); and c) installation of a new, higher-capacity condenser/ compressor
<$600/ton, from Section 157-230). This installed cost per ton is roughly indepen-
dent of the total tons of capacity. Since this estimate assumes a direct-expansion
cooling system, it will be less accurate for systems involving chillers.]
11. Compute the total cost of replacing the cooling coils
and equipment [sum of Lines 10(1) through 10(x)1 $
12. Compute the revised total heating capacity required
for each of the HVAC units in the building,
increased to handle the increased OA load.
12(1). Unit #1 [Line 4(1) + Line 8(1)]
12(2). Unit #2 [Line 4(2) + Line 8(2)]
12(3). Unit #3 [Line 4(3) + Line 8(3)]
etc.
kW
kW
kW
13. Compute the cost of replacing the pre-existing
heating elements in each HVAC unit, with enlarged
components having the capacity determined in
Item 12 above.
13(1). Unit #1 [Line 12(1) x $30/kW] $
13(2). Unit #2 [Line 12(2) x $30/kW] $
13(3). Unit #3 [Line 12(3) x $30/kW] $
etc.
[Note: The cost of $30/kW, derived from Means {1 996), includes: a) removal of the
old heating elements ($1-$2/kW, assumed to equal the average labor charges in
Section 155-408 of the citation for installation of new coils having a heating capacity
of 20 kW or greater); and b) installation of new heating elements of increased wattage
in the central unit, to increase capacity |$25-$30/kW, the average installed cost from
Section 155-408 for coils of 20 kW or greater). Since this estimate assumes electric
resistance heating, it will be less accurate for systems involving furnaces.]
(continued)
A-6
-------
Worksheet 2A (continued)!
14. Compute the total cost of replace all of the
heating elements [sum of Lines 1311) through 13(x)] $
15. Enter the total cost for increasing the cooling and
heating capacity [Line 11 + Line 14] $
Estimate Cost of Increased OA Intake Fan Capacity (if applicable)
[Note; The following portion of Worksheet 2A applies only in those
cases where an OA intake fan is already present, or must be added in
connection with the OA increase. The following assumes that a new OA
fan is added, sized to provide the OA increment. See text.]
16. Enter the total incremental increase in OA to the
building (Line 1 above) cfm
17. Refer to Table A-2 at the end of this worksheet.
Locate in Column A the fan flow rate corres-
ponding to the total additional OA flow on
Line 16. Interpolate as necessary.
18. From Column B of Table A-2, enter the installed
cost of the air handler required to provide this
additional OA flow. $
Estimate Cost of Retrofitting Additional OA Intake Ductwork (if applicable)
[Note: The following portion of Worksheet 2A applies only in systems
without economizers, where the required OA increase cannot be
achieved without supplementing the OA intake duct. The following
assumes that new ducting is installed to direct the incremental OA from
the new intake fan to each central HVAC unit, with a main trunk line
from the fan splitting into branches leading to each unit. See text.]
(continued)
-------
iiiiiiiiiiiiliiiiiiiil
19. Estimate the linear feet of ductwork that would
be required to direct the incremental additional
OA [in Lines 2(1) through 2(x) above] from the
new OA intake fan to each of the HVAC units
in the building;
19(T). Length of OA trunk line _______ ft
19{1). Branch from trunk line to Unit #1 ft
19(2). Branch from trunk line to Unit #2 ft
etc.
20. Refer to Table A-2. Locate in Column A the
incremental OA flow rates to the entire building
(Line 1), and to each HVAC unit [Lines 2(1)
through 2(x)].
21. From Column D of Table A-2, enter the installed
cost per linear foot of retrofitted insulated
duct, based on the OA flows in the trunk line
and in the branches to each HVAC unit:
21(T). OA trunk line [flow on Line 1] $/ft
21(1). Unit #1 branch [flow on Line 2(1)] $/ft
21(2). Unit #2 branch [flow on Line 2(2)] $/ft
etc.
22. Compute the installed cost of each element of the ductwork;
22{T). OA trunk line [Line 19(T) times Line 21 (T)] $
22(1). Unit #1 branch [Line 19(1) times Line 21(1)] $
22(2). Unit #2 branch [Line 19(2) times Line 21(2)] $
etc.
23, Compute the total installed cost of the new OA supply
ductwork [sum of Lines 22(T) through 22(x)] $
(continued)
A-8
-------
Worksheet 2A (continued)
Estimate Cost of Increased Exhaust Fan Capacity (if applicable)
[Note: The following portion of Worksheet 2A applies only in those
cases where a central exhaust fan is already present, or must be added
in connection with the OA increase. This will usually be the case only
in systems without economizers. The following assumes that a new
central exhaust fan is added, sized to exhaust an amount of building air
equal to the OA increment. See text,]
24. Refer to Table A-2 at the end of this worksheet.
Locate in Column A the fan flow rate corres-
ponding to the total additional OA flow on
Line 1 (or 16). Interpolate as necessary.
25. From Column B of Table A-2, enter the installed
cost of the air handler required to exhaust this
volume of building air. $
Estimate Cost of Retrofitting Additional Exhaust Ductwork (if applicable)
[Note: The following portion of Worksheet 2A applies only in systems
without economizers, where the required increase in exhaust air cannot
be achieved without supplementing the central exhaust ducting. The
following assumes that, in systems without economizers, new ducting
is installed to draw exhaust air from one zone near each central HVAC
unit, with the branches from the zones combining into a main trunk line
leading to the exhaust fan. See text.]
26. Estimate the linear feet of ductwork that would
be required to direct exhaust air - equal to the
incremental additional OA in Lines 2(1) through
2(x) — to the new exhaust fan, from zones near
each of the central HVAC units:
26{T). Length of exhaust air trunk line ft
26(1). Branch from Unit #1 zone to trunk line ft
26(2). Branch from Unit #2 zone to trunk line ft
etc.
27. Refer to Table A-2. Locate in Column A the
incremental OA flow rates to the entire building
(Line 1), and to each HVAC unit [Lines 2(1)
through 2(x)].
(continued)
A-9
-------
Worksheet 2A ^continued)
28. From Column C of Table A-2, enter the installed
cost per linear foot of retrofitted uninsulated
duct, based on the exhaust air flows in the trunk
line and in the branches from the zones near each
HVAC unit:
28{T). Exhaust trunk line [flow on Line 1] $/ft
28(1), Branch from Unit #1 zone [flow on Line 2(1}] $/ft
28(2). Branch from Unit #2 zone [flow on Line 2(2)] $/ft
etc.
29. Compute the installed cost of each element of the ductwork;
29(T). Exhaust trunk line [Line 26(T) times Line 28|T)] $
29(1). Unit #1 branch [Line 26(1) times Line 28(1)] $
29(2). Unit #2 branch [Line 26(2) times Line 28(2)] $
etc.
30. Compute the total installed cost of the new exhaust
ductwork [sum of Lines 29(T) through 29(x)] $
Estimate Total installed Cost (retrofit enlarged central unit plus, as applicable, added
OA and exhaust fans and ductwork}
31. Compute the total installed cost of the retrofitted
enlarged HVAC system (Line 1 5 plus, as applicable,
Lines 18, 23, 25, and 30). $
(continued)
A-10
-------
Worksheet 2A (continued)
TABLE A-1
Incremental Increases in Cooling and Heating Capacities
Necessitated by Increases in Outdoor Air Ventilation Rates
{by Geographical Location)
Column A Column B Column C
Required Increase in Required Increase in
Cooling Capacity1 Heating Capacity2
Citv (tons per 1,000 cfm OA) (kW per 1,000 cfm OA)
Albuquerque, NM
~0
16
Atlanta, GA
3.3
15
Boston, MA
2.7
18
Chicago, IL
3.3
22
Cincinnati, OH
3.9
18
Cleveland, OH
2.7
20
Dallas-Fort Worth, TX
3.9
14
Denver, CO
~0
21
Houston, TX
4.6
12
Los Angeles, CA
0.5
8
Miami, FL
4.6
6
Minneapolis, MN
2.7
26
New York, NY
3.3
17
Omaha, NE
3.9
23
Pittsburgh, PA
2.1
20
Raleigh, NC
3.9
16
St. Louis, MO
3.9
20
San Francisco, CA
~0
10
Seattle, WA
0.5
13
Washington, D.C.
3.9
16
Notes:
1 Computed using the 1 % design values for the cooling dry-bulb/mean wet-bulb
temperatures for the various cities, as defined by ASHRAE (ASHRAE, 1997a).
The refrigeration capacity presented here is the incremental power required to
reduce 1,000 cfm of outdoor air from the 1 % value of outdoor enthalpy to an
indoor enthalpy corresponding to 75 °F and 50% relative humidity,
2 Computed using the 99% heating dry-bulb temperatures for the various cities,
as defined by ASHRAE {ASHRAE, 1997a). The heating capacity presented here
is the incremental power required to increase 1,000 cfm of outdoor air from the
99% value of outdoor temperature to an indoor temperature of 70 °F.
(continued)
A-11
-------
Worksheet 2A ieoocluded)
TABLE A-2
Approximate Installed Costs of Air Handlers and Retrofit Ducting1
Column A
Column B
Column C
Column D
Retrofit
Retrofit
Installed
Installed Cost
Installed Cost
Flow Rate
Cost of
of Uninsulated
of Insulated
(cfm)
Fan2 (S)
Duct3 ($/linear ft)
Duct3 ($/linear ft)
500
900
66
72
1,000
1,300
77
86
2,000
1,600
91
104
4,000
2,800
113
130
6,000
3,000
128
150
8,000
3,200
143
168
10,000
4,000
155
183
Notes:
1 Includes all materials (with markup), installation labor, and installation
contractor overhead and profit.
2 Derived from Means (1996). Each figure is the average for the various cate-
gories of air handlers (centrifugal, vaneaxial, etc.) at the specified capacity,
from Section 157-290 of that citation.
3 Derived from Means (1996). The ducts are assumed to have a square cross-
section, and are sized to create 0.1 in. WG pressure loss per 100 linear feet
(ASHRAE, 1997b). The uninsulated ducts were costed using the data from
Sections R157-100 and 157-250 of the citation, assuming the use of 24-gauge
galvanized steel. Retrofit costs (including chase work and cutting the flooring)
were estimated to add S40/linear foot above the values from Means, based on
prior experience (Elder, 1998). A typical cost for insulation of $2/ft2 was
derived from Section 155-651. OA intake ducting is assumed to be insulated,
and exhaust ducting to be uninsulated.
A-12
-------
WORKSHEET 2B
Estimation of Installed Costs for Increased OA:
Dedicated-OA Unit - Retrofit Case
[For this case, it is assumed that a single new rooftop direct-expansion
HVAC unit is installed, dedicated to treating the additional OA increment
being supplied to the building. If there are multiple existing central
HVAC units serving the building and if the OA to each unit is being
increased, this one new dedicated-OA unit would supply the required OA
increment to all of the existing central units, if the building requires such
a substantia/ increase in OA volume that multiple dedicated-OA units
would be needed, the user should repeat the computations in this work-
sheet for each dedicated-OA unit.}
Enter Basic Data
1. Enter the incremental increase in OA intake rate
that is required for the entire building, in
cfm (from Line 6 of Worksheet 1). cfm
2. Enter the incremental increase in OA to each of
the HVAC units serving the building:
[Note: The sum of Lines 2(1) through 2(x)
should sum to the total on Line 1.]
Estimate Cost of Dedicated OA Rooftop Unit
3. Refer to Table A-l at the end of Worksheet 2A.
Locate in Column A the city having the climate
most closely representing the user's.
4. From Column B of Table A 1, enter the required
cooling and heating capacities per 1,000 cfm
OA for the climate of this city.
2(1). Increase in OA to Unit #1
2{2). Increase in OA to Unit #2
2(3). Increase in OA to Unit #3
etc.
cfm
cfm
cfm
4a. Cooling capacity
4b. Heating capacity
tons/1,000 cfm
kW/1,000 cfm
(continued)
A-13
-------
Worksheet 2B (continued)
5. Compute the incremental additional cooling
capacity required to treat the total increase
in OA to the building (Line 1 x Line 4a 1,000). tons
[Note: This is the required cooling capacity of the new dedicated-OA
unit.]
6. Refer to Table A-3 at the end of this worksheet.
Locate in Column A the cooling capacity defined
in Line 5 above.
7. From Column B of Table A-3, enter the total installed
cost per ton of a packaged dedicated-OA unit
having the cooling capacity in Line 5 above. S /ton
8. Compute the total installed cost (excluding heating)
of the dedicated-OA unit having the required
cooling capacity {Line 5 x Line 7). S
9. Compute the incremental additional heating
capacity required to treat the total increase
in OA to the building {Line 1 x Line 4b ^ 1,000], kW
10. Refer to Table A-4 at the end of this worksheet.
Locate in Column A the heating capacity defined
in Line 9 above.
11. From Column B of Table A-4, enter the total installed
cost per kW of installing the required heating
capacity into the dedicated-OA unit, /kW
12. Compute the total installed cost of incorporating
heating capacity into the new dedicated-OA unit
(Line 9 x Line 11). $
13. Compute the total installed cost of the new dedicated-
OA unit (cooling and heating) (Line 8 plus Line 12). $
(continued)
A-14
-------
Worksheet 2B (continued)
Estimate Cost of Retrofitting Additional OA Intake Ductwork Associated with the
Dedicated-OA Unit (if applicable)
[Mote: The following portion of Worksheet 2B applies only in systems
without economizers, where the increased OA being supplied by the
dedicated-OA unit cannot simply be delivered into the pre-existing OA
intake duct. The following assumes that, in systems without econo-
mizers, new ducting is installed to direct the incremental OA from the
dedicated-OA unit to each central HVAC unit, with a main trunk line
from the dedicated-OA unit splitting into branches leading to each HVAC
unit. See text.]
14. Estimate the linear feet of ductwork that would
be required to direct the necessary amount of
OA from the dedicated-OA unit to all of the
HVAC units in the building:
14(T). Length of OA trunk line ft
14(1). Branch from trunk line to Unit #1 ft
14(2). Branch from trunk line to Unit #2 ft
etc.
15. Refer to Table A 2 at the end of Worksheet 2A.
Locate in Column A the incremental OA flow
rates to the entire building (Line 1 above) and
to each HVAC system in the building [Lines 2(1)
through 2(x).J
16. From Column D of Table A-2, enter the installed
cost per linear foot of retrofitted insulated duct,
based on the OA flows in the trunk line and in
the branches to each HVAC unit:
16{T). OA trunk line [flow on Line 1] $/ft
16(1). Unit #1 branch [flow on Line 2(1}] S/ft
16(2). Unit #2 branch [flow on Line 2(2)] $/ft
etc.
17. Compute the installed cost of each element of the
additional OA ductwork:
17(T). OA trunk line [Line 14(T) times Line 16(T)]
17(1). Unit #1 branch [Line 14(1) times Line 16(1)]
17(2). Unit #2 branch [Line 14(2) times Line 16(2)]
etc.
$
$
$
(continued)
A-15
-------
Worksheet 2B (continued}
18. Compute the total installed cost of retrofitting the new
OA supply ductwork [sum of Lines 17(T) through 17(x)] $
Estimate Cost of Increased Exhaust Fan Capacity (if applicable)
[Note: The following portion of Worksheet 2B applies only in those
cases where a central exhaust fan is already present, or must be added
in connection with the OA increase. This will usually be the case only
in systems without economizers. The following assumes that a new
central exhaust fan is added, sized to exhaust an amount of building air
equal to the OA increment. See text.]
19. Refer to Table A-2 at the end of Worksheet 2A.
Locate in Column A the fan flow rate corres-
ponding to the total additional OA flow on
Line 1 above. Interpolate as necessary.
20. From Column B of Table A-2, enter the installed
cost of the new air handler required to exhaust
this volume of building air. $
Estimate Cost of Retrofitting Additional Exhaust Ductwork (if applicable)
[Note: The following portion of Worksheet 2A applies only in systems
without economizers, where the required increase in exhaust air cannot
be achieved without supplementing the central exhaust ducting. The
following assumes that, in systems without economizers, new ducting
is installed to draw exhaust air from one zone near each central HVAC
unit, with the branches from the zones combining into a main trunk line
leading to the exhaust fan. See text.]
21. Estimate the linear feet of ductwork that would
be required to direct exhaust air — equal to the
incremental additional OA in Lines 2(1) through
2(x} - to the new exhaust fan, from zones near
each of the central HVAC units:
21 (T). Length of exhaust air trunk line
21(1). Branch from Unit #1 zone to trunk line
21(2). Branch from Unit #2 zone to trunk line
etc.
ft
ft
ft
(continued)
A-16
-------
Worksheet 2B (continued)
22. Refer to Table A-2 at the end of Worksheet 2A.
Locate in Column A the incrementai OA flow
rates to the entire building (Line 1 above), and
to each HVAC unit [Lines 2(1) through 2(x)].
23. From Column C of Table A-2, enter the installed
cost per linear foot of retrofitted uninsulated
duct, based on the exhaust air flows in the trunk
line and in the branches from the zones near each
HVAC unit:
23{T). Exhaust trunk line [flow on Line 1 ] $/ft
23{1). Branch from Unit #1 zone [flow on Line 2(1)] $/ft
23(2). Branch from Unit #2 zone [flow on Line 2(2)] $/ft
etc.
24. Compute the installed cost of each element of the ductwork:
24(T). Exhaust trunk line I Line 21 (T) times Line 23 (T) | $
24(1). Unit #1 branch [Line 21(1) times Line 23(1)] $
24(2). Unit #2 branch [Line 21 (2) times Line 23(2)] $
etc.
25. Compute the total installed cost of retrofitting the new
exhaust ductwork [sum of Lines 24(T) through 24(x)] $
Estimate Total Installed Cost {new dedicated-OA unit plus, as applicable, added OA
ductwork, exhaust fans, and exhaust ductwork)
26. Compute the total Installed cost of the retrofitted
dedicated-OA system (Line 13 plus, as applicable,
Lines 18, 20, and 25). $
(continued)
A-17
-------
Worksheet;2B (continued)
TABLE A-3
Approximate Total and Incremental Installed Costs
for a New Rooftop Cooling System1
Column A Column B Column C
Cooling
Total
Capacity
Installed Cost
Incremental
Range
per Ton2
Installed Cost
(tons)
(S/ton)
($/ton)
0- 5
1,200
1,000
6 - 20
1,000
1,000
>20
1,000
900
Notes:
1 Includes all materials {with markup), installation labor, and installation
contractor overhead and profit. Systems include cooling capability only, with
no heating coils.
2 Derived from Means (1996). The figure for each capacity range is the average
for the various single-zone, cooling-only rooftop packaged units shown in
Section 157-180-5000 through -6070 of that citation, within the specified
range. Costs include the air handler, cooling coils, condenser/compressor, and
the associated housing. Costs do not include any ductwork.
3 The incremental installed cost is the slope of the cost-vs.-capacity curve, i.e.,
the derivative d($)/d(tons). The total installed cost (Column B) would be used
to compute the cost of a new unit of a given capacity. The incremental
installed cost (Column C) would be used to compare the incremental cost of
one unit versus another, i.e., the incremental cost of installing a unit of greater
capacity in lieu of a unit of lesser capacity within the Column A capacity range.
A-18
-------
Worksheet 2B (concluded)
TABLE A-4
Approximate Total and Incremental Installed Costs
for Heating Capacity in a New Rooftop HVAC System1
Column A
Column B
Column C
Heating
Total
Capacity
Installed Cost
Incremental
Range
per kW2
Installed Cost2,3
(kW)
(S/kW)
(S/kW)
0 - 10
100
75
11-20
65
60
21 - 40
40
40
41 -100
25
25
>100
15
15
Notes:
1 Includes all materials (with markup), installation labor, and installation
contractor overhead and profit. These figures represent the costs associated
with incorporating heating capacity into the cooling units shown in Table A-3.
2 Derived from Means (1996). The figure for each capacity range is the average
for the electric duct heaters shown in Section 1 55-408 0100 through -3300
of that citation, within the specified range.
3 The incremental installed cost is the slope of the cost-vs.-capacity curve, i.e.,
the derivative d($)/d(kW). The total installed cost (Column B) would be used
to compute the cost of incorporating a given heating capacity into a new unit.
The incremental installed cost (Column C) would be used to compare the
incremental cost of one heating element versus another, i.e., the incremental
cost of installing an element of greater capacity in lieu of an element of lesser
capacity within the Column A capacity range.
A-19
-------
WORKSHEET 3A
Estimation of Installed Costs for Increased OA:
Enlarged Central Units - New Construction Case
[In this case, it is assumed that an HVAC system of increased cooling/
heating capacity is installed in the new building in lieu of an originally
planned, lower-capacity system,]
Enter Basic Data
Enter the incremental increase in OA intake rate
that is required for the entire building, beyond
the originally designed rate, in cfm (from Line 6
of Worksheet 1).
Enter the incremental increase in OA to each of
the HVAC units serving the building, beyond the
originally designed OA rate to that unit:
cfm
2(1). Increase in OA to Unit #1
2(2). Increase in OA to Unit #2
2(3). Increase in OA to Unit #3
etc.
cfm
cfm
cfm
[Note: The sum of Lines 2(1) through 2(x)
should sum to the total on Line 1.1
Enter the originally designed cooling and heating
capacities for each of the central HVAC units
in the building.
3(1a). Original cooling capacity - Unit #1
3(1 b). Original heating capacity - Unit #1
tons
kW
3(2a). Original cooling capacity - Unit #2
3(2b). Original heating capacity - Unit #2
tons
kW
3(3a). Original cooling capacity - Unit #3
3(3b). Original heating capacity - Unit #3
etc.
tons
kW
(continued)
A-20
-------
Worksheet 3A (continued)
Estimate Cost of Increased Cooling/Heating Capacity
4. Refer to Table A-1 at the end of Worksheet 2A.
Locate in Column A the city having the climate
most closely representing the user's.
5. From Columns i and C of Table A-1, enter the
required cooling and heating capacity per
1,000 cfm OA for the climate of this city.
5a. Cooling capacity:
5b. Heating capacity:
tons/1,000 cfm
kW/1,000 cfm
6. Compute the incremental additional cooling
capacity required for each of the HVAC units
in the building, to treat the increased OA.
6(1). Unit #1 [Line 2(1) x Line 5a - 1,000]
6(2). Unit #2 [Line 2(2) x Line 5a +¦ 1,000]
6(3). Unit #3 [Line 2(3) x Line 5a - 1,000]
etc.
tons
tons
tons
Refer to Table A-3 at the end or Worksheet 2B.
Locate in Column A of Table A-3 the cooling
capacity ranges for each of the units in the
building.
From Column C in Table A-3, enter the incremental
cost per ton of increased cooling capacity corres-
ponding to the capacity of each unit.
8(1).
8(2).
8(3).
etc.
Incremental cost for Unit #1 [based
on capacity on Line 3(1 a) above].
Incremental cost for Unit #2 [based
on capacity on Line 3(2a)].
Incremental cost for Unit #3 [based
on capacity on Line 3(3a)].
/ton
/ton
/ton
(continued)
A-21
-------
Worksheet 3A (continued)
9. Compute the estimated incremental increase in
the installed cost of each HVAC unit.
9(1). Unit #1 [Line 6(1) x Line 8(1)] $
9(2). Unit #2 [Line 6(2) x Line 8(2)1 $
9(3). Unit #3 [Line 6(3) x Line 8(3)] $
etc.
[Because the costs on Line 8(x) are based on rooftop direct-expansion
units, these estimates will be less accurate for systems involving
chillers.]
10. Determine the total estimated increase in installed
HVAC cost resulting from the incremental
increase in specified cooling capacity [sum of
Lines 9(1) through 9(x)]
11. Compute the incremental additional heating
capacity for each of the HVAC units in the
building, to treat the increased OA.
11(1). Unit #1 [Line 2(1) x Line 5b +
11(2). Unit #2 [Line 2(2) x Line 5b +
11(3). Unit #3 [Line 2(3) x Line 5b h-
etc.
1,000] kW
1,000] kW
1,000] kW
12. Refer to Table A-4 at the end or Worksheet 2B.
Locate in Column A of Table A-4 the cooling
capacity ranges for each of the units in the
building.
13. From Column C in Table A-4, enter the incremental
cost per ton of increased heating capacity corres-
ponding to the capacity of each unit.
13(1). Incremental cost for Unit #1 [based
on capacity on Line 3(1 b) above], $ /kW
13(2). Incremental cost for Unit #2 [based
on capacity on Line 3{2b)], $ /kW
13(3). Incremental cost for Unit #3 [based
on capacity on Line 3(3b)|. $ /kW
etc.
(continued)
A 22
-------
Worksheet 3A (continued)
14. Compute the estimated incremental increase in
the installed cost of each HVAC unit to provide
increased heating capacity.
14(1). Unit #1 [Line 11(1} x Line 13(1)]
14(2). Unit #2 [Line 11(2) x Line 13(2)]
14(3). Unit #3 [Line 11(3} x Line 13(3}]
$
$
$
etc.
[Because the costs on Line 13(x) are based on electric duct heaters,
these estimates will be less accurate for systems involving furnaces.]
15. Determine the total estimated increase in installed
HVAC cost resulting from the incremental
increase in specified heating capacity [sum of
Lines 14(1) through 14(x)] $
16. Enter the total incremental increase in installed
cost resulting from the specification of an HVAC
system having a greater cooling and heating
capacity compared to the original design [Line 10 +
Line 15] $
Estimate Cost of Increased OA Intake Fan Capacity (if applicable)
[Note: The following portion of Worksheet 3A applies only in those
cases where an OA intake fan has been planned for the new building.
The following assumes that a larger OA fan is installed in lieu of the
originally planned fan.]
17. Enter the total incremental increase in OA to the
building (Line 1 above) cfm
18. Enter the original total OA flow to the building
(or to the portion of the building under consider-
ation), prior to the increase (Line 4 of Worksheet 1) cfm
19. Refer to Table A-5 at the end of this worksheet.
Locate in Column A the fan flow rate corres-
ponding to the total original OA flow on
Line 18.
(continued)
A-23
-------
Worksheet 3A (continued)
20. From Column B of Table A-5, enter the incre-
mental installed cost per 1,000 cfm of added
fan capacity, corresponding to the total fan
capacity on Line 18. $/1,000 cfm
21. Compute the incremental cost resulting from the
need to install a larger OA intake fan
(Line 17 x Line 20 - 1,000). $
Estimate Cost of Enlarging the OA intake Ductwork {if applicable)
[Note: The following portion of Worksheet 3A applies only in systems
without economizers, where the required OA increase cannot be
achieved without enlarging the OA intake duct. The following assumes
that OA intake ducting of larger dimensions is installed in lieu of the
originally planned intake ducting.]
22. Enter the linear feet of OA intake ductwork that
has been specified in the original system design,
delivering OA to each of the HVAC units in the
building:
22(T). Length of OA trunk line ft
22(1). Branch from trunk line to Unit #1 ft
22(2). Branch from trunk line to Unit #2 __ ft
etc.
[Note:. The above format assumes that the OA is delivered from an OA
intake fan to a main trunk line, from which branches lead to each unit.]
23. Enter the originally designed OA flow in each
branch of the OA intake ducting:
23(T). Trunk line (flow on Line 18 above) cfm
23(1). Branch to Unit #1 (original OA to Unit #1) cfm
23(2). Branch to Unit #2 cfm
etc.
24. Refer to Table A-5. Locate in Column A the
original total OA flow rates to the entire
building (Line 18) and to each HVAC unit
[Lines 23(1) through 23(x)l.
(continued)
A-24
-------
Worksheet 3A {continued)
25. From Column D of Table A-5, enter the incremental
installed cost per linear foot of insulated
duct per 1,000 cfm increase in flow, corres-
ponding to these original OA flows in the trunk
line and in the branches to each HVAC unit;
25(T). OA trunk line [flow on Line 18] $/ft/1,000 cfm
25(1). Unit #1 branch [flow on Line 23(1)] $/ft/1,000 cfm
25(2). Unit #2 branch [flow on Line 23(2)] $/ft/1,000 cfm
etc.
26. Compute the incremental increase in the installed
cost of each element of the ductwork:
26(T). OA trunk line
[Line 22(T) x Line 25{T) x Line 1 + 1,000] $
26(1). Unit #1 branch
[Line 22(1) x Line 25(1) x Line 2(1) +¦ 1,000] $
26(2). Unit #2 branch
[Lino 22(2) x Line 25(2) x Line 2(2) - 1,000] $
etc.
27. Compute the total incremental installed cost resulting
from the need to install OA supply ductwork having
larger dimensions [sum of Lines 26(T) through 26(x)]. $
Estimate Cost of increased Exhaust Fan Capacity (if applicable)
[Note: The following portion of Worksheet 3A applies only in those
cases where a central exhaust fan has been planned for the new
building. This will usually be the case only in systems without
economizers. The following assumes that a larger central exhaust fan
is installed in lieu of the originally planned fan,]
28. Enter the originally planned capacity of the
building exhaust fan. [It should approximately
equal the original OA intake rate minus the
rates of localized (e.g., bathroom) exhaust fans.] cfm
(continued)
A-25
-------
Worksheet 3A {continued)
29. Refer to Table A-5 at the end of this worksheet.
Locate in Column A the fan flow rate corres-
ponding to the total exhaust flow on Line 28.
30. From Column B of Table A-5, enter the incre-
mental installed cost per 1,000 cfm of fan
capacity corresponding to the total fan
capacity on Line 28. $/1,000 cfm
31. Compute the incremental cost resulting from the
need to install a larger central exhaust fan
(Line 1 x Line 30 -h 1,000). $
Estimate Cost of Enlarging the Exhaust Ductwork (if applicable)
[Note: The following portion of Worksheet 3A applies only in systems
without economizers, where the required increase in exhaust air cannot
be achieved without increasing the dimensions of the central exhaust
ducting. The following assumes that, in new systems without econo-
mizers, central exhaust ducting of larger dimensions is installed in lieu of
the originally planned exhaust ducting.I
32. Enter the linear feet of ductwork that has been
specified in the original system design, removing
air from the zones conditioned by each of the
HVAC units in the building:
32{T). Length of exhaust air trunk line ft
32(1). Branch from Unit #1 zones to trunk line ft
32(2). Branch from Unit #2 zones to trunk line ft
etc.
33. Enter the original design exhaust flow in each
branch of the central exhaust ducting:
33{T). Trunk line flow cfm
33(1). Flow in branch from Unit #1 zones cfm
33(2). Flow in branch from Unit #2 zones cfm
etc.
(continued)
A-26
-------
Worksheet 3A (continued)
34. Refer to Table A 5. Locate in Column A the
original total central exhaust flow rates from
the entire building [Line 33(T)] and from the
zones served by each HVAC unit [Lines 33(1)
through 33(x)].
35. From Column C of Table A-5, enter the incremental
installed cost per linear foot of uninsulated
duct per 1,000 cfm increase in flow, corres-
ponding to these original exhaust air flows in
the trunk line and in the branches from the
zones served by each HVAC unit;
35(T). Exhaust trunk line
[flow on Line 33(T)]
35(1). Branch from Unit #1 zone
[flow on Line 33(11]
35(2). Branch from Unit #2 zone
[flow on Line 33(2)]
etc.
36. Compute the incremental increase in the installed
cost of each element of the ductwork:
36{T). Exhaust trunk line
[Line 32(T) x Line 35{T) x Line 1 + 1,000] $
36(1). Unit #1 branch
[Line 32(1) x Line 35(1) x Line 2(1) + 1,000] $
36(2). Unit #2 branch
[Line 32(2) x Line 35(2) x Line 2.(2) + 1,000] $
etc.
37. Compute the total incremental installed cost
resulting from the need to install central
exhaust ductwork having larger dimensions
[sum of Lines 36(T) through 36(x)J $
$/ft/1,000 cfm
$/ft/1,000 cfm
$/ft/1,000 cfm
(continued)
A-27
-------
Worksheet 3A' (continued)
Estimate Total Installed Cost (enlarged centra! unit plus, as applicable, enlarged OA
and exhaust fans and ductwork)
38, Compute the total incremental installed cost of
the enlarged HVAC system, installed in lieu of
the originally planned system (Line 16 plus,
as applicable, Lines 21, 27, 31, and 37). $
A-28
(continued)
-------
Worksheet 3A (concluded)
TABLE A-5
Incremental Installed Costs of Air Handlers and Ducting in a New Building1
Column A
Total Flow
Rate (cfm)
500 - 1,500
1,501 - 2,500
2,501 - 5,000
>5,000
Column B
Incremental
Installed
Fan Cost2'3
($/1.000 cfm)
1,300
800
700
400
Column C
Incremental
Installed Cost
of Uninsulated Duct3,4
($/linear ft/1,000 cfm)
20
13
9
7
Column D
Incremental
Installed Cost
of Insulated Duct3,4
[$/linear ft/1,000 cfm)
26
17
11
8
Notes:
1 Includes all materials (with markup), installation labor, and installation
contractor overhead and profit.
2 Derived from Means (1996). Each figure is the average incremental installed
cost (per 1,000 cfm) for the various categories of air handlers (centrifugal,
vaneaxial, etc.) within the specified capacity range, from Section 157-290 of
that citation.
3 Incremental costs are the costs for installing a fan or ducting accommodating
a flow 1,000 cfm greater than the originally designed rate, in lieu of the
originally designed fan or ducting. This incremental cost per 1,000 cfm
increase in flow is distinguished from the total cost of the fan or ducting.
4 Derived from Means (1996). The ducts are assumed to have a square cross-
section, and are sized to create 0.1 in. WG pressure loss per 100 linear feet
(ASHRAE, 1997b). The uninsulated ducts were costed using the data from
Sections R157-100 and 157-250 of the citation, assuming the use of 24-gauge
galvanized steel. A typical cost for insulation of $2/ft2 was derived from
Section 155-651. OA intake ducting is assumed to be insulated, and exhaust
ducting to be uninsulated.
A-29
-------
WORKSHEET 3B
Estimation of Installed Costs for Increased OA:
Dedicated-OA Unit - New Construction Case
[For this case, it is assumed that a single rooftop direct-expansion HVAC
unit is installed, dedicated to treating the total OA flow being supplied
to the building. If there are multiple central HVAC units serving the
building, this one dedicated-OA unit would supply the total required OA
to all of the central units, and the original design capacity for each HVAC
unit could be reduced accordingly. If the building requires such a
substantia! OA volume that multiple dedicated-OA units would be
needed, the user should repeat the computations in this worksheet for
each dedicated-OA unit.]
Enter Basic Data
Enter the total OA intake rate that will now be
required for the entire building, after the OA
rate is increased (from Line 5 of Worksheet 1!
cfm
Enter the originally designed OA rate to each of
the HVAC units serving the building:
2(1). Original OA rate to Unit #1
2(2). Original OA rate to Unit #2
2(3). Original OA rate to Unit #3
etc.
cfm
cfm
cfm
Enter the original cooling capacity for each of
the HVAC units serving the building:
3(1). Original cooling capacity of Unit #1
3(2). Original cooling capacity of Unit #2
3(3). Original cooling capacity of Unit #3
etc.
tons
tons
tons
Enter the original heating capacity for each of
the HVAC units serving the building:
4(1). Original heating capacity of Unit #1
4(2). Original heating capacity of Unit #2
4(3), Original heating capacity of Unit #3
etc.
kW
kW
kW
(continued)
A-30
-------
Worksheet 3B {continued}
Estimate Cost of Dedicated-OA Rooftop Unit
5. Refer to Table A-1 at the end of Worksheet 2A,
Locate in Column A the city having the climate
most closely representing the user's.
6. From Column B of Table A-1, enter the required
cooling capacity per 1,000 cfm OA for the
climate of this city. tons/1,000 cfm
7. Compute the total cooling capacity required to
treat the total (increased) OA flow into the
building (Line 1 x Line 6 + 1,000). tons
[Note: This is the required cooling capacity of the dedicated-OA unit.]
8. Refer to Table A-3 at the end of Worksheet 2B.
Locate in Column A the cooling capacity defined
in Line 7 above.
9. From Column B of Table A-3, enter the total
installed cost per ton of a packaged rooftop
unit having the cooling capacity in Line 7 above. $ /ton
10. Compute the total installed cost (excluding heating)
of the dedicated-OA unit having the required
cooling capacity (Line 7 x Line 9). $
11. From Column C of Table A-1, enter the required
heating capacity per 1,000 cfm OA for the
climate of the user's city. kW/1,000 cfm
12. Compute the total heating capacity required to
treat the total (increased) OA flow into the
building (Line 1 x Line 11 1,000). kW
13. Refer to Table A-4 at the end of Worksheet 2B.
Locate in Column A the heating capacity defined
in Line 12 above.
(continued)
A-31
-------
Worksheet 3B (continued)
14. From Column B of Table A-4, enter the total
installed cost per kW of installing the required
heating capacity into the dedicated-OA unit. $ _________ /kW
15. Compute the total installed cost of incorporating
the required heating capacity into the dedicated-
OA unit (Line 13 x Line 14). $
16. Compute the total installed cost of the new dedicated-
OA unit (cooling and heating}, treating the total
(increased) OA flow entering the building
(Line 10 + Line 15). $
Estimate the Cost Savings A chieved by Reducing the Capacities of the Central HVAC
Units (since they will no longer have to condition the OA)
17. Compute the incremental decrease in cooling
capacity that will be experienced by each of
the HVAC units in the building, by virtue of
their no longer having to condition the OA.
17(1).
17(2).
17(3).
etc.
Reduced cooling capacity - Unit #1
[Line 2(1) x Line 6 + 1,000].
Reduced cooling capacity - Unit #2
[Line 2(2) x Line 6 h- 1,000].
Reduced cooling capacity - Unit #3
[Line 2(3) x Line 6 - 1,000].
tons
tons
tons
18. Refer to Table A-3 at the end of Worksheet 2B. in
Column A, locate the cooling capacity for each
HVAC unit. From Column C, enter the incremental
installed savings per ton of decreased cooling
capacity corresponding to the capacity of each unit.
18(1).
18(2).
18(3).
etc.
Incremental cost for Unit #1 [based
on capacity on Line 3(1) above].
Incremental cost for Unit #2 [based
on capacity on Line 3(2) above].
Incremental cost for Unit #3 [based
on capacity on Line 3(3) above].
/ton
/ton
/ton
(continued)
A-32
-------
Worksheet 3B (continued)
19. Compute the estimated incremental savings in
the installed cost of each HVAC unit due to
reduced cooling requirements.
19{1). Unit #1 [Line 17(1) x Line 18(1)]. S
19(2). Unit #2 [Line 17(2) x Line 18(2)]. $
19(3). Unit #3 [Line 17(3) x Line 18(3)). $
etc.
[Because the costs on Line 18(x) are based on rooftop direct-expansion
units, these estimates will be less accurate for systems involving
chillers.]
20. Determine the total estimated savings in installed
HVAC cost resulting from the incremental
reduction in specified cooling capacity [sum of
Lines 19(1) through 19(x)]. $
21. Compute the incremental decrease in heating
capacity that will be experienced by each of
the HVAC units in the building, by virtue of
their no longer having to condition the OA.
21(1). Reduced heating capacity - Unit #1
[Line 2(1) x Line 11 + 1,000]. kW
21(2). Reduced cooling capacity - Unit #2
[Line 2(2) x Line 11 - 1,000], kW
21 (3). Reduced cooling capacity - Unit #3
[Line 2(3) x Line 11 - 1,000]. kW
etc.
22. Refer to Table A-4 at the end of Worksheet 2B. In
Column A, locate the heating capacity for each
HVAC unit. From Column C, enter the incremental
installed savings per kW of decreased heating
capacity corresponding to the capacity of each unit.
22(1). Incremental cost for Unit #1 [based
on capacity on Line 4(1) above]. $ /kW
22(2). Incremental cost for Unit #2 [based
on capacity on Line 4(2) above], $ /kW
22(3). Incremental cost for Unit #3 [based
on capacity on Line 4(3) above], $ /kW
etc.
(continued)
A-33
-------
Worksheet 3B {continued)
23. Compute the estimated incremental savings in
the installed cost of each HVAC unit due to
reduced heating requirements.
23(1). Unit #1 [Line 21(1) x Line 22(1)]. $
23(2). Unit #2 [Line 21 (2) x Line 22(2)]. $
23(3). Unit #3 [Line 21(3) x Line 22(3)]. $
etc.
[Because the costs on Line 22(x) are based on electric duct heaters,
these estimates will be less accurate for systems involving furnaces.]
24. Determine the total estimated savings in installed
HVAC cost resulting from the incremental
reduction in specified heating capacity [sum of
Lines 23(1) through 23(x)|. $
25. Enter the total incremental savings in installed
cost resulting from reducing the cooling and heating
requirements of the original HVAC units [Line 20 +
Line 24]. $
Estimate Cost Savings from Elimination of OA Intake Fan (if applicable)
[Note: The following portion of Worksheet 3B applies only in those
cases where an OA intake fan had originally been planned for the new
building. The following assumes that the fan can now be eliminated,
being replaced by the air handler associated with the dedicated-OA unit.]
26. Enter the estimated installed cost for the OA
intake fan, from the estimates developed by
the designer of the mechanical system (if
available). $
27. If the designer's estimate is not available,
refer to Table A 2 at the end of Worksheet 2A.
Locate in Column A the flow rate corresponding
to the original total OA intake rate to the
building (Line 4 of Worksheet 1).
(continued)
A-34
-------
Worksheet 3B (continued)
28. From Column B of Table A-2, enter the installed
cost of the fan having this capacity. S
29. Enter the installed cost of the original OA intake
fan {from either Line 26 or Line 28, as applicable). $
Estimate Cost of Enlarging the OA intake Ductwork (if applicable}
[Note: The following portion of Worksheet 3B applies only in systems
without economizers, where the increased volume of OA being supplied
by the dedicated-OA unit cannot simpiy be delivered into the originally
designed OA intake duct. The following assumes that, in systems
without economizers, the originally designed intake ducting retains its
original configuration (presumed to be a main trunk line splitting into
branches that lead to each HVAC unit), but that ducting of enlarged
dimensions is installed in lieu of the originally designed ducting, as
necessary to handle the greater OA flow.]
30. Enter the linear feet of OA intake ductwork that
has been specified in the original system design,
delivering OA to each of the HVAC units in the
building:
30(T). Length of OA trunk line ft
30(1). Branch from trunk line to Unit #1 ft
30(2). Branch from trunk line to Unit #2 ft
etc.
31. Enter the originally designed OA flow in each
branch of the OA intake ducting:
31 (T). Trunk line (Line 4 of Worksheet 1)
31(1). Branch to Unit #1 [from Line 2(1)]
31(2). Branch to Unit #2 [from Line 2(2)]
etc.
32. Enter the incremental increase in OA flow that must
be accommodated in each branch of the ducting.
32(T). OA increase to bldg. (Line 6, Worksheet 1). cfm
32(1). Increase in OA to Unit #1 cfm
32(2). Increase in OA to Unit #2 cfm
etc.
(continued)
A-35
cfm
cfm
cfm
-------
Worksheet 3B {continued)
33. Refer to Table A-5 at the end of Worksheet 3A.
Locate in Column A the original total OA flow
rates to the entire building [Line 31 (T)] and to
each HVAC unit [Lines 31(1} through 31 (x)].
34. From Column D of Table A-5, enter the incremental
installed cost per linear foot of insulated
duct per 1,000 cfm increase in flow, corres-
ponding to these original OA flows in the trunk
line and in the branches to each HVAC unit:
34(T). OA trunk line [flow on Line 31 (T)l $/ft/1,000 cfm
34(1). Unit #1 branch [flow on Line 31(1)] $/ft/'1,000 cfm
34(2). Unit #2 branch [flow on Line 31(2)] $ /ft/1,000 cfm
etc.
35. Compute the incremental increase in the installed
cost of each element of the ductwork:
35(T). OA trunk line
[Line 30(T) x Line 34(T) x Line 32(T)
35(1). Unit #1 branch
[Line 30(1) x Line 34(1) x Line 32(1)
35(2). Unit #2 branch
[Line 30(2) x Line 34(2) x Line 32(2)
etc.
36. Compute the total incremental installed cost resulting
from the need to install OA supply ductwork having
larger dimensions [sum of Lines 35(T) through 35(x)]. $
- 1,000] $
- 1,000] $
- 1,000] $
Estimate Cost of Increased Exhaust Fan Capacity (if applicable)
[Note: The following portion of Worksheet 3B applies only in those
cases where a central exhaust fan had originally been planned for the
new building. This will usually be the case only in systems without
economizers. The following assumes that a larger central exhaust fan
is installed in lieu of the originally designed fan.]
(continued)
A-36
-------
Worksheet 3B (continued}
37, Enter the originally planned capacity of the
building exhaust fan. [it should approximately
equal the original OA intake rate minus the
rates of localized (e.g., bathroom) exhaust fans.] cfm
38. Refer to Table A-5 at the end of Worksheet 3A
Locate in Column A the fan flow rate corres-
ponding to the total exhaust flow on Line 37.
39. From Column B of Table A-5, enter the incre-
mental installed cost per 1,000 cfm of fan
capacity corresponding to the total fan
capacity on Line 37. $/1,000 cfm
40. Compute the incremental cost resulting from the
need to install a larger central exhaust fan
[Line 32(T) x Line 39 + 1,000]. $
Estimate Cost of Enlarging the Exhaust Ductwork (if applicable)
[Note; The following portion of Worksheet 3B applies only in systems
without economizers, where the required increase in exhaust air cannot
be achieved without increasing the dimensions of the central exhaust
ducting. The following assumes that, in new systems without econo-
mizers, the exhaust ducting retains its original design configuration, but
that ducting of enlarged dimensions is installed in lieu of the originally
designed ducting, as necessary to handle the greater exhaust flow.]
41. Enter the linear feet of ductwork that has been
specified in the original system design, removing
air from the zones conditioned by each of the
HVAC units in the building.
41 (T). Length of exhaust air trunk line ¦ ft
41(1). Branch from Unit #1 zones to trunk line ft
41(2). Branch from Unit #2 zones to trunk line ft
etc.
(continued)
A-37
-------
Worksheet 3B (continued)
42. Enter the original design exhaust flow in each
branch of the central exhaust ducting:
42(1). Trunk line flow cfm
42(1). Flow in branch from Unit #1 zones cfm
42(2). Flow in branch from Unit #2 zones cfm
etc.
43. Refer to Table A-5 at the end of Worksheet 3A.
Locate in Column A the original total central
exhaust flow rates from the entire building
[Line 42(T}] and from the zones served by each
HVAC unit [Lines 42(1) through 42(x)].
44. From Column C of Table A-5, enter the incremental
installed cost per linear foot of uninsulated
duct per 1,000 cfm increase in flow, corres-
ponding to these original exhaust air flows in
the trunk line and in the branches from the
zones served by each HVAC unit:
44(T). Exhaust trunk line
[flow on Line 42(T)]
44(1). Branch from Unit #1 zone
[flow on Line 42(1)]
44(2). Branch from Unit #2 zone
[flow on Line 42(2)]
etc,
45. Compute the incremental increase in the installed
cost of each element of the ductwork:
45{T). Exhaust trunk line
[Line 41 (T) x Line 44(T) x Line 32(T)
45(1). Unit #1 branch
[Line 41(1) x Line 44(1) x Line 32(1)
45(2). Unit #2 branch
[Line 41(2) x Line 44(2) x Line 32(2)
etc.
(continued)
$/ft/1,000 cfm
$/ft/1,000 cfm
$/ft/1,000 cfm
- 1,000] $
+ 1,000] $
- 1,000] $
A-38
-------
Worksheet 3B (concluded)
46. Compute the total incremental installed cost
resulting from the need to install central
exhaust ductwork having larger dimensions
[sum of Lines 45{T) through 45{x}] S
Estimate Total Installed Cost {new dedicated OA unit plus, as applicable, added OA
ductwork, exhaust fans, and exhaust ductwork)
47. Compute the total Incremental installed cost of
the dedicated-OA system, installed in lieu of
the originally designed system (Line 16 minus
Line 25; minus, if applicable, Line 29; plus,
as applicable, Lines 36, 40, and 46). $
A-39
-------
WORKSHEET 4
Estimation of Annual Operating Costs for Increased OA
Enter Basic Data
1. Enter the incremental increase in OA intake rate
that is required for the entire building, beyond
the originally designed rate, in cfm (from Line 6
of Worksheet 1). cfm
2. Enter the overall Energy Efficiency Ratio (EER) for
the cooling system in the building, i.e., the
Btu/h of cooling output per W of electric input.
(As a default, assume EER = 10 Btu/h/W.) Btu/h/W
[Note: If the compressor/condenser of the cooling system is driven by
a source other than an electric motor (e.g., by a gas or diesel engine, or
a gas or steam turbine) — or if an absorption chiller is used — the cooling
system efficiency should be expressed in the appropriate units, of Btu/hr
cooling output per unit energy input.]
3. Enter the overall efficiency of the heating system
in the building, i.e., the Btu/h of heating output
per Btu/h of fuel or electricity input. (As a
default, assume and efficiency of 1.0 for electri
city and 0.7 for gas or oil.) Btu/h per Btu/h
4. Enter the unit costs of the applicable utilities
used as energy sources in the building:
4a. Cost of electricity, if applicable
(Default: $0.08/kWh). $/kWh
4b, Cost of natural gas, if applicable
(Default: $0.60/therm). $/therm
4c. Cost of fuel oil, if applicable
(Default: $1.00/gal). $/gal
[Note: Utility costs will sometimes not be a simple function of the
amount used. For example, costs of electricity will commonly include a
demand charge based on peak kW usage, in addition to the unit cost per
kWh. For this simple estimation, the user should utilize an average cost
per unit consumed.]
(continued)
A-40
-------
Worksheet 4 (continued)
Enter the average number of hours per day, and
days per week, that OA is being supplied to the
building.
5a. Hours per day hours/day
5b. Days per week days/week
Estimate Annua! Cost of Cooling and Heating the incremental increased OA
6. Refer to Table A-6 at the end of this worksheet.
Locate in Column A the city having the climate
closest to that of the user.
7. From Column B of Table A-6, enter the value for
the annual cooling energy that is required by
the air stream, per incremental cfm of OA. Btu/yr/cfm
8. The annual cooling energy from Table A-6 is based
on operation at 13 hours/day, 5 days/week. If
the user's system operates on a significantly
different cycle, correct the figure on Line 7:
(Line 7) x (Line 5a -f- 13) x (Line 5b -s- 5} Btu/yr/cfm
9. Calculate the total energy input required to the
cooling system, considering system efficiency;
(Line 1) x (Line 8) - (Line 2} +¦ 1,000 W/kW kWh/yr
[Note: The form of this equation assumes that the cooling system is
driven by a compressor having an electric motor, and that Line 9 thus
has the units of kWh/yr. If this is not the case, modify the units of
Line 2 (and thus of Line 9) accordingly.]
10. Calculate the annual energy cost associated cooling
the incremental additional OA (Line 9 x Line 4a). $ _____
11. From Column C of Table A-6, enter the value for
the annual heating energy that is required by
the air stream, per incremental cfm of OA. Btu/yr/cfm
(continued)
A-41
-------
Worksheet 4 {continued}
12. Correct the annual heating energy on Line 11 if
the user's system operates on a significantly
different cycle from 13 hr/day, 5 days/wk:
{Line 11) x (Line 5a + 13) x (Line 5b -s- 5) Btu/yr/cfm
13. Calculate the total energy input required to the
heating system, considering system efficiency:
(Line 1) x (Line 12} -f- (Line 3) Btu/yr
14. Compute the amount of input energy to the system
that is required to provide the Btu's indicated
on Line 13:
14a. Line 13 x (1 kWh/3413 Btu)
(for electric heat)
14b. Line 13 x (1 therm/100,000 Btu)
(for gas heat)
14c. Line 13 x (1 gal./140,000 Btu)
(for fuel oil heat)
15. Calculate the annual energy cost associated heating
the incremental additional OA (Line 14a x Line 4a
for electric; Line 14b x Line 4b for gas; Line 14c
x Line 4c for oil). $ /yr
16. Calculate the total annual energy cost associated
with cooling and heating the incremental addi-
tional OA (Line 10 plus Line 15). $ _____ /V
Estimate Incremental Annual Energy Cost for New or Enlarged OA Intake Fans (if
applicable)
17. Enter the flow rate for any new OA intake fan,
or the incremental increase in flow through any
enlarged intake fan, if applicable. cfm
(continued)
_ kWh/yr
therms/yr
gal./yr
A-42
-------
Worksheet 4 (continued)
Note; Obtain this value on Line 17 from:
Worksheet 2A, Line 14; or
Worksheet 2B, Line 1; or
Worksheet 3A, Line 17; or
Worksheet 3B, Line 32(T).
In the cases of the dedicated-OA units (Worksheets 2B and 3B), the "OA intake
fan" addressed here is the air handler associated with the new dedicated-OA
unit.
18. Enter the actual linear feet of ducting through
which the OA must flow. ft
Note: Obtain this value from:
Worksheet 2A, Line 17(T) plus the average
of Lines 17(1) through 17(x); or
Worksheet 2B, Line 14C0 plus the average
of Lines 14(1) through 14(x); or
Worksheet 3A, Line 22{T) plus the average
of Lines 22(1) through 22{x); or
Worksheet 3B, Line 30(T) plus the average
of Lines 30(1) through 30(x).
19. Enter the additional equivalent linear feet of
intake ducting, beyond the actual linear feet,
created by elbows and other fittings in the ducting:
Average number of fittings between the intake
fan and the typical HVAC unit in the building
( ) times 20 equivalent feet per
fitting. ft
20. Compute the total equivalent linear feet of intake
ducting (Line 18 + Line 19). ft
21. Compute the total static pressure increase required
across the OA intake fan:
21a. Due to duct loss (Line 20 x 0.1 in. WG/ft). in. WG
21b. Due to HVAC coils and air filter (applies
to dedicated-OA cases only) -- enter
design value, if available.
(Default: 0.5 in. WG) in. WG
21c. Total (Line 21a + Line 21b). in. WG
(continued)
A-43
-------
Worksheet 4 {continued)
22. Enter the overall fan energy efficiency.
(Defaults: 0.50 for fans < 1,000 cfm;
0.65 for fans > 1,000 cfm) hp out/hp in
23. Compute the required power input to the fan, to
provide the output power required raise the
incremental OA flow on Line 17 by the pressure
increment on Line 21;
(Line 17) x (Line 21) x [5.19 (lb/ft2)/(in. WG)]
x [(1 hp)/(33,000 ft-lb/min)] + (Line 22) hp in
24. Enter the number of hours that the fan will be
operating per year.
(Default: 3,276 hr/yr, for 13 hr/day, 5 day/wk
excluding holidays.) hr/yr
25. Compute the annual energy consumption by any
new OA intake fan, or by the incremental increase
in flow through any enlarged intake fan.
(Line 23) x (0.746 kW/hp) x (Line 24) kWh/yr
[Note: This calculation assumes that the OA intake fan will be operating at full
load whenever it is operating.]
26. Calculate the incremental annual energy cost
associated with the operation of this new or
incrementally enlarged OA intake fan
(Line 25) x (Line 4a) $ /yr
Estimate Incremental Annual Energy Cost for New or Enlarged Exhaust Fans (if
applicable)
27. Enter the flow rate for any new exhaust fan, or
the incremental increase in flow through any
enlarged exhaust fan, if applicable. cfm
Note: Obtain this value from:
Worksheet 2A, Line 1, or
Worksheet 2B, Line 1; or
Worksheet 3A, Line 1; or
Worksheet 3B, Line 32(T).
(continued)
A-44
-------
Worksheet 4 (continued)
28. Enter the actual linear feet of ducting through
which the exhaust air must flow. ft
Note: Obtain this value from;
Worksheet 2A, Line 24{T) plus the average
of Lines 24(1) through 24 1,000 cfm) hp out/hp in
33. Compute the required power input to the fan, to
provide the output power required raise the
exhaust flow on Line 27 by the pressure
increment on Line 31:
(Line 27) x (Line 31) x [5.19 (lb/ft2)/(in. WG)]
x [(1 hp)/(33,000 ft-lb/min)] + (Line 32) hp in
(continued)
A-45
-------
Worksheet 4 (continued)
34. Enter the number of hours that the exhaust fan
will be operating per year.
(Default: 3,276 hr/yr, for 13 hr/day, 5 day/wk
excluding holidays.) hr/yr
35. Compute the annual energy consumption by any
new exhaust fan, or by the incremental increase
in flow through any enlarged exhaust fan.
(Line 33) x (0.746 kW/hp) x (Line 34) kWh/yr
[Note: This calculation assumes that the exhaust fan will be operating at full
load whenever it is operating.]
36. Calculate the Incremental annual energy cost
associated with the operation of this new or
incrementally enlarged exhaust fan
(Line 35) x (Line 4a) $ /yr
Estimate Total Incremental Annual Operating Cost (increased cooling and heating
energy plus, as applicable, increased energy for OA and exhaust fans)
37. Compute the total incremental annual operating
cost associated with the increase in OA
ventilation rate (Line 16 plus, as applicable,
Lines 26 and 36). $ /yr
A-46
(continued)
-------
Worksheet 4 (concluded)
TABLE A-6
Incremental Annual Cooling and Heating Energy Requirements
per Unit Increase in OA Ventilation Rate1,2
(by Geographical Location)
Column A
Citv
Column B
Incremental Additional Annua!
Cooling Energy Required per
Incremental Increase in
Outdoor Air Intake Rate
(Btu/vr per incremental cfm)
Column C
incremental Additional Annual
Heating Energy Required per
Incremental Increase in
Outdoor Air Intake Rate
?Btu/vr per incremental cfm)
Chicago, IL
Miami, FL
Minneapolis, MN
Northern Virginia
Raleigh, NC
Seattle, WA
13,000
67,000
13,000
20,000
26,000
3,000
41,000
200
63,000
25,000
16,000
28,000
Notes:
Computed using the DOE-2 computer model for simulating building energy
consumption (York, 1981), assuming a small office building for which an input
file was already available (Henschel, 1997), The figure for each geographical
location is an average for alternative variable-volume and constant-volume
mechanical systems, and for OA flow rates over the range of 5 to 60 cfm/
person at an occupant density of 7 persons per 1,000 ft2. The modeling
assumed that OA was supplied to the building 13 hours/day (6 am to 7 pm) on
weekdays only (excluding holidays).
Addresses the energy that must be supplied to the incremental outdoor air.
The energy that must be supplied as input to the cooling and heating equipment
(in the form of fuel or electricity), to provide this cooling/heating of the
incremental OA, will depend on the efficiency of the equipment.
A-47
-------
WORKSHEET 5
Estimation of Annual Maintenance Costs for Increased OA
1. Enter the number of new OA intake fans assumed
in Worksheets 2A or 3B, if applicable, fans
[Note: Intake fans that have been enlarged, as assumed in Worksheet 3A,
should not be included here; only fans that have been added are assumed to
add to maintenance costs. Only Worksheet 2A assumes the addition of new
intake fans; in Worksheet 3B, any previously designed intake fans would be
deleted, in which case the number entered here would be negative. The
formats of Worksheets 2A and 3B assume that only a single intake fan is being
added (or deleted}; in larger buildings, this number might be greater than one.
As noted in those prior tables, there will often not be any intake fan, in which
case the number entered here would be zero.]
2. Enter the number of new central exhaust fans
assumed in Worksheets 2A or 2B, if applicable. fans
[Note: Exhaust fans that have been enlarged, as assumed in Worksheets 3A
and 3B, should not be included here. As noted in the prior tables, central
exhaust fans will usually be required only in systems without economizers.]
3. Enter the total number of new fans (sum of
Line 1 plus Line 2). fans
4. Enter the estimated additional maintenance labor
hours per year per new fan.
(Default: 5 hours/year/fan} hr/yr/fan
5. Enter the estimated hourly labor rates for fan
maintenance personnel.
(Default: 535/hour, including overhead) $ /hr
6. Compute the annual maintenance cost increase
for the additional fans
(Line 3 x Line 4 x Line 5). $ /yr
(continued)
A-48
-------
Worksheet 5 (concluded)
7. Enter the number of new dedicated-OA units
assumed in Worksheets 2B or 3B, if applicable. units
[Note: HVAC units that have been enlarged, as assumed in Worksheets 2A and
3A, are not be included here; only units that have been added are assumed to
add to maintenance costs. The formats of Worksheets 2B and 3B assume that
only a single dedicated-OA unit is being added; in larger buildings, this number
might be greater than one.]
8. Enter the estimated additional maintenance labor
hours per year per new dedicated-OA unit.
(Default: 20 hours/year/unit) hr/yr/unit
9. Enter the estimated hourly labor rates for HVAC
maintenance personnel.
(Default: $35/hour, including overhead) $ /hr
10. Compute the annual maintenance cost increase
for the new dedicated-OA units
(Line 7 x Line 8 x Line 9). $ /yr
Estimate Total Annual Maintenance Costs (for new OA and exhaust fans and
dedicated-OA units, as applicable)
11. Compute the total incremental annual mainten-
ance cost associated with the increase in OA
ventilation rate (Line 6 plus Line 10, as
applicable). $
A 49
-------
WORKSHEET 6
Estimation of Total Annualized Costs for Increased OA
Enter Results from Other Worksheets
1. Enter the total installed cost of the equipment
required for the increase in ventilation rate. $ _______
Note: Obtain this value from:
Worksheet 2A, Line 29; or
Worksheet 2B, Line 26; or
Worksheet 3A, Line 38; or
Worksheet 3B, Line 47.
2. Enter the total incremental annual operating cost
associated with the increase in ventilation rate
(Worksheet 4, Line 37). $ /yr
3. Enter the total incremental annual maintenance
cost associated with the increase in ventilation
rate {Worksheet 5, Line 11). $ /yr
Determine the Capital Recovery Factor (CRFI
[Note: The CRF is the fraction of the initial installed cost that must be
amortized each year if, after n years (i.e., after n equal "payments"), the
initial cost is to be recovered with an i percent annual interest rate
charged on the unpaid balance.]
4. Enter the equipment lifetime, n, that will be
assumed for these calculations (commonly
10 to 20 years). yr
5. Enter the annual interest rate, i, that will be
assumed for these calculations. %
6. From these values for n and i, identify the
appropriate value of the CRF from Table A-7
at the end of this worksheet.
(continued)
A-50
-------
Worksheet 6 (continued)
Compute the Total Annualized Cost for Increased Ventilation
7. Compute the average annual capital charge
(Line 1 x Line 6),
8. Compute the annual operating and maintenance
(O&M) costs associated with the increase in
ventilation rate (Line 2 + Line 3),
9. Compute the total annualized cost associated
with the increase in OA ventilation rate
(Line 7 plus Line 8).
A-51
-------
Worksheet 6 {concluded)
TABLE A-7
Capital Recovery Factors1
Number of Years, n,
Over Which the Compound Interest Rate, i, to Be Charged
Initial Investment on the Unpaid Balance
to Be Amortized
5%
6%
7%
8%
10%
1
1.0500
1.0600
1.0700
1.0800
1.1000
2
0.5378
0.5454
0.5531
0.5608
0.5762
3
0.3672
0.3741
0.3811
0.3880
0.4021
4
0.2820
0.2886
0.2952
0.3019
0.3155
5
0.2310
0.2374
0.2439
0.2505
0.2638
6
0.1970
0.2034
0.2098
0.2163
0.2296
7
0.1728
0.1791
0.1856
0.1921
0.2154
8
0.1547
0.1610
0.1648
0.1740
0.1874
9
0.1407
0.1470
0.1535
0.1601
0.1736
10
0.1295
0.1359
0.1424
0.1490
0.1628
11
0.1204
0.1268
0.1334
0.1401
0.1540
12
0.1128
0.1193
0.1259
0.1327
0.1468
13
0.1065
0.1130
0.1196
0.1265
0.1408
14
0.1010
0.1076
0.1143
0.1213
0.1358
15
0.0963
0.1030
0.1098
0.1168
0.1315
16
0.0923
0.0990
0.1059
0.1130
0.1278
17
0.0887
0.0954
0.1024
0.1096
0.1247
18
0.0856
0.0924
0.0994
0.1067
0.1219
19
0.0828
0.0896
0.0968
0.1041
0.1196
20
0.0802
0.0872
0.0944
0.1018
0.1175
Note:
1 The figures presented in the table above are the values of the Capital Recovery
Factor (CRF), computed from the specified values of n and i using the equation:
CRF = [i(1 + i)n] / 1(1 +i)n - 1].
A-52
-------
WORKSHEET 7
Estimation of Air Cleaner Efficiency Required
to Achieve Desired Reduction in Contaminant Concentration
Using a Central Indoor Air Cleaner
Enter Basic Data
1. Enter the current average indoor concentration,
C1No, of the contaminant of concern in the
building (or in that portion of the building
served by a given air handler), with no air
cleaner in place. mg/m3
2. Enter the average concentration, C,Nr to which
the level in Line 1 above should be reduced
after the air cleaner is installed, mg/m3
3. Enter the average concentration, C0A, of the
contaminant in the outdoor air, mg/m3
4. Enter the volumetric flow of outdoor air, Q0A,
into the building (or into that portion of the
building being addressed here). cfm
5. Enter the total volume of air, Qs, being supplied
to the space within the building, including the
outdoor air Q0A plus the recirculating air, GR. cfm
6. Compute the rate, QR, at which building air is
being recirculated (Line 5 minus Line 4). cfm
7. Quantify the rate, S, at which the contaminant
of concern is being generated by sources inside
the building, in Ib/min. Ib/min
(continued)
A-53
-------
Calculate the Required Air Cleaner Efficiency
8. Refer to Figure A-1 at the end of this worksheet.
Select which alternative location in that figure
is to be used for the air cleaner.
9. Refer to Table A-8 at the end of this worksheet.
For the selected air cleaner location, identify in
the table the equation that defines the required
air cleaner efficiency, q, as a function of ClN,
Coa' ^oA< ®rsd S.
10. Compute the required air cleaner efficiency, /?,
using the appropriate equation selected on
Line 9, using the parameters defined on Lines
2, 3, 4, 6, and 7.
A-54
(continued)
-------
Worksheet 7 (continued)
Outdoor
Air,
OA' OA
Exhaust
Qoa 'C|
Recirculating
Air
Location
#2
Location
#3
Possible Air
Cleaner Locations
Supply
Air
HVAC
System
Location
Contains source (S)
ZONE
Key:
Q = air flow rate (cfm)
C = contaminant concentration (mg/m3)
[Note: 1 mg/m3 = 6.2 x 10 ° lb/ft3]
S - source term for contaminant generated indoors (Ib/rnin)
Subscripts:
OA = outdoor air
S = supply air to zone
R = recirculating air
IN = desired indoor concentration with air cleaner in place
Figure A-1. Alternative locations for central indoor air cleaners within the HVAC system,
(continued!
A-55
-------
TABLE A-8
Equations 1-2 to Compute Air Cleaner Efficiency, r\,
Required to Achieve Desired Indoor Concentration, CN
Air cleaner Location #13:
Qoa(^oa " ^ ^
n
QoA^oaK
Air cleaner Location #2:
Qoa(Coa^Cin)K + S
0
cink
Air cleaner Location #3:
Qqa(Coa - cIN)K + s
QoaCoaK - QrCinK
Air cleaner locations, and terms in equations, as defined in Figure A-1,
K = concentration conversion factor = 6.2 x 10'8 !lb/ft3)/(mg/m3).
Equations derived based upon a mass balance around the zone. See text.
Equation for Location #1 applies only when outdoor air is a meaningful
contributor to indoor concentrations.
A 56
-------
WORKSHEET 8
Estimation of Installed Costs for Central Indoor Air Cleaners
Enter Basic Data
1. Enter the required per-pass removal efficiency
for the air cleaner (from Line 10 of Worksheet
7).
2. Enter the total flow through the air cleaner. cfm
Note: Obtain this value from the following lines
on Worksheet 7:
Line 4 (Q0A) for Location #1; or
Line 6 (QR) for Location #2; or
Line 5 (Qs) for Location #3.
Estimate Installed Cost for Particulate Air Cleaners
[Note: The following portion of Worksheet 8 applies only when the air
cleaner is being installed to remove particulate matter. It is assumed
that the HVAC system already includes basic particulate air cleaners for
protecting the fan and coils and for controlling coarse particles, and that
any air cleaner being costed here is to remove greater amounts of finer
particulate.]
3. Refer to Table A-9 at the end of this worksheet.
Considering the air cleaner efficiency defined
in Line 1 above and the size range of the
particulate to be removed, select an air cleaner
from the table that will provide the desired
efficiency.
4. Estimate the installed cost per unit air flow for
a particulate air cleaner of the type selected
in Line 3 above.
[Note: This would include the installed cost of the cleaning device itself
plus any housing required to mount the device in the ductwork, plus any
increase in the horsepower of the central fan drive motor necessary to
handle the increase in pressure drop created by the air cleaner.]
(continued)
A-57
-------
Worksheet 8 {continued)
4a. Obtain a quote from a vendor,
including installation. S /1,000 cfm
or
4b. Refer to Table A-10 at the end of
this worksheet. Identify in
Column A the air cleaner closest
to the one selected in Line 3. From
Column B of the table, enter the
unit installed cost of this cleaner. $ /1,000 cfm
Compute the estimated installed cost for the
particulate air cleaner (Line 2 x Line 4a or 4b
+ 1,000). $
If there are multiple HVAC units in the building
requiring an air cleaner, repeat the procedure
on Lines 3 through 5 for each unit.
Estimate Installed Cost of Air Cleaners for Gaseous Contaminants
INote; The following portion of Worksheet 8 applies only when the air
cleaner is being installed to remove gaseous contaminants.]
7. Estimate the installed cost per unit air flow for
a gaseous contaminant air cleaner, suitable for
removing the contaminant(s) of concern.
7a. Obtain a quote from a vendor,
including installation. $ /1,000 cfm
or
7b. Enter $680/1,000 cfm $ /1,000 cfm
[Note: The default value of $680/1,000 cfm consists of the following
components: 1) $660/1,000 cfm for an installed granular activated carbon
filter, derived independently from vendor quotes (Henschel, 1998) and also
obtained from Section 157-401-0050 of Means (1996); and 2) $20/1,000 cfm
as the incremental cost for an enlarged motor to drive the central air handler,
to accommodate an assumed 1 in. WG pressure loss across the air cleaner,
derived from Section 1 63-140 of Means (1996).I The installed cost of
increased cooling capacity, to remove the additional heat generated by the
larger fan motor, is neglected. Complications in installation, such as
inadequate space to accommodate the new air cleaner within the
existing mechanical room, are not included in these costs.
(continued)
A-58
-------
Worksheet 8 (continued)
Compute the estimated installed cost for the
gaseous air cleaner (Line 2 x Line 7a or 7b
+ 1,000).
If there are multiple HVAC units in the building
requiring an air cleaner, repeat the procedure
on Lines 3 through 5 for each unit.
A-59
-------
Worksheet
anue
TABLE A-9
Approximate Fractional Efficiency of
Various In-Duct Particulate Indoor Air Cleaners1'2
Type of Air Cleaner
Air Cleaner Efficiency in Removing Particles
Having the Following Diameters3
0.01 um 0.1 um 1.0 um
Media Air Cleaners
Pleated panel cartridge filter; 90 20 40
6 in, deep; paper media;
ASHRAE 654
Pleated panel cartridge filter; 90-95 + 40-50 80-90
6 in. deep; paper media;
ASHRAE 85
Pleated panel cartridge filter; 95 + 50-60 95
6 in. deep; paper media;
ASHRAE 95
Pocket filter; 22 in. deep; 95+ 70-95+ 90-95 +
non-woven fiber media;
ASHRAE 95
High-efficiency particulate air 99.97% efficient on particles of 0.3 pm
(HEPA) pleated panel filter;
12 in. deep; glass fiber media;
DOP 99.975
Electronic Air Cleaners
Electrostatic precipitator;
2 stages
- 90-180 ft/min face velocity 40-70 80-90 80-90
- 350 ft/min face velocity 40 60 70
(continued)
A-60
-------
Worksheet 8 (continued)
TABLE A-9 (concluded)
Approximate Fractional Efficiency of
Various In-Duct Particulate Indoor Air Cleaners
Notes:
1 The particulate air cleaners addressed here are designed for mounting in the
HVAC ductwork, as illustrated in Figure A-1, as distinguished from self-
contained or in-room stand-alone units. Only air cleaners having an ASHRAE
dust spot average efficiency of 65% or greater (ASHRAE, 1992) are addressed,
assuming that less efficient filters to control coarse particles are already
incorporated into the system.
2 The fractional efficiency data presented in this table (excluding the value for the
HEPA filter) were obtained from Hanley et al. (1994).
3 Fractional efficiencies on the various particle sizes vary, to greater or lesser
extents, with air velocity through the air cleaner and, for media air cleaners,
with filter loading. The value shown here represents a typical value. The air
cleaners are consistently least efficient for particles around 0.1 to 0.3 //m;
efficiencies improve for smaller as well as larger particles.
4 The ASHRAE specification (e.g., ASHRAE 65) refers to the dust spot average
efficiency determined using the procedure for testing air cleaning devices
defined in ASHRAE Standard 52.1-1992 (ASHRAE, 1992).
5 The DOP (dioctyl phthalate) specification for the performance of HEPA filters
refers to the percentage removal of 0.3 pm DOP particles using the procedure
defined in U. S. Military Standard MIL-STD-282 (U. S. Department of Defense,
1956).
A-61
-------
Worksheet 8 (continued)
TABLE A-10
Approximate Installed Costs of
Various ln-Duct Particulate Indoor Air Cleaners
Column A
Type of Air Cleaner
Pleated panel cartridge
filter, ASHRAE 6512
Pleated panel cartridge
filter, ASHRAE 851,2
Pleated panel cartridge
filter, ASHRAE 9512
Pleated panel HEPA filter
Electronic air cleaner2,4
Column B
Total Unit
Installed Cost
($/1.000 cfm)
115
115
120
*3
400
Installed costs for ASHRAE 65 through 95 media filters are based on cartridge filter
units, and thus might be less accurate for bag or pocket filters. Costs include; the
cartridge ($35-$40/1,000 cfm for 2,000 cfm cartridges), based on vendor quotes
(Flanders Filters, Inc., Washington, NO and Section 157-401-3000 of Means (1996);
the frame, based on vendor quotes of about $50/1,000 cfm for a unit capable of
supporting four 2,000 cfm cartridges (Air Seal Filter Housing, Houston, TX); installa-
tion labor for the frame into the ductwork (assumed to require 2 labor hours at the rate
charged for a sheet metal worker in Means, 1996); and the incremental installed cost
for an enlarged drive motor for the air handler, to handle the increased pressure drop
across the filter (estimated to be about 1 in. WG on average over the filter lifetime).
The incremental cost for enlarged drive motors (about $20/1,000 cfm) was derived
from Section 163-140 of Means (1996). The installed cost of increased cooling
capacity, to remove the additional heat generated by the larger fan motor, is neglected.
Complications resulting from, e.g., inadequate space to accommodate the new air
cleaner within the existing mechanical room, are not considered in these costs.
Quotes for HEPA filters should be obtained directly from the vendor. Due the quality
required in materials and fabrication, HEPA units will cost significantly more than the
other media filters.
Installed cost per 1,000 cfm for an electronic air cleaner was obtained from Section
157-401-2000 of Means (1996), based on a 2,000 cfm unit.
A-62
-------
WORKSHEET 9
Estimation of Annual Operating Costs
for Central Indoor Air Cleaners
Enter Basic Data
1. Enter the total flow through the air cleaner.
cfm
Note: Obtain this value from the following lines
on Worksheet 7;
Line 4 (Q0A) for Location #1; or
Line 6 (QB) for Location #2; or
Line 5 (Qs) for Location #3.
2. Enter the number of hours per year that the
central air handler (and the indoor air cleaner)
will be operating.
(Default: 3,276 hr/yr, for 13 hr/day, 5 day/wk,
[Note: Electricity costs will sometimes not be a simple function of the
number of kWh used. For example, a demand charge based on the peak
kW usage rate will commonly be included. For this simple estimation,
the user should utilize an average cost per kWh consumed.]
4. Enter the Electric Input Ratio (EIR) for the cooling
system on which the air cleaner is to be installed,
i.e., the kW of electric input per kW of cooling
input.
(Default: EIR = 0.34 kW/kW.) kW/kW
[Note: If the compressor/condenser of the cooling system is driven by
a source other than an electric motor (e.g., by a gas or diesel engine, or
a gas or steam turbine) -- or if an absorption chiller is used -- the cooling
system efficiency should be expressed in the appropriate units, of Btu/hr
cooling output per unit energy input.]
excluding holidays).
hr/yr
3. Enter the unit cost of electricity.
(Default: $0.08/kWh).
/kWh
(continued)
A-63
-------
Worksheet 9 (continued)
5. Enter the overall energy efficiency of the central
air handler (fan/motor combination).
(Defaults: 0.50 for fans < 1,000 cfm;
0.65 for fans > 1,000 cfm) hp out/hp in
Estimate AnnuaI Operating Cost of Media Air Cleaners for Particulate Matter
[Note: The following portion of Worksheet 9 applies for particulate air cleaners
utilizing media cartridges, pockets, or bags. The annual operating costs consist
of: the increased fan energy required to overcome the pressure drop associated
with the new filter; and the incremental increase in cooling energy required to
remove the heat produced by this increase in fan power.]
6. Enter the average pressure drop across the filter
over its lifetime (ranging from unloaded at the
outset, to completely loaded with collected
particulate prior to replacement of the media).
(Default: 1 in. WG). in. WG
7. Compute the required incremental additional
power input to the fan/motor, required to
enable the flow on Line 1 to overcome the
added pressure drop identified in Line 6:
(Line 1) x (Line 6) x [(5.19 lb/ft2)/(in. WG)3
x [(1 hp)/(33,000 ft-lb/min)] -s- (Line 5) hp in
8. Compute the incremental annual energy consump-
tion resulting from this added fan power:
(Line 7) x (0.746 kW/hp) x (Line 2) kWh/yr
9. Compute the incremental annual energy cost
associated with the increased fan power
required to handle the filter pressure drop
(Line 8 x Line 3). $ /yr
10. Compute the incremental additional energy input
required to the cooling system, to remove the
additional heat created by this increase in
fan power. (Assume that, on average over the
cooling and heating seasons, essentially ali of
the heat added to the air stream by the fan must
be removed by the cooling system.)
(Line 8 x Line 4) kWh/yr
(continued)
A-64
-------
Worksheet 9 {continued)
11. Compute the incremental annual energy cost
associated with the increased cooling energy
consumption necessitated by the increase in
fan power (Line 10 x Line 3). $ /yr
12. Compute the total incremental annual operating
cost associated with the addition of a media
filter for indoor particulate control (Line 9
plus Line 11). $ /yr
Estimate AnnuaI Operating Cost of Electronic Air Cleaners for Particulate Matter
[Note: The following portion of Worksheet 9 applies for particulate air cleaners
utilizing electrostatic precipitation. The annual operating costs consist of: the
electrical energy required to operate the precipitator: and the incremental
increase in cooling energy required to remove the heat produced by this
electrical input. It is assumed that there is no pressure drop across the
precipitator.]
13. Enter the average electric power consumption by
the precipitator per unit air flow, as stated by
the vendor.
[Default: 30 W/1,000 cfm (ASHRAE, 1996)] W/1,000 cfrn
14. Compute the total annual power consumption to
operate the electrostatic precipitator:
(Line 13) x (Line 1) - (1,000 cfm/MCFM)
x (Line 2) + (1,000 W/kW) kWh/yr
15. Compute the annual electrical power cost
associated with operating the precipitator
(Line 14 x Line 3). $ /yr
16. Compute the incremental additional energy input
required to the cooling system, to remove the
additional heat generated by the power input to
the precipitator. (Assume that, on average over
the cooling and heating seasons, essentially all
of the heat added to the air stream by the pre-
cipitator must he removed by the cooling system.)
(Line 14 x Line 4) kWh/yr
(continued)
A-65
-------
Worksheet $ (continued)
17. Compute the incremental annual energy cost
associated with the increased cooling energy
consumption necessitated by the power input
to the precipitator (Line 16 x Line 3). $ /yr
18. Compute the total incremental annual operating
cost associated with the addition of an
electronic air cleaner for indoor particulate
control {Line 15 plus Line 17). $ /yr
Estimate Annua/ Operating Cost of Air Cleaners for Gaseous Contaminants
[Note: The following portion of Worksheet 9 applies for air cleaners designed
to remove gaseous contaminants, utilizing dry granular sorbents or catalysts
(e.g., granular activated carbon or activated alumina). The annual operating
costs consist of: the increased fan energy required to overcome the pressure
drop across the granular bed; and the incremental increase in cooling energy
required to remove the heat produced by this increase in fan power.]
19. Enter the estimated pressure drop across the air
cleaner, based on vendor specifications.
(Default: 1 in. WG). in. WG
20. Compute the required incremental additional
power input to the fan/motor, required to
enable the flow on Line 1 to overcome the
added pressure drop identified in Line 19:
(Line 1) x (Line 19) x [(5.19 lb/ft2)/(in. WG)]
x [(1 hp)/(33,000 ft-lb/min)] -4- (Line 5) hp in
21. Compute the incremental annual energy consump-
tion resulting from this added fan power:
(Line 20) x (0.746 kW/hp) x (Line 2) kWh/yr
22. Compute the incremental annual energy cost
associated with the increased fan power
required to handle the air cleaner pressure
drop (Line 21 x Line 3). $ /yr
(continued)
A-66
-------
Worksheet 9 (concluded)
23. Compute the incremental additional energy input
required to the cooling system, to remove the
additional heat created by this increase in
fan power, (Assume that, on average over the
cooling and heating seasons, essentially all of
the heat added to the air stream by the fan must
be removed by the cooling system.)
(Line 21 x Line 4).
24. Compute the incremental annual energy cost
associated with the increased cooling energy
consumption necessitated by the increase in
fan power (Line 23 x Line 3).
25. Compute the total incremental annual operating
cost associated with the addition of an air
cleaner for indoor gaseous contaminant control
(Line 22 plus Line 24).
Summation of Annual Operating Costs for AH Air Cleaners
26. If multiple air cleaners must be installed in a
given building, repeat the calculations above
for each one as necessary. Sum the total
annual operating costs (on Lines 12, 18,
and/or 25) for all air cleaners, and enter the
sum here.
A-67
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WORKSHEET 10
Estimation of Annual Maintenance Costs
for Central Indoor Air Cleaners
[Note: For this estimation, it is assumed that the only maintenance costs
are those associated with; replacing the filter media in media filters for
particulate matter; removing the collected particulate matter from an
electronic air cleaner; or replacing the granular sorbent/catalyst in air
cleaners for gaseous contaminants.]
Compute the Mass of Contaminant to Be Removed by the Air Cleaner
1. From Worksheet 7, enter:
1a. The flow rate entering the air cleaner. cfm
[Qoa (Line 4) for Location #1;
Qr (Line 6) for Location #2;
Gs = Qr + Goa (Line 5) for Location #3]
lb. The contaminant concentration entering
the air cleaner. mg/m3
[C0A (Line 3) for Location #1;
CIN (Line 2) for Location #2;
(GrC|N + Q0AC0A)/(Qr + Qoa) for Location #3]
1c. The fractional efficiency, o, of the
air cleaner (Line 10).
2. From Worksheet 9, Line 2, enter the number of
hours per year that the central air cleaner
will be operating. hr/yr
3. Compute the mass of contaminant that will be
removed per year by the air cleaner:
(Line 1a) x (Line 1b) x [6.2 x 10~8 (lb/ft3)/(mg/m3)]
x (Line 1c) x (60 min/hr) x (Line 2). Ib/yr
(continued)
A-68
-------
Worksheet 10 (continued)
Estimate Annua/ Maintenance Cost of Media Air Cleaners for Particulate Matter
4. From the vendor of the media air cleaner, obtain
an estimate of the mass of particulate that can
be collected on the filter under consideration,
before the pressure drop would be expected to
exceed the vendor's (or the user's) specifications. lb
5. Compute the number of times per year that the
filter media will need to be replaced;
(Line 3] + (Line 4) /yr
6. Refer to Table A-11 at the end of this worksheet.
Identify in Column A the ASHRAE dust spot
efficiency of the media filter. From Column B,
enter the unit cost per replacement filter
cartridge. [MCFM = 1,000 cfm] $ /MCFM
[Note: Since these cost estimates are based on cartridge filters, they
will be less accurate for bag or pocket filters. These replacement costs
include the cost of the cartridge only, assuming that the labor costs
involved in physically replacing the cartridges is small for the purposes
of this rough estimate.]
7. Compute the annual cost of replacing the media
in particulate media filters:
(Line 6} x (Line la) - 1,000 cfm/MCFM x (Line 5). $ /yr
Estimate Annua! Maintenance Cost of Electronic Air Cleaners for Particulate Matter
8. From the vendor of the electronic air cleaner,
obtain an estimate of the mass of particulate
that can be collected on the plates of the
precipitator under consideration, before precipi-
tator performance would be expected to drop
below the vendor's (or the user's) specifications. lb
(continued)
A-69
-------
Worksheet 10 (continued)
9. Compute the number of times per year that the
precipitator will need to be cleaned;
(Line 3} (Line 8) /yr
10. Estimate the number of labor hours that wii! be
required to clean the precipitator. hr/cleaning
11. Enter the labor rate for the personnel who will
clean the precipitator.
[Default: $32/hr for building laborers, inci.
overhead, from Means (1996)] $ /hr
12. Compute the annual cost of cleaning the
electronic air cleaners:
(Line 9) x (Line 10} x (Line 11). $ /yr
Estimate Annua! Maintenance Cost of Air Cleaners for Removing Gaseous Contam-
inants
[Note: The following is based on gaseous air cleaners utilizing dry
granular sorbents and catalysts.]
13. From the vendor or from vendor literature,
define the mass of sorbent (or catalyst) that
is present in the air cleaner, per unit air
throughput. lb sorbent/MCFM
14. Compute the Ib/yr of gaseous contaminant that
is removed by the air cleaner, per unit air
throughput:
(Line 3) ¦+¦ (Line 1a) x (1,000 cfm/MCFM). lb contam./yr/MCFM
15. For the specific gaseous compounds to be
removed by the air cleaner, determine the
mass of contaminant that can be removed per
unit mass of sorbent, before the sorbent must
be replaced:
(continued)
A-70
-------
Worksheet 10 (continued)
15a. Obtain a rigorous estimate from
the vendor.
or
lb contam./lb sorbent
15b. Refer to Table A-12 at the end of
this worksheet. Identify in Column
A the contaminant that is closest
to the one that must be removed in
the case at hand. Select from
Column B the corresponding sorbent
capacity for the contaminant
concentration that the user is
anticipating. lb contam./lb sorbent
[Note: Table A-12 is based on the performance of 8 x 16
mesh coconut shell granular activated carbon in removing
individual organic compounds. Thus, the figures in this
table will be less accurate for other sorbents (impregnated
carbons, impregnated activated alumina, etc.) and for
compound mixtures. See table footnotes.]
16. Compute the number of times per year that the
sorbent/catalyst in the air cleaner wilt have
to be replaced:
(Line 14) ¦+¦ (Line 13) (Line 15a or 15b).
/yr
17. Enter the unit cost of replacement sorbent or
catalyst purchased from the supplier.
(Default: $3/lb for activated carbon)
/lb
18. Enter the number of labor hours required to
replace the sorbent, per unit air throughput.
(Default: 1 labor hr/MCFM)
hr/MCFM
19. Enter the labor rate for the personnel who will
replace the sorbent.
[Default: $32/hr for building laborers, incl.
overhead, from Means (1996)]
$
/ hr
(continued)
A-71
-------
Worksheet 10 (continued)
20. Enter the cost per unit mass for disposing of
the spent sorbent that is removed from the
air cleaner.
[Default: $0.05/lb for landfilling (Henschel,
1998)] $ /lb
21. Compute the cost incurred per unit air throughput
each time the sorbent is replaced:
[(Line 13) x (Line 17)] + [(Line 18) x (Line 19)]
+ [(Line 13) x (Line 20)]. $ /MCFM/replacement
22. Compute the annual cost of replacing the
sorbent In air cleaners for gaseous
contaminants:
(Line 21) x (Line 16) x (Line 1a) 1,000 cfm/MCFM. $ /yr
Summation of Annual Maintenance Costs for All Air Cleaners
23. If multiple air cleaners must be installed in a
given building, repeat the calculations above
for each one as necessary. Sum the total
annual maintenance costs {on Lines 7, 12,
and/or 22) for all air cleaners, and enter the
sum here. $ /yr
A-72
-------
Worksheet 10 (continued)
TABLE A-11
Approximate Replacement Costs of Media Cartridges
for Particulate Media Air Cleaners
Column A
Type of Air Cleaner
Pleated panel cartridges,
ASHRAE 652
Pleated panel cartridges,
ASHRAE 852
Pleated panel cartridges,
ASHRAE 952
Pleated panel HEPA filter,
DOP 99.97
Column B
Unit Cost of
Replacement Cartridges
(S/MCFM1)
35
35
40
Notes:
1 MCFM = 1,000 cfm.
2 Replacement costs for ASHRAE 65 through 95 media filters based on cartridge
filter units, and thus might be less accurate for bag or pocket filters. Costs
include the cartridge {$35-S40/MCFM for 2,000 cfm cartridges), based on
vendor quotes (Flanders Filters, Inc., Washington, NC) and based on Section
157-401-3000 of Means (1996). For this rough estimate, it is assumed that
only minimal labor is required to install the replacement cartridges.
3 Obtain quotes for HEPA filters directly from the vendor. Due the quality
required in materials and fabrication, HEPA units will cost more than the other
media filters.
A-73
-------
Worksheet 10 (concluded)
E} L. 1
Sorption Capacity of Granular Activated Charcoal Air Cleaners
for Various Organic Compounds12-3 4
Column A Column B
Sorption Capacity (lb organic
compound per lb carbon), at the
following inlet concentrations
Oraanic Compound
0.1 DDfTlV
1 DDmv
10 DDmv
Decane
0.14
0.15
0.16
1,1-Dichloroethane
0.0004
0.004
0.01
Hexane
0.02
0.04
0.10
Methyl ethyl ketone
0.01
0.03
0.06
Toluene
0.05
0.09
0.17
Notes:
1 Figures derived from logarithmic extrapolation of data obtained with the indicated
organic compounds in the concentration range of 0.1 to 10 ppmv, reported by
VanOsdell et al. (1996).
2 The figures shown here represent the lb of organic compound that will be adsorbed per
lb of 8 x 16 mesh coconut shell carbon, at the point where 10% of the compound in
the inlet stream breaks through the carbon bed, appearing in the outlet. The figures
are based on a feed stream containing only the indicated organic compound in
otherwise pure air at room temperature and 50% relative humidity. Carbon sorption
capacity will likely be reduced for coarser carbon or higher relative humidities than the
values used here. Also, performance for a given compound will likely be reduced when
other compounds are simultaneously present in the inlet stream.
3 Capacities are based on activated coconut shell carbon without any impregnant.
Performance would likely be different with, e.g., carbons impregnated with activating
agents, or other sorbents or catalysts (e.g., impregnated activated alumina).
4 Any attempt to interpolate to organic compounds not on the above list should be
generally based on the size of the molecule and the functional groups that are present.
Non-impregnated activated carbon is not a good sorbent for compounds having fewer
than four atoms (exclusive of hydrogen). Note that sorption capacity can vary
substantially with inlet concentration to the air cleaner.
A-74
-------
WORKSHEET 11
Estimation of Total Annualized Costs for Central Indoor Air Cleaners
Enter Results from Other Worksheets
1. Enter the total installed cost of the equipment
required for the central indoor air cleaner(s). $
Note: Obtain this value from:
Worksheet 8, Line 6; and/or
Worksheet 8, Line 9.
2. Enter the total incremental annual operating cost
associated with the central indoor air cleaner(s)
(Worksheet 9, Line 26). $ /yr
3. Enter the total incremental annual maintenance
cost associated with the central indoor air
cleaner(s) (Worksheet 10, Line 23). $ /yr
Determine the Capital Recovery Factor (CRFj
[Note: The CRF is the fraction of the initial installed cost that must be
amortized each year if, after n years {i.e., after n equal "payments"), the
initial cost is to be recovered with an i percent annual interest rate
charged on the unpaid balance.]
4. Enter the equipment lifetime, n, that will be
assumed for these calculations (commonly
10 to 20 years). yr
5. Enter the annual interest rate, i, that will be
assumed for these calculations. %
6. From these values for n and i, identify the
appropriate value of the CRF from Table A-7
at the end of Worksheet 6.
(continued)
A-75
-------
Worksheet 11 (concluded)
Compute the Total Annualized Cost for Indoor Air Cleaners
1. Compute the average annual capital charge
(Line 1 x Line 6).
8. Compute the annual operating and maintenance
(O&M) costs associated with the indoor air
cleaner(s) (Line 2 + Line 3).
9. Compute the total annualized cost associated
with the central indoor air cleaner(s)
(Line 7 plus Line 8).
A 76
-------
WORKSHEET 12
Estimation of Costs for Self-Contained Indoor Air Cleaners
Enter Basic Data
1. Enter the current average indoor concentration,
C[Noz< °f the contaminant of concern in the
zone that is to be treated by the self-
contained air cleaner, with no air cleaner in
place. mg/m3
2. Enter the average concentration, CIN_2, to which
the level on Line 1 above should be reduced
after the air cleaner is installed. mg/m3
3. Enter the average concentration, C0A, of the
contaminant in the outdoor air. mg/m3
4. Enter the total volume of air, Gs.z, being supplied
to the zone of interest, including the outdoor air
to the zone, Q0AZ' P'us ^he recirculating air, QK?. cfm
5. Enter the volumetric flow of outdoor air, Q0AZ,
into the zone being addressed here. cfm
[Note: This OA flow to this zone will be a fraction of the total OA being
supplied by the HVAC system, proportional to the ratio of the supply air
flow to this zone, Qs_z, to the total supply air being provided by the
system to all of the zones it is serving.]
6. Quantify the rate, Sz, at which the contaminant
of concern is being generated by sources inside
the zone, in Ib/min. _ Ib/min
7. Enter the fractional efficiency, r\, of the air
cleaner in removing the contaminant of concern,
based on data from the vendor or independent
sources.
(continued]
A-77
-------
Worksheet 12 {continued)
Calculate the Required Flow, Q(y Through the Air Cleaner
8. Refer to Figure A-2 at the end of this worksheet.
Using the equation in that figure, compute the
required total rate, Qc, at which zone air must
be circulated through the air cleaner in order
to achieve the desired zone concentration, C,N_2. cfm
Estimate the Installed Cost for Self-Contained Air Cleaners
10.
Enter the flow capacity for the self-contained
air cleaners being considered.
Compute the number of air cleaners that will
be required to provide the total capacity
calculated on Line 8 (Line 8 Line 9).
cfm/air cleaner
air cleaners
11. Enter the uninstalled cost per air cleaner, based
on vendor quotes.
12. Estimate the installation cost for each air cleaner,
including the cost for mounting and electrical
wiring.
13. Calculate the total installed cost per air cleaning
unit (Line 11+ Line 1 2).
/air cleaner
/air cleaner
/air cleaner
14. Compute the total installed cost of the self-
contained air cleaning system:
(Line 13) x (Line 1 0).
Estimate the Annual Operating Cost for Self-Contained Air Cleaners
15. Enter the electric power consumption by each
self-contained air cleaner, based on vendor
specifications. kW/air cleaner
[Note; This power consumption will include, as a minimum, the power
to operate the air circulation fan within the air cleaner.]
(continued)
A-78
-------
Worksheet 12 (continued)
16. Enter the number of hours per year that the self-
contained air cleaner will be operating.
(Default: 3,276 hr/yr, for 13 hr/day, 5 day/wk,
excluding holidays).
17. Enter the unit cost of electricity.
(Default; $0,08/kWh).
18. Compute the incremental annual energy cost
associated with the electricity to operate
the self-contained air cleaner(s):
(Line 15) x (Line 10) x (Line 16) x (Line 17).
19. Enter the Electric Input Ratio (EIR) for the cooling
system serving the zone in which the air cleaner
is to be installed, i.e., the kW of electric input
per kW of cooling input.
(Default: EIR = 0.34 kW/kW.)
20. Compute the incremental additional energy input
required to the cooling system, to remove the
additional heat created by the power input to
the air cleaner. (Assume that, on average over
the cooling and heating seasons, essentially all
of the heat added to the space by the air cleaner
must be removed by the cooling system.)
(Line 15) x (Line 10) x (Line 16) x (Line 19)
21. Compute the incremental annual energy cost
associated with the increased cooling energy
consumption necessitated by the power input
to the air cleaner(s) (Line 20 x Line 17).
22. Compute the total incremental annual operating
cost associated with the addition of self-
contained indoor air cleaner(s) (Line 18 plus
Line 21).
A-79
-------
Worksheet 12 (continued)
Estimate the Annua! Maintenance Cost for Self-Contained Air Cleaners
23. Compute the mass of contaminant that wiil be
removed per year by the air cleaner system:
(Line 8) x (Line 2) x (Line 7). Ib/yr
24. Complete Lines 4 through 22, as applicable, in
Worksheet 10 for central air cleaners. To
adapt that worksheet to self-contained air
cleaners, make the following adjustments:
- use Line 8 above in lieu of Line 1a of Worksheet 10;
- use Line 23 above in lieu of Line 3 of Worksheet 10;
- for media filters, use vendor quotes in lieu of the
filter costs in Table A-11 on Line 6 of Worksheet 10.
25. Based on the use of Worksheet 10, as specified
on Line 24 above, enter the total incremental
annual maintenance cost associated with the
addition of self-contained indoor air cleaner(s)
(from Line 7, 12, or 22 of Worksheet 10). $ /yr
Estimate the Total Annualized Cost for Self-Contained Air Cleaners
26. Determine the CRF, according to Lines 4 through
6 of Worksheet 11.
27. Compute the average annual capital charge
(Line 14 x Line 26). $ /yr
28. Compute the annual operating and maintenance
(O&M) costs associated with the self-contained
air cleaner(s) (Line 22 plus Line 25). $ /yr
29. Compute the total annualized cost associated
with the self-contained indoor air cleaner(s)
(Line 27 plus Line 28}. $ /yr
(continued)
A-80
-------
Worksheet 12 (concluded)
Qsz
ZONE
C IN-Z
Contains source (S z)
Supply
Air
Qs-z
Q c
u IN-Z
Self-contained |
air cleaner \
Qqa z(Coa Gin z) K +
n cin_zk
Key:
Qs z = supply air flow to the zone to be treated using a self-contained
air cleaner (cfm)
Qc = flow rate of zone air being circulated through the air cleaner
(cfm)
Qoa.z = flow rate of outdoor air into the zone (cfm)
C0A = contaminant concentration in outdoor air (mg/m3)
CiN.z = desired contaminant concentration in the zone (mg/m3)
K = concentration conversion factor = 6.2 x 10"8 (lb/ft3)/(mg/m3)
Sz = source term for contaminant generated in zone (Ib/min)
H = fractional efficiency of the air cleaner
Figure A-2. Schematic diagram and mass balance equation for a zone being
treated using a self-contained air cleaner.
A-81
-------
WORKSHEET 13
Estimation of Costs for Source Management:
Source Replacement by Low-Emitting Materials (LEMs)
[Note; For simplicity, this worksheet addresses a single type of source
that is to be replaced by a lower-emitting substitute -- e.g., carpeting,
wall paint, or a specific item of furniture (such as office desks) — where
the emission characteristics of the original product and of the lower-
emitting substitute are known. Where multiple source types are being
considered for replacement, this worksheet would have to filled out for
each source type.]
Enter Basic Data
1. Enter the source type that is being addressed
in this analysis (carpeting, wall paint,
furniture item, photocopiers, etc.).
2. Enter amount of source area/number of sources
for sources of this type (ft2 of carpeted
floor area, ft2 of painted wall surface,
number of furniture items or photocopiers,
etc.). _____ ___
(units)
3. Enter the installed cost per unit area, or the
cost per item, for the originally planned high-
emitting materials/equipment items, assuming
that the materials are being installed in a new
building (no retrofit complications). $ /(unit)
4. Enter the installed cost per unit area, or the
cost per item, for the low-emitting materials
with which the original units are to be replaced,
assuming that the LEM is being installed in a
new building (no retrofit complications). $ /(unit)
[Note: Line 4 will not necessarily be greater than Line 3. The installed
costs on these two lines should include: the uninstalled cost of the
material; and the labor/supplies required for installation in a new building,
where there are no installation complications associated with retrofit.
These costs would be expressed, for example, as $/ft2 or $/furniture
item, depending upon the material/equipment item being addressed.]
(continued)
A-82
-------
Worksheet 13 (continued)
5. Enter the estimated useful lifetime of the
originally planned high-emitting materials/
equipment items, yr
6. Enter the estimated useful lifetime of the
low-emitting materials with which the original
units are to be replaced. yr
[Note: Line 5 will not necessarily be greater than Line 6. As a default,
assume that Line 6 equals Line 5.]
RETROFIT CASE
[Note: For the case of new construction, skip directly to Line 17.]
Compute the Installed Cost for the LEMs - Retrofit Case
7. For existing buildings (retrofit cases), estimate
the cost per unit for removing the original
materials or equipment items, if applicable. $ /(unit)
[Note: This removal cost could include, for example: clearing the area
to provide working access to the original material; physical removal of
the old material; disposal of the old material, as applicable; any repairs
or surface preparation required before new material can be installed; and,
as applicable, moving back into place any furniture, etc., that had been
cleared to allow access to the original material.]
8. Estimate the total unit installed cost of the LEM,
including the complications of installation in
the retrofit case (Line 4 plus Line 7). $ /(unit)
9. Compute the total installed cost of retrofitting
a LEM into the existing building:
(Line 8} x (Line 2). $
(continued)
A-83
-------
Worksheet 13 (continued)
Compute the Total Annualized Cost for Retrofitting the LEM
10. Refer to Table A-7 at the end of Worksheet 6
(page A-52). Identify the Capital Recovery
Factor for the number of years, nL, corres-
ponding to the expected LEM lifetime entered
on Line 6 (and for the interest rate, i,
selected by the user). Enter that CRF here. /yr
11. Compute the total annualized cost for retro-
fitting the LEM into this building
(Line 9 times Line 10). S /yr
Back-Calculation of Premium That Coulcf Be Paid for LEMs (Retrofit)
[Note: The preceding calculations assume that the price of the LEM is
known, and the objective is to compute the annualized cost that will
enable the subsequent calculation of the cost-effectiveness of this
approach (see Section 7). The following calculations consider the
reverse situation, where the absolute cost-effectiveness of ventilation
and/or air cleaning is known (Section 7.1), and the user wishes to
determine what premium could be paid for a LEM that will accomplish
the same contaminant reduction, before this source management
approach becomes less cost-effective than those competing alternatives.
That is, the user wishes to back-calculate what the acceptable entry
wouid be on Line 4.]
12. Enter the incremental reduction in exposure
lA(exposure)] that is desired to protect the
occupants [in units of (mg/rrr) person-hr per
year]. (See Section 1.4, page 1-5.) (mg/m3)-p-hr/yr
[Note: Computer modeling may be necessary to determine whether LEM
replacement may in fact be capable of providing this degree of reduction.
See Section 6.1.]
13. Enter the cost-effectiveness ICE = - A (cost)/
A(exposure)] with which ventilation or air
cleaning can provide this desired reduction in
exposure [in annualized dollars expended per
(mg/m3)-person-hr per year reduction]. $/(mg/m3) p hr/yr
(continued)
A-84
-------
Worksheet 13 (continued)
14. Compute the maximum annualized cost that
can be paid for LEM replacement before this
approach becomes less cost-effective than the
competing alternatives (Line 12 x Line 13).
15. Back-calculate the maximum allowable total
installed cost for retrofitting a LEM into the
building, that will not exceed the maximum
annualized cost on Line 14:
(Line 14) - (Line 10).
16. Back-calculate the maximum allowable unit
installed cost of the LEM (under the no-
retrofit-complication case) that can be
entered on Line 4 without exceeding the
allowable total installed cost on Line 15:
[(Line 1 5) - (Line 2)] - (Line 7). $ /(unit)
[Note: The user must now determine whether a suitable low-emitting
material can be obtained for this unit price.]
NEW CONSTRUCTION CASE
Compute the Incremental Installed Cost for the IF Ms in New Construction
17. Compute the cost that would have been incurred
had the originally planned material been
installed in the new building:
(Line 3) x (Line 2). $
18. Compute the cost that will be incurred if the
LEM is installed instead:
(Line 4) x (Line 2), $
(continued)
/ yr
A-85
-------
19. Compute the total incremental installed cost of
installing a LEWI into a new building during
construction:
(Line 18) - (Line 17). S
Compute the Incremental Annualized Cost of Substituting a LEM in New Construction
20. Refer to Table A-7 at the end of Worksheet 6
(page A-52). For the interest rate, i,
selected by the user, enter:
20a. The CRF for the number of years,
n0, corresponding to the expected
lifetime entered on Line 5 for the
originally planned high-emitting
material. /yr
20b. The CRF for the number of years,
nL, corresponding to the expected
lifetime entered on Line 6 for the
LEM. /yr
21. Compute the total annualized cost that would
have been incurred with the originally planned
material:
(Line 17) x (Line 20a). $ /yr
22. Compute the total annualized cost that will be
incurred with LEM:
(Line 18) x (Line 20b). $ /yr
23. Compute the incremental increase in the
total annualized cost for installing the LEM
into this new building (Line 22 minus Line 21). $ /yr
(continued)
A-86
-------
Worksheet 13 {continued)
Back-Calculation of Premium That Could Be Paid for LEMs iNew Construction}
[Mote: The following procedure back-calculates the maximum unit price
for a LEM that can be entered on Line 4, if the cost-effectiveness of the
LEM replacement approach is to match that for ventilation or air cleaning
steps achieving the same reduction in exposure.]
24. Enter the incremental reduction in exposure
[ A(exposure)] that is desired to protect the
occupants [in units of (mg/m3)-person-hr
per year]. (mg/m3)-p-hr/yr
[Note: Computer modeling may be necessary to determine whether LEM
replacement may in fact be capable of providing this degree of reduction.
See Section 6,1,]
25. Enter the cost-effectiveness [CE = - A(cost)/
A(exposure)] with which ventilation or air
cleaning can provide this desired reduction in
exposure [in annualized dollars expended per
(mg/m3)-person hr per year reduction]. $/(mg/m3) p-hr/yr
26. Compute the maximum annualized cost that
can be paid for LEM replacement before this
approach becomes less cost-effective than
competing alternatives {Line 24 x Line 25). $ /yr
27. Back-calculate the maximum allowable total
annualized cost for using a LEM in the new
building (i.e., the maximum allowable entry
on Line 22), that will ensure that the
incremental annualized cost for using a LEM
(the value on Line 23) does not exceed the
maximum annualized cost on Line 26:
(Line 26) + [(Line 17) x (Line 20a)]. $ /yr
A-87
(continued)
-------
illllsheet 13 (concluded)
28. Back-calculate the maximum allowable unit
installed cost of the LEM in the new
building, that can be entered on Line 4
without exceeding the allowable total
annualized cost for using a LEM on Line 27:
[{Line 27) -h- (Line 20b)] 4- {Line 2). $ /{unit)
[Note: The user must now determine whether a suitable low-emitting
material can be obtained for this unit price.]
A-88
-------
WORKSHEET 14
Absolute Reduction in Exposure Resulting from
Implementation of an IAQ Control Measure:
Simplified Calculation
1. Enter the annual average concentration of the
contaminant of concern in each individual zone
of interest during working hours, prior to
implementation of the IAQ control measure:
1(1). In Zone #1 mg/m3
1(2). In Zone #2 mg/m3
1(3}. In Zone #3 mg/m3
etc.
[Note: Obtain these average concentrations from: Line 1 of Worksheet 1; Line 1
of Worksheet 7; or CD in Section 5.2.1, if those entries represent annual average
concentrations.]
2. Enter the annual average concentration of the
contaminant of concern in each individual zone
of interest during working hours, after
implementation of the IAQ control measure:
2(1). In Zone #1 mg/m3
2(2). In Zone #2 mg/m3
2(3). In Zone #3 mg/m3
etc.
[Note: Obtain these average concentrations from: Line 2 of Worksheet 1; Line 2
of Worksheet 7; or CEm in Section 5.2.1, if those entries represent annual average
concentrations.]
3. Compute the incremental change in concentration
being achieved in each zone of interest by
implementing the IAQ control measure:
3(1). In Zone #1 [Line 2(1) minus Line 1(1)] mg/m3
3(2). In Zone #2 [Line 2(2) minus Line 1(2)] mg/m3
3(3). In Zone #3 [Line 2(3) minus Line 1(3)] mg/m3
etc.
[Note: These numbers should be negative - i.e., Line 2(x) should be
smaller than Line 1 (x) - reflecting a reduction in the concentration to
which occupants are being exposed.]
(continued)
A-89
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Worksheet 14 (continued)
Enter the number of occupied hours during days
when the building is occupied.
hr/day
[Note: If there are hours when very few persons are in the building --
e.g., overnight or on weekends - the user may wish to consider, for this
simplified calculation, only those hours when the number of occupants
is significant.]
Enter the average number of persons in each
zone during the occupied hours in Line 4 above:
5(1). In Zone #1
5(2). In Zone #2
5(3). in Zone #3
etc.
persons
persons
persons
[Note: If, for example, 10 persons worked in Zone X during the 9-hour
period between 8 am and 5 pm, but each left for a 1-hour lunch break
on a staggered schedule around mid-day, the user might wish to simply
enter "8 hr" on Line 4 above, and enter "10 persons" on Line 5(X).
Alternatively, the user could enter "9 hr" on Line 4 and, on Line 5(X),
(10 x 8) person-hr total occupancy/day 9 hr/day =
8,9 persons per hour on average.]
6. Compute the total number of occupied hours per year:
{[(number of occupied days/week) x (52 weeks/yr)]
- (number of holidays/yr)} x Line 4.
Compute the change in occupant exposure in
each of the individual zones of interest:
hr/yr
7(1). in Zone #1
I Line 3(1) x Line 5(1) x Line 61
7(2). In Zone #2
[Line 3(2) x Line 5(2) x Line 6]
7(3). In Zone #3
[Line 3(3! x Line 5(3) x Line 61
etc.
(mg/m3)-person-hr/yr
(mg/m3)-person-hr/yr
(mg/m3)-person-hr/yr
(continued)
A-90
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Worksheet 14 {concluded}
8. Compute the total change in occupant exposure
summed over all zones of interest
[Line 7(1) + Line 7(2) + . . Line 7(x)]. (mg/m3)-person-hr/yr
[Note: If one wishes instead to express this exposure result in terms of
the change in exposure for the average person in the zones of interest,
divide the figure on Line 8 by the total number of persons in the zones,
i.e., the sum of Lines 5(1) through 5(x). The figures on Lines 7 and 8
should be negative, representing a reduction in exposure achieved by
implementing the IAQ control measure.]
A-91
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WORKSHEET 15
Relative Reductions in Exposure Achieved by
One IAQ Control Measure Compared Against Alternative Measures
1. For each of the IAQ control measures under
consideration, enter the ratio of the annual
average indoor concentration expected to be
achieved by implementing the control (Cccntro))
divided by the annual average concentration
without this control (Cno contro,):
1(1). C00ntr0|/Cn0 contr0| with
1(2) . Cconfro|/CnQ corral With
1(3). CcontrO|/Cn0 control with
etc.
Alternative Measure #1
Alternative Measure #2
Alternative Measure #3
[Note: For example, if a given control measure reduced the indoor
concentration to 20% of the level it would otherwise have been without
control, enter 0.2 here for that measure. These fractional efficiencies
could be obtained from the preceding worksheets as follows:
(Line 3) in Worksheet 1;
[(Line 2) h- (Line 1)1 in Worksheet 7;
(Csm/CQ) in Section 5.2.1.]
2. Compute the fractional change in annual exposure
resulting from implementing each of the alterna-
tive control measures [(Ccontrol/CnocOTltrol) - 1].
2(1). (Ccontrol/Cno control), - 1 (Measure #1)
2(2). (Ccontro,/Cnocontrol)2- 1 (Measure #2)
2(3). !Ccontro,/CnoCDntrol)3 - 1 (Measure #3)
etc.
[Note: For example, if (Ccontrol/Cno contJx = 0.2, then (Cconlrol/C
no control )x
1 = -0.8, reflecting an 80% reduction in annual exposure with Measure
x, relative to the case of no control.]
(continued)
A-92
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Worksheet 15 {concluded}
3. Enter the fractional effectiveness of each
alternative control measure:
3(1). Effectiveness of Measure #1 {-[Line 2{1)J}
3(2). Effectiveness of Measure #2 {-[Line 2(2)]} _____
3(3). Effectiveness of Measure #3 {-[Line 2(3)]}
etc.
[Note: This step is intended simply to emphasize the relationship,
effectiveness = - A(exposure). A control measure causing a fractional
change in annual exposure of -0.8 would have an effectiveness of
+ 0.8.]
4. Compute the relative effectiveness of any one
of these control measures (e.g., Measure #1}
relative to each of the others:
4(1). Measure #1 relative to Measure #2
[Line 3(1)]/[Line 3(2)].
4(2). Measure #1 relative to Measure #3
[Line 3(1 )]/[Line 3(3)].
etc.
[Note: For example, if Measure #1 had an effectiveness of 0.8 and
Measure #2 an effectiveness of 0.6, the effectiveness of Measure #1
relative to Measure #2 would be 0.8/0.6 = 1.33, indicating that
Measure #1 is 33% more effective in reducing exposure than Measure
#2.]
A-93
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