United States Indoor Environments Division EPA-4-2-S-01-001
Environmental (6609J) January 2000
Protection Office of Air and Radiation
Agency
Energy Cost and IAQ
Performance of Ventilation
Systems and Controls
Executive Summary
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Energy Cost and IAQ Performance of Ventilation Systems and Controls
Executive Summary
PURPOSE AND SCOPE OF THIS REPORT
In it's 1989 Report to Congress on Indoor Air Quality, the United States Environmental
Protection Agency provided a preliminary assessment of the nature and magnitude of indoor air
quality problems in the United States, the economic costs associated with indoor air pollution,
and the types of controls and policies which can be used to improve the air quality in the
nation's building stock. In that report, EPA estimated that the economic losses to the nation due
to indoor air pollution was in the "tens of billions" of dollars per year, and suggested that
because of the relative magnitude of operating costs, labor costs, and rental revenue in most
buildings, it is possible that modest investments toward improved indoor air quality would
generate substantial returns. Since that time, EPA has attempted to further define the costs and
benefits to the building industry of instituting indoor air quality controls.
This project - Energy Cost and IAQ Performance of Ventilation Systems and Controls - is part
of that effort. Adequate ventilation is a critical component of design and management practices
needed for good indoor air quality. Yet, the energy required to run the heating, ventilating, and
air conditioning (HVAC) system constitutes about half of a building's energy cost. Since energy
efficiency can reduce operating costs and because the burning of fossil fuels is a major source
of greenhouse gases, energy efficiency has become an important concern to the building
industry and the promotion of efficient energy utilization has become a matter of public policy. It
is important, therefore, to examine the relationship between energy use and indoor air quality
performance of ventilation systems.
This project represents a substantial modeling effort whose purpose is to assess the
compatibilities and trade-offs between energy, indoor air quality, and thermal comfort objectives
in the design and operation of HVAC systems in commercial buildings, and to shed light on
potential strategies which can simultaneously achieve superior performance on each objective.
This project seeks to examine three related fundamental questions:
1. How well can commonly used HVAC systems and controls be relied upon to satisfy
generally accepted indoor air quality standards for HVAC systems when they are
operated according to design specifications?
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2. What is the energy cost associated with meeting ASHRAE indoor air quality
performance standards for HVAC systems?
3. How much energy reduction would have to be sacrificed in order to maintain minimum
acceptable indoor air quality performance of HVAC systems in the course of energy
efficiency projects?
The outdoor air flow rates contained in ANSI/ASHRAE Standard 62-1989 (and subsequently
Standard 62-1999)1 Ventilation for Acceptable indoor Air Quality, along with the temperature
and humidity requirements of ANSI/ASHRAE Standard 55-1992, Thermal Environmental
Conditions for Human Occupancy were used as the indoor air quality design and operational
criteria for the HVAC system settings in this study. The outdoor air flow rates used were 20 cfm
per occupant for office spaces, and 15 cfm per occupant for educational buildings and
auditoriums as per ANSI/ASHRAE Standard 62-19992. The flow rates were established for
design occupancy conditions and were not assumed to vary as occupancy changed during the
day. Space temperature set points were designed to maintain space temperatures between
70° F - 79° F and relative humidity levels not to exceed.60%, consistent with ANSI/ASHRAE
Standard 55-19923. With these design and operational settings, the actual outdoor airflows,
space temperatures, and space relative humidity were then compared with these criteria to
assess the indoor air quality performance of the system. When the design or operational set
points were not maintained, operational changes were selectively undertaken to insure that the
criteria were met so that the associated changes in energy cost could be examined.
While indoor air quality can arguably be controlled by different combinations of source control,
ventilation control, and/or air cleaning technologies, no attempt was made in this project to study
the potential for maintaining acceptable indoor air quality at reduced ventilation rates through
the application of source control and air cleaning methods. In addition, while the impact of
polluted outdoor air on the indoor environment is noted in discussions of outdoor airflow rates,
no attempt was made to assess the implications of treating the outdoor air prior to entry into the
building. In general, this project attempted to examine issues facing HVAC design and
This project was initiated while ASHRAE Standard 1989 was in effect. However, since the outdoor air flow rates
for both the 1989 and 1999 versions are the same, all references to ASHRAE Standard 62 in this report are stated as ASHRAE
Standard 62-1999.
The outdoor air flow rates specified in ASHRAE 62-1999 are designed to dilute indoor generated contaminants to
acceptable levels where no significant indoor sources of pollution are present, and where the outdoor air quality meets applicable
pollution standards. Thus, where significant indoor sources of pollution are present, these would have to be controlled. In
addition, unacceptable concentrations of contaminants in the outdoor air would have to be removed prior to its entering occupied
spaces. These issues were not specifically addressed in this modeling project.
ASHRAE Standard 55-1992 describes several factors which affect thermal comfort, including air temperature,
radiant temperature, humidity, air speed, temperature cycling and uniformity of temperature, when establishing criteria for
thermal comfort. The modeling in this project addresses only the air temperature and relative humidity factors.
Energy Cost and IAQ 2 Executive Summary
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operational engineers during the most common applications of the indoor air quality and
thermal comfort standards as prescribed by ASHRAE.
In addition, since outdoor air flow rates of 5 cfm per occupant were allowed by ASHRAE
Standard 62-1981, energy costs for both 5 cfm per occupant (which were commonly used prior
to 1989) as well as the above referenced 15 and 20 cfm per occupant, were
estimated in order to determine the cost implications of raising the outdoor airflow rates from
the previously allowed to the current ASHRAE outdoor air requirements.
This is a modeling study, subject to all the limitations and inadequacies inherent in using models
to reflect real world conditions that are complex and considerably more varied than can be fully
represented in a single study. Nevertheless, it is hoped that this project will make a useful
contribution to understanding the relationships studied, so that together with other information,
including field research results, professionals and practitioners who design and operate
ventilation systems will be better able to save energy without sacrificing thermal comfort or
outdoor air flow performance.
METHODOLOGY
The process of investigating indoor air quality (IAQ) and energy use can be time-consuming and
expensive. In order to streamline the process, this study employed a building simulation computer
modeling procedure. The computer modeling approach enabled the investigation of multiple
variations of building configurations and climate variations at a scale which would not otherwise be
possible with field study investigations.
The methodology used in this project has been to refine and adapt the DOE-2.1 E building energy
analysis computer program for the specific needs of this study, and to generate a detailed
database on the energy use, indoor climate, and outdoor air flow rates of various buildings,
ventilation systems and outdoor air control strategies.
Buildings and Climate
One large office building, an education building, and an auditorium formed the basis for most of
this study. Summary characteristics of these buildings are presented in Exhibit 1. In addition,
however, thirteen variations of the office building were used to examine how these variations
impacted the energy costs of increasing outdoor air flow rates from 5 to 20 cfm per occupant, while
slight modifications to the education building were made to examine the combined application of
energy efficiency and indoor air quality controls.
Each building was modeled with (1) a dual duct constant volume (CV) system with temperature
reset; and (2) a single duct variable volume (VAV) system with reheat. The CV system was
included to represent many existing CV systems rather than current applications. Outdoor air
controls include a fixed outdoor air fraction (FOAF), and a constant outdoor air (COA) flow. The
FOAF strategy maintains a constant outdoor air fraction (percent outdoor air) irrespective of the
Energy Cost and IAQ 3 Executive Summary
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supply air volume. For VAV systems, the FOAF could potentially be approximated in field
applications by an outdoor damper in a fixed position (Cohen 1994; Janu 1995; and Solberg
1990), but specific field applications are not addressed in this study. The FOAF strategy was
modeled so that the design outdoor air flow rate is met at the design cooling load, and diminishes
in proportion to the supply flow during part-load. The COA strategy maintains a constant volume of
outdoor air irrespective of the supply air volume. In a CV system, the FOAF and the COA
strategies are equivalent, and are referred to in this report as CV (FOAF). In a VAV system, the
COA strategy might be represented in field applications by a modulating outdoor air damper which
opens wider as the supply air volume is decreased in response to reduced thermal demands.
Specific control mechanics which would achieve a VAV (COA) have been addressed by other
authors, (Haines 1986, Levenhagen 1992, Solberg 1990) but are not addressed in this modeling
project.
In this study two types of air-side economizer strategies were also modeled: one controlled by
outdoor air temperature (ECONT) and one controlled by outdoor air enthalpy (ECONE). The
economizer is designed to override the minimum outdoor air flow called for by the prevailing
strategy (FOAF or the COA) by bringing in additional quantities of outdoor air to provide "free
cooling" when the outdoor air temperature (or enthalpy) is lower than the return air temperature
(or enthalpy). In addition, the temperature economizer is prevented from operating when
outdoor air temperatures exceed 65°F in order to avoid potential humidity problems. While the
enthalpy economizer was modeled for comparison purposes, the temperature economizer was
the primary economizer control used in various parts of this study.
Climates and Utility Rates
Each building was modeled using TMY formatted weather data for three different cities, each
representing distinctly different climate regions: Minneapolis, MN (cold climate regions),
Washington, DC (temperate climate regions), and Miami, FL (hot and humid climate regions).
Five different utility rate structure were modeled to determine the extent to which energy cost
impacts from various parametric changes were dependent on utility rate structures. The base
utility rate structure represents the average of prices taken from utilities in 17 major cities
around the country in 1994. The price of electricity was modeled at $0.044 per kilowatt-hour,
and $7.89 per kilowatt. Gas for space heating and DHW service was modeled at $0.49 per
therm. The absolute, rather than the percentage increase in the cost of raising outdoor air flow
rates, and the absolute dollar savings of energy efficiency projects, for example, would be
greater (less) with higher (lower) utility rates. The sensitivity of the results in this study to
alternative utility rate structures (varying relationships between gas and electric rates) was also
tested.
LIMITATIONS
Any analysis, however thorough, is inevitably constrained by the state of the art and resources
available. Several fundamental limitations to the analysis in this project must be recognized.
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• The analysis is ultimately constrained by the extent to which the model used accurately
reflects real world performance.
• While a large number of building and ventilation parameters were used, they are
limited in comparison to the many and varied building and ventilation characteristics in
the nation's building stock. While the parameters were chosen to capture important
variations, they are not necessarily representative.
• The model assumes that all equipment functions as it was intended to function. Faulty
design, improper installation, and malfunctioning equipment due to poor maintenance,
which are not uncommon in buildings, were not modeled.
ISSUES ADDRESSED IN THE PROJECT
Seven reports, covering the following questions describe the issues addressed in this project:
Project Report #1: Project Objectives and Methodology
• What is the purpose of the project?
• What modeling tool was used and what modifications were made to meet the needs of
this project?
• What buildings, HVAC systems, outdoor air control strategies, and utility rate
structures were used, and how were they combined in simulations which constitute the
database for this project?
Project Report #2: Assessment of CV and VAV Ventilation Systems and Outdoor Air
Control Strategies for Large Office Buildings-- Outdoor Air Flow Rates and Energy Use
• Are there significant differences in outdoor airflow and energy cost among different
HVAC systems and outdoor air control strategies?
• What HVAC system/outdoor air control strategy combinations offer the best and the
worst results?
• What are the trade-offs and compatibilities between energy cost and outdoor air
performance among the combinations studied?
Project Report #3: Assessment of CV and VAV Ventilation Systems and Outdoor Air
Control Strategies for Large Office Buildings- Zonal Distribution of Outdoor Air and
Thermal Comfort Control
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• How well do HVAC systems and outdoor air control strategies deliver design
quantities of outdoor air to individual zones?
• Can shortfalls in particular zones be easily corrected and at what energy cost?
Project Report #4: Energy Impacts of Increasing Outdoor Air Flow Rates from 5 to 20
cfm per Occupant in Large Office Buildings
• What are the energy costs of raising outdoor air flow rates from 5 to 20 cfm per
occupant for office buildings?
• How does the cost impact vary among different ventilation systems, outdoor air control
strategies, and climates?
Project Report #5: Peak Load Impacts of Increasing Outdoor Air Flow Rates from 5 to
20 cfm per Occupant in Large Office Buildings
• Do HVAC system capacity problems result when outdoor air flow rates are raised in
existing buildings (designed for 5 cfm of outdoor air per occupant) to conform with
ASHRAE 62-1999?
• How significant are such problems and when are they most likely to occur?
• What implications do peak load impacts have on desires to downsize equipment in
order to reduce first costs and save energy?
Project Report #6: Potential Problems in IAQ and Energy Performance of HVAC
Systems When Outdoor Air Flow Rates Are Increased from 5 to 15 cfm per Occupant in
Education Buildings, Auditoriums, and Other Very High Occupant Density Buildings
• What operational difficulties are presented by the requirement for large quantities of
outdoor air for schools, auditoriums and other buildings with high occupant densities and
how can these difficulties best be solved?
• What are the energy costs of increasing outdoor air flow from 5 to 15 cfm per occupant
as per ASHRAE Standard 62-1999 for schools, auditoriums, and other buildings with
high occupant densities, and how much can these costs be mitigated?
Project Report #7: The Impact of Energy Efficiency Strategies on Energy Use, Thermal
Comfort, and Outdoor Air Flow Rates in Commercial Buildings
• What energy efficiency measures are compatible and what measures are incompatible
with indoor environmental quality?
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• What are the energy savings and penalties associated with measures to protect the
indoor environments during energy efficiency projects?
• What protections and enhancements to indoor environmental quality can reasonably be
employed in energy management and retrofit projects without sacrificing energy
efficiency?
KEY RESULTS
* VAV Systems Save Energy: The variable air volume systems provided $0.10 - $0.20
energy savings per square foot over constant volume systems modeled for a savings of !0% to
21 % of HVAC energy cost. Since the modeled CV system is much more energy efficient than
other CV systems, the results tend to underestimate the advantages of conversion from CV to
VAV systems. See Report #2.
* VAV with Fixed Outdoor Air Fractions Caused Outdoor Air Flow Problems: VAV
systems may require a different outdoor air control strategy at the air handler to maintain
adequate outside air for indoor air quality than the constant volume predecessor. Because the
fixed outdoor damper strategy of the CV system, which is commonly used in the VAV systems,
was modeled to provide a fixed outdoor air fraction, the outdoor air delivery rate at the air
handler was cut to about one half to two thirds the design level during most of the year. See
Report #2.
* Core Zones Received Significantly Less Air than Perimeter Zones and space
temperatures tended to be higher: Both the CV and VAV systems provided an unequal
distribution of supply air and outdoor air to zones. The south zone received the highest and the
core zone received the least outdoor air. The core zone received only about two thirds of the
building average outdoor air flow and had higher space temperatures. The impact of zonal
differences on indoor air quality in the under-ventilated zones will depend on the degree of air
mixing between zones. See Report #3.
* Core Zones in VAV Systems with a Fixed Outdoor Air Fraction Received Very Little
Outdoor Air: The VAV system with fixed outdoor air fraction diminished the outdoor air
delivery to the core zone to only about one third of the design level. Wth a design level of 20 cfm
of outdoor air pe occupant, the core zone received only 6-8 cfm per occupant, and only 2-3 cfm
per occupant with a design level of 5 cfm per occupant. Along with higher temperatures in the
core zone, this shortfall could contribute to higher indoor air quality complaint rates in the core
relative to the perimeter zones in some circumstances. See Report #3.
* VAV with Constant Outdoor Air Control Displayed Improved Indoor Air Performance
without any Meaningful Energy Penalty. The VAV system with an outdoor air control
strategy that maintains the design outdoor airflow at the air handler all year round had slightly
lower energy cost in the cold climate, and slightly more energy cost in the hot and humid climate.
Energy Cost and IAQ 7 Executive Summary
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It is therefore comparable in energy cost, but preferred for indoor air quality. See Reports #2
and #3.
* Economizers on VAV Systems May Be Advantageous for Both Indoor Air Quality and
Energy in Cold and Temperate Climates. By increasing the outdoor airflow when the
outside air temperature (or enthalpy) is less than the return air temperature(or enthalpy),
economizers can reduce cooling energy costs. For office buildings, economizers may operate
to provide free cooling even at winter temperatures (e.g. at zero degrees Fahrenheit), provided
that coils are sufficiently protected from freezing. For the office building, energy savings of
about $0.05 per square foot were experienced by the VAV system economizer over the non-
economizer VAV system in cold and temperate climates. The economizer on the CV system
modeled was much less advantageous due to increases in heating energy costs for this
particular system, and was actually more expensive under some utility rate structures. However,
this would not likely be the case for dual fan, dual duct CV systems with separate economizers
for the hot and cold coils. The need to control relative humidity and the potential introduction of
outdoor contaminants are potential disadvantages of economizer systems. See Reports #2 and
#3.
* VAV with Constant Outdoor Air Control and an Economizer Offers Significant
Advantages, while VAV with Fixed Outdoor Air Fraction and No Economizer offers
offers Significant Disadvantages: Of all the ventilation systems and controls studied, the
VAV system with constant outdoor air flow, which in cold and temperate climates is combined
with an economizer and proper freeze control and humidity control, provided good overall
performance considering outdoor air flow, thermal comfort and energy efficiency. The VAV
system with a fixed outdoor air fraction and no economizer provided poor overall performance
because it failed to deliver adequate outdoor air and displayed no energy benefit. See Reports
#2 and #3.
* Raising Outdoor Air to Meet ASHRAE Standard 62-1999 in Most of the Office
Buildings Resulted in Very Modest Increases in Energy Costs. The main factor affecting
the energy cost of raising outdoor airflow was occupant density, such that buildings with higher
occupant density experienced higher energy cost increases. But for office buildings with 7
persons per thousand square feet, with moderate chiller and boiler efficiencies, and operating
in daytime mode for 12 hours per work day, raising outdoor air flow from 5-20 cfm (2-9 L/s) per
occupant raised HVAC energy costs by 2% -10% depending upon system and climate
variations. Considering the total energy bill, this increase amounted to approximately 1% - 4%.
This is generally less than is commonly perceived and suggests that the issue needs a more
careful examination by practitioners. The cooling cost increases in the summer months were
counterbalanced by cooling cost savings during cooler weather. Cost increases were higher for
economizer systems than systems without economizers because much of the cost savings from
higher outdoor air flow rates during cooler weather was already captured by the economizer
system. For buildings with occupant densities of 3 persons per thousand square feet, energy
costs increases were less. By contrast, office buildings modeled with 15 persons per 1000
Energy Cost and IAQ 8 Executive Summary
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square feet experienced up to 21 % increase in HVAC energy (or up to 8% increase in the total
energy bill). See report #4.
* VAV Systems in Education, Auditoriums, and Other Buildings with Very High
Occupant Densities May Require Special Adjustments for Meeting the High Outdoor Air
Flow Rates of ASHRAE 62-1999. In the education and auditorium buildings, the higher per
occupant outdoor air requirements sometimes exceeded the total supply air needed to control
thermal comfort. Even with the constant outdoor air damper control on the VAV system, the VAV
box minimum settings had to be raised to what appear to be uncommonly high levels (e.g. 50%
-100% of peak flow), in order to maintain 15 cfm per occupant during part load. See Report #6.
* Controlling Humidity Can be a Problem for Education Buildings, Auditoriums or
Other Buildings with Very High Occupant Densities where HVAC Systems Must
Deliver High Outdoor Air Flows to Meet ASHRAE Standard 62-1999. Relative humidity
frequently exceeded 60% and occasionally exceeded 70% in all climates in the education
buildings and the auditoriums even though the cooling coils were adequately sized to handle
peak loads and the indoor temperatures were well controlled. Problems occurred at part load
during mild weather when the outdoor relative humidity was high. The increased dominance of
the outdoor air at 15 cfm per occupant meant that the heating and cooling system had to deal
with wide ranges in the sensible to latent heat ratio, so that humidity as well as temperature had
to be part of the control regime. Controlling humidity may be a subject of special concern in
buildings with very high occupant densities which meet the outdoor airflow requirements of
ASHRAE Standard 62-1999. See Report #6.
* The Outdoor Air Requirements of ASHRAE Standard 62-1999 for Education
Buildings, Auditoriums and Other Buildings with Very High Occupant Densities Can
Create a Significant Energy Burden. When outdoor air ventilation rates were raised from 5
to 15 cfm per occupant in the education building and the auditorium, and when all adjustments
were made to insure adequate outdoor airflow rates at part load, and relative humidity was
controlled to 60% or below, HVAC energy costs rose by $0.13 -$0.27 per square foot (15%-
32%) in the education building, and by $0.36 -$0.88 per square foot (26% - 67%) in the
auditorium. This was judged to be a significant energy burden. See report #6.
* Peak Loads, and therefore Equipment Capacity Requirements, may be Significantly
Impacted when Outdoor Air Ventilation Rates are Raised. Raising the rate from 5 to 20
cfm per occupant in office buildings often raised peak coil requirements by 15% - 25%, and
created preheat requirements where none had previously existed. Raising the outdoor air flow
rate from 5 to 15 cfm increased the peak loads by 25%-35% in the education building, and by
35% - 40% in the auditorium. This could provide real limits to downsizing strategies which are
often part of an energy efficiency strategy, and calls for specific steps to reduce peak loads
without sacrificing outdoor air requirements. It also suggests indoor air consultants advise
clients of existing buildings to raise outdoor airflow rates in order to reduce indoor air quality
complaints, should first consider the potential need to either increase capacity or reduce peak
loads. Buildings without sufficient capacity may find themselves unable to maintain thermal
Energy Cost and IAQ 9 Executive Summary
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comfort in the face of these higher outdoor ventilation rates, or in the worst scenario, may
experience coil damage. See Report #5.
* Energy Recovery Technologies May Potentially Reduce or Eliminate the Humidity
Control, Energy Cost and Sizing Problems Associated with ASHRAE Standard 62-1999
in Education Buildings, Auditoriums, and Other Buildings with Very High Occupant
Density. While DOE-2 has limited capabilities to adequately model energy recovery
technologies, some literature suggests that both latent and sensible energy recovery systems
may significantly reduce or eliminate the associated problems of controlling thermal comfort,
reducing energy costs, and downsizing equipment needs while meeting the outdoor air
requirements of ASHRAE Standard 62-1999 in high occupant density buildings. Cost issues
would include the capital cost of the energy recovery equipment, capital cost savings from
downsizing, and the annual energy savings from the energy recovery system. Corroborating
research could be of great value. See Report #7.
* Protecting or Improving Indoor Environmental Quality During Energy Efficiency
Projects Need Not Hamper Energy Reduction Goals. Many energy efficiency measures
with the potential to degrade indoor environmental quality appear to require only minor
adjustments to protect the indoor environment. When energy efficiency measures (including
lighting upgrades), which were adjusted to either enhance or not degrade indoor environmental
quality, were combined with measures to meet the outdoor air requirements of ASHRAE
Standard 62-1999, total energy costs were cut by 42% - 43% for the office building, and 22% -
37% for the school. Not included were savings from reduced lighting during unoccupied hours
that could provide 12% - 22% savings, or improved equipment operations that could provide
5% -15% savings. Operational measures that could degrade IAQ such as widening the daytime
temperature deadband, relaxing the nighttime temperature setback, and reducing HVAC
operating hours were not included. Cumulatively, these three measures that are not compatible
with IEQ would have reduced total energy costs by only 3%-5% in the office building, and 7%-
10% in the education building. Therefore, there appears to be demonstrable compatibility
between indoor environmental goals and energy efficiency goals, when energy saving
measures and retrofits are applied wisely. See Report #7.
DISCUSSION
Relative Performance of Alternative HVAC Systems and Outdoor Air Control
Strategies
Exhibit 2 presents the average outdoor air flow rate by outdoor air temperature for the
CV and VAV systems. The design outdoor air flow for each system was set at 20 cfm per
occupant. The CV(FOAF) and the VAV(COA) configurations provided 20 cfm of outdoor air
per occupant at all times and in all climates. However, the VAV(FOAF) system never provided
20 cfm of outdoor air per person - except on the design day - because as the supply air flow
rate is throttled back from design conditions, the outdoor air flow into the building is reduced
proportionally, to between one third to two thirds the design flow rate most of the time.
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Exhibit 3 presents the proportion of occupied hours that each HVAC system in the base
office building experiences an outdoor air flow within designated ranges. The outdoor air
performance of the VAV(FOAF) systems varied with climate location. The system's outdoor air
performance was best in the hot Miami climate, and worst in the cold Minnesota climate. This is
because a larger portion of the year is spent at low cooling load conditions in Minneapolis
relative to Washington D.C. and Miami. An economizer significantly improved the outdoor air
performance of the VAV(FOAF) system for Minneapolis and Washington D.C., but only when
the economizer was operational. As expected, the economizer made little difference in the
outdoor air performance in the Miami climate.
Variations in outside air distribution due to variations in the thermal loads on the base
office building4 with VAV(COA) in Washington, D.C. are shown in Exhibit 4. For the VAV(COA)
system, the outdoor air flow at the air handler is consistently at the design level of 20 cfm (9.2
L/s) per occupant, but there is wide divergence in the outdoor airflow rate to the zones, with the
divergence depending on the outdoor temperature. At all temperatures, the core zone is being
consistently under ventilated relative to the building design flow rate and receives the least
outdoor air during hot weather, when a large portion of the supply air flows to the south zone
because of its high cooling load. The zonal pattern would be similar for the VAV(FOAF) system,
except that the outdoor airflow rate for each zone is lower, corresponding to the reduced air
flow into the building described above.
Since the ventilation disparity between zones is seasonal, the extent to which each zone
is over ventilated or under ventilated over the course of the year depends in part on the
proportion of occupied hours the building is experiencing various outdoor air temperatures.
Exhibit 5 presents the proportion of occupied hours that each zone experiences various outdoor
air ventilation rates for different ventilation systems. This table shows that for a design outdoor
air flow rate of 20 cfm (9 L/s) per occupant, the core zone of the CV(FOAF) system consistently
receives 11-15 cfm (5-7 L/s) per occupant, while the core zone for the VAV(COA) system
receives this amount about half the time. However, the core zone for the VAV(FOAF) system
received only 6-10 cfm (2-4 L/s) of outdoor air per occupant all year round. While not shown
here, patterns for other climates are similar. Also, adjusting VAV box settings (not shown here)
did not resolve this potential problem.
Operational modifications (not shown here) to improve the performance of the
VAV(FOAF) system were also modeled. Raising the outdoor air setting at design to 30 cfm
(14 L/s) per occupant in Miami was sufficient to achieve at least 15 cfm (7 L/s) per occupant
year round, but raised HVAC energy costs by $.03 per square foot. For Minneapolis and
Washington D.C., raising the design setting to 45 cfm (21 L/s) per occupant was necessary to
achieve 15 cfm per occupant year round, raising HVAC energy costs by $ .05 - $.06 per square
foot respectively. A seasonal reset strategy was also modeled with similar results. However,
making operational adjustments such as these runs the risk of exceeding capacity during
extreme weather conditions and may not be advisable.
The occupant density is the same for each zone.
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Exhibit 6 shows the energy costs for the CV system and the VAV systems with and
without economizers. Comparisons of the energy costs of the CV(FOAF) and the VAV(COA)
demonstrates the energy advantage of the VAV over the CV system. Both systems provide 20
cfm (9 L/s) under all operating conditions, but the energy cost for the VAV system was $0.10 -
$0.20 per square foot less than the CV system. Much of this is due to the reduction in fan energy
costs.
It is also useful to compare the VAV(FOAF) with the VAV(COA). The VAV(FOAF)
system consistently delivered less than 20 cfm (9 L/s) of outdoor air, but offered no energy
advantage over the VAV(COA) system which delivered a constant 20 cfm (9 L/s) per occupant.
That is, the diminished outdoor air flow of the VAV(FOAF) system did not reduce energy costs
over the VAV (COA) system. In fact, for the cold and temperate climates of Minneapolis and
Washington D.C., energy costs of the VAV(FOAF) system were marginally greater than the
VAV(COA) system, and only marginally less than the VAV(COA) system in Miami. This result is
consistent with the fact that additional outside air during cooler weather provides some degree
of free cooling, which is the concept underlying the economizer outdoor air control strategy. The
added cooling benefit of the additional outdoor air in the VAV(COA) system tends to offset the
added cooling burden during the hot summer season. However, when economizers were added
to both systems, both systems experienced free cooling. The VAV(FOAF)Econ saved about
$.02 per square foot over the VAV(COA)Econ.
Economizers reduced HVAC energy costs 6% -10% on VAV systems compared to
only 1 % to 2% for the CV system modeled. The economizer for the CV system provided
significant savings in cooling energy for the core zone, but this is partially counterbalanced by a
heating penalty for the perimeter zones. While the economizer brings in sufficient outdoor air to
reduce the mixed air temperature to 55° F in both systems, the supply air quantity of the CV
system is considerably higher than that of the VAV system, and this resulted in a substantial
heating penalty for the CV system economizer. Since gas is used for space heating, the
advantage of the CV economizer was sensitive to the price of gas relative to electricity. In fact,
while not shown here, for pricing structures involving high gas and low electricity prices , the CV
economizer raised rather than lowered energy costs. However, this may be unique to the CV
system modeled, and would not be expected to apply to a CV system with dual fan, dual ducts
and a separate economizer for the hot and cold coils. As expected, economizers have a
meaningful impact on energy costs only in cold and temperate climates. Because the Miami
climate offers little opportunity for economizer operation, energy savings of the economizer in
Miami were minimal.
Impacts of Increased Outdoor Air Flows on Annual HVAC Energy Costs
It is commonly held that raising outdoor air flow rates to accommodate indoor air quality
needs will dramatically increase energy use because this increased outdoor air must be
conditioned. However, this conventional wisdom ignores the dynamics of energy use of
different systems during different seasons. By way of explanation, Exhibit 7 shows the
variations on the coil loads at different seasons for selected systems. Exhibit 7 suggests that
Energy Cost and IAQ 12 Executive Summary
-------
the annual average change in energy use resulting from increasing the outdoor airflow rate in
an office building from 5-20 cfm per occupant depends on the relative impact of increases in
energy use and decreases in energy use during different seasons. Significant reductions in
cooling energy can occur in mild to cold temperatures which offset increases during warm
weather, but heating penalties may also occur in some CV systems during cold weather
periods. The actual impact depends on the nature of the energy impact during each season,
the utility rate structure, and the amount of time the system is operating within each seasonal
range. Increases in CV systems modeled tended to be higher than VAV systems because of
the heating penalty in winter, while economizer systems tended to result in higher energy cost
increases because much of the cooling cost savings in the mild to cold weather is already
accounted for in the economizer system.
Exhibit 8a presents the HVAC energy cost changes when outdoor air flow rates were
raised from 5 cfm (2 L/s) per occupant to 20 cfm (9 L/s) per occupant for the office building, and
to 15 cfm (7 L/s) per occupant for the education and assembly buildings. All buildings have
VAV(COA) systems with economizers. For the office building shown, the outdoor air increase
resulted in only a 6% -10% increase in HVAC energy cost, (or approximately 2% - 4% increase
of total energy cost). While not shown here, altering the HVAC system and controls and using
alternative energy pricing structures did not significantly change this range for the base building;
however, lowering the occupant density reduced the energy impact, while raising the occupant
density raised the energy impact considerably (see Project Report #4).
Raising outdoor airflow rates resulted in a considerably higher HVAC energy cost
increase in the school, amounting to 15% - 31% (5% -14% total energy cost), while the
auditorium experienced an HVAC energy cost increase of 26% - 67% (9% - 25% total energy
cost), for the HVAC system shown. The range of increase for other systems was very similar.
This large increase was due to many factors. Because of the high occupant densities in these
buildings, the required per occupant outdoor air flows may exceed supply air flow during
periods of the year when thermal loads are low. In these cases, supply air flows must be
increased to maintain minimum outdoor air flows in the building, increasing annual fan energy
costs. This was done by adjusting the VAV box minimum settings. In addition, the large
volumes of outdoor air subjected the cooling system to wide ranges in the sensible to latent heat
ratio, making it difficult for the system to keep indoor air relative humidity below 60% when
controlling only for temperature. Particularly on mild but humid days, indoor relative humidity
frequently rose above 60% and occasionally rose above 70%. As a result, cooling coil
temperatures had to be lowered when needed to insure that indoor relative humidity did not
exceed 65%.
Surprisingly, the total increase in HVAC energy cost from raising the outdoor airflow rate in the
education building and auditorium was least in Miami. While heating energy costs did not
increase in the office buildings with a VAV system in any climate, heating cost penalties in the
education and assembly buildings were substantial, often accounting for more than half of the
increase in total HVAC energy cost in the cold and temperate climates. However, in the hot and
humid climate of Miami, heating energy and fan energy penalties were very low. As a result, the
Energy Cost and IAQ 13 Executive Summary
-------
total energy cost increase in Miami was less than it was in either Minneapolis or Washington,
D.C. This result may be a function of the limitations of DOE-2 and modeling parameters
established for this project and should therefore be interpreted cautiously.
Exhibit 8b shows annual HVAC energy cost increases when outdoor airflow was raised from 5
to 20 cfm (2-9 L/s) per person for various office building configurations. It suggests that
occupant density is the single most important factor affecting the energy penalty from raising
outdoor air flow rates. The occupant density of the base building was 7 persons per 1000
square feet. Dropping occupant density to 3 persons per 1000 square feet reduced the energy
penalty to about a third of that in the base building, while raising the occupant density to15
persons per 1000 square feet approximately doubled the energy penalty. Other building
variations that were modeled included changes in building shell efficiency, changes in boiler
and chiller efficiency, increased exhaust, changes in building shape, and increases in HVAC
operating hours. None of these variations showed consistent and significant effects on the
energy penalty.
Impacts of Increased Outdoor Air Flows on HVAC System Capacity
Research on the impact of increased outdoor air flows on HVAC system capacity is
important because ASHRAE Standard 62-1999 and the IAQ litigation environment may have
the effect of forcing building operators to increase outdoor airflow rates in buildings in response
to occupant complaints. When these situations occur, the existing cooling and heating systems
(designed for 5 cfm of outdoor air per occupant) may not have the capacity to handle the
increased load caused by the increased outdoor air flows.
Exhibit 9 presents DOE-2.1E predicted peak load impacts for the 3 types of buildings
for VAV(COA) and the CV (FOAF) systems with economizers. While only economizer systems
are presented, there were no meaningful differences in the results between systems with and
without economizers Peak cooling load increases tended to be higher for the CV system than
the VAV system, and also higher in the education and assembly buildings when compared to
the office building. Increases in peak cooling loads ranged from 15% - 21% in the office
building, from 20% - 33% in the education building, and from 26% to 45% in the assembly
building. Increases tended to be higher in warmer climates5. Since increases in peak cooling
loads caused by the increase in outdoor air occured during the day, capacity limitations on the
cooling coil would most likely bring about thermal discomfort of occupants from midday to late
afternoon.
Absolute increases in peak heating loads are modest (below 500 kBTU/hr) for all
buildings in all climates, but percentage increases can be substantial due to relatively small
initial peak loads. Peak preheat coil load increases can be higher (0 -1100 kBTU/hr) and often
occurred in situations where no preheat was required at the lower outdoor air flow rate. The
Peak cooling load increases show the same climatic pattern in Eto (1988).
Energy Cost and IAQ 14 Executive Summary
-------
increase in both the peak heating and peak preheat coil load caused by the increase in outdoor
air occurred consistently at the first hour of occupancy when the outdoor air damper was first
opened. This suggests that heating and preheat coil capacity limitations may therefore prevent
the system from maintaining thermal comfort in the morning, and, with high outdoor air flow
rates, potentially throughout the day. In the worst scenario, inadequate preheat capacity could
result in coil damage if the outdoor dampers are not closed. But closing the outdoor dampers
would add indoor air quality problems to the thermal comfort problems.
The Energy Consequences of Protecting Indoor Environmental Quality in
Energy Efficiency Projects
The indoor environmental factors that most influence occupant health and welfare are the
thermal conditions, the lighting, and the concentrations of indoor pollutants. Thermal control and
lighting are familiar subjects in energy management. Accordingly, energy professionals are in a
strong position to affect these two important aspects of indoor environmental quality (IEQ) while
they are often less knowledgeable about indoor pollutant concentrations. Energy activities that
are compatible with IEQ, either because they are likely to enhance or have little effect on IEQ if
properly instituted, are identified in Exhibit 10. In general, the compatibility with IEQ is
dependent on the cautions and adjustments which are outlined in this exhibit. In this modeling
project, unless otherwise stated, the cautions and limitations described in this exhibit were
either directly or implicitly incorporated into the modeling runs when energy efficiency measures
were modeled.
Much of the perceived conflict between IEQ and energy efficiency results from just two
elements of an energy strategy- the tendency to minimize outdoor air ventilation rates and the
willingness to relax controls on temperature and relative humidity to save energy. Energy
reduction activities that are generally recognized as having a significant potential for degrading
the indoor environment and causing problems for the building owner (client) and the occupants
are identified in Exhibit 11.
A staged energy retrofit on an office building and education building was modeled to
quantify the energy gains and losses from energy activities which protect or enhance indoor
environmental quality and which avoid measures that compromise it. The office building had a
VAV system with fixed outdoor air damper and an economizer, while the education building
had a VAV system, constant outdoor airflow control and an economizer. The parameters of
these buildings and the energy measures taken are presented in Exhibit 12. The staged retrofit
included operational (tune-up) measures in Stage 1, load reduction measures in Stage 2, air
distribution system upgrades in Stage 3, central plant upgrades in Stage 4, and selected IEQ
upgrades in Stage 5. For analytic convenience, most of the operational measures normally
included in Stage 1 were modeled and analyzed separately and not included in Stage 1.
Exhibits 13-14 present the energy cost results from the staged energy activities for the
office building (Exhibit 13) and the education building (Exhibit 14). Exhibit 15 presents the
Energy Cost and IAQ 15 Executive Summary
-------
percent savings (from the base and from the previous stage) of the total energy cost for both
buildings6.
Stage 1 included only a simple seasonal supply air temperature reset strategy which
increased the supply air temperature from 55° F to 65°F from January 1 to March 31 in each
climate. Therefore, it does not reflect an optimal control logic for the fans and chiller. As a
result, the energy savings for Stage 1 (-2% -1 %) are not substantial and not uniformly positive,
and do not reflect values that would normally be achieved with a more sophisticated control
strategy (See discussion of other operational measures below).
A further reduction beyond Stage 1 of 28% - 33% was achieved in this building through a
lighting retrofit and increased efficiency of office equipment in Stage 2. The Stage 3 upgrades
relied solely on variable speed drives which reduced the energy costs an additional 5% -10%.
Finally, in Stage 4, central plant efficiency upgrades (including down-sizing the equipment
because of reduced loads7) added another 13% -15% to the total energy savings, bringing the
combined savings to 44% - 45% for the office building. The results for the education building
were similar but less dramatic, resulting in a total energy savings of 31 % - 40%. While many of
these activities implemented in Stages 1 through 4 above could adversely impact IEQ, all the
necessary adjustments identified in Exhibit 10 were made or are implicit in the model's
algorithms to insure that IEQ would not be degraded.
The base buildings provided only 5 cfm of outdoor air per occupant (i.e. does not meet
the current ASHRAE ventilation requirements for indoor air quality (ASHRAE Standard 62-
1999)). To meet the requirements of ASHRAE Standard 62-1999, a set of IEQ controls were
instituted as part of Stage 5. The first control was to raise the outdoor air setting from 5 cfm per
occupant to 20 cfm per occupant in the office building, and 15 cfm per occupant in the
education building. The second control was to provide a constant outdoor air control damper to
the office building to insure 20 cfm of outdoor air per occupant at all times. In the education
building, VAV boxes were adjusted to insure 15 cfm per occupant at all times, and relative
humidity was controlled so as not to exceed 60%.
When compared to the previous stage, meeting these indoor environmental
requirements raised total energy costs 3% -4% for the office building and 5% -14% for the
education building. When compared to from the base building, the IAQ requirements amounted
to a sacrifice of 2%-3% of annual energy savings for the office building, and 3%-9% for the
education building. Accordingly, the staged energy retrofits which include provisions to protect
indoor environmental quality and which provide additional outdoor air to meet ASHRAE
Standard 62-1999 achieved total energy savings of 42% - 43% for the office building, and 22%
- 37% for the education building. While the modeling capability in DOE-2.1E does not allow
adequate representation of energy recovery systems, some literature suggests that the energy
Total energy costs are defined here to include only energy from HVAC, lighting, and office equipment.
The equipment was downsized, but not below that necessary to accommodate increased outdoor air flow in Stage 5 of
20 cfm/occ for the office building, and 15 cfm per occupant for the education building, as per ASHRAE Standard 62-1999.
Energy Cost and IAQ 16 Executive Summary
-------
burden of providing additional outdoor air may be substantially reduced or eliminated through
energy recovery technology (Rengarajan, el al. 1996; Shirey and Rengarajan, 1996). This issue,
including the capital cost of the energy recovery equipment, the capital saving due to
downsizing, and the potential energy saving is worthy of further research.
Many energy measures with significant potential to adversely impact IEQ occur in Stage
1, and involve either relaxing temperature (and humidity) controls and/or reducing HVAC
operating hours. Exhibit 16 summarizes the results of these modeling runs. Widening the day
time temperature dead band from 71 - 77° F to 68-80° F reduced energy costs by 2% -3% in
the office building, and by 7% - 8% in the education building. Relaxing the night time
temperature setback from +/-10°F to +/-15°F reduced energy costs from 0% -1 % in the office
and from 1 % - 2% in the education building. Reducing the HVAC operating time by two hours
(including a reduction of startup time from 2 hours to 1 hour), reduced the energy costs by 0% -
1 % for the office building and by 2% - 4% in the education building. All of these operational
measures are attractive because they are inexpensive to implement. However, the savings are
small relative to other operational measures or retrofit measures, and cumulatively amount to
savings of only 3%-5% for the office building and to 7% -10% in the education building.
In contrast, other operational measures for Stage 1 that do not degrade IEQ can provide
significant savings. For example, simply commissioning the building to insure that controls and
equipment are functioning properly (not modeled) have been shown to typically reduce total
energy costs by 5% -15%, and also tend to improve IEQ (Gregerson, 1997). Reducing lighting
and office equipment usage during unoccupied hours can also result in significant savings. The
base office building was modeled with lighting during unoccupied hours operated at 20% of
daytime use and office equipment operated at 30% of daytime use. Exhibit 17 compares the
modeling results for this case (20%/30%) with both greater usage during unoccupied hours
(40% 750%) in Stage 1, and reduced usage (10%715%) after Stage 4 modifications.
As indicated in Exhibit 17, had the usage of the lighting/office equipment during
unoccupied hours been at 40%/50% of day time levels and then reduced to the original levels of
20%/30% that was modeled in the office building, 12% savings would have been possible in
Stage 1 from this activity. This result is consistent with field data which showed that energy
savings of 15% on average are associated with operational controls (mostly lighting) during
unoccupied hours (Herzog, et al.1992). In addition, an aggressive program to reduce nighttime
use of lights and office equipment after the building is made energy efficient and IEQ
compatible could provide additional reductions of equal magnitude.
In sum, the energy savings from operational controls that could degrade IEQ amounted to only
3% -10% of total energy costs. Considering the energy savings of 31 % - 45% associated with
lEQ-compatible upgrades through Stage 4, plus the potential for additional savings of 12% or
more from reduced use of lights, and savings of 5% -15% from improved equipment
performance, the energy savings of 3% -10% from controls that are incompatible with IEQ are
very small in comparison. It appears to make little sense to pursue energy reduction activities
that compromise IEQ and run the risk of potential liability of lEQ-related illnesses and
Energy Cost and IAQ 17 Executive Summary
-------
complaints, when the energy saving potential for compatible measures is so much greater in
comparison.
SUMMARY
This study contains DOE-2.1 E modeling data and analysis which shed light on several
important issues related to the performance of ventilation systems in terms of energy use,
thermal comfort, and outdoor air flow. Three fundamental questions were examined.
1. How well can commonly used HVAC systems and controls be relied upon to satisfy
generally accepted indoor air quality standards for HVAC systems when they are
operated according to design specifications?
2. What is the energy cost associated with meeting ASHRAE indoor air quality
performance standards for HVAC systems?
3. How much energy reduction would have to be sacrificed in order to maintain minimum
acceptable indoor air quality performance of HVAC systems in the course of energy
efficiency projects?
The results suggest that VAV systems with fixed outdoor air fraction (VAV(FOAF)) do
not provide adequate outdoor air to the building even when design settings are consistent with
ASHRAE 62-1999. CV and VAV (COA) do not pose such a problem. However, all systems
provide less than average outdoor air to the core zones and more than average outdoor air to
the perimeter zones. For the VAV (FOAF) system the core zone was particularly vulnerable to
being starved for outdoor air even with design settings meeting ASHRAE Standard 62-1999.
The cost of increasing outdoor air flow to meet ASHRAE standards can be modest for office
buildings, except that the energy penalty can rise substantially with higher occupant densities.
For schools and auditoriums, with high occupant densities, the energy penalty can be
substantial. Controlling humidity could also be a problem with higher outdoor airflow rates in
schools and auditoriums. It was noted, however, that energy recovery ventilation may have the
potential to significantly improve humidity control and reduce the energy penalty.
Finally, the study suggests that protecting indoor environmental quality in energy efficiency
projects need not hamper the achievement of energy reduction goals, provided that the projects
are instituted wisely. Avoiding measures that could degrade IEQ involved energy sacrifices that
were small compared to the potential for energy savings from measures that are compatible
with IEQ. Some guidelines for insuring that energy efficiency measures do not degrade IEQ
were also presented.
Energy Cost and IAQ 18 Executive Summary
-------
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Energy Cost and IAQ 19 Executive Summary
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Energy Cost and IAQ 22 Executive Summary
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Exhibit 1: Characteristics of the Base Buildings Modeled in this Study
Building Characteristics
shape
zones/floor
floor area (ft2)
number of floors
floor height (ft)
wall construction
net window area (%)
window U-value (Btu/hr ft2 °F)
window shading coefficient
wallR-value (hr ft2 °F/Btu)
roof R-value (hr ft2 °F/Btu)
perimeter/core ratio*
infiltration rate (ach)
Occupancy
number of occupants
occupant density (occup/1 000ft2)
HVAC
air distribution system
heating and DHW
cooling
Office
square
5
338,668
12
12
steel-reinforced
concrete, curtain wall
42%
0.75
0.8
R-7
R-8
0.5
0.25**
2,130
7
central (CVor VAV)
central gas boiler - 70%
efficiency
chiller - 3 COP
w/cooling tower
Education
L-shaped
6
50,600
2
15
concrete block
34%
0.59
0.6
R-8
R-12
1.0
0.25
1,518
30
central (CVor VAV)
central gas boiler - 80%
efficiency
chiller - 4 COP
w/cooling tower
Assembly
square
5
19,600
1
30
concrete block
7%
0.59
0.6
R-8
R-12
0.6
0.25
588
60
central (CVor VAV)
central gas boiler - 80%
efficiency
chiller - 4 COP
w/cooling tower
* Ratio of perimeter to core floor area, where perimeter space is up to 15 ft. from the exterior walls
**0.5 when HVAC is not operating
Energy Cost and IAQ
23
Executive Summary
-------
Building: Office
Location: Washington, DC
System: VAV & CV
OA Control: FOAF & COA
Design OA Flow: 20 cfm/person
40
35
(0
0)
•+J
ro
I
30
25
<2 20
r
§f
•o £
»*- ,11-
".15
0)
o
5
0)
>
10
0
10
Exhibit 2
Comparison of Seasonal Variations
in Outdoor Air Flow Rates for
VAV & CV Systems
20
30
40 50 60 70
Outdoor Air Temperature, (deg F)
80
90
100
-------
Exhibit 3: Comparison of Outdoor Air Flows {design = 20 cfm (9 L/s) per person} for
a Large Office Building with Alternative HVAC Systems
(% of Occupied Hours ]
HVAC System Type
and
Climate Location
CV(FOAF)
Minneapolis, MN
Washington, DC
Miami, FL
VAV(COA)
Minneapolis, MN
Washington, DC
Miami, FL
VAV(FOAF)
Minneapolis, MN
Washington, DC
Miami, FL
VAV(FOAF) Econ
Minneapolis, MN
Washington, DC
Miami, FL
Outdoor Air Flow Rates Achieved
(cfm per person)
<=5
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
6-10
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
42.0%
16.6%
0.0%
0.0%
0.1%
0.0%
11-15
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
56.3%
78.1%
42.5%
32.5%
48.6%
62.3%
16-19
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
1.7%
5.3%
57.5%
0.0%
0.5%
31.9%
>=20
100.0%
100.0%
100.0%
100.0%
100.0%
100.0%
0.0%
0.0%
0.0%
67.4%
50.8%
5.8%
Energy Cost and IAQ
25
Executive Summary
-------
Building: Office
Location: Washington, DC
System: VAV
VAV Box Min: 30% All Zones
OA Control: Constant Flow
Design OA Flow: 20 cfm/person
Exhibit 4
Comparison of Zone Level Outdoor Air
Flow Rates for VAV (COA) System
;: 15
o
o
5 10
3
5
0
10
20
30
40 50 60 70
Outdoor Air Temperature, (deg F)
80
90
100
•Core
•East
North
South
•West
•Building
-------
Exhibit 5: Comparison of Zone Level Outdoor Air Flow Rates {design = 20 cfm (9
L/s) per person} for Three Types of HVAC Systems in Office Buildings in
Washington, DC.
(% of Occupied Hours)
System Type
and Zone
CV(FOAF)
Core
East
North
West
South
VAV(COA)
Core
East
North
West
South
VAV(FOAF)
Core
East
North
West
South
without Economizer
OA Flow Rate Achieved (cfm/person)
<6 6-10 11-15 16-19 >19
100.0
100.0
100.0
100.0
100.0
0.2 51.5 48.3 0.0
100.0
14.4 85.6
100.0
100.0
0.7 99.3 0.0 0.0 0.0
46.4 15.3 38.3
69.4 24.4 6.2
54.2 15.0 30.8
35.2 10.7 54.1
with Economizer
OA Flow Rate Achieved (cfm/person)
<6 6-10 11-15 16-19 >19
49.9 0.6 49.5
100.0
100.0
100.0
100.0
39.0 10.4 50.6
100.0
4.1 95.9
100.0
100.0
49.3 0.1 0.1 50.6
6.3 13.5 80.2
3.5 19.4 23.8 53.2
9.7 14.5 75.7
6.1 8.8 85.1
Energy Cost and IAQ
27
Executive Summary
-------
Exhibit 6: Comparison of Annual Energy Costs for the Base Office Building
with Alternative HVAC Systems and in Different Climates
HVAC System Type and
Climate Location
CV(FOAF)
Minneapolis, MN
Washington, DC
Miami, FL
CV(FOAF) Econ
Minneapolis, MN
Washington, DC
Miami, FL
VAV(COA)
Minneapolis, MN
Washington, DC
Miami, FL
VAV(COA) Econ
Minneapolis, MN
Washington, DC
Miami, FL
VAV(FOAF)
Minneapolis, MN
Washington, DC
Miami, FL
VAV(FOAF) Econ
Minneapolis, MN
Washington, DC
Miami, FL
Annual HVAC
Energy Use Summary
Fan
($/SF)
0.32
0.29
0.30
0.32
0.29
0.30
0.19
0.17
0.18
0.19
0.17
0.18
0.19
0.17
0.18
0.19
0.17
0.18
Cooling
($/SF)
0.52
0.56
0.72
0.45
0.50
0.71
0.49
0.52
0.65
0.43
0.47
0.64
0.49
0.52
0.62
0.42
0.46
0.61
Heating
($/SF)
0.04
0.01
0.00
0.10
0.06
0.00
0.10
0.05
0.00
0.11
0.05
0.00
0.10
0.05
0.00
0.11
0.05
0.00
Total
($/SF) (KBtu/sf)
0.88
0.86
1.02
0.87
0.85
1.01
0.78
0.74
0.83
0.73
0.69
0.83
0.79
0.74
0.81
0.71
0.68
0.80
47.4
41.1
50.6
53.7
46.4
50.7
49.7
38.9
38.9
45.9
35.8
38.5
50.6
39.5
38.3
45.7
35.5
37.8
Energy Cost and IAQ
28
Executive Summary
-------
Exhibit 2
Change in Coil Loads with Increased Outdoor Air Flow Rate for Building
A with CV (FOAF) in
""500
2000
1500
_ 1000
^
1 500
—
=! -500
o
0 -1000
-1500
-2000
9cinn
Washington, DC
,...jim
^
rcdUl
^m
1
iiif
iiouu
Bin1 (<55°F) Bin2 (56-65°F) Bin3 (66-79°F) Bin4 (>80°F) Annual
Outdoor Air Temperature (°F)
E3 Heating
H Cooling (S)
H Cooling (L)
Exhibit 3
Change in (
A with CV (
2500 -,
2000 -
1500 -
_ 1000 -
S
1 500
- -500
o
0 -1000
-1500 -
-2000 -
-2500
2oil Loads with Increased Outdoor Air Flow Rate for Building
FOAF) EconT in Washington, DC
JSSSJ
[•••j
JH]
Bin1 (<55°F) Bin2 (56-65°F) Bin3 (66-79°F) Bin4 (>80°F) Annual
Outdoor Air Temperature (°F)
ED Heating 0
El Cooling (S)
H Cooling (L)
-------
Exhibit 7a
Change in Coil Loads with Increased Outdoor Air Flow Rate for Building
A with VAV
2500 -,
2000
1500
_ 1000
| 500
(0
=! -500
'o
0 -1000
-1500
-2000
(COA) in Minneapolis, MN
^Sit1
^Sit1
^Sit1
mwn
I
mwwm
mmm*
Bin1 (<55°F) Bin2 (56-65°F) Bin3 (66-79°F) Bin4 (>80°F) Annual
Outdoor Air Temperature (°F)
S Heating
0 Cooling (S)
H Cooling (L)
Exhibit 7b
Change in
A with VAV
2500 -,
2000 -
1500 -
_ 1000 -
3
1 500
| ° -
= -500
0 -1000
-1500 -
-2000 -
-2500
Coil Loads with Increased Outdoor Air Flow Rate for Building
(COA) EconT in Minneapolis, MN
im-rfnn
nrwn
^^•- - - JlHJ
Bin1 (<55°F) Bin2 (56-65°F) Bin3 (66-79°F) Bin4 (>80°F) Annual
Outdoor Air Temperature (°F)
El Heating
El Cooling (S)
H Cooling (L)
-------
Exhibit 9: Impacts of Increased Outdoor Air Flows on Peak HVAC Coil Loads
for the CV(FOAF) and VAV(COA) Systems with Economizers
Climate
End Use
Office Building
5 cfm Increase
kBTU/Hr kBTU/hr
Percent
Increase
(%)
Education Building
5 cfm Increase
kBTU/hr kBTU/hr
Percent
Increase
(%)
Assembly Building
5 cfm Increase
kBTU/hr kBTU/hr
Percent
Increase
(%)
CV(FOAF) EconT
Minneapolis, MN
Cooling
Heating
Preheat
Washington, DC
Cooling
Heating
Preheat
Miami, FL
Cooling
Heating
Preheat
9288 1421
6707 623
0 0
9017 1756
3936 35
0 0
9258 1876
3446 0
0 0
15.0%
9.0%
0.0%
19.0%
1 .0%
0.0%
20.0%
0.0%
0.0%
2068 679
2609 588
0 0
2071 562
1884 234
0 77
2409 503
17 560
0 0
33.0%
23.0%
0.0%
27.0%
12.0%
Increase
21.0%
3366.0%
0.0%
1193 527
1476 41
0 44
1157 522
1153 74
0 38
1394 611
63 478
0 0
44.0%
3.0%
Increase
45.0%
6.0%
Increase
44.0%
758.0%
0.0%
VAV(COA) EconT
Minneapolis, MN
Cooling
Heating
Preheat
Washington, DC
Cooling
Heating
Preheat
Miami, FL
Cooling
Heating
Preheat
8688 1336
6148 444
0.00 897
8517 1659
4638 None
0.00 None
8670 1862
1949 None
0.00 None
15%
7%
Increase
19%
None
None
21%
None
None
1841 370
2819 1
246 1282
1951 488
1935 93
90 750
2213 529
397 271
0.00 200
20%
0%
521%
25%
5%
832%
24%
68%
Increase
958 271
1134 106
330 919
1067 275
822 177
224 553
1229 349
99 291
0.00 151
28%
9%
279%
26%
22%
247%
28%
293%
Increase
Energy Cost and IAQ
32
Executive Summary
-------
Exhibit 10: Energy Measures that are Compatible with IEQ
Measure
Improve building
shell
Reduce internal
loads (e.g. lights,
office equipment)
Fan/motor/drives
Chiller/ boiler
Energy recovery
Air-side
economizer
Night pre-cooling
Preventive
Maintenance (PM)
of HVAC
CO2 controlled
ventilation
Reducing demand
(KW) charges
Supply air
temperature reset
Comment
- May reduce infiltration. May need to increase mechanically supplied
outdoor air to ensure applicable ventilation standards are met.
- Reduced loads will reduce supply air requirements in VAV systems. May
need to increase outdoor air to meet applicable ventilation standards.
- Lighting must be sufficient for general lighting and task lighting needs
- Negligible impact on IEQ
- Negligible impact on IEQ
- May reduce energy burden of outdoor air, especially in extreme climates
and/or when hiqh outdoor air volumes are required (e.q. schools, auditoria).
- Uses outdoor air to provide free cooling. Potentially improves IEQ when
economizer is operating by helping to ensure that the outdoor air ventilation
rate meets IEQ requirements.
- On/off set points should be calibrated to both the temperature and moisture
conditions of outdoor air to avoid indoor humidity problems. May need to
disengage economizer during an outdoor air pollution episode.
- Cool outdoor air at night may be used to pre-cool the building while
simultaneously exhausting accumulated pollutants. However, to prevent
microbiological growth, controls should stop pre-cooling operations if dew
point of outdoor air is high enough to cause condensation on equipment.
- PM will improve IEQ and reduce energy use by removing contaminant
sources (e.g. clean coils/drain pans), and insuring proper calibration and
efficient operation of mechanical components (e.g. fans, motors,
thermostats, controls)..
- CO2 controlled ventilation varies the outdoor air supply in response to CO2
which is used as an indicator of occupancy. May reduce energy use for
general meeting rooms, studios, theaters, educational facilities etc. where
occupancy is highly variable, and irregular. A typical system will increase
outdoor air when CO2 levels rise to 600-800 ppm to ensure that maximum
levels do not exceed 1 ,000 ppm. The system should incorporate a
minimum outside air setting to dilute building related contaminants during
low occupancy periods.
- Night pre-cooling and sequential startup of equipment to eliminate demand
spikes are examples of strategies that are compatible with IEQ. Caution is
advised if load shedding strategies involve changing the space temperature
set points or reducing outdoor air ventilation during occupancy.
- Supply air temperature may sometimes be increased to reduce chiller
energy use. However, fan energy will increase. Higher supply air
temperatures in a VAV system will increase supply air flow and vice versa.
Energy Cost and IAQ
33
Executive Summary
-------
Exhibit 10 (continued)
Equipment down-
sizing
- Prudent avoidance of over-sizing equipment reduces first costs and energy
costs. However, capacity must be sufficient for thermal and outdoor air
requirements during peak loads in both summer and winter. Latent load should
not be ignored when sizing equipment in any climate. Inadequate humidity
control has resulted in thermal discomfort and mold contamination so great as
to render some buildings uninhabitable.
- Energy recovery systems may enable chillers and boilers to be further
downsized by reducing the thermal loads from outdoor air ventilation.
Exhibit 11: Energy Measures that May Degrade IEQ
Measure
Comment
Reducing outdoor
air ventilation
- Applicable ventilation standards usually specify a minimum continuous
outdoor air flow rate per occupant, and/or per square foot, during occupied
hours. They are designed to ensure that pollutants in the occupied space are
sufficiently diluted with outdoor air. Reducing outdoor air flow below applicable
standards can degrade IEQ and has low energy saving potential relative to
other energy saving options.
Variable Air
Volume (VAV)
Systems with fixed
percentage
outdoor air
- VAV systems can yield significant energy savings over Constant Volume (CV)
systems in many applications. However, many VAV systems provide a fixed
percentage of outdoor air (e.g. fixed outdoor air dampers) so that during part
load conditions when the supply air is reduced, the outdoor air may also be
reduced to levels below applicable standards.
- VAV systems should employ controls which maintain a continuous outdoor air
flow consistent with applicable standards. Hardware is now available from
vendors and involves no significant energy penalty.
Reducing HVAC
operating hours
Delayed start-up or premature shutdown of the HVAC can evoke IEQ problems
and occupant complaints.
- An insufficient lead time prior to occupancy can result in thermal discomfort
and pollutant-related health problems for several hours as the HVAC system
must overcome the loads from both the night-time setbacks and from current
occupancy. This is a particular problem when equipment is downsized.
Shutting equipment down prior to occupants leaving may sometimes be
acceptable provided that fans are kept operating to ensure adequate ventilation.
However, the energy saved may not be worth the risk .
Relaxation of
thermal control
Some energy managers may be tempted to allow space temperatures or
humidity to go beyond the comfort range established by applicable standards.
Occupant health, comfort and productivity are compromised. The lack of overt
occupant complaints is NOT an indication of occupant satisfaction.
Energy Cost and IAQ
34
Executive Summary
-------
Exhibit 12: Modeling Parameters for the Office and Education Building
Building Parameter
Office Building
Base
Modification
Education Building
Base*
Modification
Stage 1: Operational/Tune-up Measures
Day Temp. Set Points
Night Set Back
Day HVAC Hours
Seasonal Reset
71°-77°F
+/- 1 0° F
Sam -6pm
No
(68°- 80° F)
(+/-15°F)
(9am - 5pm)
Yes
71°-77°F
+/- 1 0° F
7am -10pm
No
(68°- 80° F)
(+/- 15°F)
(Sam - 9pm)
Yes
Entries in parentheses were modeled separately-not part of the retrofit project
Stage 2: Load Reduction Measures
Lighting
Office Equipment
2.5 W/f2
1 .0 W/f2
30% reduction
30% reduction
3.0 W/f2 rms
2.0 W/f2 co rr
0.25 W/f2
30% reduction
30% reduction
Stage 3: Air distribution System Upgrades
VSD
no
yes
no
yes
Stage 4: Central Plant Upgrades
Chiller COP
Boiler Efficiency
3.0
70%
5.5
85%
3.0
70%
5.5
85%
Stage 5: IEQ Ventilation Modifications Required to meet ASHRAE 62-1999
Outdoor Air Setting
Outdoor Air Control
Humiditv Control
5 cfm/occ
fixed damper
not needed
20 cfm/occ
constant flow
not needed
5 cfm/occ
constant flow
not needed
1 5 cfm/occ
const. flow-VAV box
adjustment
60% RH
*Forthe base education building used for the energy retrofit: infiltration rate = O.Sach; window U value = 0.99 (Btui/hr
ft2 °F); and window shading coeff. = 0.90.
Exhibit 13: Energy Cost for Office Building with Energy and IEQ Modifications
Building
Parameter
Base Bldg
Stage 1
Seas. Reset
Stage 2
Ltng/Off Equip
Stage 3
VSD
Stage 4
Chiller/Boiler
Stage 5
OA Setting
OA Control
Washington D.C.
($/sf)
Fan
0.17
0.18
0.15
0.09
0.09
0.09
0.09
Cool
0.42
0.41
0.30
0.28
0.16
0.18
0.19
Heat
0.05
0.04
0.08
0.06
0.05
0.06
0.06
Total
HVAC
0.64
0.63
0.52
0.43
0.30
0.32
0.33
Lights
Off.
Equip
0.94
0.94
0.57
0.57
0.57
0.57
0.57
Total
1.58
1.57
1.08
1.00
0.87
0.89
0.90
Minneapolis
($/sf)
Total
HVAC
0.68
0.66
0.58
0.47
0.33
0.36
0.37
Lights
Off.
Equip
0.94
0.94
0.57
0.57
0.57
0.57
0.57
Total
1.62
1.60
1.16
1.04
0.90
0.93
0.94
Miami
($/sf)
Total
HVAC
0.74
0.78
0.57
0.52
0.35
0.38
0.40
Light
&Off.
Equip
0.94
0.94
0.57
0.57
0.57
0.57
0.57
Total
1.68
1.72
1.15
1.09
0.93
0.95
0.9
Energy Cost and IAQ
35
Executive Summary
-------
Exhibit 14: Energy Cost for the Education Building with Energy and IEQ Modifications
Building
Parameter
Base Bldg
Stage 1
Seasonal Reset
Stage 2
Lights/off equip
Stage 3
VSD
Stage 4
Chiller/boiler
Stage 5*
OA Setting
OA & RH control
Washington D.C.
($/f2)
Fan
0.21
0.21
0.19
0.11
0.11
0.12
0.13
Cool
0.62
0.61
0.53
0.50
0.29
0.35
0.36
Heat
0.28
0.25
0.33
0.33
0.28
0.35
0.38
Total
HVAC
1.11
1.07
1.04
0.94
0.67
0.82
0.87
Light
&Off
Equip
0.97
0.97
0.67
0.67
0.67
0.67
0.67
Total
2.08
2.04
1.71
1.62
1.35
1.49
1.54
Minneapolis
($/f2)
Total
HVAC
1.42
1.38
1.42
1.30
0.98
1.19
1.20
Light
&Off
Equip
0.97
0.97
0.67
0.67
0.67
0.67
0.67
Total
2.40
2.36
2.10
1.97
1.65
1.68
1.87
Miami
($/f2)
Total
HVAC
1.22
1.23
1.08
0.98
0.64
0.73
0.71
Light
&Off.
Equip
0.97
0.97
0.67
0.67
0.67
0.67
0.67
Total
2.19
2.21
1.76
1.65
1.31
1.40
1.38
* Only the education building required RH control
Exhibit 15: Percent Savings in Total Energy Cost from Energy and IEQ Modifications
(Top figure in each cell is for office building; bottom figure is for education building)
Base Bldg
Stage 1
Seasonal Reset
Stage 2
Lights/Off Equip
Stage 3
VSD
Stage 4
Chiller/boiler
Stage 5*
OA setting with OA
& RH control
Washington
$/f2
1.58
2.08
1.57
2.04
1.08
1.71
1.00
1.62
0.87
1.35
0.90
1.54
From
Base
01%
02%
32%
18%
37%
22%
45%
35%
43%
26%
From
Prev.
Stage
01%
02%
31%
16%
07%
05%
13%
17%
-03%
-14%
Minneapolis
$/f2
1.62
2.40
1.60
2.36
1.16
2.10
1.04
1.97
0.90
1.65
0.94
1.87
From
Base
01%
2%
28%
13%
36%
18%
44%
31%
42%
22%
From
Prev.
Stage
01%
2%
28%
11%
10%
6%
13%
16%
-04%
-13%
Miami
$/f2
1.68
2.19
1.74
2.21
1.15
1.76
1.09
1.65
0.93
1.31
0.97
1.38
From
Base
-02%
-01%
32%
20%
35%
25%
45%
40%
42%
37%
From
Prev.
Stage
-02%
-01%
33%
20%
5%
6%
15%
21%
-04%
-05%
' Only the education building required RH control
Energy Cost and IAQ
36
Executive Summary
-------
Exhibit 16: Energy Costs of Operational Measures that May Have Adverse Effects on IEQ
Building
Parameter
Base Off. Bldg
Day Temp. Set
Night Set Back
Day HVAC Mrs.
Base Edu. Bldg
Day Temp. Set
Night Set Back
Day HVAC Mrs
Washington D.C.
$/sf
Fan
0.17
0.17
0.16
0.17
0.21
0.18
0.21
0.20
Cool
0.42
0.40
0.41
0.42
0.62
0.55
0.62
0.61
Heat
0.05
0.04
0.04
0.04
0.28
0.22
0.27
0.25
Total
HVAC
0.64
0.61
0.62
0.63
1.11
0.95
1.10
1.06
Light
&Off
Equip
0.94
0.94
0.94
0.94
0.97
0.97
0.97
0.97
Total
1.58
1.56
1.56
1.57
2.08
1.93
2.07
2.02
%
Save
01%
01%
01%
07%
00%
03%
Minneapolis
$/sf
Total
HVAC
0.68
0.64)
0.66
0.66
1.42
1.25
1.40
1.34
Total
1.62
1.58
1.60
1.60
2.40
2.23
2.38
2.31
%
Save
03%
01%
01%
07%
01%
04%
Miami
$/sf
Total
HVAC
0.74
0.71
0.72
0.75
1.22
1.06
1.22
1.18
Total
1.68
1.65
1.66
1.69
2.19
2.03
2.19
2.15
%
Save
02%
01%
00%
01%
00%
02%
Exhibit 17: Savings from Reduced Lights and Office Equipment when Unoccupied
Operational Control
% of daytime use during unoccupied hours
Stage 1
40% lights/50% office eguipment (base case)
20% lights/30% office eguipment
Stage 4 (retrofitted building)
20% lights/30% office eguipment
15%lights/20% office eguipment
Office Building in Washington D.C.
Enerav Cost ($/f 2)
HVAC
0.71
0.64
0.33
0.29
Light/off eguip
1.08
0.94
0.57
0.40
Total
1.79
1.58
0.90
0.70
Sa
S/f2
0.21
0.20
I/ing
%
12%
22%
Energy Cost and IAQ
37
Executive Summary
------- |