United States	Indoor Environments	liPA-402-S-01-OOI13
Environmental	Division (6609J)	January 2000
Protection	Office of air and Radiation
Agency	
Energy Cost and IAQ
Performance of Ventilation
Systems and Controls
Project Report # 2
Assessment of CV and VAV Ventilation
Systems and Outdoor Air Control Strategies
for Large Office Buildings
Outdoor Air Flow and Energy Use

-------
Energy Cost and IAQ Performance of Ventilation Systems
and Controls
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
Indoor Environments Division
Office of Radiation and Indoor Air
Office of Air and Radiation
United States Environmental Protection Agency
Washington, D.C. 20460
January 2000

-------
Energy Cost and IAQ Performance of Ventilation Systems and Controls
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
INTRODUCTION
Purpose and Scope of this Report
Constant volume (CV) air handling systems provide a constant flow of ventilation air at all operating
conditions, and were the staple of the HVAC design community for many years. Because the
ventilation air quantities in these systems do not change, maintaining a minimum outdoor airflow is
a matter of establishing a minimum outdoor air damper setting. In the last fifteen years, variable air
volume (VAV) ventilation systems have become more popular with design engineers because of
their improved energy efficiency ever CV systems. When VAV systems were introduced as being
more energy efficient, they often employed outdoor air controls similar to those of the older CV
systems. However, since the total supply airflow in a VAV system varies in response to varying
thermal loads, the outdoor air flow rate into the building may also be expected to vary, unless
specific provisions are introduced to maintain a constant outdoor airflow rate. Thus, the variations
in airflow have created new challenges for maintaining minimum outdoor airflow.
Using the DOE-2.1E energy simulation model, this report systematically compares the outdoor air
flow quantities of CV and VAV air handling systems in a large office building under a variety of
outdoor air control and economizer strategies, and examines the energy implications of these
strategies. This assessment is conducted for three climate regions representing cold
(Minneapolis), temperate (Washington, D.C.) and hot/humid (Miami) weather conditions. A
companion report (Project Report #3) examines how these systems distribute outdoor air and
control thermal comfort in individual zones.
Background
This report is part of a larger modeling project to assess the compatibilities and trade-offs between
energy, indoor air, 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.
Energy Cost and MQ
1
Report # 2

-------
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.
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 ventilation
systems and control strategies. Constant volume (CV) and variable air volume (VAV) systems in
different buildings and with different outdoor air control strategies under alternative climates
provided the basis for parametric variations in the database.
Seven reports, covering the following topics, describe the findings of this project:
	Project Report #1: Project objective and detailed description of the modeling methodology and
database development
	Project Report #2: Assessment of energy and outdoor air flow rates in CV and VAV ventilation
systems for large office buildings:
	Project Report #3: Assessment of the distribution of outdoor air and the control of thermal
comfort in CV and VAV systems for large office buildings
	Project Report #4: Energy impacts of increasing outdoor air flow rates from 5 to 20 cfm per
occupant in large office buildings
	Project Report #5: Peak load impacts of increasing outdoor air flow rates from 5 to 20 cfm per
occupant in large office buildings
	Project Report #6: Potential problems in IAQ and energy performance of HVAC systems when
outdoor airflow rates are increased from 5 to 15 cfm per occupant in
auditoriums, education, and other buildings with very high occupant density
	Project Report #7: The energy cost of protecting indoor environmental quality during energy
efficiency projects for office and education buildings.
DESCRIPTION OF THE BUILDING AND VENTILATION SYSTEMS MODELED
A large 12 story office building was modeled in three different climates representing cold
(Minneapolis), temperate (Washington, D.C.), and hot/humid (Miami) climate zones. The building
has an air handler on each floor servicing four perimeter zones corresponding to the four compass
Energy Cost and MQ
2
Report it 2

-------
orientations, and a core zone. A dual duct constant volume (CV) system with temperature reset,
and a single duct variable volume (VAV) system with reheat were modeled. Constant volume
systems control the thermal conditions in the space by altering the temperature of a constant
volume of supply air. VAV systems provide control by altering the supply air volume while
maintaining a constant supply air temperature.
Three basic outdoor air control strategies were modelled: fixed outdoor air fraction (FOAF),
constant outdoor air (COA), and air-side economizer (ECON). The FOAF strategy maintained a
constant outdoor air fraction (percent outdoor air) irrespective of the supply air volume. The FOAF
strategy maintained a constant outdoor air fraction (percent outdoor air) irrespective of the supply
air volume. For VAV systems, the FOAF may 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 airflow 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.
Two air-side economizer strategies are used, one based on temperature (ECONt) and one on
enthalpy (ECONe). The economizer strategies override the 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). The quantity of outdoor air is adjusted so that the desired supply air
discharge temperature (or enthalpy) can be achieved with minimum mechanical cooling. Because
outdoor air humidity levels are sometimes high during warm weather, the temperature economizer
in this project is shut off at outdoor temperatures above 65 F.
A more detailed description of the building and ventilation system is provided in Report#!
APPROACH
In this report, the outdoor air quantities for each HVAC system and OA control strategy are
determined over the full range of thermal loads. The systems design setting is 20 cfm of outdoor
air per occupant, which is prescribed for office spaces by ASHRAE Standard 62-19991. The
outdoor air flow rates were established for design occupancy levels and were not changed as
occupancy varied during the day.
1 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 ASHRAF, Standard 62-1999.
Energy Cost and MQ
3
Report it 2

-------
Annual energy use (KBtu/ft2) is converted to energy cost under the base price structure of $.044 per
kilowatt-hour, and $7.89 per kilowatt and $0.49 per therm. A sensitivity analysis is also conducted
to determine how sensitive the conclusions are to relative utility prices. Since Minneapolis,
Washington, D.C. and Miami are used only to represent different climate conditions, no attempt
was made to use the actual energy prices in these individual cities. Derivation of the pricing
scenarios is provided in Report #1
RESULTS
The presentation of results is organized to shed light on the following questions:
a.	Do the energy savings in VAV systems justify the potential shortfall in delivering desired
quantities of outdoor air? What are optimal outdoor air control strategies for CV and VAV
systems?
b.	How significant are advantages of economizer strategies in energy savings and outdoor
airflow rates? When do enthalpy economizers make sense?
c.	How might operating engineers change outdoor air flow settings to improve the
performance of existing HVAC systems?
Comparing CV and VAV Systems
Energy Advantage of VA V Systems
Exhibit 1 presents the annual energy use and annual energy costs for operating each of the CV and
VAV systems modeled without economizers. The data confirm the energy savings associated with
VAV systems. For example, the annual energy cost of the CV(FOAF) system is $.86/sf, while the
annual cost ofVAV(FOAF) system is only $.74/sf, or 14% less for the Washington, D C. climate.
The VAV(FOAF) system is 10% less in Minneapolis and 21% less in Miami compared to the CV
(FOAF) system. As expected, most of the savings results because fan energy is cut almost in half.
The modeled CV system is a dual duct system with temperature reset capabilities, which is much
more energy efficient than other CV systems, and therefore the results tend to underestimate the
advantages of conversion from CV to VAV systems.
Except in Miami where heating is negligible, more heating energy is used in the VAV than in the
comparable CV systems. This is because the VAV system modeled reheats the supply air at the
VAV box after it is cooled at the central air handler.
Outdoor Air Shortfall with VAV(FOAF) Systems
Exhibit 2 compares the outdoor airflow rate of CV(FOAF), VAV(FOAF) and the VAV(COA)
systems set to deliver 20 cfm of outdoor air per person at the design cooling load. This plot is
based on hourly data over the full year, and shows the average OA flow rate delivered by the air
Energy Cost and MQ
4
Report it 2

-------
handler for all the hours associated with each outdoor air temperature - Winter at the left end of the
horizontal axis, Spring/Fall in the middle, and Summer at the right end.
Since the CV system operates on a constant supply air volume, the CV(FOAF) strategy brings in a
constant supply of outdoor air, and is therefore comparable to the VAV(COA) system. Most of the
year, the VAV(FOAF) system operates at considerably less than the design setting of 20 cfm per
person and only approaches this value as the supply air increases toward its design cooling flow
rate (far right of the graph). At off-peak conditions (periods of mild or cool weather), the
requirement for supply air is reduced, and the OA flow rate is reduced proportionately. At Spring
and Fall conditions, the amount of OA delivered from the air handler is almost one half of this
design value. The OA flow rate in the summer is at or near the required 20 cfm per occupant which
is reached at design load2.
How often the flow of outdoor air in the VAV(FOAF) system is significantly below design depends
on the outdoor climate - the proportion of the year that the outdoor temperature is substantially
below summer design temperature. Exhibits 3A and 3B presents this information for the three
climates, along with the proportion of time the VAV(FOAF) system delivered outdoor air flow rates
at various levels. In this case, the performance was worse in the colder climate (Minneapolis)3
where the system almost never delivered more than 15 cfm of outdoor air per person, delivering
only 6 -10 cfm per person 42% of the time, and 11-15 cfm per person 56% of the time. The
performance was marginally better in the temperate climate of Washington, D.C., but even here,
the VAV(FOAF) system exceeded 15 cfm of outdoor air only 5% of the time. The ventilation
system performed best in Miami because of cooling load dominance, where it never delivered less
than 10 cfm, and most often delivered more than 15 cfm of outdoor air per occupant. But in no
case did the VAV(FOAF) system provide the 20 cfm of outdoor air per person that the system was
"designed" to achieve.
Outdoor Air and Energy Trade-offs
What, if any, of the energy savings of VAV(FOAF) system can be associated with this shortfall in
the delivery of outdoor air? To examine this question, it is useful to compare the energy
performance of the VAV(COA) system which continuously provides 20 cfm/occupant to that of the
VAV(FOAF) system which delivers considerably less outdoor air. A glance at Exhibit 1 reveals
that the diminished outdoor airflow of the VAV(FOAF) system did not reduce energy consumption
2	The design load is an estimate of the peak or close to peak load based on anticipated internal loads, and
outdoor temperature and relative humidity which is published for major cities and climate regions. Since the
design load is an estimate, it may never be experienced in a given year.
3
It would not always be worse in the colder climates, because as the outdoor temperature gets colder, the
supply air and outdoor air volumes may rise. When the heating load rises sufficiently in cold weather to offset the
declining cooling load, the VAV(FOAF) system would increase the supply air volume, and consequently the
outdoorair volume. This did not occurtc any substantial degree in the base building for the Minneapolis climate.
The outdoor temperature at which this offset point occurs is colder for more efficient building shells or for
buildings with low perimeter to core ratios.
Energy Cost and MQ
5
Report # 2

-------
or reduce energy costs. In fact, for the cold and temperate climates of Minneapolis and
Washington, D.C., energy use and 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
strategies. This added cooling benefit of the additional outdoor air in the VAV(COA) system was
more than enough to offset the added cooling burden during the hot summer season. The
VAV(COA) system, therefore, provided net energy advantages equivalent to the VAV(FOAF)
system while providing quantities of outdoor air equal to the older CV systems. It appears,
therefore, to be highly advantageous to design control mechanisms to achieve the VAV(COA)
strategy for both energy efficiency and indoor air quality purposes in all climates.
Conversely, the VAV system with fixed fraction outdoor air offered no energy or indoor air quality
advantage to recommend it. Rather, the analysis suggests reasons for avoiding control
mechanisms that approximate the VAV(FOAF) system4.
Economizer Strategies
Both temperature economizers and enthalpy economizers were modeled with the CV(FOAF),
VAV(FOAF), and VAV(COA) systems. The energy data for the economizer systems is presented
in Exhibit 4. Exhibit 5 presents the percent difference in HVAC energy use and energy costs
associated with each economizer over its base system. Economizers on the CV systems modeled
offered energy cost savings on the order of 1 % - 2% in the cold and temperate climate, while
economizers in VAV systems offered savings of 6% -10% in these climates. Enthalpy
economizers provided only marginal increased savings over the temperature economizer
modeled.
Economizers offered significant energy savings in the cold and temperate climates of Minneapolis
and Washington, D.C., but have no meaningful affect on energy use in the hot humid climate of
Miami. This is because hot humid climates offer little opportunity for economizing. Exhibit 3B
shows the proportion of time each climate experiences cold, temperate, and hot weather
conditions. Opportunities for economizers to provide "free cooling" exist only about 10% of the
time in Miami compared to approximately 70% of the time in Minneapolis and 60% of the time in
Washington, D C.
Since air-side economizers both increase the quantity of outdoor air and, in most cases, save
energy, they would appear to be advantageous. However, temperature economizers can create
humidity problems in some climates. In this modeling study, the temperature economizer was shut
4 All the central HVAC systems studied created an unequal distribution of outdoor air to different occupied
zones where the core zone received a lower than average airflow. Because of this, the reduced outdoor airflow at
the air handler with the VAV(FOAF) system exacerbated potential problems caused by this outdoor air shortfall in
the core zone (see Project Report #3),
Energy Cost and MQ
6
Report it 2

-------
off at temperatures above 65 F to avoid bringing in excessively humid air in the spring and
summer periods (See Project Report #1). Economizers also increase the potential for
contaminating the indoor environment with outdoor pollutants. Where outdoor pollution is a
problem, the indoor air quality impact of economizers would have to be carefully examined.
High Outdoor Air Flow and Heating Penalties of CV Economizers
The energy use data on Exhibit 5 shows that for the CV system, economizers actually increased
the energy use by up to 13% even while the energy costs were reduced. This is because,
particularly in cold climates, increasing outdoor air quantities carries with it a heating penalty, even
while the cooling burden is reduced. The cost savings for cooling exceeded the added costs for
heating and thus a net energy cost savings was achieved. This is particularly significant for the CV
systems modeled. Exhibit 6 compares the outdoor air flow rates at various outdoor temperatures
for the temperature economizers of a CV and a VAV system in the Minneapolis climate5. In both
the CV and VAV system, more than 20 cfm of outdoor air per occupant is brought into the building,
even at sub-zero temperatures as a means of cooling the supply air to achieve a desired discharge
temperature6. However, the economizing outdoor air flow rates are considerably higher in the CV
system than in the VAV system. This is because the part-load supply airflow in the CV system is
higher, and therefore requires a higher outdoor air quantity to achieve the desired mixed air
temperature.
The added quantity of cool outdoor air in the CV system provided free cooling for the core of the
building, but it carried with it a heating penalty for the perimeter zones. This added heating penalty
diminished the advantage of the economizer in overall energy costs for the CV system. However,
this would not likely be the case for dual fan, dual duct CV systems with separate economizers for
the hot and cold coils. Since the heating energy in the systems modeled is gas rather than
electricity, the energy cost advantage of economizers is sensitive to the relative price of these two
fuels. Exhibit 7 demonstrates that with relatively high gas and low electricity prices, economizers
on the CV system modeled could actually increase energy costs when gas prices are high relative
to electricity prices.
Outdoor Air and Energy Performance of VA V Economizers
Exhibit 8 presents economizer outdoor air flow rates for the VAV systems in Minneapolis. The
outdoor air flow rates for both temperature and enthalpy economizers are identical below 65 F at
5	The pattern is similar for all climates. The differences in annual average outdoor air flow rates between
climates depends mostly on the proportion of the yearthat a climate will experience cold, temperate, or hot
outdoor temperatures.
6	In cold weather, the economizer causes the outdoor air damperto open sufficiently to provide a mixed air
temperature of about 55F, so theoretically, there should be no problem in freezing the coil. However, because of
imperfect mixing, coil freezing may still occur. Therefore, the outdoor air flow is sometimes purposely reduced in
extreme cold conditions, or the outdoor air may have to be preheated, to avoid freezing of the coll. See Project
Report #5 for a discussion of the capacity constraints associated with raising outdoor air flow rates.
Energy Cost and MQ
7
Report # 2

-------
which point the temperature economizer is modeled to shut off. The enthalpy economizers
continue to operate to temperatures as high as 80 F, bringing in additional outdoor air7. The
pattern is similar for all climates.
The annual average outdoor air performance of the VAV(FOAF) system was considerably
improved when an economizer was added but significant shortfalls still remained. Exhibit 9
compares the outdoor airflow rates of VAV systems. Without the economizer, the VAV(FOAF)
system never achieved the design 20 cfm of outdoor air, and was below 11 cfm per person 42% of
the occupied hours for Minneapolis and 17% of the occupied hours for Washington, D.C. Adding
the temperature economizer kept the outdoor air flow rate above 10 cfm/occupant during all
occupied hours, but still showed significant shortfalls. Adding the enthalpy economizer improves
the performance more, but the outdoor air flow rate was between 11 and 15 cfm per occupant 19%
of the time in Minneapolis and 28% of the time in Washington D.C.
As was the case without economizers, the shortfalls in outdoor air supply of the VAV(FOAF)
system with economizers were not counterbalanced by meaningful energy savings when compared
to economizers applied to the VAV(COA) system. This suggest that a control mechanism which
approximates the VAV(FOAF) system, even with economizer operation, is not a mechanism which
is easily justified based on its performance characteristics.
Systems which approximate the VAV(COA)(ECON) strategy appear to offer the best overall
performance in terms of providing requisite outdoor airflow over the full year while attaining
significant energy advantages or no meaningful energy disadvantage over alternative systems. In
hot humid/climates, the VAV(COA) system is equally advantageous since there is little opportunity
for economizer operations. All economizers may need to incorporate humidity controls, and
economizer advantages may be compromised when outdoor air pollution levels are high.
Possible Corrections for Existing VAV(FOAF) Systems
Increasing Outdoor Air Flow Setting
Short of installing a new outdoor air control system, owners of buildings with VAV(FOAF) systems
may wish to improve the ventilation and/or energy performance of this system by simply resetting
the system to bring in larger amounts of outdoor air. In addition to the design load setting of 20 cfm
per occupant, higher design load settings of 30, and 45 cfm per occupant were also modeled to
determine the impact on both outdoor air flow rates and energy consumption. Exhibits 10 and 11
display the outdoor airflow rates in graphical and tabular formats. Exhibit 12 show the energy
implications of these settings.
7 The temperature economizer is modeled to shut off at 65F. Above 65F, the outdoor humidity could be too
high. In practice, this shut off temperature would be climate dependent (e.g., in dry climates it might be set at
75F, The enthalpy economizer has no automatic shut off since it will automatically shut off when the outdoor
humidity is too high. Exhibit 8 shows the average outdoor air flow rate for the economizer systems at each
outdoor air temperature. On average, the enthalpy is operational between 65F and SOT even though it does not
operate under high humidity conditions.
Energy Cost and MQ
8
Report it 2

-------
The results are surprising. Raising the design outdoor air flow rate to 30 cfm per occupant
improved the outdoor air performance of the VAV(FOAF) system considerably at a cost of only
$0.01 - $0.02 per square foot in Minneapolis and Washington, D.C, and $0.03 per square foot in
Miami. At a design setting of 45 cfm per occupant in Minneapolis and Washington, D.C. energy
costs rose by $0.05 - $0.06 per square foot, while 20 cfm of outdoor air was provided all year
round.
These cost increases are modest, and may be worthwhile to insure adequate outdoor airflow. A
potential problem is that raising the design outdoor air setting requires large increases in the
outdoor air flow rate at peak cooling and heating conditions. The additional burden of this outdoor
air on the heating and cooling coils could exceed the original coil design loads. If this should
happen in the summer, space conditions may become excessively warm. Increasing the outdoor
air flow on very cold winter days could cause freezing and permanent damage to the coils in the
central air handlers.
Resetting the Outdoor Air Flow Rate Each Season for VAV(FOAF)
A more effective strategy might be to reset the outdoor air control system at each season in an
attempt to mimic a VAV(COA) enthalpy economizer. This could avoid some of the capacity
problems mentioned above, while improving the energy performance of the system. For ease of
interpretation by operating engineers, Exhibit 13 translates the outdoor air flows of the VAV(COA)
enthalpy economizer to percent outdoor air. Exhibits 8 and 13 suggest that using a setting of 40%
outdoor air during the winter (e.g., below 40 F) a setting of 85 % outdoor air during the spring and
fall, (e.g., 40-79 F), and a setting of 20% outdoor air during the hot summer period (e.g., above 80
F and above), would approximately mimic the VAV(COA) enthalpy economizer. To model this
strategy, the settings specified in Exhibit 14 were used.
The effects of this outdoor airflow reset strategy, relative to the VAV(FOAF) control strategy, are
presented in Exhibits 15 and 16. These Exhibits suggest that a four season reset strategy has the
potential of achieving improved outdoor air performance at little energy expense in temperate
climates like Washington, D.C. In Exhibit 15, the energy used by the two control strategies is
almost identical in all three climates. However, the cooling costs were 10 to 20 percent higher in
Minneapolis and Miami. This increase is due to the increase in peak loads and peak demand in
these two climates. As expected, Exhibit 16 shows that the outdoor air flow rates were significantly
improved when the reset strategy was used. The reset strategy is less effective in Miami, since the
economizer is not operational during a large part of the year (i.e., when the outdoor air temperature
is above 75F).
Summer Reset for VA V(FOAF)(ECON)
For existing VAV(FOAF) systems with temperature or enthalpy economizers, a simple
improvement would be to reset the system to bring in 20 cfm per occupant (18% outdoor air) for a
modest summer load (e.g., 90 F), rather than at design load. Effectively, this amounts to resetting
the design load damper setting to 30 cfm per occupant. Exhibits 17 and 18 present the results of
Energy Cost and MQ
9
Report # 2

-------
this modification. Provided that there is sufficient capacity in the cooling system, this should not
have a significant effect on energy, but it would improve the outdoor air performance of this system
during summer months.
This simple resetting of the outdoor air flow to achieve 20 cfm per person at 90F rather than at
design load improved the outdoor air performance in all climates, insuring that this system
achieved at least 15 cfm per occupant all year round. The cost for such an improvement ranged
from $0.02 to $0.03 per square foot (3-4%) in Minneapolis and Washington, D.C. and from $0.03
to $0.05 per square foot (4-6%) in Miami. A major portion of this increment occurred during very
hot summer days. Some reduction in cost would likely be achieved if the damper were manually
reset to its original minimum position during these very hot days.
EFFECTS OF UTILITY RATES ON ENERGY COSTS
Exhibits 19-24 compares the energy costs of the base office building under the different utility price
structures outlined in Exhibit 7a. As expected, the results reflect the greater sensitivity of energy
costs to electric prices relative to gas, because the HVAC systems employed use gas only for
heating, while most commercial buildings are cooling dominated. However, as previously
demonstrated with CV economizers, when alterations to the HVAC system dramatically change the
relative use of heating and cooling energy, the effect on energy costs can be substantial.
These exhibits also demonstrate the relative importance of electric demand charges. For
example, in Exhibit 7a which shows the utility prices used under the different rate structures, there is
a 48% difference between the high (or low) demand charges and the base rate. Exhibit 20 shows
that this increase (or decrease) in demand charges resulted in an increase (or decrease) in
energy costs of about 20% in Miami where gas usage is minimal, and somewhat lower in
Washington D.C. and Minneapolis where gas usage is higher. Thus, approximately 40% of electric
energy cost (20/48 = 0.20), was from electric demand charges, which reflect peak load rather than
actual kilowatt hours of electricity consumed.
SUMMARY & CONCLUSIONS
Constant volume ventilation systems provide a constant flow of ventilation air at all operating
conditions, and were the staple of the HVAC design community for many years. The fact that
ventilation air quantities in these systems do not change both simplifies the task of maintaining
system balance, and assures that designated quantities of outdoor air enter the building under all
operating conditions.
In the last fifteen years, variable air volume ventilation systems have become more popular with
design engineers because of their improved energy efficiency over constant volume systems.
These systems vary the amount of supply air in response to variations in thermal demand, and use
less energy primarily because they move less air. This report suggests that the energy cost savings
are are conservatively 10% -21 % compared with CV systems. However, the variations in airflow
can create new challenges for maintaining system balance, and have raised a number of issues
Energy Cost and MQ
10
Report it 2

-------
concerning the ability of these systems to adequately dilute indoor contaminants at part load
conditions.
Maintaining system balance in VAV systems is a challenge which is not addressed in this project.
However, the ability of VAV systems to adequately dilute contaminants with outdoor air is
addressed. Serious questions regarding VAV system outdoor air control relate to whether
commonly used control mechanisms approximate a fixed outdoor air fraction or a constant outdoor
air flow. The results of this study suggest that the implications of this question are more related to
indoor air quality than they are related to energy consumption.
This report suggests that the outdoor air quantities actually supplied by systems which approximate
VAV(FOAF) can be significantly less than the design quantity. When set to deliver 20 cfm of
outdoor air at design conditions, VAV(FOAF) actually deliver only 6-10 cfm a substantial portion of
the time in cold and temperate climates, and almost never exceeded 15 cfm in those climates. In
warmer climates, the outdoor air performance was improved, but was only between 10 and 15 cfm
per occupant almost half the time. Adding an economizer improved the overall outdoor air
performance, but still left the buildings with less than design quantities of outdoor air during a
significant portion of the year.
This study suggests that the energy cost savings of VAV systems are not compromised if the
outdoor control strategy provides 20 cfm of outdoor air under all operating conditions. In fact, only in
the cold climate of Minneapolis, was the energy cost of the VAV(FOAF) system greater than for the
VAV(COA) system, and the difference was marginal. In the temperate climate of Washington,
D.C., and in the Miami climate, providing 20 cfm of outdoor air year round, resulted in a marginal
energy cost saving. It is therefore not likely that the systems which approximate VAV(FOAF) could
be justified on either energy or indoor air grounds. Control mechanisms which approximate the
VAV(COA) system, on the other hand, appear to be a highly advantageous for both energy
efficiency and indoor air quality. It would appear to be the preferred system for both retrofit and
new construction.
Adding either an air-side temperature or enthalpy economizer to the VAV(COA) strategy provided
significant additional savings in energy cost of $ 0.04 - $0.06 per square foot (6% - 8%) in the cold
and temperate climates of Minneapolis and Washington, D C. Economizers did not offer
advantages in hot/humid climates where there is little opportunity for economizer operations.
Provided that humidity is controlled and outdoor pollution is not excessive, economizers appear to
offer the advantages from both energy conservation and indoor air quality perspectives.
Operational modifications for existing VAV(FOAF) systems could improve their outdoor air
performance without retrofit, at what appears to be little to no energy cost, and in some cases could
possibly result in an energy savings. For VAV(FOAF) systems, a four season reset strategy was
modeled and produced favorable results. The operation of the VAV(FOAF) system with
temperature and enthalpy economizers were modified with a simple reset of the outdoor air
damper during the summer period when the economizers are not operating to improve their
Energy Cost and MQ
11
Report it 2

-------
outdoor air performance. Doing this likely to increased energy costs only marginally 3 - 4% per
square foot in cold and temperate climates.
Energy Cost and MQ
12
Report # 2

-------
BIBLIOGRAPHY
Bearg, D, W. 1995. Demand-controlled ventilation. Engineered Systems April 1995:28-32.
Brambley, Michael; Pratt, Robert; Chassin, David; and Cartipamuia, Srinivas. 1998. Diagnostics for Outdoor
Air Ventilation and Economizers. ASHRAE Journal 40(10): 49-55.
Cohen, T. 1994. Providing constant ventilation in variable air volume systems. ASHRAE Journal 34(7): 43-50.
Elovitz, D. ML, 1995. Minimum outside air control methods for VAV systems. ASHR4E Transactions 101(2):
613-618.
Filardo, M. J. 1993. Outdoor air - how much is enough? ASHRAE Journal 35(1): 34-38.
Haines, R. W. 1994. Ventilation air, the economy cycle, and VAV. Heating/Piping/Air Conditioning
October 1994: 71-73.
Janu, G. J., Wenger, J. D., Nesler, C. G. 1995. Outdoor air flow control for VAV systems. ASHRAE Journal
37(4): 62-68.
Kettler, J. P. 1998. Controlling minimum ventilation volume in VAV Systems. ASHRAE Journal 40(5): 1-7.
Levenhagen, J. 1. 1992. Control systems to comply with ASHRAE Standard 62-1989. ASHRAE Journal
34(9):40-44.
Marshall say, P. G, Luxton, R. E., Shaw, A. 1993. Ventilation air quantity indoor air quality and energy.
CLIMA 2000 Conference, November 1993.
Mumma, S. A., Wong, Y. M. 1990. Analytical evaluation of outdoor airflow rate variation vs. supply airflow
rate variation in variable air volume systems when the outdoor air damper position is fixed. ASHRAE
Transactions 96(1): 1197-1208
Mutammara, A.W., and 1 little, D.C. 1990. Energy effects of various control strategies for variable air volume
systems. ASHRAE Transactions 96(1): 98-102.
Reddy, T. A, Liu, M,, Claridge, D. E. 1996. Synergism between energy use and indoor air quality in terminal
reheat variable air volume systems. ACEEE 1996 Draft Paper.
Sauer. H. J., Howell, R. H. 1992. Estimating the indoor air quality and energy performance of VAV systems.
ASHRAE Journal 34(7): 43-50
Energy Cost and MQ
13
Report it 2

-------
Warden, D. 1996. Outdoor air: calculation and delivery. ASHRAE Journal 37(6): 54-61,
Warden, D. 1996. Dual fan, dual duct systems. ASHRAE Journal 38(1): 36-41.
Energy Cost and 1AQ
14
Report 4 2

-------
Exhibit 1
Variations in Annual Energy Use
for HVAC Systems
in Three Climate Locations
HVAC System Type
Annual HVAC Energy Use Summary
f
arid
Climate Location

Fan
Cooling
Heating

Total

S/sf
kbtu/sf
S/sf
kbtu/sf
S/sf
kbtu/sf
$/sf
kbtu/sf
CV (FOAF)








Minneapolis, MN
0.32
18.3
0.52
19.9
0.04
9.2
0.88
47.4
Washington, DC
0.29
16.4
0.56
22.2
0.01
2.4
0.86
41.1
Miami, FL
0.30
17.6
0.72
33.0
0.00
0.1
1.02
50.6
VAV(FOAF)








Minneapolis, MN
0.19
9.8
0.49
20.0
0.10
20.9
0.79
50.6
Washington, DC
0.17
8.7
0.52
21.0
0.05
9.8
0.74
39.5
Miami, FL
0.18
9.3
0.62
28.5
0.00
0.5
0.81
38.3
VAV(COA)








Minneapolis, MN
0.19
9.8
0.49
18.7
0.10
21.2
0.78
49.7
Washington, DC
0.17
8.7
0.52
20.3
0.05
9.9
0.74
38.9
Miami, FL
0.18
9.3
0.65
29.0
0.00
0.5
0.83
38.9
Energy Cost and IAQ
15
Report # 2

-------
Building: Office A
Location: Washington, DC
System: VAV & CV
OA Control: FOAF & COA
Design OA Flow: 20 cfm/person
40
Exhibit 2
Comparison of Seasonal Variations
in Outdoor Air Flow Rates for
VAV & CV Systems

m
IS
EC
I
35
30
25
CV (FOAF)
20
VAV (COA)
VAV (FOAF)
10 20	30	40	50 60	70
Outdoor Air Temperature, (deg F)
80
90
100

-------
Exhibit 3A
Variation in OA Flow Rates for VAV(FOAF)
in Three Climate Locations
HVAC System Type
and
Outdoor Air Flow Rates Achieved
(cfm per person)
Location
<= 5
6-10
11-15
16-19
>= 20
VAV(FOAF)





Minneapolis, WIN
0.0%
42.0%
56.3%
1.7%
0.0%
Washington, DC
0.0%
16.6%
78.1%
5.3%
0.0%
Miami, FL
0.0%
0.0%
42.5%
57.5%
0.0%
Exhibit 3B
Variation in Temperature for VAV(FOAF)
in Three Climate Locations
Location
Outdoor Air Temperature Bins
Winter
<10 - 39F
# of hours % of
hours
Spring/Fall
40 - 69'" F
# of hours % of
hours
Summer
70 - >90F
# of % of
hours hours
Minneapolis, MN
979 41.4%
736 31.1%
649 27.5%
Washington, DC
411 17.4%
1028 43.5%
925 39.1%
Miami, FL
0 0.0%
219 9.3%
2145 90,7%
Energy Cost and MQ
17
Report # 2

-------
Exhibit 4
Variations in Annual Energy Use
for HVAC Systems with Economizers
HVAC System Type
Annual HVAC Energy Use Summary
f
and
Climate Location

Fan
Cooling
Heating

Total

S/sf
kbtu/sf
S/sf
kbtu/sf
S/sf
kbtu/sf
S/sf
kbtu/sf
CV (FOAF) Econ,








Minneapolis, MN
0.32
18.2
0.45
14.7
0.10
20.7
0.87
53.7
Washington, IX
0.29
16.4
0.50
17.4
0.06
12.5
0.85
46.4
Miami, FL
0.30
17.5
0.71
32.3
0.00
0.9
1.01
50.7
CV (FOAF) Econc








Minneapolis, MN
0.32
18.2
0.45
14.1
0.10
20.7
0.87
53.1
Washington, DC
0.29
16.4
0.49
16.8
0.06
12.5
0.84
45.7
Miami, FL
0.30
17.5
0.70
31.9
0.00
0.8
1.01
50.2
VAV(FOAF) EconT








Minneapolis, MN
0.19
9.7
0.42
14.2
0.11
21.8
0.71
45.7
Washington, DC
0.17
8.6
0.46
16.4
0.05
10.4
0.68
35.5
Miami, FL
0.18
9.3
0.61
27.9
0.00
0.5
0.80
37.8
VAV(FOAF) EconE








Minneapolis, MN
0.19
9.7
0.41
13.8
0.11
21.8
0.71
45.3
Washington, DC
0.17
8.6
0.45
15.8
0.05
10.4
0.68
34.9
Miami, FL
0.18
9.3
0.61
27.6
0.00
0.5
0.79
37.4
VAV(COA) Ecorv








Minneapolis, MN
0.19
9.7
0.43
14.3
0.11
21.8
0.73
45.9
Washington, DC
0.17
8.6
0.47
16.7
0.05
10.4
0.70
35.8
Miami, FL
0.18
9.3
0.64
28.6
0.00
0.5
0.83
38.5
VAV(COA) EconE








Minneapolis, MN
0.19
9.7
0.43
14.0
0.11
21.8
0.72
45.5
Washington, DC
0.17
8.6
0.47
16.1
0.05
10.4
0.69
35.2
Miami, FL
0.18
9.3
0.64
28.3
0.00
0.5
0.82
38.2
Energy Cost and IAQ
18
Report # 2

-------
Exhibit S
Annual HVAC Energy and HVAC Energy Cost
Savings* of Temperature and Enthalpy
Economizers Compared to the Base Case

Minneapolis, MN
Washington, DC
Miami, FL
System
Temp
Enth
Temp
Enth
Temp
Enth
Energy (kBTU/sq ft)






CV (FOAF)
-13.3%
-12.0%
-13.0%
-11.3%
-0.2%
0.8%
VAV(FOAF)
9,8%
10.6%
10.1%
11.6%
1.5%
2.5%
VAV(COA)
7.7%
8.4%
8.0%
9.5%
1.0%
1.9%
Energy Costs ($/sq ft)






CV (FOAF)
1.3%
2.1%
1.4%
2.4%
0.5%
1.1%
VAV(FOAF)
9.3%
9.9%
7.8%
8.9%
1.2%
1.8%
VAV(COA)
6.9%
7.5%
6.0%
7.0%
0.6%
1.2%
* Negative values represent increases
Energy Cost and 1AQ
19
Report 4 2

-------
Building: Office A
Location: Minneapolis, MN
Systems: CV & VAV w/ Economizers
OA Control: COA
Design OA Flow: 20 cfm/person
200
190
180
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
c
o
e

(0
a:
Z
o
t
<
o
o
T3
Exhibit 6
Comparison of Seasonal Variations
in Outddor Airflow Rates
for CV and VAV Systems with Ecomomizers
CV (FOAF) Econ
VAV (COA) Econ-,
-20 -10 0 10 20 30 40 50 60 70
Outdoor Air Temperature, (deg F)
80
90
100

-------
Exhibit 7a
Utility Rate Structures

Rate Class
Rate Structure
Rate
Structures
Gas
Rate
Electric
Rate
Electric
Deman
d
Gas
Rate
Electric
Rate
Electric
Deman
d
Ratchet
Clause
Base
Average
Average
Average
$0,490
$0,044
$7,890
No
Option 1
Low
(-33%)
High
(+43%)
Average
$0,330
$0,063
$7,890
No
Option 2
High
(+33%)
Low
(-43%)
Average
$0,650
$0,025
$7,890
No
Option 3
Average
Average
High
(+48%)
$0,490
$0,044
$11,710
No
Option 4
Average
Average
Low
(-48%)
$0,490
$0,044
$4,070
No
Energy Cost and MQ
21
Report # 2

-------
Exhibit 7b
Price Sensitivity of CV Systems with Economizers
in Three Climates
Location and Utility
Price Structure
CV (FOAF) System with Temperature and Enthalpy Economizers
Base
$/sf
EconT
EconF
$/sf
% Change
$/sf
% Change
Minneapolis, WIN





Base
1.02
1.01
-0.5%
1.01
-1.1%
Lo Gas/Hi Elec
1.30
1.29
-0.8%
1.28
-1.4%
Hi Gas/Lo Elec
0.74
0.74
0.0%
0.74
-0.5%
Hi Demand
1.20
1.19
-0.5%
1.19
-0.9%
Lo Demand
0.84
0.84
-0.6%
0.83
-1.3%
Washington, DC





Base
0.88
0.87
-1.3%
0.87
-2.1%
Lo Gas/Hi Elec
1.08
1.02
-5.5%
1.01
-6.4%
Hi Gas/Lo Elec
0.69
0.72
5.3%
0.72
4.7%
Hi Demand
1.05
1.04
-1.1%
1.03
-1.8%
Lo Demand
0.72
0.71
-1.6%
0.70
-2.6%
Miami, FL





Base
0.86
0.85
-1.4%
0.84
-2.4%
Lo Gas/Hi Elec
1.07
1.02
-5.1%
1.01
-6.3%
Hi Gas/Lo Elec
0.65
0.68
4.7%
0.68
4.0%
Hi Demand
1.03
1.02
-1.2%
1.01
-2.0%
Lo Demand
0.69
0.68
-1.8%
0.67
-3.0%
Energy Cost and IAQ
22
Report # 2

-------
Building: Office A
Location: Minneapolis, MN
System: VAV w/ Temp & Enth Economizer
OA Control: COA & FOAF
Design OA Flow: 20 cfm\person
100
Exhibit 8
Comparison of Seasonal Variations
in Outddor Airflow Rates for
VAV Systems with Economizers
90
80
70
60
50
O 40
30
C
O
(2
0
Q.
E
H
U)
CD
n:
oc

o
<
o
o
B 20
3
o
10
0
m--
.. .srw
-J.-
v,, ;i5: .m
... M
<  A m
>
fm
mm
/ss
/m
J 3
-W
./H
S n 
:i
VAV (COA) Eicon-,
VAV (COA) EconE
! I ! I i
-+-
.y
-------
Exhibit 9
Variation in OA Flow Rates for VAV Systems
in Three Climate Locations
HVAC System Type
arid
Outdoor Air Flow Rates Achieved
(efm per person)
Location
A
II
Ol
6-10
11-15
16-19
>= 20
VAV(FOAF)





Minneapolis, MN
0.0%
42.0%
56.3%
1.7%
0.0%
Washington, DC
0.0%
16.6%
78.1%
5.3%
0.0%
Miami, FL
0.0%
0.0%
42.5%
57.5%
0.0%
VAV(FOAF) Econ-





Minneapolis, MN
0.0%
0.0%
32.5%
0.0%
67.4%
Washington, DC
0.0%
0.1%
48.6%
0.5%
50.8%
Miami, FL
0.0%
0.0%
62.3%
31.9%
5.8%
VAV(FOAF) Econc





Minneapolis, MN
0.0%
0.0%
18.9%
0.0%
81.1%
Washington, DC
0.0%
0.0%
28.1%
0.5%
71.4%
Miami, FL
0.0%
0.0%
48.2%
29.7%
22.1%
VAV(COA)





Minneapolis, MN
0.0%
0.0%
0.0%
0.0%
100.0%
Washington, DC
0.0%
0.0%
0.0%
0.0%
100.0%
Miami, FL
0.0%
0.0%
0.0%
0.0%
100.0%
Energy Cost and IAQ
24
Report # 2

-------
Building: Office A
Location: Washington, DC
System: VAV	Exhibit 10
Design oa Flow: 20,30, & 45 ctm>person Comparison of Seasonal Variations
in Outdoor Airflow Rates for
Various OA Damper Settings
5 cfm/person
30 cfm/person
20 cfm/person
10	20	30	40	50	60	70
Outdoor Air Temperature, (deg F)
80
90
100

-------
Exhibit 11
Comparison of Variations
in Outdoor Air Flow Rates for VAV (FOAF) Systems
with Various OA Damper Settings
in Three Climate Locations
OA Damper Setting
and
Location
Outdoor Air Flow Rates Achieved
(cfm per person)
<= 5
6-10
11-15
16-19
o
CM
II
A
20 dm/person





Minneapolis, MN
0.0%
42.0%
56.3%
1.7%
0.0%
Washington, DC
0.0%
16.6%
78.1%
5.3%
0.0%
Miami, FL
0.0%
0.0%
42.5%
57.5%
0.0%
30 cfm/person





Minneapolis, MN
0.0%
0.9%
39.5%
30.2%
29.3%
Washington, DC
0.0%
0.1%
14.1%
41.3%
44.5%
Miami, FL
0.0%
0.0%
0.0%
7.6%
92.4%
45 cfm/person





Minneapolis, MN
0.0%
0.0%
1.0%
19.2%
79.8%
Washington, DC
0.0%
0.0%
0.3%
1.8%
98.0%
Miami, FL
0.0%
0.0%
0.0%
0.0%
100.0%
Energy Cost and IAQ
26
Report # 2

-------
Exhibit 12
Variations in Annual Energy Costs
for VAV(FOAF) at Alternative Damper Settings
in Three Climate Locations
HVAC System Type
Annual HVAC Energy Cost Summary
and
Climate Location
Fan
Cooling
Heating
Total

$/sf
$/sf
S/sf
$/sf
VAV(FOAF)




Minneapolis, MN
0.19
0.49
0.10
0.79
Washington, DC
0.17
0.52
0.05
0.74
Miami, FL
0.18
0.62
0.00
0.81
VAV(FOAF)
@ 30 cfm/person




Minneapolis, MN
0.19
0.51
0.11
0.80
Washington, IX
0.18
0.54
0.05
0.76
Miami, FL
0.18
0.66
0.00
0.84
VAV(FOAF)
@ 45 cfm/person




Minneapolis, MN
0.19
0.53
0.11
0.84
Washington, IX
0.18
0.57
0.05
0.80
Miami, FL
0.18
0.72
0.00
0.90
Energy Cost and MQ
27
Report # 2

-------
Building: Office A
Location: Minneapolis, MN
Systems: VAV w/ Enthalpy Economizer
OA Control: COA
Design OA Flow: 20 cfm/person
Exhibit 13
Seasonal Variations
in Outdoor Air Fractions for
VAV (COA) with Enthalpy Economizer
C
O
o
re
o
o
o
3
o
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
-20 -10 0 10 20 30 40 50 60 70
Outdoor Air Temperature, (deg F)
80
90
100

-------
Exhibit 14
Outdoor Air Settings for VAV(FOAF) Seasonal Reset Strategy
In Three Climates
Season
OA Setting
Minneapolis, MN
Washington, DC
Miami, FL
cfm/person
%OA
Winter
30-40
28-30
Nov-Mar
Dec-Feb
N/A
Spring
70-120
100
Apr-May
Mar-May
Jan-Feb
Summer
10-20
12-14
Jun-Aug
Jun-Sep
Mar-Oct
Fall
70-120
100
Sep-Oct
Oct-Nov
Nov-Dec
Energy Cost and MQ
29
Report # 2

-------
Exhibit 15
Variations in Annual Energy Use
for VAV(FOAF) Using a 4 Season Reset Strategy
HVAC System Type
Annual HVAC Energy Use Summary
/
and
Climate Location
$/sf
Fan
kbtu/sf
Cooling
S/sf kbtu/sf
Heating
S/sf kbtu/sf
$/sf
Total
kbtu/sf
VAV(FOAF)








Minneapolis, MN
0.19
9.8
0.49
20.0
0.10
20.9
0.79
50.6
Washington, DC
0.17
8.7
0.52
21.0
0.05
9.8
0.74
39.5
Miami, FL
0.18
9.3
0.62
28.5
0.00
0.5
0.81
38.3
VAV(FOAF)
w/Reset








Minneapolis, MN
0.19
9.8
0.58
18.6
0.11
22.5
0.88
50.9
Washington, DC
0.17
8.6
0.52
19.7
0.05
10.1
0.74
38.4
Miami, FL
0.18
9.2
0.70
29.2
0.00
0.6
0.88
39.0
Energy Cost and IAQ
30
Report # 2

-------
Exhibit 16
OA Flow Rates for VAV(FOAF)
with 4 Season Reset in Three Climate Locations
HVAC System Type
arid
Outdoor Air Flow Rates Achieved
(efm per person)
Location
A
II
Ol
6-10
11-15
16-19
>= 20
VAV(FOAF)





Minneapolis, IV! N
0.0%
42.0%
56.3%
1.7%
0.0%
Washington, DC
0.0%
16.6%
78.1%
5.3%
0.0%
Miami, FL
0.0%
0.0%
42.5%
57.5%
0.0%
VAV(FOAF)
w/Reset





Minneapolis, MN
0.0%
0.0%
25.1%
8.5%
66.4%
Washington, DC
0.0%
0.0%
30.6%
4.6%
64.7%
Miami, FL
0.0%
0.0%
28.8%
39.3%
31.9%
Energy Cost and IAQ
31
Report # 2

-------
Exhibit 17
Variations in Annual Energy Use
for VAV(FQAF) w/Economizers
and OA Reset for 20 cfm/person at 90F
HVAC System
Annual HVAC Energy Use Summary
Type and
Climate Location

Fan
Cooling
Heating

Total

$/sf
kbtu/sf
S/sf
kbtu/sf
$/sf
kbtu/sf
$/sf
kbtu/sf
VAV(FOAF) Econ-








Minneapolis, WIN
0,19
9.7
0.42
14.2
0.11
21.8
0.71
45.7
Washington, DC
0,17
8.6
0.46
16.4
0.05
10.4
0.68
35.5
Miami, FL
0.18
9.3
0.61
27.9
0.00
0.5
0.80
37.8
VAV(FOAF) Econ
w/OA Reset








Minneapolis, MN
0.19
9.7
0.44
14.5
0.11
22.4
0.74
46.6
Washington, DC
0.17
8.6
0.48
16.8
0.05
10.6
0.71
36.1
Miami, FL
0.18
9.2
0.65
28.7
0.00
0.6
0.83
38.5
VAV(FOAF) Econfc








Minneapolis. MN
0.19
9.7
0.41
13.8
0.11
21.8
0.71
45.3
Washington, DC
0.17
8.6
0.45
15.8
0.05
10.4
0.68
34.9
Miami, FL
0.18
9.3
0.61
27.6
0.00
0.5
0.79
37.4
VAV(FOAF) EconE
w/OA Reset








Minneapolis, MN
0.19
9.7
0.43
14.1
0.11
22.4
0.73
46.3
Washington, DC
0.17
8.6
0.48
16.2
0.05
10.6
0.70
35.5
Miami, FL
0.18
9.3
0.65
28.7
0.00
0.5
0.84
38.6
Energy Cost and IAQ
32
Report # 2

-------
Exhibit 18
Variations in OA Flow Rates
for VAV(FQAF) w/Economizers
and OA Reset for 20 cfm/person at 90F
HVAC System Type
and
Outdoor Air Flow Rates Achieved
(cfm per person)
Location
<=5
6-10
11-15
16-19
o

-------
Exhibit 19
Variations in Annual Energy Costs
for Various Utility Pricing Schemes
in Washington, DC
HVAC System
Annual HVAC Energy Cost Summary
Type
Base
Low Gas/
High Electric
High Gas/
Low Electric
High
Demand
Low
Demand

S/sf
S/sf
S/sf
$/sf
S/sf
CV (FOAF)
0.86
1.07
0.65
1.03
0.69
CV (FOAF) EconT
0,85
1.02
0.68
1.02
0.68
CV (FOAF) Econ,.
0.84
1.01
0.68
1.01
0.67
VAV(FOAF)
0.74
0.89
0.59
0.89
0.59
VAV(FOAF) Econ-
0.68
0.81
0.56
0.83
0.53
VAV(FOAF) Econr
0.68
0.79
0.56
0.82
0.53
VAV(COA)
0.74
0.89
0.60
0.90
0.59
VAV(COA) Econ,
0.70
0.82
0.57
0.85
0.54
VAV(COA) Econ_
0.69
0.81
0.57
0.85
0.54
VAV(FOAF)
@ 30 cfm OA/per
0.76
0.91
0.61
0.92
0.60
@ 45 cfm OA'per
0.80
0.95
0.65
0.98
0.62
@ 2 Season Fixed
0.73
0.87
0.58
0.88
0.58
@ 4 Season Fixed
0.74
0.88
0.60
0.90
0.58
VAV(FOAF) Econr
@ 30 cfrn OA/per
0.71
0.83
0.59
0.87
0.55
@ 45 cfrn OA/per
0.75
0.88
0.63
0.93
0.58
@ 2 Season Fixed
0.68
0.81
0.56
0.83
0.53
Energy Cost arid 140
34
Report # 2

-------
Exhibit 20
Variations in Annual Energy Costs
for Various Utility Pricing Schemes
in Miami, FL
HVAC System
Annual HVAC Energy Cost Summary
Type
Base
Low Gas/
High Electric
High Gas/
Low Electric
High
Demand
Low
Demand

S/sf
S/sf
S/sf
$/sf
S/sf
CV (FOAF)
1.02
1.30
0.74
1.20
0.84
CV (FOAF) EconT
1.01
1.29
0.74
1.19
0.84
CV (FOAF) Econ,.
1.01
1.28
0.74
1.19
0.83
VAV(FOAF)
0.81
1.02
0.60
0.96
0.65
VAV(FOAF) Econ-
0.80
1.00
0.59
0.95
0.65
VAV(FOAF) Econr
0.79
1.00
0.59
0.95
0.64
VAV(COA)
0.83
1.04
0.62
0.99
0.67
VAV(COA) Econ,
0.83
1.04
0.62
0.99
0.66
VAV(COA) Econ_
0.82
1.03
0.61
0.98
0.66
VAV(FOAF)
@ 30 cfm OA/per
0.84
1.05
0.63
1.00
0.67
@ 45 cfrn OA'per
0.90
1.12
0.68
1.08
0.71
@ 2 Season Fixed
0.80
1.01
0.59
0.95
0.65
@ 4 Season Fixed
0.88
1.09
0.67
1.06
0.69
VAV(FOAF) Econr
@ 30 cfrn OA/per
0.83
1.04
0.62
0.99
0.67
@ 45 cfrn OA/per
0.89
1.11
0.67
1.07
0.71
@ 2 Season Fixed
0.79
1.00
0.59
0.94
0.64
Energy Cost arid 140
35
Report # 2

-------
Exhibit 21
Variations in Annual Energy Costs
for Various Utility Pricing Schemes
in Minneapolis, MN
HVAC System
Annual HVAC Energy Cost Summary
Type
Base
Low Gas/
High Electric
High Gas/
Low Electric
High
Demand
Low
Demand

S/sf
S/sf
S/sf
$/sf
S/sf
CV (FOAF)
0,88
1.08
0.69
1.05
0.72
CV (FOAF) EconT
0,87
1.02
0.72
1.04
0.71
CV (FOAF) Econ,.
0.87
1.01
0.72
1.03
0.70
VAV(FOAF)
0.79
0.92
0.65
0.93
0.64
VAV(FOAF) Econ-
0.71
0.81
0.62
0.86
0.57
VAV(FOAF) Econr
0.71
0.80
0.61
0.85
0.56
VAV(COA)
0.78
0.91
0.66
0.93
0.63
VAV(COA) Econ,
0.73
0.83
0.63
0.88
0.58
VAV(COA) Econ_
0.72
0.82
0.63
0.88
0.57
VAV(FOAF)
@ 30 cfm OA/per
0.80
0.93
0.67
0.96
0.65
@ 45 cfrn OA'per
0.84
0.96
0.71
1.00
0.67
@ 2 Season Fixed
0.77
0.89
0.64
0.91
0.62
@ 4 Season Fixed
0.88
1.00
0.76
1.07
0.68
VAV(FOAF) Econr
@ 30 cfrn OA/per
0.74
0.84
0.64
0.89
0.58
@ 45 cfrn OA/per
0.78
0.88
0.68
0.94
0.61
@ 2 Season Fixed
0.71
0.81
0.61
0.86
0.57
Energy Cost arid 140
36
Report # 2

-------
Exhibit 22
Change in Annual Energy Costs
for Various Utility Pricing Schemes
in Washington, DC
HVAC System
Change in Annual HVAC Energy Cost from Base
Type
Base
Low Gas/
High Electric
High Gas/
Low Electric
High
Demand
Low
Demand

S/sf
%
%
%
%
CV (FOAF)
0.86
24.5%
-24.5%
19.8%
-19.8%
CV (FOAF) EconT
0,85
19.8%
-19.8%
20.1%
-20.1%
CV (FOAF) Econ,.
0.84
19.6%
-19.6%
20.3%
-20.3%
VAV(FOAF)
0.74
20.2%
-20.2%
20.3%
-20.3%
VAV(FOAF) Econ-
0.68
18.0%
-18.0%
21.9%
-21.9%
VAV(FOAF) Econr
0.68
17.7%
-17.7%
22.1%
-22.1%
VAV(COA)
0.74
19.6%
-19.6%
20.9%
-20.9%
VAV(COA) Econ,
0.70
17.8%
-17.8%
22.3%
-22.3%
VAV(COA) Econ_
0.69
17.5%
-17.5%
22.5%
-22.5%
VAV(FOAF)
@ 30 cfm OA/per
0.76
19.5%
-19.5%
21.1%
-21.1%
@ 45 cfm OA'per
0.80
18.6%
-18.6%
22.1%
-22.1%
@ 2 Season Fixed
0.73
19.7%
-19.7%
20.6%
-20.6%
@ 4 Season Fixed
0.74
19.2%
-19.2%
21.2%
-21.2%
VAV(FOAF) Econr
@ 30 cfrn OA/per
0.71
17.5%
-17.5%
22.5%
-22.5%
@ 45 cfrn OA/per
0.75
17.0%
-17.0%
23.3%
-23.3%
@ 2 Season Fixed
0.68
17.9%
-17.9%
21.9%
-21.9%
Energy Cost arid 140
37
Report # 2

-------
Exhibit 23
Change in Annual Energy Costs
for Various Utility Pricing Schemes
in Miami, FL
HVAC System
Change in Annual HVAC Energy Cost from Base
Type
Base
Low Gas/
High Electric
High Gas/
Low Electric
High
Demand
Low
Demand

S/sf
%
%
%
%
CV (FOAF)
1.02
27.6%
-27.6%
17.5%
-17.5%
CV (FOAF) Ecorv
1,01
27.2%
-27.2%
17.6%
-17.6%
CV (FOAF) Ecorip
1.01
27.1%
-27.1%
17.7%
-17.7%
VAV(FOAF)
0.81
25.9%
-25.9%
19.1%
-19.1%
VAV(FOAF) Ecorv
0,80
25.9%
-25.9%
19.1%
-19.1%
VAV(FOAF) Econr
0.79
25.8%
-25.8%
19.3%
-19.3%
VAV(COA)
0,83
25.6%
-25.6%
19.5%
-19.5%
VAV(COA) EconT
0.83
25.5%
-25.5%
19.6%
-19.6%
VAV(COA) Econc
0.82
25.4%
-25.4%
19.7%
-19.7%
VAV(FOAF)
@ 30 cfm OA/per
0.84
25.4%
-25.4%
19.7%
-19.7%
@ 45 cfrn OA/per
0.90
24.6%
-24.6%
20.5%
-20.5%
@ 2 Season Fixed
0.80
26.1%
-26.1%
18.9%
-18.9%
@ 4 Season Fixed
0.88
24.2%
-24.2%
21.0%
-21.0%
VAV(FOAF) Econ-
@ 30 cfm OA/per
0.83
25.4%
-25.4%
19.7%
-19.7%
@ 45 cfm OA/per
0.89
24.6%
-24.6%
20.5%
-20.5%
@ 2 Season Fixed
0.79
26.0%
-26.0%
19.0%
-19.0%
Energy Cost and IAQ
38
Report # 2

-------
Exhibit 24
Change in Annual Energy Costs
for Various Utility Pricing Schemes
in Minneapolis, MN
HVAC System
Change in Annual HVAC Energy Cost from Base
Type
Base
Low Gas/
High Electric
High Gas/
Low Electric
High
Demand
Low
Demand

S/sf
%
%
%
%
CV (FOAF)
0.88
22.4%
-22.4%
19.0%
-19.0%
CV (FOAF) Ecorv
0,87
17.2%
-17.2%
19.3%
-19.3%
CV (FOAF) Ecorip
0.87
17.0%
-17.0%
19.4%
-19.4%
VAV(FOAF)
0.79
16.8%
-16.8%
18.5%
-18.5%
VAV(FOAF) EconT
0,71
13.8%
-13.8%
20.3%
-20.3%
VAV(FOAF) Econr
0.71
13.6%
-13.6%
20.4%
-20.4%
VAV(COA)
0,78
16.0%
-16.0%
19.3%
-19.3%
VAV(COA) EconT
0.73
13.6%
-13.6%
20.7%
-20.7%
VAV(COA) Econc
0.72
13.4%
-13.4%
20.8%
-20.8%
VAV(FOAF)
@ 30 cfm OA/per
0.80
16.1%
-16.1%
19.1%
-19.1%
@ 45 cfrn OA/per
0.84
15.2%
-15.2%
19.9%
-19.9%
@ 2 Season Fixed
0.77
16.3%
-16.3%
18.9%
-18.9%
@ 4 Season Fixed
0.88
13.9%
-13.9%
22.2%
-22.2%
VAV(FOAF) Econ-
@ 30 cfm OA/per
0.74
13.4%
-13.4%
20.7%
-20.7%
@ 45 cfm OA/per
0.78
13.0%
-13.0%
21.2%
-21.2%
@ 2 Season Fixed
0.71
13.9%
-13.9%
20.3%
-20.3%
Energy Cost and IAQ
39
Report # 2

-------