Technical Report

NREL/TP-550-41955

April 2009 

Assessment of the Energy 

Impacts of Outside Air in the 

Commercial Sector 

K. Benne, B. Griffith, N. Long, and P. Torcellini

National Renewable Energy Laboratory 

D. Crawley and T. Logee

U.S. Department of Energy 
National Renewable Energy Laboratory

1617 Cole Boulevard, Golden, Colorado 80401-3393

303-275-3000 • www.nrel.gov

NREL is a national laboratory of the U.S. Department of Energy

Office of Energy Efficiency and Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC

Contract No. DE-AC36-08-GO28308

Technical Report

NREL/TP-550-41955

April 2009 

Assessment of the Energy 

Impacts of Outside Air in the 

Commercial Sector 

K. Benne, B. Griffith, N. Long, and P. Torcellini

National Renewable Energy Laboratory 

D. Crawley and T. Logee

U.S. Department of Energy 

Prepared under Task No. BEC7.1006
NOTICE

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iii

Contents

CONTENTS ............................................................................................................................................. III

FIGURES...................................................................................................................................................IV

TABLES ...................................................................................................................................................... V

NOMENCLATURE................................................................................................................................ VII

ACKNOWLEDGMENTS ........................................................................................................................IX

EXECUTIVE SUMMARY ....................................................................................................................... X

PRINCIPAL FINDINGS.............................................................................................................................. XII

RESEARCH PRIORITIES .......................................................................................................................... XIII

1. INTRODUCTION............................................................................................................................... 1

1.1 PROBLEM DEFINITION................................................................................................................... 1

1.2 PROJECT SCOPE............................................................................................................................. 2

1.3 REPORT ORGANIZATION ............................................................................................................... 2

2. ANALYSIS METHODOLOGY ........................................................................................................ 3

2.1 ENERGY IMPACT MODELING ........................................................................................................ 3

2.2 SCENARIOS.................................................................................................................................... 4

3. RESULTS AND DISCUSSION ......................................................................................................... 8

3.1 90.1-2004 SCENARIOS................................................................................................................... 8

3.2 EXISTING STOCK......................................................................................................................... 22

3.3 MAX TECH .................................................................................................................................. 30

4. SUMMARY AND RECOMMENDATIONS.................................................................................. 38

5. REFERENCES .................................................................................................................................. 40
iv

Figures

Figure ES-1 Sector-Wide Average EUI versus Total ACH for 90.1-2004 Scenarios.............................xiii

Figure 3-1 Sector-Wide Average EUI versus Total ACH for the 90.1-2004 Construction Group........ 10

Figure 3-2 Summary of Percentage Decreases in Sector-Wide Averages............................................. 14

Figure 3-3 PDF of Change in Sector Average EUI for 90.1-2004, No Minimum Mechanical 

Ventilation ........................................................................................................................... 15

Figure 3-4 PDF of Change in Sector Average EUI for Existing Stock, No Minimum Mechanical 

Ventilation ........................................................................................................................... 23

Figure 3-5 PDF of Change in Sector Average EUI for Max Tech, No Minimum Mechanical 

Ventilation ........................................................................................................................... 31
v 

Tables

Table ES-1 Scenarios Examined.............................................................................................................. xi

Table 2-1 Default Outside Air Mechanical Ventilation Rates by PBA.................................................. 5

Table 2-2 Scenarios Examined............................................................................................................... 7

Table 3-1 90.1-2004, Sector-Wide Average Total Site EUI .................................................................. 9

Table 3-2 90.1-2004, Sector-Wide Average ACH ............................................................................... 10

Table 3-3 90.1-2004, Sector-Wide Average Gas EUI.......................................................................... 11

Table 3-4 90.1-2004, Sector-Wide Average Electricity Site EUI ........................................................ 12

Table 3-5 90.1-2004, Sector-Wide Average Peak Electric Power ....................................................... 13

Table 3-6 Number of Models by Subsectors and Climate Zones......................................................... 16

Table 3-7 90.1-2004, No Minimum Mechanical Ventilation Scenario, Percent Change in EUI by 

Climate Zone and Subsector................................................................................................ 17

Table 3-8 90.1-2004, No Minimum Mechanical Ventilation, Percent Change in ACH by Climate 

Zone and Subsector ............................................................................................................. 18

Table 3-9 90.1-2004, No Minimum Mechanical Ventilation, Percent Change in Gas EUI by 

Climate Zone and Subsector................................................................................................ 19

Table 3-10 90.1-2004, No Minimum Mechanical Ventilation, Percent Change in Electricity EUI by 

Climate Zone and Subsector................................................................................................ 20

Table 3-11 90.1-2004, No Minimum Mechanical Ventilation, Percent Change in Peak Electrical 

Power by Climate Zone and Subsector ............................................................................... 21

Table 3-12 Existing Stock, Sector-Wide Average Total Site EUI ......................................................... 22

Table 3-13 Existing Stock, Sector-Wide Average ACH ........................................................................ 23

Table 3-14 Existing Stock, Sector-Wide Average Gas EUI................................................................... 24

Table 3-15 Existing Stock, Sector-Wide Average Electricity EUI ........................................................ 24

Table 3-16 Existing Stock, Sector-Wide Average Peak Electric Power ................................................ 24

Table 3-17 Existing Stock, No Minimum Mechanical Ventilation, Total EUI Percent Change for 

Climate Zone and Subsector................................................................................................ 25

Table 3-18 Existing Stock, No Minimum Mechanical Ventilation, ACH Percent Change for 

Climate Zone and Subsector................................................................................................ 26

Table 3-19 Existing Stock, No Minimum Mechanical Ventilation, Gas EUI Percent Change for 

Climate Zone and Subsector................................................................................................ 27

Table 3-20 Existing Stock, No Minimum Mechanical Ventilation, Electric EUI Percent Change for 

Climate Zone and Subsector................................................................................................ 28

Table 3-21 Existing Stock, No Minimum Mechanical Ventilation, Peak Electrical Power Percent 

Change for Climate Zone and Subsector............................................................................. 29

Table 3-22 Max Tech, Sector-Wide Average Total Site EUI ................................................................ 30

Table 3-23 Max Tech, Sector-Wide Average ACH ............................................................................... 31

Table 3-24 Max Tech, Sector-Wide Average Gas EUI.......................................................................... 32

Table 3-25 Max Tech, Sector-Wide Average Electric EUI.................................................................... 32

Table 3-26 Max Tech, Sector-Wide Average Peak Electrical Power..................................................... 32

Table 3-27 Max Tech, No Minimum Mechanical Ventilation, Total EUI Percent Change for 

Climate Zone and Subsector................................................................................................ 33

Table 3-28 Max Tech, No Minimum Mechanical Ventilation, ACH Percent Change for Climate 

Zone and Subsector ............................................................................................................. 34

Table 3-29 Max Tech, No Minimum Mechanical Ventilation, Gas EUI Percent Change for Climate 

Zone and Subsector ............................................................................................................. 35

Table 3 –30 Max Tech, No Minimum Mechanical Ventilation, Electric EUI Percent Change for 

Climate Zone and Subsector................................................................................................ 36
vi

Table 3-31 Max Tech, No Minimum Mechanical Ventilation, Peak Electrical Power Percent 

Change for Climate Zone and Subsector............................................................................. 37
vii

Nomenclature

ACH—Air Changes per hour. 

AEO—Annual Energy Outlook, from EIA. 

EIA—Energy Information Administration. 

ASHRAE—American Society of Heating, Refrigerating and Air-Conditioning Engineers. 

90.1-2004 Construction Group—A group of scenarios that are derived from CBECS, but have 

modifications to comply with ANSI/ASHRAE/IESNA 90.1-2004. Abbreviated as 90.1-2004 in some 

contexts.

BT—Building Technologies Program within DOE/EERE. 

CBECS—Commercial Buildings Energy Consumption Survey.

DOE—U.S. Department of Energy. 

EERE—Energy Efficiency and Renewable Energy. 

EUI—Energy Use Intensity. 

Existing Stock Construction Group—A group of scenarios that are derived from CBECS to represent the 

commercial stock of buildings as currently constructed. Abbreviated as Existing Stock in some contexts. 

HRV—Heat Recovery Ventilation (include energy and enthalpy recovery). 

HVAC—Heating, Ventilating, and Air-Conditioning. 

Infiltration—Outside air that is passively introduced through openings in a building’s shell. 

Max Tech Construction Group—A group of scenarios that are derived from CBECS, but have 

modifications to better represent expected building technology in the year 2025. Abbreviated as Max 

Tech in some contexts. 

Maximum Mechanical Ventilation—Outside air that can optionally be introduced by the mechanical 

system for the purpose of economizing, building models that are not equipped with economizers will have 

a maximum ventilation rate equal to the minimum. 

Minimum Mechanical Ventilation—Outside air that is introduced by the mechanical system to meet the 

fresh air requirements. 

NREL—National Renewable Energy Laboratory. 

PDF—Probability Distribution Function. 

Perturbation Scenario—A scenario that is based on a reference scenario, but has an adjustment to the 

outside air. 

Reference Scenario—A scenario that is used as a point of comparison in an analysis of the effects of 

outside air. 

Scenario—A group of 4,820 building models derived from CBECS data. 

Sector—Energy consumption in the United States is classified by three sectors: transportation, buildings, 

and industrial. 

Subsector—Disaggregation of the sector energy use. As defined by CBECS (EIA 2006b), there are 20 

subsectors, or principal building activities, in commercial buildings. These include retail, office, and food 

sales buildings, and others. Complete listings are provided by Griffith et al. (2008). 
viii

ZEB—Zero energy building (or net zero energy building). A building with net zero energy consumption 

over one year. Assumed to be based on site energy use. 
ix

Acknowledgments

This document was prepared under the auspices of Drury Crawley and Terrence Logee of the Building 

Technologies (BT) Program within the Office of Energy Efficiency and Renewable Energy (EERE) at the 

U.S. Department of Energy (DOE). The authors would like to thank Michael Brambley, Steven 

Emmerich, and Michael Deru for reviewing this work, and Stefanie Woodward and Devin Egan for 

editing.
x 

Executive Summary 

We conducted simulation-based research to study the energy impacts of outside air on U.S. commercial 

buildings stock. We derived detailed building models from 4,820 buildings in the 2003 Commercial 

Buildings Energy Consumption Survey (CBECS). Combined with the appropriate weighting factors

these 4,820 models form the basis of this national scale study. The energy effects of outside air on 

commercial buildings were analyzed according to three types of construction. 

• The commercial sector was analyzed based on a set of models called the Existing Stock 

Construction Group, which is designed to represent the current CBECS buildings. 

• A set of models called the 90.1-2004 Construction Group was created by making the appropriate 

changes to the existing stock models to make them comply with ANSI/ASHRAE/IESNA 

standard 90.1-2004 (hereafter simply 90.1-2004). 

• A third set of models called the Max Tech Construction Group was created by applying changes 

to the existing stock models to reflect the technology and construction practices expected by

2025. 

The developments of the basic models used in this study are documented in two related studies, Griffith et 

al. (2008) and Griffith et al. (2007). EnergyPlus version 2.1 was used to conduct all simulations. 

For each building model, two simulations were compared to isolate the energy affects of outside air from 

the full integrated load. One is established as a reference case, the other has an adjustment to the outside 

air levels. The only difference between the two models is the outside air rates; thus, it is possible to 

compare the full integrated energy consumption of the two models and determine the energy impacts 

related to the change in outside air. 

Outside air is analyzed based on two general categories: 

• Infiltration, which is uncontrolled, is introduced through openings in the building's shell. The rate 

depends on relatively complex physics that are related to many variables, including the 

temperature gradients in the building, relative inside pressure, and the wind exposure of the 

facade. We simplified the physics by treating infiltration as an empirically derived constant 

average rate for each annual simulation. 

• Mechanical ventilation. A minimum level of ventilation is provided by mechanical systems to 

provide adequate indoor air quality as specified by ANSI/ASHRAE standard 62.1-2004 (hereafter 

simply 62.1-2004) and Turk et al. (1989). Some buildings’ mechanical systems have economizer 

controls that can bring in more outside air than the minimum requirement in order to help

condition the indoor space. A subset of the buildings in this study also has energy recovery 

devices that can recover energy from the exhaust air stream of the building through energy 

transfer to the outdoor air stream. Of the three types of construction we considered, the models in 

the Existing Stock Construction Group have, on average, the highest levels of minimum 

ventilation and infiltration. Furthermore, relatively few buildings in the Existing Stock

Construction Group have economizer controls and energy recovery devices. The minimum 

ventilation rates are generally lower in the 90.1-2004 Construction Group models than in the 

Existing Stock Construction Group. The infiltration rates in the 90.1-2004 Construction Group

models remain unchanged. More buildings in 90.1-2004 Construction Group have economizers 

and energy recovery systems than in the Existing Stock Construction Group. The Max Tech

Construction Group, predictably, has the most advanced management of outside air. The 

minimum ventilation rates are the same as in 90.1-2004 Construction Group, but the infiltration 

rates are reduced by a factor of 4 to reflect tighter construction. The Max Tech Construction 

Group models have economizers and energy recovery devices in every building. 
xi

We created a reference set of models for each construction group to establish a point of comparison. 

Each set of models, called a reference scenario, contains 4,820 models derived from the buildings in the 

CBECS survey. Each construction group had one perturbation scenario where the minimum ventilation 

was removed from each of the models. The 90.1-2004 Construction Group was analyzed in more detail

then the Existing Stock Construction Group and Max Tech Construction Group. For 90.1-2004 

Construction Group, perturbation scenarios were created to analyze the effects of increasing and 

decreasing the minimum ventilation levels. An additional perturbation scenario was created without any

mechanical ventilation, and without the ability to economize. One scenario has infiltration removed so 

that its effects could be examined. In total, seven scenarios have an adjustment to some aspect of the 

outside air. All the scenarios used in this study are outlined in Table ES-1. 

Table ES-1 Scenarios Examined

Construction 

Group Scenario

Infiltration Rate

(at 4 Pa) Ventilation 

Rate Economizer

Heat 

Recovery 

m Ventilation 3/s·m2 cfm/ft2

Existing 

Stock Reference 2.68E-04 0.060 Turk et al. (1989)

Varies by 

building

Varies by 

building

Existing 

Stock

No Minimum 

Mechanical 

Ventilation

2.68E-04 0.060

Zero unless 

in economizer 

mode

Varies by

building

Varies by 

building

90.1-2004 Reference 2.68E-04 0.060 As required 

by 62.1-2004

Where 

required by 

90.1-2004

Where 

required by 

90.1-2004

90.1-2004 No Infiltration 0.00 0.000 As required 

by 62.1-2004

Where 

required by 

90.1-2004

Where 

required by 

90.1-2004

90.1-2004

No 

Mechanical 

Ventilation

2.68E-04 0.060 0.0 No Not 

Applicable

90.1-2004

No Minimum 

Mechanical 

Ventilation

2.68E-04 0.060

Zero unless 

in economizer 

mode

Where 

required by 

90.1-2004

Where 

required by 

90.1-2004

90.1-2004

Half 

Minimum 

Mechanical 

Ventilation

2.68E-04 0.060

Half of 62.1-

2004 

requirements

Where 

required by 

90.1-2004

Where 

required by 

90.1-2004

90.1-2004

Double 

Minimum 

Mechanical 

Ventilation

2.68E-04 0.060

Double 62.1-

2004 

requirements

Where 

required by 

90.1-2004

Where 

required by 

90.1-2004

Max Tech Reference 6.69E-05 0.015 As required 

by 62.1-2004 Yes Yes

Max Tech

No Minimum 

Mechanical 

Ventilation

6.69E-05 0.015

Zero unless 

in economizer 

mode

Yes Yes
xii

Principal Findings

• The minimum mechanical ventilation in the reference models increases the commercial sector 

average energy use intensity (EUI) by 6.6%, 5.2%, and 0.7% for the Existing Stock, 90.1-2004, and 

Max Tech construction groups, respectively. The relative magnitude of the effect is smallest for the 

Max Tech Construction Group and greatest for the Existing Stock Construction Group. The impact

of mechanical ventilation is more significant on older vintages of construction because outside air 

management in new buildings is improved. Heat recovery devices are included in many new 

construction (90.1-2004 Construction Group) buildings and in all Max Tech Construction Group

buildings. 

• The natural gas EUIs follow a similar trend as the total EUIs. Minimum mechanical ventilation 

increases the energy consumption by 21.4%, 20.3%, and 8.9% for the Existing Stock, 90.1-2004, and 

Max Tech construction groups, respectively. 

• The required ventilation decreases or has no effect on the electricity EUIs. The change is

undetectable, 0.0%, for the Existing Stock and a 2.8% and 3.1% decrease for the 90.1-2004, and Max 

Tech Construction Groups respectively. Surprisingly, the minimum ventilation reduces the average 

electric EUI even for the Max Tech Construction Group, where all buildings are equipped with

economizers. Controls in the economized buildings should bring in outside air when it is beneficial, 

even if the minimum ventilation rate is zero. The economizer controls in the simulations presumably 

missed opportunities to economize. 

• The sector average EUI is plotted versus the air change rate, expressed in air changes per hour 

(ACH), for the 90.1-2004 Construction Group in Figure ES-1. The series of connected points from 

left to right represents scenarios in the 90.1-2004 Construction Group with no minimum, half 

minimum, reference, and double minimum levels of ventilation. A significant amount of information 

can be obtained from this figure by differencing two points. It is probably most significant that the 

relationship between the total EUI and ACH is nonlinear among the scenarios with varying 

ventilation rates. The nonlinear outcome reveals that outside ventilation air is costlier at higher 

ventilation rates. 

• Figure ES-1 also shows two outlying points corresponding to scenarios in the 90.1-2004 Construction 

Group with no mechanical ventilation and no infiltration. Comparing the two points to the reference 

scenario suggests that, based on the sector average, a quantity of outside air provided by mechanical 

ventilation consumes less energy than an equivalent volume of outside air passively introduced 

because of infiltration. The outcome is consistent with expectations, because mechanical ventilation 

systems can take advantage of heat recovery. The trend is based purely on the overall sector average 

(and constant, annual average infiltration) and does not apply to every climate and building. The 

detailed results contained in the body of this report show that for some climates infiltration actually

reduces the overall EUI of a building, presumably because of passive economizing.
xiii

0

10

20

30

40

50

60

70

80

90

0 0.2 0.4 0.6 0.8 1 1.2 1.4

ACH 

EUI (kBtu/ft2•yr)

Variable Minimum Ventilation

90.1-2004, No Infiltration

90.1-2004, No Mechanical Ventilation

Figure ES-1 Sector-Wide Average EUI versus Total ACH for 90.1-2004 Scenarios

• Detailed results based on climate zone and subsector are included in the body of this report; however, 

we concluded that in many cases there are too few building models in the CBECS data set to provide 

a statistically accurate sample. In climate zones and subsectors that have only a few building models,

a single non-prototypical building may skew the results. 

Research Priorities

This assessment shows that the energy consumed as a result of outside air is a significant fraction of a 

building’s overall energy consumption. When gas energy is associated primarily with heating, and 

electric energy is associated mostly with cooling, the results can provide a basic indicator of the effect 

outside air has on heating and cooling energy. It was found that gas energy consumption is particularly 

affected by outside air, especially in colder climates. We also found that on average electrical energy 

decreased as a result of mechanical ventilation, but for buildings with economizers this outcome seems to 

be attributed to poor economizer controls. This research shows that the energy associated with ventilation 

increases slightly nonlinearly with the ventilation rate, so the energy impact of increasing the rate would 

be underestimated if a linear extrapolation with a narrow perturbation range were used. Despite the

significant energy penalty, there is continuing pressure to increase ventilation rates to improve occupant 

health. We recommend several areas where further research would be beneficial.

• Investigate advanced energy recovery systems to reduce the energy consumed by

mechanical ventilation. Developments in fundamental heat transfer would apply to energy 

recovery in buildings and to a wide range of mechanical systems. Current technology could 

benefit from a study of the most effective building types and locations to apply energy recovery 

devices. The performance of all heat recovery systems could be improved by implementing 

advanced controls that could bypass the system when the associated increase in fan energy was 

greater than the savings achieved by energy recovery. 

• Develop improved economizing controls. We identified instances where required ventilation

reduces cooling energy consumption, even when economizers are installed. Economizing 

systems could be improved by developing control mechanisms that more effectively identify 

conditions when economizing can save energy. The optimal system should identify economizing 

90.1-2004, Reference
xiv

opportunities and provide ventilation independent of the fresh air requirement. Although the 

conclusion that economizing control should be improved is based on simulation, the control 

systems in real buildings are thought to have the same shortcomings. 

• Improve infiltration modeling. The effect of infiltration was given less emphasis, but the 90.1-

2004 Construction Group simulations predict that a significant energy penalty is associated with 

infiltration. Infiltration is sometimes beneficial, but it typically consumes more energy per 

volume of outside air than mechanical ventilation. Nevertheless, building infiltration is a 

complex phenomenon that is modeled crudely in the present methodology, which uses constant 

annual average rates. The infiltration rates specified in the models of this study are merely 

estimates, and research is needed to more accurately model this form of outside air. Models are 

available in EnergyPlus to develop a detailed air flow network; however, applying these methods 

to the large number of unique buildings in this study is impractical.

• Improve the accuracy of detailed results. The limited number of buildings in the CBECS 

survey reduces the accuracy of detailed results. This deficiency could be improved by either 

developing a set of building models based on a larger number of samples, or more practically by 

using a set of prototypical benchmark buildings as the basis of the investigation. A smaller set of 

prototypical buildings would make it feasible to focus on individual models.

• Investigate alternative methods of producing a healthy indoor environment. Advanced 

filters and ultraviolet light might reduce the necessary ventilation rates, but at the expense of new 

parasitic losses. The energy implications of these alternatives should be investigated and 

compared to the cost of conventional ventilation.

• Fully implement building standards and ensure compliance. Significant energy savings can 

be achieved simply by ensuring that standards are followed. Much of this report focuses on 

improving on a very optimistic scenario where all buildings are tightly sealed and have 

economizers and heat recovery. Improved governance based on current understanding is at least 

as important as technical advancements. 
1 

1. Introduction 

1.1 Problem Definition

The Energy Information Agency (EIA 2006a) reports that in 2005, U.S. commercial buildings consumed 

18 quads of energy, accounting for nearly 18% of the nation’s total energy consumption. The energy 

supply is becoming increasingly limited, and the energy demand continues to increase. The energy used 

by commercial buildings places a significant burden on the nation’s finite energy supply. To address this

concern, the U.S. Department of Energy has set an aggressive goal to reduce the energy consumption of 

the commercial sector of buildings to net zero. Research on how best to achieve net zero energy 

buildings (ZEBs) is ongoing although a recent study by the National Renewable Energy Laboratory 

(NREL) found that net zero energy across the sector is possible if the current best technologies are used in 

combination with an integrated, whole-building design approach (Griffith et al. 2008). 

The purpose of this study is to analyze the effects of outside air on the energy performance of a building. 

There is as yet no consensus, but the viability of ZEBs could be significantly influenced by the effects of

outside air. A detailed assessment of these effects is needed to determine the significance of outside air

and to direct future study toward the most viable ways to achieve energy savings, assuming the effects of 

outside air are significant. 

A study of the energy implications of outside air presents two significant challenges. 

• We need to accurately quantify the amount of outside air that enters a building. There is not a 

direct method to physically measure the amount of outside air entering a building. One approach

is to use various tracer gas techniques (Harrje et al. 1985), which can determine the amount of 

outside air—although these are typically short-term tests and extrapolation can be problematic 

because of the variables affecting the rate. Experimental techniques are also very expensive to 

apply on a reasonably-sized sample of the U.S. commercial buildings stock. 

• There is no method to directly measure the energy impacts of outside air, because the system 

loads related to outside air are coupled with the full integrated load on the HVAC equipment. 

The difficulty in isolating outside air loads and the challenge in simply measuring outside air 

rates can be at least partially overcome with energy simulations, but even with simulation

isolating the effects of the outside air is difficult. 

Assuming these obstacles can be overcome, a detailed national scale analysis remains complicated by the 

sheer number of dependent variables involved. Two important variables that this study attempts to isolate 

are the outdoor climate and the means by which outside air is introduced to the building. 

A few publications address the energy implications of outside air, but many more focus on the benefits of 

increased ventilation without fully taking into account the energy requirements (Fisk 2000). One study

that does address the energy associated with outside air is by Eto et al. (1988). Eto used the DOE 2.1C 

modeling software to study the energy implications of outside air for a single office building swept over 

13 climates in the United States and Canada. They concluded that increasing the ventilation rate has only 

a small impact on a building’s overall energy consumption. Nevertheless, a fourfold increase in the 

ventilation rate resulted in an 8% heating energy increase and a 14% cooling energy increase in the most 

extreme climates. 

Colliver (1995) used a theoretical analysis to determine the annual energy required to condition a 

specified rate of outside air to the indoor set point conditions. This analysis used hourly weather data to 

determine realistic outdoor conditions; both sensible and latent energy were taken into account. In Los 

Angeles, the annual normalized energy requirement of outside air was determined to be 22.1 MJ·h/kg; in 

Omaha it was 102.5 MJ·h/kg. Colliver concluded that the energy associated with ventilation was 

significant.
2 

Emmerich et al. (2005) published a report on the energy effects of outside air using an analysis based on 

three building types swept across five representative U.S. cities. This study was carried out using detailed 

simulations based on the Multizone Airflow and Contaminant Transport Analysis Software 

(CONTAMW), coupled with a detailed multi-zone building model in the Transient Energy System 

Simulation Tool (TRNSYS). An analysis was made of the energy cost savings potential of increasing the 

air tightness of each building. The results predicted a 3% to 36% savings in annual heating and cooling 

energy.

This study uses a much simpler airflow model compared to the work of Emmerich et. al.; however, the 

focus here is to assess a large representative sampling of the U.S. commercial buildings stock. This work

is based around several sets of building models derived from the 4,820 buildings in the 2003 Commercial 

Buildings Energy Consumption Survey (CBECS) (2006b). 

1.2 Project Scope

This report provides a detailed analysis of the effects of outside air on U.S. commercial buildings. The 

objectives are to quantify the energy use associated with various forms of outside air and to identify 

research areas that have potential to advance high-performance building technology. 

The means by which outside air is brought into a building is important. For this research, three methods

of introducing outside air are studied: 

• Infiltration through the building’s shell. 

• Mechanical ventilation necessary to provide suitable indoor air quality as specified by 

ANSI/ASHRAE standard 62.1-2004 and Turk et al. (1989). 

• Mechanical ventilation used for economizing. 

The effects of each form of outside air are analyzed individually. We aggregated the results into 14 

climate zones and 18 subsectors of the U.S. commercial buildings stock. 

The commercial sector is further analyzed, based on three levels of construction quality. One level of 

construction is designed to represent the existing stock of commercial buildings. Another level of 

construction is based on a generally improved set of buildings based on ASHRAE 90.1-2004. The third 

level is based on the expected technology and construction practices in 2025.

The intent of this work is specifically to identify the energy impacts of outside air. The analysis is based 

on answering a series of “what if” questions. We look at what happens if building construction quality

and mechanical equipment are improved. What happens if mechanical ventilation is cut in half? What if 

it is doubled? It is not in the scope of this work to assess the appropriate levels of outdoor air. We aim to 

inform decision makers of the national-scale energy impacts of decisions related to changing outside air 

requirements. 

1.3 Report Organization

This report is divided into five sections: 

Section 1 introduces the problem and identifies the research motivation and objectives. 

Section 2 outlines the methodology used to evaluate the effects of outside air. 

Section 3 presents the results of the study along with a discussion of important outcomes. 

Section 4 includes a discussion of the recommendations based on this research, including suggestions 

for future research. 

Section 5 is a list of references. 
3 

2. Analysis Methodology

For an assessment of the energy impacts of outside air, national-scale results based on a large number of 

buildings are valuable. To meet this need, we carried out detailed building simulations based on 4,820 

buildings in the 2003 CBECS public-use data using EnergyPlus version 2.1. By applying the appropriate 

weighting factors, the buildings in the CBECS data set were used to represent the entire U.S. commercial 

buildings stock. The methodology used to create detailed models from the survey data has been 

thoroughly documented in two previous NREL studies: Griffith et al. (2007; 2008). The models created 

for those works form the basis of this analysis. 

2.1 Energy Impact Modeling

Modeling the energy impacts of outside air is difficult because of the complex interactions between 

HVAC components and the thermal zone. The difficulty arises in determining exactly how one small 

portion of an integrated load is supposed to be propagated back through all the components of an 

arbitrarily complex HVAC system. The ventilation load data from a single model might be used to make 

simplifying assumptions and model the energy impacts; however, our approach is to use multiple 

simulations. A methodology based on adjusting inputs and comparing multiple runs is common when 

detailed, whole-building simulation programs such as EnergyPlus are used. Calculating the differences in 

energy use results between simulations appears to be the most useful way to apply EnergyPlus to the 

question of outside air impact on energy. The basic method used here is to run two simulations: one

reference simulation with a typical rate for outside air, and another simulation with a prescribed change in 

the outside air rate. The whole-building integrated energy use results are compared, and because the only 

difference in the models is in the outside air rate, we attribute all the changes in energy use to that change. 

The method of comparing energy use across multiple simulations is an obvious choice for modeling the 

energy impacts of outside air with EnergyPlus, but in practice the issue of autosizing HVAC systems 

complicates the approach. Outside air is an important contributor to the integrated load calculations used 

to size system component capacities. If two models with different levels of outside air are automatically 

sized, the simulations will differ in many more ways, because the system capacities would be different. 

For example, a constant volume air system that provides no outside air will be smaller than a similar 

system that does provide outside air. The air system with a smaller design will have less fan energy than 

the larger air system. Although the implications of outside air could be evaluated in such a way that the 

system size differences are taken into account, it is simpler not to allow such secondary and complex 

changes to occur. When using perturbation and differencing methods to calculate integrated effects on 

whole-building energy use, it is preferable to control exactly how the models differ.

To avoid the complexities of autosizing, in most cases we used hard sizes in the EnergyPlus input files. 

The building models are derived from models that were initially autosized, but then hard size files were 

created by using the results from previous autosizing. In the hard-sized EnergyPlus models, all the inputs 

are fixed and there are no input objects related to sizing. In theory, the hard-sized and autosized 

simulations should be identical; in practice, negligible differences are observed because of round-off 

differences. The one exception for autosizing is when outside air was increased from the levels in the 

reference simulation. In this case the model was autosized to allow adequate system capacity to meet the 

required indoor conditions.

For each building model, three parameters are used to control the outside air rates that are important to 

this work: 

• Infiltration rate. This prescribes the amount of outside air that is unintentionally introduced 

through openings in the building’s shell. Our modeling approach treats infiltration as a constant 

annual rate. The physical complexities of infiltration are simplified by our approach. Detailed air 
4 

flow models are available; however, they were considered impractical to implement for the large 

number of models in this study. 

• Minimum mechanical ventilation rate. This controls the amount of outside air that is 

introduced by the mechanical system to provide fresh air. 

• Maximum mechanical ventilation rate. This comes into play with an economizer system. It 

determines the rate of outside air that the building’s mechanical system is capable of delivering. 

The building is modeled without an economizer by setting the maximum ventilation rate equal to the 

minimum. When the maximum ventilation rate is set above the minimum, controls in the HVAC system 

can provide ventilation up to the maximum rate for economizing. The maximum ventilation rate is not a 

requirement. Buildings in poor economizing climates can remain at the minimum ventilation rate for the 

entire simulation if controls determine that economizing does not save energy.

2.2 Scenarios

For this study, the commercial stock of buildings is analyzed based on three levels of construction quality

and building technology. Each group of models belonging to a particular level is referred to as a 

construction group. One construction group, which we call the Existing Stock Construction Group, aims 

to represent the commercial sector as it is constructed today. Another construction group, the 90.1-2004 

Construction Group, has the necessary changes to make the existing stock of buildings comply with 90.1-

2004. A third construction group, called the Max Tech Construction Group, is based on reconstructing 

the current stock of buildings using future advanced technology and construction practices. 

Within each construction group several sets of 4,820 models are created based on the CBECS data. We 

call each group of 4,820 models a scenario. Each construction group contains a “reference scenario” and 

at least one “perturbation scenario” that has a change to the outside air levels. The reference scenarios 

most correctly represent each construction group. The scenarios with changes to the outside air levels are 

necessitated by our approach in determining the effects of outside air. 

The process of creating complete building models for the Existing Stock Construction Group is 

documented by Griffith et al. (2008). Griffith et al. (2007) documents the series of changes that were 

made to the existing stock models in order to create the 90.1-2004 and Max Tech construction groups. In 

this report, our intent is to investigate the effects of outside air, so we focus on the details of the models 

pertaining to infiltration and mechanical ventilation. 

2.2.1 Existing Stock

Complete details about the Existing Stock Construction Group models are documented in previous work, 

but here we focus on the details pertaining to outside air. Following the previous work, infiltration is 

modeled as a simple constant air change rate that is the result of combining a flow rate per exterior area 

with a whole-zone air change rate that is the same for all zones. Based on Persily (1998) we assumed a 

leakage rate per exterior area of 0.4 cfm/ft2 at 75 Pa. The leakage rate is a factor of 4 lower than the mean 

value of 1.67 cfm/ft2 at 75 Pa reported by Persily. Leakage rates are typically characterized at relatively 

high pressure differences (75 Pa); however, in practice the differential pressure seen by a building is 

lower and variable depending on stack, wind, and mechanical ventilation effects. We used the 

relationship n  / ∆= PCAV , where n = 65.0 , combined with the infiltration rate at 75 Pa, to arrive at the 

infiltration rate for the existing stock models, 0.0002677 m3

/s·m2 at 4 Pa. 

In addition to the infiltration rate that is a function of the building envelope area, a whole-zone air change 

rate is applied to all zones. The magnitude of the whole zone infiltration rate was assigned, by 

assumption, by taking 10% of a randomly assigned level determined using a lognormal probability 

distribution for infiltration found by Chan (2006). Chan’s modeling study found infiltration rates in the 

commercial sector to have a lognormal distribution with geometric mean of 0.35 and a geometric standard 

deviation of 2.1.
5 

Most HVAC systems use outside air ventilation to gradually purge the impurities in stale indoor air. Like 

infiltration, data pertaining to real world ventilation rates are limited, and much of the information 

combines mechanical ventilation and infiltration. Turk et al. (1989) used tracer gas techniques to measure 

combined infiltration and ventilation rates in 38 commercial buildings in the Pacific Northwest. They 

found mean outside air rates of 1.5 air changes per hour (ACH) or 28 l/s·person (59.3 cfm/person), and 

provided a breakdown for educational, libraries, small and large offices, and multi-use buildings. We 

modeled ventilation by assuming that the infiltration portion is equivalent to 9.3 l/s·person (19.7 

cfm/person), then subtracted the rate for infiltration from the whole-building ventilation rates reported by 

Turk et al. to assemble default rates for mechanical ventilation. For activity types not covered, the mean 

rate without infiltration of 18.8 l/s·person (39.8 cfm/person) was used. The mechanical ventilation rates 

that are used for each principal building activity (PBA) of the existing stock models are given by Table 2-

1. The rates are generally in excess of the minimum levels specified in 62.1-2004, except for education, 

which is close but slightly low.

Table 2-1 Default Outside Air Mechanical Ventilation Rates by PBA 

PBA 

Code PBA Name

Default Outside 

Air Rate

(cfm/person)

Default Outside 

Air Rate

(l/s·person)

Data Source

1 Vacant 0.0 0.0 (assumption)

2 Office/professional < 9300 m2 55.3 26.1 Turk et al. 1989

2 Office/professional > 9300 m2 45.3 21.4 Turk et al. 1989

4 Laboratory 39.6 18.7 Turk et al. 1989

5 Nonrefrigerated warehouse 10.6 5.0 (assumption)

6 Food sales 39.6 18.7 Turk et al. 1989

7 Public order and safety 39.6 18.7 Turk et al. 1989

8 Outpatient health care 39.6 18.7 Turk et al. 1989

11 Refrigerated warehouse 4.2 2.0 (assumption)

12 Religious worship 39.6 18.7 Turk et al. 1989

13 Public assembly 39.6 18.7 Turk et al. 1989

14 Education 13.4 6.3 Turk et al. 1989

15 Food service 39.6 18.7 Turk et al. 1989

16 Inpatient health care 39.6 18.7 Turk et al. 1989

17 Skilled nursing 39.6 18.7 Turk et al. 1989

18 Lodging 39.6 18.7 Turk et al. 1989

25 Retail 39.6 18.7 Turk et al. 1989

26 Service 39.6 18.7 Turk et al. 1989

91 Other 39.6 18.7 Turk et al. 1989

The minimum ventilation rate is the minimum level of outside air that is required for occupant health. 

When an airside economizing system is present, the minimum rate can be exceeded to provide

inexpensive cooling. Only a subset of the existing stock is equipped with economizer controls, and in this 

study the presence of economizing controls is determined from the CBECS data. In order to model an 

airside economizer, the maximum ventilation rate is set to the capacity of the supply fan, thereby allowing 

the system to provide up to 100% outside air when it is advantageous to economize. 

Only a subset of the existing stock also has energy recovery systems. For the Existing Stock Construction 

Group modeling scenarios, the presence of these devices is again determined from the CBECS survey 

data. 
6 

2.2.2 90.1-2004

The models in the 90.1-2004 Construction Group are created by applying the necessary changes to make 

the Existing Stock Construction Group models comply with the 90.1-2004 standard. As documented by 

Griffith et al. (2007), changes are made to items such as lighting power density (LPD), thermal envelope 

constructions, and mechanical efficiencies. System types are also modified to reflect the eight system 

types specified in Table G3.1.1A of 90.1-2004 Appendix G. Most pertinent to this study is that minimum 

mechanical ventilation rates are set to the minimum specified by 62.1-2004. For the 90.1-2004 reference 

scenario, infiltration rates remain the same as in the Existing Stock Construction Group models, because 

90.1-2004 has no air tightness requirements. Economizers and heat recovery devices are used where they 

are required by 90.1-2004. There are more buildings in the 90.1-2004 Construction Group with 

economizers and heat recovery devices than in the Existing Stock Construction Group. 

2.2.3 Max Tech

The models in the Max Tech Construction Group were developed by applying changes to the existing 

stock models that reflect the best available technology and energy-saving practices expected in 2025. 

Similar to the 90.1-2004 Construction Group models, changes are made to items such as LPD, thermal 

envelope constructions, and mechanical efficiencies. Again, the system types are modified to reflect the 

eight system types specified in Table G3.1.1.A of 90.1-2004. The reference scenario models in the Max 

Tech Construction Group are also fully documented by Griffith et al. (2007). 

For the reference models in the Max Tech Construction Group, infiltration rates are reduced by a factor of 

4 compared to the existing stock models to reflect an improved envelope construction. The minimum 

mechanical ventilation rates are set to the minimum specified by 62.1-2004, the same as the 90.1-2004 

reference scenario. The reference models in the Max Tech Construction Group have economizers and 

heat recovery devices for all buildings. 

2.2.4 Summary of Outside Air Scenarios

The details pertaining to the outside air of each scenario are summarized in Table 2-2. There are three 

reference scenarios, one corresponding to each construction group. The infiltration rate is the same for 

the Existing Stock and 90.1-2004 reference scenarios; the Max Tech reference scenario has reduced 

infiltration to reflect a tighter envelope. Ventilation is the same for the 90.1-2004 and Max Tech 

reference scenarios, and slightly higher for the existing stock reference scenario. A larger number of 

buildings in the 90.1-2004 reference include economizers and heat recovery devices compared to the 

Existing Stock. All buildings in the Max Tech reference have economizers and heat recovery devices. 

In addition to the three reference scenarios, seven perturbation scenarios are created, which modify the

reference outside air rates. Each construction group has a scenario that removes all minimum mechanical 

ventilation. The 90.1-2004 Construction Group is analyzed in more detail than the other two groups. For 

the 90.1-2004 Construction Group, five perturbation scenarios adjust the outside air rates from the 

reference. 

All infiltration rates reported in Table 2-2 include only the infiltration per shell area. As noted in previous 

discussion, there is a statistically random whole zone infiltration rate applied to all models in addition to 

the rates reported in the table. 
7 

Table 2-2 Scenarios Examined

Construction 

Group Scenario

Infiltration Rate

(at 4 Pa) Ventilation 

Rate Economizer 

Heat 

Recovery 

m Ventilation 3/s·m2 cfm/ft2

Existing 

Stock Reference 2.68E-04 0.060 Turk et al. (1989)

Varies by 

building

Varies by 

building

Existing 

Stock

No Minimum 

Mechanical 

Ventilation

2.68E-04 0.060

Zero unless 

in economizer 

mode

Varies by 

building

Varies by 

building

90.1-2004 Reference 2.68E-04 0.060 As required 

by 62.1-2004

Where 

required by 

90.1-2004

Where 

required by 

90.1-2004

90.1-2004 No Infiltration 0.00 0.000 As required 

by 62.1-2004

Where 

required by 

90.1-2004

Where 

required by 

90.1-2004

90.1-2004

No 

Mechanical 

Ventilation

2.68E-04 0.060 0.0 No Not 

Applicable

90.1-2004

No Minimum 

Mechanical 

Ventilation

2.68E-04 0.060

Zero unless 

in economizer 

mode

Where 

required by 

90.1-2004

Where 

required by 

90.1-2004

90.1-2004

Half 

Minimum 

Mechanical 

Ventilation

2.68E-04 0.060

Half of 62.1-

2004 

requirements

Where 

required by 

90.1-2004

Where 

required by 

90.1-2004

90.1-2004

Double 

Minimum 

Mechanical 

Ventilation

2.68E-04 0.060

Double 62.1-

2004 

requirements

Where 

required by 

90.1-2004

Where 

required by 

90.1-2004

Max Tech Reference 6.69E-05 0.015 As required 

by 62.1-2004 Yes Yes

Max Tech

No Minimum 

Mechanical 

Ventilation

6.69E-05 0.015

Zero unless 

in economizer 

mode

Yes Yes
8 

3. Results and Discussion 

3.1 90.1-2004 Scenarios

The 90.1-2004 Construction Group scenarios that were described in Section 2.2 were used to investigate 

the effects of outside air on new 2005 construction. The 90.1-2004 scenarios were derived from CBECS 

data with adjustments to meet 90.1-2004. The six scenarios that represent new construction include a 

reference scenario and five additional scenarios that modify the prescribed quantity of outside air in the 

reference scenario. We determined the effect of outside air by evaluating the difference between the 90.1-

2004 reference scenario and another scenario that has a change in the outside air rates. Aggregate results 

for the entire commercial sector are shown in Table 3-1 through Table 3-5. Table 3-7 through Table 3-11

show a selection of the results based on climate zone and building subsector. Sector averages were 

determined by applying a weighting factor, based on the total floor area of similar buildings in the sector. 

The average energy use intensities (EUIs) for the sector are shown in Table 3-1. EUIs are displayed as 

absolute quantities and as relative and percent changes compared to the reference scenario. Interpreting 

the relative quantities is generally straightforward; however, a brief explanation of the results is 

important. In most scenarios some outside air is removed from each model, so the relative values can be 

interpreted as the EUI associated with the quantity of outside air that is removed. For example, based on 

the relative decrease in EUI for the No Minimum Mechanical Ventilation Scenario, providing the 

minimum level of ventilation increases the average EUI for the commercial sector by 3.7 kBtu/ft2

·yr (42.0 

MJ/m2

·yr). The Double Minimum Mechanical Ventilation scenario is interpreted differently, because 

outside air is added to, instead of subtracted from, the reference set of models. Doubling the minimum 

ventilation increases the EUI by 8.7 kBtu/ft2

·yr (98.8 MJ/m2·yr) compared to the reference. 

The relative changes in total energy are informative; however, percentages, which are the relative 

differences normalized by the reference values, are a simpler measure of the effects attributed to outside 

air. Providing the minimum level of mechanical ventilation required by 90.1-2004 increases the total 

average EUI by 5.2%, and supplying double the required ventilation rate increases the EUI by 12.4%,

compared to the reference model. Percentages from the full set of 90.1-2004 Construction Group 

scenarios are included in Table 3-1. 
9 

Table 3-1 90.1-2004, Sector-Wide Average Total Site EUI

Scenario

Absolute Decrease Relative to 

Reference

Percent 

Decrease

Relative to 

Reference (kBtu/ft2

·y) (MJ/m2·y) (kBtu/ft2·y) (MJ/m2·y) 

Reference 71.0 806.7 – – – 

No Infiltration 64.1 728.4 6.90 78.37 9.7%

No Mechanical Ventilation 71.1 807.3 –0.05 –0.56 –0.1%

No Minimum Mechanical 

Ventilation 67.3 764.9 3.69 41.86 5.2%

Half Minimum Mechanical 

Ventilation 68.4 777.4 2.59 29.37 3.7%

Double Minimum Mechanical 

Ventilation 79.8 905.7 –8.72 –98.99 –12.4%

The total ACH averaged across the sector are presented in Table 3-2. The format mirrors the method

used to display results pertaining to the total EUI. The values are given as an absolute quantity, the

decrease relative to the reference, and the percent decrease relative to the reference. The simulations 

predict that infiltration accounts for 31% of the total air change rate, and that minimum mechanical 

ventilation accounts for 53% of the total. The remaining balance of outside air is introduced by the 

HVAC system for economizing. 

Figure 3-1 combines the data pertaining to total EUI and outside air change rate into a single illustration. 

In order from left to right, the series of connected points represent the scenarios with no minimum 

ventilation, half minimum ventilation, the reference quantity, and double ventilation. As discussed in the 

methodology, the equipment sizes are based on the reference models, except for the double ventilation 

scenario, where the equipment is resized to meet set point. The plot of EUI versus the total outside air 

change rate suggests a nonlinear relationship between EUI and the minimum mechanical ventilation rate. 

Interestingly, the data indicate that ventilation air has an increasing impact on energy use as the minimum

ventilation rate increases. Admittedly, some of this nonlinearity is a result of resizing the double 

ventilation scenario; however, even neglecting that scenario there is a slight nonlinearity. Figure 3-1 also 

shows two outlying points that represent the scenarios with no mechanical ventilation and no infiltration. 

Compared to the 90.1-2004 reference point, these data points illustrate that significantly more energy is

consumed by infiltration than by mechanical ventilation, even though mechanical ventilation introduces 

outside air at a higher rate. Simply put, a quantity of outside air provided by mechanical ventilation 

consumes less energy than the same quantity of outside air introduced through infiltration. We attribute 

this difference to the fact that outside air introduced by mechanical ventilation is engineered to take 

advantage of economizing and heat recovery in many of the 90.1-2004 Construction Group models. 
10

Table 3-2 90.1-2004, Sector-Wide Average ACH

Scenario Absolute 

Decrease

Relative to 

Reference

(1/h)

Percent Decrease

Relative to 

Reference

Reference 0.80 – – 

No Infiltration 0.55 0.24 31.25%

No Mechanical Ventilation 0.27 0.53 66.25%

No Minimum Mechanical 

Ventilation 0.38 0.42 52.50%

Half Minimum Mechanical 

Ventilation 0.58 0.22 27.50% 

Double Minimum Mechanical 

Ventilation 1.19 –0.40 –48.75%

0

10

20

30

40

50

60

70

80

90

0 0.2 0.4 0.6 0.8 1 1.2 1.4

ACH 

EUI (kBtu/ft2•yr)

Variable Minimum Ventilation

90.1-2004, No Infiltration

90.1-2004, No Mechanical Ventilation

Figure 3-1 Sector-Wide Average EUI versus Total ACH for the 90.1-2004 Construction Group

Outside air has a different effect on the natural gas EUI (see Table 3-3) and the electricity EUI (see Table 

3-4), so these components are analyzed one at a time. Infiltration increases the natural gas EUI by 26.8% 

and the minimum mechanical ventilation increases the gas EUI 20.3%. In contrast, infiltration increases 

the electricity EUI by only 0.9% and the minimum ventilation reduces the electricity EUI by 2.8%. The 

varying effect of outside air on the gas and electric EUIs can be explained by associating gas energy with 

heating, and electrical energy with cooling. Under such an assumption the diminished effect of outside 

air on the electricity EUI can be attributed to economizing, or nearly free cooling that can be provided by 

90.1-2004, reference 90.1-2004, Half Minimum 

Mechanical Ventilation 90.1-2004, No 

Minimum Mechanical 

90.1-2004, 

Double Minimum 

Mechanical Ventilation
11

outside air under some outdoor conditions. In other words, outside air can sometimes actually save 

cooling energy with economizing; however, rarely can outside air reduce heating energy. The effects of 

outside air on total annual electric energy and peak electric power are markedly different. In contrast to 

electric energy where outside air decreases the quantitative intensity, Table 3-5 shows that outside air 

increases the peak electric power in every scenario. 

Table 3-3 90.1-2004, Sector-Wide Average Gas EUI

Scenario

Absolute Decrease Relative to 

Reference

Percent 

Decrease

Relative to 

Reference (kBtu/ft2

·y) (MJ/m2·y) (kBtu/ft2·y) (MJ/m2·y)

Reference 24.6 279.4 – – – 

No Infiltration 18.0 204.9 6.56 74.47 26.8%

No Mechanical Ventilation 21.3 241.9 3.30 37.50 13.4%

No Minimum Mechanical 

Ventilation 19.6 222.4 5.01 56.95 20.3%

Half Minimum Mechanical 

Ventilation 21.7 246.6 2.89 32.78 11.8%

Double Minimum Mechanical 

Ventilation 31.7 360.4 –7.13 –80.99 –28.9%
12

Table 3-4 90.1-2004, Sector-Wide Average Electricity Site EUI

Scenario

Absolute Decrease Relative to 

Reference

Percent 

Decrease

Relative to 

Reference (kBtu/ft2

·y) (MJ/m2·y) (kBtu/ft2·y) (MJ/m2·y)

Reference 46.2 524.2 – – – 

No Infiltration 45.8 520.3 0.34 3.89 0.9%

No Mechanical Ventilation 49.5 562.3 –3.35 –38.06 –7.1%

No Minimum Mechanical 

Ventilation 47.5 539.3 –1.33 –15.09 –2.8%

Half Minimum Mechanical 

Ventilation 46.5 527.6 –0.30 –3.41 –0.6%

Double Minimum Mechanical 

Ventilation 47.7 542.2 –1.58 –18.00 –3.2%
13

Table 3-5 90.1-2004, Sector-Wide Average Peak Electric Power

Scenario

Absolute Decrease Relative to 

Reference

Percent 

Decrease 

Relative to 

Reference (W/ft2

) (W/m2) (W/ft2) (W/m2) 

Reference 5.12 55.07 – – – 

No Infiltration 4.76 51.27 0.35 3.80 7.03%

No Mechanical Ventilation 4.81 51.72 0.31 3.34 6.06%

No Minimum Mechanical 

Ventilation 4.82 51.84 0.30 3.23 5.86%

Half Minimum Mechanical 

Ventilation

4.95 53.26 0.17 1.81 3.32%

Double Minimum Mechanical 

Ventilation 5.84 62.91 –0.73 –7.84 –14.06%

The previous results present several of the most relevant metrics regarding the effects of outside air. The 

sector average total EUI, ACH, gas EUI, electric EUI, and peak electric power are presented in absolute 

and relative terms and in SI and IP units. These data have been presented in tables to accommodate the 

large amount of information; however, it is difficult to see the relative nature of the results in tabular

format. To address this difficulty, Figure 3-2 presents percent changes of the metrics in a chart to better 

illustrate the comparison between each 90.1-2004 scenario. 

 
14

-60%

-40%

-20%

0%

20%

40%

60%

80%

EUI ACH Gas EUI Electric EUI Peak Electric 

Power

Percent Decrease

90.1-2004, No Infiltration

90.1-2004, No Mechanical Ventilation

90.1-2004, No Minimum Mechanical Ventilation

90.1-2004 Half Minimum Mechanical Ventilation

90.1-2004, Double Minimum Mechanical Ventilation

Figure 3-2 Summary of Percentage Decreases in Sector-Wide Averages

The U.S. commercial buildings sector is diverse, and the buildings vary by many factors, including 

geometry, type of construction, purpose, and climate zone. Sector averages provide a simple indicator of 

a particular metric such as total site EUI, but these averages do not show the entire picture. Figure 3-3

illustrates the variation of total site EUI in the commercial sector using a probability density function 

(PDF) of the relative change in total EUI. Most buildings have a change in EUI near the average for the 

sector (3.7 kBtu/ft2

·yr) (42.0 MJ/m2·y), but some differ significantly. For some buildings, the minimum

ventilation actually results in energy savings, presumably due to uncontrolled economizing due to the 

minimum outside air requirement. Although PDFs are not given for all metrics, we expect similar 

variation across the sector for the other metrics that have been shown as sector averages.

 
15

0

0.05

0.1

0.15

0.2

0.25

-40 -30 -20 -10 0 10 20 30 40

Change in EUI (kBtu/ft2

•yr) (1.0 kBtu/ft2

•yr = 11.4 MJ/m2

•yr)

Probability Density

Figure 3-3 PDF of Change in Sector Average EUI for 90.1-2004, No Minimum Mechanical

Ventilation

The PDF of the change in total EUI due to the minimum ventilation indicates a significant variation in 

this quantity across the sector. A significant portion of the variation is believed to be associated with the 

building subsector and climate zone. To address the possibility that climate and subsector are important 

variables, select results are presented in a tabular format that shows the effect of minimum ventilation

based on climate zone and building subsector. Table 3-7 through Table 3-11 show the percent change in 

total EUI, ACH, gas EUI, electricity EUI, and peak electric demand, respectively, when the minimum 

mechanical ventilation is set to zero.

The detailed tables based on climate zone and subsector should be used cautiously, because sometimes 

only a few buildings are associated with each table entry. As a result, a single building simulation can 

have a significant impact on the results. The exact number of buildings in the CBECS survey is broken 

down by climate zone and subsector in Table 3-6. 
16

Table 3-6 Number of Models by Subsectors and Climate Zones

Subsector

Climate Zone

All 1A 2A 2B 3A 3B 3C 4A 4B 4C 5A 5B 6A 6B 7 

All 4,820 40 542 24 464 452 52 982 64 50 1,152 262 519 120 97

Office/professional 976 6 99 7 73 108 18 211 6 21 253 33 93 26 22

Nonrefrigerated warehouse 473 5 77 0 49 50 2 93 6 6 94 21 50 10 10

Education 649 4 91 5 62 59 8 124 9 8 139 58 61 17 4 

Retail (except malls) 355 4 34 2 52 36 4 80 6 0 73 23 27 7 7 

Public assembly 279 3 36 0 25 26 3 47 5 5 62 14 37 6 9 

Service 370 2 20 0 43 21 2 76 5 0 100 20 54 13 13

Religious worship 311 0 31 0 35 29 0 64 6 0 82 11 45 6 0 

Lodging 260 7 31 0 20 22 0 58 7 3 51 15 26 8 10

Food services 242 2 34 0 27 22 2 49 0 2 57 12 28 2 4 

Inpatient health care 217 2 25 3 19 22 5 45 2 0 53 12 21 6 2 

Public order and safety 85 0 7 0 4 4 0 23 0 0 22 9 9 3 0 

Food sales 125 0 13 0 16 8 2 23 0 0 35 8 13 0 4 

Inpatient health care 144 3 15 0 10 15 0 28 4 0 35 10 12 7 2 

Vacant 134 0 17 2 18 10 2 24 3 2 29 3 20 0 3 

Other 64 0 6 0 3 4 0 10 2 0 21 4 8 2 4 

Skilled nursing 73 0 5 0 5 7 0 16 0 0 22 6 8 3 0 

Laboratory 43 0 0 0 2 8 0 5 0 0 19 0 4 2 0 

Refrigerated warehouse 20 0 0 0 0 0 0 6 0 0 5 3 3 0 0 
17

 

Table 3-7 90.1-2004, No Minimum Mechanical Ventilation Scenario, Percent Change in EUI by Climate Zone and Subsector

Subsector

Climate Zone

All 1A 2A 2B 3A 3B 3C 4A 4B 4C 5A 5B 6A 6B 7 

All 5.2 2.8 –3.7 –2.2 –2.3 0.9 1.2 1.2 9.5 6.4 9.6 9.4 15.1 19.1 15.9

Office/professional 2.1 4.2 –1.4 –0.7 1.6 0.0 –0.8 –0.2 2.4 4.4 4.3 4.0 5.9 9.0 4.3

Nonrefrigerated warehouse 6.9 3.5 –5.0 5.3 5.6 1.0 6.4 7.5 7.6 10.1 10.0 9.8 11.0 12.5

Education 7.7 –10.6 –14.4 7.0 –3.2 3.7 11.7 –3.5 5.4 12.9 19.7 17.8 27.7 37.0 30.8

Retail (excluding mall) 7.4 5.2 –3.9 5.0 2.4 –0.4 2.5 4.3 1.9 15.2 12.3 17.0 16.8 23.5

Public assembly 6.9 –0.6 –0.1 –4.0 1.1 1.1 0.7 12.7 10.3 15.4 6.4 15.7 3.8 15.4

Service 16.9 –9.2 –5.1 9.4 9.3 –2.0 10.1 11.2 19.3 19.9 30.0 28.7 29.1

Religious worship 12.6 –7.5 8.4 5.4 12.4 18.5 17.3 13.3 17.1 19.8

Lodging 11.2 1.9 4.4 5.0 3.5 11.6 13.5 6.9 14.9 10.0 16.4 17.5 20.8

Food services –0.2 3.0 –1.9 –1.8 –1.2 –0.7 –2.3 –1.1 1.2 0.1 4.8 7.0 7.7

Health care (inpatient) –2.7 2.2 3.6 –2.4 –24.3 –2.2 –3.1 –3.3 –0.7 3.3 3.8 17.9 21.9 –6.3

Public order and safety 2.2 1.3 3.9 1.3 –1.2 5.0 0.3 7.3 –1.6

Food sales 1.2 –0.1 –2.0 0.4 0.0 –1.7 2.8 3.3 6.6 4.0

Health care (outpatient) 8.1 12.2 –15.3 –12.4 –14.4 5.8 18.8 15.3 11.9 27.2 20.0 40.3

Vacant 12.1 18.6 –0.8 9.1 8.2 2.8 4.9 13.0 11.3 17.7 7.2 12.9 18.3

Other 3.5 –3.2 –1.8 1.0 –0.5 8.2 5.9 5.8 8.1 11.6 10.2

Skilled nursing –0.6 –4.3 –18.7 –1.1 –28.3 7.7 13.3 24.5 27.4

Laboratory –1.4 –0.5 –4.4 –1.4 –1.7 0.1 0.4

Refrigerated warehouse 4.4 1.7 8.4 7.2 8.4
18

Table 3-8 90.1-2004, No Minimum Mechanical Ventilation, Percent Change in ACH by Climate Zone and Subsector

Subsector

Climate Zone

All 1A 2A 2B 3A 3B 3C 4A 4B 4C 5A 5B 6A 6B 7 

All 52.6 65.6 64.1 44.4 64.8 47.4 34.3 62.2 50.8 39.3 44.7 43.2 46.9 45.9 41.8

Office/professional 38.4 57.5 49.7 30.2 50.6 34.1 26.8 56.5 24.2 24.9 29.6 25.4 32.4 30.7 30.1

Nonrefrigerated warehouse 35.2 42.2 33.0 36.4 34.0 17.8 40.3 24.9 39.5 33.0 31.7 36.4 33.9 36.9

Education 69.0 78.8 76.9 67.5 75.2 66.0 53.9 77.0 63.8 63.5 62.9 58.5 63.6 63.0 68.6

Retail (excluding mall) 53.3 58.3 58.4 48.6 54.5 50.6 48.4 56.6 43.8 51.4 42.3 54.9 43.7 52.9

Public assembly 45.6 35.7 56.8 51.2 43.0 42.5 54.9 41.4 32.0 43.1 34.7 44.7 20.3 33.9

Service 59.0 62.6 57.9 61.6 56.7 47.4 65.2 59.7 56.2 51.1 60.2 55.7 56.1

Religious worship 51.6 49.6 53.2 50.9 55.7 51.1 50.1 46.9 50.0 51.3

Lodging 33.7 53.9 37.9 28.4 26.1 33.3 46.7 19.6 34.4 25.8 30.9 28.0 30.9

Food services 44.3 84.8 77.2 78.3 37.0 20.5 75.6 48.7 22.7 9.2 20.5 9.9 28.3

Health care (inpatient) 78.2 88.4 89.6 71.0 87.6 74.1 75.3 88.8 88.7 64.9 71.4 68.8 57.6 86.0

Public order and safety 38.3 55.2 45.2 34.5 52.7 25.6 20.0 28.6 9.3

Food sales 32.9 34.7 37.9 31.0 24.1 35.0 32.6 24.8 33.6 27.7

Health care (outpatient) 66.8 80.5 68.4 67.2 58.9 74.6 61.6 64.2 61.5 67.9 60.7 67.3

Vacant 49.9 0.0 36.9 52.1 55.3 0.0 59.5 0.0 33.0 26.2 50.2 52.2 44.0

Other 36.8 36.5 35.6 28.3 48.4 36.5 29.8 28.5 29.5 36.3 32.5

Skilled nursing 64.5 82.3 77.2 56.4 81.4 55.0 49.2 57.2 56.2

Laboratory 31.2 84.0 25.0 73.6 14.5 12.7 8.5

Refrigerated warehouse 37.9 43.9 37.5 33.1 28.8
19

Table 3-9 90.1-2004, No Minimum Mechanical Ventilation, Percent Change in Gas EUI by Climate Zone and Subsector

Subsector

Climate Zone

All 1A 2A 2B 3A 3B 3C 4A 4B 4C 5A 5B 6A 6B 7 

All 20.4 –0.1 1.3 3.5 3.7 13.0 9.3 14.3 35.9 25.3 23.6 30.6 30.4 40.4 32.0

Office/professional 14.4 –1.4 4.3 –0.4 21.0 6.9 4.2 10.0 8.7 22.3 15.3 22.7 16.5 27.5 15.4

Nonrefrigerated warehouse 16.7 –1.5 4.4 15.3 22.5 0.0 15.7 15.4 25.8 16.8 21.8 16.7 15.3 20.1 

Education 30.4 20.1 –15.5 60.0 15.4 45.7 42.2 7.7 63.9 37.1 37.2 47.2 45.2 59.5 65.7

Retail (excluding mall) 33.0 9.7 3.2 –0.8 24.3 17.7 30.0 31.8 33.1 36.8 37.0 38.0 36.7 42.5

Public assembly 23.7 0.0 21.5 –8.6 18.2 22.8 11.5 28.5 45.6 31.3 34.6 34.2 8.7 24.2

Service 42.2 4.0 24.9 41.0 44.0 17.1 36.4 36.3 40.0 44.6 44.9 58.0 47.7

Religious worship 29.7 32.6 33.0 35.3 30.0 54.2 29.2 29.5 27.2 28.0

Lodging 40.1 1.6 3.1 26.7 25.6 46.1 59.7 25.7 46.7 32.3 40.4 38.8 38.9

Food services 3.2 0.0 0.5 1.5 0.4 –0.6 1.3 4.0 4.4 3.7 10.2 14.7 27.4

Health care (inpatient) 7.8 0.0 5.1 1.0 –44.2 10.9 11.5 9.4 19.8 24.5 25.9 50.9 47.9 5.0

Public order and safety 14.1 –3.6 22.7 13.9 3.5 19.7 19.2 22.4 7.6

Food sales 20.5 5.7 9.1 14.1 19.4 16.1 22.6 29.7 22.3 33.0

Health care (outpatient) 38.1 –5.5 7.3 19.7 18.7 40.6 45.1 36.2 36.2 49.9 50.3 66.1

Vacant 20.7 35.0 –2.8 17.8 37.9 10.3 9.1 21.3 34.0 27.9 25.3 17.3 36.7

Other 11.3 –11.5 7.9 7.4 4.0 20.5 13.1 13.7 15.4 31.3 24.1

Skilled nursing 20.6 –4.5 3.1 2.6 –26.7 25.1 53.5 58.4 60.5

Laboratory –2.5 0.0 –7.8 0.9 –3.9 0.2 0.5

Refrigerated warehouse 27.8 19.7 34.1 33.4 33.3
20

Table 3-10 90.1-2004, No Minimum Mechanical Ventilation, Percent Change in Electricity EUI by Climate Zone and Subsector

Subsector

Climate Zone

All 1A 2A 2B 3A 3B 3C 4A 4B 4C 5A 5B 6A 6B 7 

All –2.9 3.4 –4.7 –2.8 –4.7 –3.2 –2.7 –4.8 –2.3 –1.2 –1.0 –1.0 –0.7 –0.9 1.2

Office/professional –1.0 4.6 –1.7 –0.7 –1.1 –0.6 –1.6 –2.2 0.4 –0.5 0.1 0.0 –0.1 –1.0 –2.2

Nonrefrigerated warehouse –1.5 3.6 –6.5 –1.1 0.8 1.0 –1.9 0.1 –0.5 0.0 1.6 –0.8 0.8 –0.7

Education –6.6 –10.9 –14.3 0.0 –10.1 –8.7 –5.5 –10.5 –15.6 –2.7 1.8 0.0 2.7 –0.5 –0.3

Retail (excluding mall) –3.0 5.2 –4.4 6.0 –4.7 –4.1 0.5 –5.1 –5.2 0.3 –1.0 –0.8 0.2 –5.1

Public assembly –2.2 –0.6 –1.8 –2.4 –3.2 –4.4 –4.9 –1.3 –1.3 –0.2 –3.1 –2.9 –0.4 6.7

Service –2.6 –10.0 –8.4 –2.3 –4.6 –7.3 –3.6 1.0 –1.3 0.5 –0.9 0.6 1.6

Religious worship –2.3 –10.9 –2.6 –1.3 –2.2 0.1 0.1 1.4 0.5 0.4

Lodging 1.4 2.0 4.5 0.1 –1.8 0.1 –0.4 –0.1 1.5 –0.4 3.6 –1.2 10.1

Food services –2.9 5.3 –3.1 –3.7 –2.9 –1.0 –5.0 –8.3 –1.8 –2.6 –0.6 –2.1 –4.3

Health care (inpatient) –9.1 3.0 3.1 –3.8 –12.1 –8.3 –12.0 –10.1 –9.4 –11.0 –10.3 –10.7 –7.1 –16.0

Public order and safety –1.3 1.7 –1.9 –0.2 –2.5 –0.7 –3.5 –0.9 –3.4

Food sales –2.1 –0.5 –2.9 –1.3 –3.0 –3.8 –2.2 –1.4 –1.1 –1.3

Health care (outpatient) –8.4 14.0 –17.3 –19.0 –22.1 –11.6 1.3 –4.1 1.4 0.5 –5.8 –2.5

Vacant –0.1 8.2 –0.1 –1.6 –6.9 –8.1 –1.0 1.7 2.5 0.8 3.4 0.6 –1.3

Other –1.0 –1.5 –2.7 0.6 –2.3 1.0 –0.3 0.3 0.5 –0.2 1.5

Skilled nursing –11.8 –4.2 –21.7 –2.3 –29.3 –5.4 –7.4 –5.5 –1.7

Laboratory –0.7 –0.8 –1.7 –2.9 0.1 0.1 0.3

Refrigerated warehouse 0.0 –0.5 0.8 0.4 –0.4
21

Table 3-11 90.1-2004, No Minimum Mechanical Ventilation, Percent Change in Peak Electrical Power by Climate Zone and 

Subsector 

Subsector

Climate Zone

All 1A 2A 2B 3A 3B 3C 4A 4B 4C 5A 5B 6A 6B 7 

All 5.9 5.4 3.9 1.6 7.3 4.1 3.7 6.0 9.3 4.3 5.8 6.9 7.6 5.2 9.2

Office/professional 3.1 2.1 2.5 0.3 5.1 1.8 3.3 3.3 3.3 3.5 3.1 2.1 3.5 3.4 4.0

Nonrefrigerated warehouse 4.9 1.6 3.2 3.0 4.4 8.0 5.9 4.6 3.8 4.8 8.9 8.2 3.2 6.1

Education 9.7 1.8 5.4 9.1 15.0 4.7 3.0 10.9 16.5 5.0 9.6 11.8 10.2 5.3 11.9

Retail (excluding mall) 4.4 0.2 4.3 6.8 3.8 4.4 10.4 3.4 5.2 5.4 3.6 7.3 2.7 8.6

Public assembly 4.3 0.0 1.9 4.9 3.4 3.4 2.9 3.7 4.4 5.1 2.2 7.4 2.4 9.0

Service 6.5 0.2 1.4 6.1 6.3 –0.6 5.9 8.8 6.0 5.8 11.2 10.5 13.4

Religious worship 5.0 1.2 3.5 6.7 4.0 6.2 7.0 9.9 5.5 3.2

Lodging 14.5 14.0 9.8 14.2 9.4 16.3 12.6 21.2 16.1 9.6 18.6 7.4 19.2

Food services 2.6 8.8 2.1 3.9 3.1 1.3 2.1 2.3 3.0 0.9 3.1 –0.6 1.5

Health care (inpatient) 11.6 9.6 21.7 8.9 11.5 5.9 1.6 17.6 6.0 8.0 3.1 9.3 3.0 7.0

Public order and safety 2.9 2.7 3.7 2.3 3.2 3.3 0.9 3.5 0.9

Food sales 1.4 1.5 1.8 1.2 0.0 0.8 1.4 1.4 2.2 2.9

Health care (outpatient) 6.6 14.2 0.2 0.5 –1.3 6.3 12.5 8.8 17.8 11.6 4.3 13.6

Vacant 7.5 9.6 2.6 9.7 11.5 7.8 4.3 4.9 9.2 8.7 17.5 6.4 8.3

Other 4.4 2.9 5.5 4.4 4.6 4.0 5.3 1.9 3.5 3.7 4.5

Skilled nursing 12.7 15.3 10.4 7.7 9.6 9.7 11.6 19.9 5.7

Laboratory 3.4 6.0 0.0 5.3 1.8 2.6 4.5

Refrigerated warehouse 7.8 7.5 7.4 5.1 6.7
22

 

3.2 Existing Stock

The results pertaining to new construction will help us to assess the effect of outside air in the future; 

however, an assessment of the existing stock of buildings is needed to determine the role of outside air in 

the sector today. The Existing Stock Construction Group models are composed of a reference scenario

and one other scenario where the minimum mechanical ventilation is set to zero. The effects of outside 

air on the aggregate of the commercial sector as it is constructed today are shown in Table 3-12 through 

Table 3-16. 

The trends pertaining to the existing stock are generally similar to those observed for the 90.1-2004

Construction Group scenarios. Table 3-12 shows that the average total EUI across the sector is increased 

by 6.6% because of the minimum ventilation rate. The results of the 90.1-2004 and Existing Stock 

construction group scenarios indicate that the required ventilation has a greater impact on the Existing 

Stock. We suggest that this difference is a result of the improved outside air management of the newer 

buildings, specifically, the use of economizers and heat recovery systems in the 90.1-2004 scenarios. The

PDF in Figure 3-4 shows significant variation across the sector, but to a lesser extent for the Existing 

Stock Construction Group models. 

Table 3-12 Existing Stock, Sector-Wide Average Total Site EUI

Scenario

Absolute Decrease Relative to 

Reference

Percent Decrease

Relative to 

(kBtu/ft Reference 2·y) (MJ/m2·y) (kBtu/ft2·y) (MJ/m2·y) 

Reference 74.2 842.6 – – – 

No Minimum Mechanical 

Ventilation 69.3 787.0 4.90 55.64 6.6
23

0

0.1

0.2

0.3

0.4

0.5

0.6

-30 -20 -10 0 10 20 30

Change in EUI (kBtu/ft2

•yr) (1.0 kBtu/ft2•yr = 11.4 MJ/m2•yr)

Probability Density

Figure 3-4 PDF of Change in Sector Average EUI for Existing Stock, No Minimum Mechanical

Ventilation

The air change rate for the Existing Stock Construction Group is slightly lower than for the 90.1-2004

Construction Group buildings (see Table 3-13). Again the gas EUI (Table 3-14) is affected more by the 

required ventilation than by the electricity EUI. Table 3-15 shows that the electricity EUI is unaffected 

by the required ventilation, although the peak electric power is increased by almost 6%. 

Table 3-13 Existing Stock, Sector-Wide Average ACH

Scenario Absolute 

(1/h)

Decrease 

Relative to 

Reference (1/h)

Percent Decrease 

Relative to 

Reference

Reference 0.76 – – 

No Minimum Mechanical 

Ventilation 0.35 0.41 53.95%
24

Table 3-14 Existing Stock, Sector-Wide Average Gas EUI

Scenario

Absolute Decrease Relative to 

Reference

Percent 

Decrease 

Relative to 

Reference (kBtu/ft2

·yr) (MJ/m2·yr) (kBtu/ft2·yr) (MJ/m2·yr)

Reference 21.0 238.5 – – – 

No Minimum Mechanical 

Ventilation 16.5 187.4 4.5 51.1 21.4%

Table 3-15 Existing Stock, Sector-Wide Average Electricity EUI

Scenario

Absolute Decrease Relative to 

Reference

Percent 

Decrease 

Relative to 

Reference (kBtu/ft2

·yr) (MJ/m2·yr) (kBtu/ft2·yr) (MJ/m2·yr)

Reference 50.8 576.9 – – – 

No Minimum Mechanical 

Ventilation 50.8 576.9 0 0 0 

Table 3-16 Existing Stock, Sector-Wide Average Peak Electric Power

Scenario

Absolute Decrease Relative to 

Reference

Percent 

Decrease 

Relative to 

Reference (kBtu/ft2

·yr) (MJ/m2·yr) (kBtu/ft2·yr) (MJ/m2·yr)

Reference 5.25 56.47 – – – 

No Minimum Mechanical 

Ventilation 4.94 53.13 0.31 3.34 5.91%

The results of the previous five tables are more thoroughly presented, by climate zone and subsector, in 

Table 3-17 through Table 3-21. 
25

Table 3-17 Existing Stock, No Minimum Mechanical Ventilation, Total EUI Percent Change for Climate Zone and Subsector

Subsector

Climate Zone

All 1A 2A 2B 3A 3B 3C 4A 4B 4C 5A 5B 6A 6B 7 

All 6.5 3.6 2.2 –0.6 4.7 1.4 0.2 5.9 10.5 9.5 8.0 11.5 9.9 11.7 11.1

Office/professional 3.2 1.1 1.1 0.7 2.5 1.1 –2.5 1.9 1.7 2.9 4.5 4.7 7.0 11.1 7.3

Nonrefrigerated warehouse 2.1 1.2 0.8 1.6 0.6 –1.1 1.3 2.9 1.9 2.6 1.7 3.1 4.0 6.5

Education 4.4 7.4 –1.7 1.0 6.3 4.4 –1.9 5.1 16.1 2.9 3.7 10.9 3.4 13.5 14.5

Retail (excluding mall) 8.4 2.9 4.0 2.3 8.7 2.5 –0.1 9.0 6.0 10.0 12.7 10.8 12.0 11.5

Public assembly 10.6 5.5 6.4 3.9 7.2 11.2 7.5 11.9 22.3 12.0 18.4 15.7 16.9 7.7

Service 3.2 2.7 1.2 2.3 0.8 0.2 2.3 1.2 3.6 4.5 2.7 4.3 3.2

Religious worship 9.9 6.1 8.8 4.8 8.3 19.8 9.7 10.7 12.6 11.9

Lodging 10.2 2.7 4.9 2.4 0.0 14.0 11.8 5.5 9.9 16.6 10.6 24.5 4.4

Food services 6.4 8.1 3.0 4.8 –2.1 0.2 4.5 26.7 9.4 12.0 11.0 5.8 33.3

Health care (inpatient) 21.5 –12.0 1.9 –23.5 15.5 4.6 8.1 18.0 27.8 28.3 35.3 41.7 31.3 53.4

Public order and safety 5.6 1.3 3.1 –4.1 3.1 4.5 20.4 11.7 5.1

Food sales 6.2 3.2 2.9 0.5 –2.7 4.5 10.2 6.2 8.6 3.3

Health care (outpatient) 9.8 0.7 5.0 4.3 –0.2 10.4 –4.7 14.4 17.8 10.1 7.2 38.5

Vacant 10.2 4.1 3.7 2.3 –3.7 0.0 17.5 8.0 –0.2 16.6 9.0 1.6 –0.1

Other 0.2 1.5 0.3 0.0 –0.9 5.9 1.3 3.7 0.6 –0.1 –0.2

Skilled nursing 6.5 4.4 3.1 –0.4 4.5 8.7 18.8 2.5 34.2

Laboratory –0.9 –0.4 1.7 0.2 –0.1 –13.4 –14.5

Refrigerated warehouse 1.3 0.9 –0.3 1.5 2.5
26

Table 3-18 Existing Stock, No Minimum Mechanical Ventilation, ACH Percent Change for Climate Zone and Subsector

Subsector

Climate Zone

All 1A 2A 2B 3A 3B 3C 4A 4B 4C 5A 5B 6A 6B 7 

All 54.0 72.2 66.7 66.6 56.8 53.1 45.5 54.0 45.1 42.2 49.6 48.1 50.9 50.3 41.8

Office/professional 42.0 43.5 56.8 42.5 41.1 34.7 43.6 41.9 33.9 29.9 42.9 32.9 39.9 51.3 28.7

Nonrefrigerated warehouse 11.0 14.3 7.9 9.4 5.9 25.1 9.3 21.9 15.3 13.4 6.3 14.1 21.1 26.8

Education 58.2 79.7 73.8 79.1 61.3 60.4 38.5 59.0 64.8 –3.0 40.4 53.8 45.0 54.1 46.9

Retail (excluding mall) 47.4 20.8 54.5 58.1 48.0 49.7 33.7 46.7 45.0 46.5 47.8 47.1 50.4 42.7

Public assembly 55.7 62.6 63.2 40.9 64.0 –40.9 48.7 56.6 63.8 48.5 63.7 69.1 65.2 38.3

Service 18.1 39.3 18.6 20.1 10.7 23.3 22.6 12.6 13.7 23.5 14.7 23.6 10.0

Religious worship 49.5 59.6 51.7 60.6 45.0 66.5 43.7 41.2 42.5 46.7

Lodging 60.0 76.6 69.0 59.5 55.9 65.8 38.9 32.4 57.1 51.3 49.4 55.8 42.0

Food services 78.9 94.7 79.8 78.7 78.9 86.8 81.3 94.4 72.7 79.6 72.6 60.8 88.3

Health care (inpatient) 82.9 96.9 92.4 90.5 80.1 87.6 82.1 81.9 65.0 83.2 69.6 81.9 55.1 60.7

Public order and safety 33.9 52.1 39.8 51.8 58.0 32.9 –42.8 18.7 16.8

Food sales 51.3 52.7 56.9 42.7 43.9 47.9 54.3 50.5 41.4 27.8

Health care (outpatient) 60.1 23.2 61.4 45.2 62.3 71.2 42.7 61.7 55.2 42.2 68.9 70.0

Vacant 32.1 0.0 70.8 0.0 0.0 0.0 0.0 0.0 61.1 64.9 71.8 52.2 21.3

Other 15.2 29.6 10.3 6.3 15.0 40.6 17.0 31.8 7.0 14.6 10.2

Skilled nursing 62.4 81.1 66.1 63.4 50.7 64.3 55.4 59.6 65.1

Laboratory 42.2 67.2 –7.5 52.1 37.8 87.6 54.5

Refrigerated warehouse 21.2 19.3 4.1 25.2 30.1
27

Table 3-19 Existing Stock, No Minimum Mechanical Ventilation, Gas EUI Percent Change for Climate Zone and Subsector

Subsector

Climate Zone

All 1A 2A 2B 3A 3B 3C 4A 4B 4C 5A 5B 6A 6B 7 

All 21.3 0.0 7.5 29.6 18.3 12.9 10.5 20.1 38.3 41.4 22.5 33.3 22.4 26.9 25.1

Office/professional 18.6 0.0 10.7 2.3 13.5 15.4 0.7 15.1 13.4 12.5 20.4 25.2 20.8 32.2 15.1

Nonrefrigerated warehouse 8.7 0.0 5.2 7.5 5.4 7.0 6.0 22.1 7.5 8.9 7.7 7.7 6.7 21.3

Education 16.4 0.3 10.7 0.0 34.6 25.3 0.0 19.0 59.1 12.2 8.8 30.7 5.6 37.2 31.5

Retail (excluding mall) 27.8 0.0 30.5 35.1 36.0 29.1 7.9 29.1 20.2 25.7 39.0 24.4 32.6 18.8

Public assembly 27.7 –1.3 32.1 17.1 41.5 46.3 15.7 44.8 74.8 26.9 36.4 27.9 18.7 12.5

Service 9.8 0.0 4.3 9.7 4.6 4.7 10.2 6.7 10.6 11.6 5.2 9.6 7.2

Religious worship 17.3 22.8 22.6 27.8 16.0 52.6 13.8 17.2 18.3 15.3

Lodging 25.3 0.0 –4.8 14.0 5.9 27.6 41.1 0.0 31.1 42.4 22.7 43.8 16.9

Food services 16.1 0.0 3.4 11.7 2.6 0.3 14.1 42.2 21.3 28.7 26.8 14.6 60.8

Health care (inpatient) 56.2 0.0 24.3 18.8 47.6 39.8 43.1 54.9 67.7 62.7 65.2 71.0 57.3 76.8

Public order and safety 25.2 –8.7 7.8 18.9 19.3 14.5 50.6 41.2 19.9

Food sales 29.8 17.5 29.1 8.0 4.8 22.9 40.4 28.9 23.6 10.6

Health care (outpatient) 26.1 0.0 10.9 12.5 5.3 39.9 –11.7 27.9 49.5 18.8 34.6 50.5

Vacant 29.9 19.3 2.3 10.1 9.4 0.0 37.0 0.0 –0.8 35.8 46.6 5.5 3.7

Other 1.4 5.3 2.7 0.0 –5.0 19.2 4.1 10.2 1.7 –0.1 –3.9

Skilled nursing 26.9 10.1 0.0 3.5 25.9 35.3 41.7 14.3 62.0

Laboratory 0.4 0.0 3.1 2.1 –0.8 1.8 0.2

Refrigerated warehouse 9.8 6.9 –5.2 0.0 14.7
28

Table 3-20 Existing Stock, No Minimum Mechanical Ventilation, Electric EUI Percent Change for Climate Zone and Subsector

Subsector

Climate Zone

All 1A 2A 2B 3A 3B 3C 4A 4B 4C 5A 5B 6A 6B 7 

All 0.0 5.7 3.2 0.3 0.4 –1.0 –3.2 –0.1 0.3 –1.8 –0.8 –0.8 –1.0 –0.6 0.4

Office/professional 0.1 1.1 2.0 0.6 0.9 0.1 –2.8 –0.7 0.1 –1.2 0.0 –0.4 0.7 0.8 3.9

Nonrefrigerated warehouse 0.3 1.2 0.5 0.2 0.0 –3.0 0.1 0.0 1.6 0.3 0.3 0.8 0.0 0.0

Education 1.3 7.5 4.4 0.4 2.2 0.5 –2.5 0.9 3.5 0.6 0.2 –0.2 –0.2 –1.8 6.3

Retail (excluding mall) 1.2 3.0 3.0 1.7 2.0 0.0 –0.8 2.1 1.0 0.3 –0.1 –0.2 –0.9 –0.6

Public assembly 0.4 5.7 3.3 1.6 0.4 1.1 2.4 0.2 –8.3 0.2 0.1 –4.2 –0.1 0.9

Service 0.1 2.9 0.9 0.5 0.2 –0.7 0.1 0.0 –0.3 –0.1 0.6 0.0 0.0

Religious worship 2.3 5.2 3.7 0.7 3.3 0.3 1.8 1.3 0.6 –0.1

Lodging 1.3 7.8 6.9 –0.1 –1.3 1.0 –0.2 6.7 0.1 –2.3 1.2 –1.9 –1.8

Food services –2.5 13.5 3.1 –1.0 –7.0 0.0 –3.8 –1.2 –4.8 –4.8 –8.3 –3.4 –5.4

Health care (inpatient) –4.5 7.4 4.5 –1.6 –2.3 –7.5 –22.5 –2.4 –10.9 –10.8 –8.7 –1.7 –2.5 –3.5

Public order and safety 0.7 2.0 1.5 0.1 0.2 –0.2 3.0 0.5 –0.2

Food sales 0.2 2.0 –0.3 –0.3 –3.4 0.8 –0.3 –0.4 –0.5 0.0

Health care (outpatient) 1.1 0.7 3.9 2.5 –1.7 1.3 –0.3 2.1 –0.8 2.0 –3.1 –2.9

Vacant –0.2 2.6 3.9 0.2 –4.0 0.0 1.0 8.0 –0.2 –0.2 –0.3 –0.2 –0.4

Other 0.0 1.0 0.1 0.0 –0.3 0.4 0.0 0.1 0.2 –0.1 0.1

Skilled nursing –0.7 3.4 3.5 –1.0 –3.0 –3.2 1.3 –2.1 –0.2

Laboratory –0.2 –0.6 0.9 –1.6 0.3 –1.0 0.0

Refrigerated warehouse 0.3 0.5 0.0 0.1 –0.4
29

Table 3-21 Existing Stock, No Minimum Mechanical Ventilation, Peak Electrical Power Percent Change for Climate Zone and 

Subsector 

Subsector

Climate Zone

All 1A 2A 2B 3A 3B 3C 4A 4B 4C 5A 5B 6A 6B 7 

All 5.8 5.9 7.1 5.7 7.3 4.7 2.6 6.7 5.4 8.1 4.9 4.1 5.3 2.5 2.1

Office/professional 3.7 0.1 3.4 1.9 4.5 2.6 1.8 4.1 3.0 9.6 3.9 3.8 3.6 5.7 1.9

Nonrefrigerated warehouse 0.9 0.0 1.1 0.5 1.0 1.5 0.9 0.0 0.3 1.2 1.1 0.6 0.2 0.1

Education 7.4 18.6 8.4 8.0 12.0 8.8 5.6 7.8 11.3 5.0 3.9 3.4 4.4 2.7 5.3

Retail (excluding mall) 4.4 0.0 6.8 9.6 4.2 3.8 3.3 6.2 2.2 2.6 4.3 2.3 4.4 2.3

Public assembly 6.8 4.2 8.7 5.7 0.9 –3.0 7.3 1.5 10.3 2.5 3.0 16.9 0.0 –0.9

Service 1.1 0.1 1.3 2.5 1.8 0.1 0.9 0.0 1.0 1.8 0.2 0.4 0.0

Religious worship 5.5 9.2 8.8 5.0 5.1 8.2 3.9 0.9 1.6 1.8

Lodging 13.1 14.2 13.7 10.0 9.4 21.1 2.9 30.5 6.3 10.6 8.7 1.9 1.4

Food services 7.8 21.5 6.8 7.3 6.8 0.0 8.8 6.8 8.2 3.3 8.3 0.0 7.9

Health care (inpatient) 14.9 –0.5 26.5 24.0 9.4 15.6 11.2 10.4 –0.8 21.2 5.6 8.7 3.3 –14.4

Public order and safety 3.8 2.0 6.7 3.0 4.0 3.4 6.7 3.9 1.7

Food sales 4.8 5.0 5.6 2.1 3.3 5.2 6.1 2.3 2.5 2.8

Health care (outpatient) 8.1 0.1 5.6 12.7 4.3 9.4 0.3 9.7 6.4 3.5 2.6 25.4

Vacant 6.5 8.5 3.5 4.7 5.2 0.0 11.0 29.4 8.4 8.5 0.0 2.0 3.7

Other 1.0 3.3 1.4 1.2 1.6 3.1 0.3 0.0 0.2 1.3 0.0

Skilled nursing 15.2 18.4 12.9 10.4 20.0 12.1 29.1 14.0 0.4

Laboratory 6.7 8.9 4.2 5.5 6.5 1.3 0.1

Refrigerated warehouse 3.1 3.3 0.1 1.7 4.4
30

3.3 Max Tech

The effects of outside air could change significantly for high-performance buildings. To address this 

possibility, we studied a set of building models based on projected construction in 2025. These models 

are the Max Tech Construction Group scenarios described in Section 2.2. For the Max Tech Construction

Group, a reference scenario and a scenario with the minimum mechanical ventilation requirement set to 

zero are simulated. The aggregate results for the entire commercial sector are presented in Table 3-22

through Table 3-26. The results are again shown in absolute terms and as percent and relative changes. 

Table 3-22 shows the total site EUIs. The minimum ventilation has a lesser effect on the 90.1-

2004Construction Group than the Existing Stock Construction Group. The trend continues here; the 

required ventilation has an even lesser effect on the Max Tech Construction Group than it had on the 

90.1-2004 Construction Group. The reduced impact of ventilation is attributed to the fact that the Max 

Tech buildings have the best outside air management through the use of economizer and heat recovery 

systems in every building. Insight into the commercial sector variation is again shown for total site EUI 

with the PDF of Figure 3-5. 

Table 3-22 Max Tech, Sector-Wide Average Total Site EUI

Scenario

Absolute Decrease Relative to 

Reference

Percent 

Decrease 

Relative to 

Reference (kBtu/ft2

·yr) (MJ/m2·yr) (kBtu/ft2·yr) (MJ/m2·yr)

Reference 38.5 437.0 0.00 0.00 0.0%

No Minimum Mechanical 

Ventilation 38.2 434.1 0.26 2.91 0.7%
31

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

-15 -10 -5 0 5 10 15

Probability Density

Change in EUI (kBtu/ft2·yr) (1.0 kBtu/ft2·yr = 11.4 MJ/m2·yr)

 

Figure 3-5 PDF of Change in Sector Average EUI for Max Tech, No Minimum Mechanical

Ventilation

The diminished impact of minimum ventilation is perhaps more pronounced, considering that required 

ventilation is a larger fraction of the air change rate compared to the 90.1-2004 and Existing Stock

construction groups. Table 3-23 shows that minimum ventilation is 63.6% of the total outside air rate. 

The effect on the gas EUI is 8.9% (see Table 3-24). Table 3-25 shows that the minimum ventilation rate

improves the electricity EUI by 8.9%, which was observed for the 90.1-2004 Construction Group, 

although to a lesser extent. The electrical energy savings from minimum ventilation suggest missed 

opportunities for economizing. In terms of electrical power, required ventilation again increases the peak 

demand (Table 3-26). 

Table 3-23 Max Tech, Sector-Wide Average ACH

Scenario Absolute 

(1/h)

Decrease Relative 

to Reference 

(1/h)

Percent Decrease 

Relative to 

Reference

Reference 0.59 0.00 0.00%

No Minimum Mechanical 

Ventilation 0.22 0.38 63.58%
32

Table 3-24 Max Tech, Sector-Wide Average Gas EUI

Scenario

Absolute Decrease Relative to 

Reference

Percent 

Decrease 

Relative to 

Reference (kBtu/ft2

·yr) (MJ/m2·yr) (kBtu/ft2·yr) (MJ/m2·yr)

Reference 11.9 135.4 0.00 0.00 0.0%

No Minimum Mechanical 

Ventilation 10.9 123.3 1.07 12.10 8.9%

Table 3-25 Max Tech, Sector-Wide Average Electric EUI

Scenario

Absolute Decrease Relative to 

Reference

Percent 

Decrease 

Relative to 

Reference (kBtu/ft2

·yr) (MJ/m2·yr) (kBtu/ft2·yr) (MJ/m2·yr)

Reference 26.3 298.6 0.00 0.00 0.0%

No Minimum Mechanical 

Ventilation 27.1 307.7 -0.81 -9.19 -3.1%

Table 3-26 Max Tech, Sector-Wide Average Peak Electrical Power

Scenario

Absolute Decrease Relative to 

Reference

Percent 

Decrease 

Relative to 

Reference (kBtu/ft2

·yr) (MJ/m2·yr) (kBtu/ft2·yr) (MJ/m2·yr)

Reference 2.45 26.39 0.00 0.00 0.00%

No Minimum Mechanical 

Ventilation 2.40 25.78 0.06 0.61 2.32%

We used the format established for the 90.1-2004 and Existing Stock construction group models to 

present the climatic and programmatic influences in Table 3-27 through Table 3-31 and to observe similar 

trends. 
33

Table 3-27 Max Tech, No Minimum Mechanical Ventilation, Total EUI Percent Change for Climate Zone and Subsector

Subsector

Climate Zone

All 1A 2A 2B 3A 3B 3C 4A 4B 4C 5A 5B 6A 6B 7 

All 0.7 0.3 –3.4 –2.6 0.9 –1.1 0.3 1.1 2.6 2.5 1.4 2.4 2.2 5.4 2.5

Office/professional –0.1 1.8 –1.7 –0.7 0.3 –0.5 –0.8 –0.2 0.0 0.9 0.0 0.5 0.7 1.5 2.2

Nonrefrigerated warehouse 3.3 1.6 –4.0 3.9 3.7 –3.1 7.1 9.8 12.4 2.9 6.2 3.8 8.7 0.1

Education –0.3 –19.2 –11.2 –2.9 –4.2 –7.0 2.1 2.1 –1.7 14.6 5.2 8.4 0.6 13.0 23.1

Retail (excluding mall) 2.2 3.4 –6.7 3.4 0.8 –5.0 3.9 3.6 –3.0 7.8 2.2 7.8 0.8 10.3

Public assembly –0.4 –0.8 –3.3 –3.9 –1.2 –0.5 0.3 1.8 –1.6 3.7 –0.8 –1.1 –1.0 –0.1

Service 6.2 –8.3 –11.4 5.8 –1.6 –2.6 7.5 9.0 5.9 11.2 11.5 12.5 15.3

Religious worship 5.0 –15.4 3.2 1.6 10.2 13.0 6.6 8.2 7.9 11.3

Lodging 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Food services –0.6 1.4 –0.5 –0.5 0.0 –0.1 –0.9 –0.2 –0.4 –1.8 –0.4 –2.4 –10.3

Health care (inpatient) 4.7 2.0 5.5 0.1 14.6 1.6 0.4 3.3 3.9 –1.3 0.9 5.2 6.9 –3.8

Public order and safety –0.1 0.9 –0.3 0.0 –0.8 0.3 –0.8 0.7 –2.7

Food sales –1.3 –1.2 –2.5 –1.6 –2.6 –2.2 –1.1 –0.8 1.5 –1.5

Health care (outpatient) –1.8 6.1 –15.4 –11.1 –16.1 –0.1 5.2 –0.1 8.0 12.0 7.7 19.0

Vacant 0.7 0.0 1.4 0.8 0.0 0.0 0.0 0.0 1.1 0.1 2.2 –0.9 7.2

Other –0.8 –2.8 –2.6 0.7 –1.4 6.9 4.5 3.6 –6.0 6.7 –2.7

Skilled nursing –4.3 –6.6 –16.4 2.8 –9.3 –1.0 –8.0 1.7 9.4

Laboratory –0.4 0.1 –0.1 0.2 –1.1 –0.4 0.5

Refrigerated warehouse 1.4 0.4 1.9 0.9 3.3
34

Table 3-28 Max Tech, No Minimum Mechanical Ventilation, ACH Percent Change for Climate Zone and Subsector

Subsector

Climate Zone

All 1A 2A 2B 3A 3B 3C 4A 4B 4C 5A 5B 6A 6B 7 

All 63.6 80.7 72.0 57.0 64.4 62.0 38.3 60.6 69.5 48.3 63.5 60.1 66.9 65.3 58.8

Office/professional 50.6 77.8 60.4 49.6 53.0 49.8 31.0 47.7 36.4 35.3 52.8 42.2 58.2 55.4 54.4

Nonrefrigerated warehouse 60.9 69.1 58.1 61.1 60.3 35.2 61.7 49.1 70.6 60.3 60.1 64.6 66.0 61.6

Education 80.7 89.5 86.8 79.6 79.6 81.6 66.0 78.4 84.9 80.7 80.0 77.3 80.5 75.3 84.9

Retail (excluding mall) 76.4 84.5 76.2 65.6 76.0 72.6 71.2 76.4 72.8 78.0 68.6 80.6 72.5 81.7

Public assembly 63.0 71.5 72.8 59.9 60.2 48.0 61.0 67.1 41.6 66.2 53.0 66.4 45.4 65.3

Service 80.1 84.6 81.0 82.9 80.9 78.1 78.9 81.3 79.0 76.0 83.5 80.3 81.8

Religious worship 77.4 74.4 79.5 75.0 77.6 79.5 78.3 76.1 78.0 76.6

Lodging 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Food services 43.1 93.6 57.7 43.9 45.2 23.5 38.4 28.7 41.1 24.0 41.0 32.1 40.5

Health care (inpatient) 66.6 97.0 78.9 48.4 71.9 58.0 48.2 66.7 63.3 63.9 51.0 70.4 62.6 56.1

Public order and safety 47.3 63.2 54.0 46.8 44.5 46.8 35.1 49.8 27.9

Food sales 55.9 57.6 54.5 54.3 49.5 54.5 59.3 42.9 62.4 47.8

Health care (outpatient) 81.0 92.5 84.6 83.2 74.1 78.5 81.1 80.5 80.4 85.4 79.9 83.8

Vacant 65.9 0.0 57.9 76.0 84.0 0.0 49.0 0.0 37.1 56.2 68.5 72.1 63.7

Other 57.5 57.0 52.0 48.0 54.0 70.7 58.8 57.3 62.2 66.4 63.9

Skilled nursing 71.0 79.8 73.2 65.2 69.8 70.9 58.9 72.8 68.9

Laboratory 29.8 29.7 32.0 28.2 30.9 33.4 18.5

Refrigerated warehouse 57.5 57.5 63.6 56.5 58.3
35

Table 3-29 Max Tech, No Minimum Mechanical Ventilation, Gas EUI Percent Change for Climate Zone and Subsector

Subsector

Climate Zone

All 1A 2A 2B 3A 3B 3C 4A 4B 4C 5A 5B 6A 6B 7 

All 8.9 0.6 1.6 0.6 9.0 5.1 3.9 11.3 19.6 15.5 8.5 15.0 9.8 18.1 14.0

Office/professional 7.1 –2.7 0.3 –0.4 10.4 3.3 1.2 7.7 1.2 13.1 5.7 13.9 8.3 13.2 17.8

Nonrefrigerated warehouse 11.3 1.0 5.0 14.0 22.8 0.0 18.3 24.5 44.2 7.2 18.6 8.4 13.7 3.6

Education 18.3 1.0 3.0 29.6 12.0 15.9 24.5 22.4 60.4 46.6 17.9 35.8 9.2 33.0 66.8

Retail (excluding mall) 25.8 –4.2 1.9 –3.7 26.3 11.5 39.8 37.7 25.5 26.6 17.2 26.7 9.0 29.8

Public assembly 10.0 0.0 5.4 –4.5 6.8 20.4 10.3 10.4 21.8 15.4 20.4 12.8 0.5 1.7

Service 25.7 0.2 7.6 31.7 21.9 13.9 31.5 32.9 20.3 33.8 22.7 37.3 34.1

Religious worship 21.0 10.5 31.4 29.8 31.2 55.9 16.0 23.0 15.9 17.1

Lodging 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Food services 0.0 0.0 0.0 0.0 0.0 0.0 –0.4 0.1 –0.1 0.0 0.4 0.0 0.0

Health care (inpatient) 18.4 0.0 10.0 1.6 32.2 9.4 8.0 17.9 18.8 10.2 12.7 26.9 25.9 0.2

Public order and safety 4.3 –2.0 6.9 1.5 0.7 9.4 1.3 6.5 –0.2

Food sales 6.1 1.9 2.7 2.9 4.7 4.8 6.6 7.4 12.2 8.2

Health care (outpatient) 20.4 15.6 2.0 9.9 16.4 23.3 15.8 15.7 25.4 29.9 30.2 55.5

Vacant 2.2 0.0 1.6 2.0 0.8 0.0 0.3 0.0 0.0 0.6 15.7 –0.7 31.1

Other 1.1 7.4 6.5 6.0 –2.4 17.1 12.0 12.3 –11.3 30.5 –3.8

Skilled nursing 19.8 2.5 1.4 17.6 21.0 24.2 16.0 23.1 36.3

Laboratory –0.5 0.0 –0.2 0.4 –1.3 0.0 1.0

Refrigerated warehouse 17.5 15.4 15.3 8.1 24.9
36

Table 3 –30 Max Tech, No Minimum Mechanical Ventilation, Electric EUI Percent Change for Climate Zone and Subsector

Subsector

Climate Zone

All 1A 2A 2B 3A 3B 3C 4A 4B 4C 5A 5B 6A 6B 7 

All –3.1 0.2 –4.8 –3.1 –2.8 –3.5 –1.6 –2.9 –2.5 –1.5 –2.7 –2.8 –2.9 –2.2 –3.6

Office/professional –1.1 2.2 –1.7 –0.7 –0.5 –0.8 –0.9 –1.0 –0.2 –0.5 –1.1 –1.0 –1.3 –1.3 –2.4

Nonrefrigerated warehouse –2.0 1.7 –5.7 –1.7 –0.3 –3.1 –0.9 –0.6 0.3 –1.8 –0.6 –1.6 –0.1 –3.3

Education –8.1 –19.4 –13.9 –5.5 –8.5 –11.5 –3.7 –6.0 –13.2 –5.9 –3.2 –4.9 –6.7 –6.9 –3.7

Retail (excluding mall) –4.7 3.6 –7.3 5.5 –5.3 –8.2 –0.3 –5.2 –9.2 –2.0 –2.9 –2.6 –3.3 –6.3

Public assembly –3.4 –0.8 –3.8 –3.8 –3.0 –3.7 –2.8 –1.9 –4.1 –1.8 –5.1 –6.4 –2.0 –1.0

Service –3.8 –9.1 –13.8 –3.5 –8.7 –8.7 –2.7 –0.2 –3.2 –1.1 –1.5 –0.7 –0.9

Religious worship –5.0 –17.0 –5.2 –4.1 –2.2 –1.0 –3.1 –0.7 –2.0 –0.1

Lodging 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Food services –1.3 3.1 –1.0 –1.1 0.0 –0.2 –1.5 –0.9 –0.8 –3.7 –1.4 –6.0 –16.1

Health care (inpatient) –2.7 3.1 3.9 –0.6 2.8 –2.4 –4.8 –3.5 –2.8 –8.0 –6.2 –5.9 –5.9 –7.5

Public order and safety –0.8 1.2 –1.3 –0.2 –1.1 –1.0 –1.2 –1.0 –2.9

Food sales –2.5 –1.5 –3.0 –2.2 –3.8 –3.1 –2.6 –2.1 –1.5 –2.9

Health care (outpatient) –11.4 4.1 –17.5 –17.0 –26.6 –10.1 –0.2 –9.7 –0.2 –1.5 –5.7 –6.0

Vacant –0.3 0.0 1.3 0.0 –0.1 0.0 –0.1 0.0 1.2 –0.2 –0.1 –1.0 –0.8

Other –1.5 –4.5 –3.5 0.2 –1.0 0.6 –0.1 –0.3 –3.4 –0.2 –2.4

Skilled nursing –13.9 –8.6 –20.1 –3.3 –21.6 –14.3 –15.7 –8.5 –2.7

Laboratory –0.3 0.1 0.0 0.1 –0.9 –0.7 –0.2

Refrigerated warehouse –0.9 –1.3 –0.4 0.1 –1.6
37

Table 3-31 Max Tech, No Minimum Mechanical Ventilation, Peak Electrical Power Percent Change for Climate Zone and 

Subsector 

Subsector

Climate Zone

All 1A 2A 2B 3A 3B 3C 4A 4B 4C 5A 5B 6A 6B 7 

All 2.3 2.7 1.2 –0.8 2.8 1.3 0.7 2.2 3.1 3.3 2.5 3.3 4.1 2.5 3.0

Office/professional 1.1 2.6 0.6 0.0 1.5 0.8 –0.3 1.2 1.4 0.2 1.4 0.8 1.1 0.6 1.5

Nonrefrigerated warehouse 3.4 0.7 3.5 0.5 3.5 23.9 3.9 2.2 2.1 2.9 5.6 5.4 1.9 2.9

Education 4.4 1.2 2.1 2.3 7.0 0.8 –1.3 4.3 5.2 14.6 4.6 7.3 5.6 2.4 16.6

Retail (excluding mall) 3.1 1.1 0.7 4.5 1.2 4.4 3.2 3.1 2.2 4.5 2.5 7.9 0.4 –1.4

Public assembly 1.5 –0.1 –0.8 1.2 0.9 1.2 0.8 1.6 2.4 2.7 –1.2 4.0 –3.6 3.5

Service 4.7 –0.1 –2.5 4.9 1.8 5.1 4.2 5.6 5.4 7.4 9.2 7.7 8.3

Religious worship 3.2 –1.6 2.8 0.5 4.3 3.7 5.1 8.4 5.7 1.4

Lodging 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Food services 1.2 3.9 1.2 1.8 1.3 0.2 0.8 1.5 1.6 0.1 1.4 0.1 0.9

Health care (inpatient) 5.5 5.9 11.4 5.4 4.0 3.9 0.3 7.8 4.4 4.1 –0.4 8.0 1.7 4.2

Public order and safety 1.1 0.8 1.6 2.0 0.9 2.3 –1.2 1.2 1.0

Food sales –0.5 0.6 –1.2 0.0 0.2 –1.2 –1.1 0.2 2.1 –0.4

Health care (outpatient) 0.9 10.0 –6.8 –5.0 –12.4 3.4 8.2 2.2 8.9 9.0 5.6 8.9

Vacant 0.7 0.0 2.2 2.2 0.5 0.0 –0.9 0.0 –1.2 0.0 0.3 1.8 4.3

Other 1.4 1.0 5.6 3.2 0.7 2.0 2.3 0.4 1.0 0.6 0.5

Skilled nursing 0.6 5.5 –1.6 4.9 –3.3 –1.2 –4.1 6.2 0.9

Laboratory 1.9 3.0 1.1 1.8 1.5 1.7 0.7

Refrigerated warehouse 2.5 1.7 3.4 2.3 3.0
38

4. Summary and Recommendations

This research suggests that outside air has a significant impact on the energy consumption of commercial 

buildings. Depending on the level of construction quality, providing the minimum level of mechanical 

ventilation for indoor air quality increases the total energy consumption of the commercial buildings 

sector by 0.7% to 6.6%. Outside air due to infiltration increases the energy consumption of the sector 

9.7% for construction based on 90.1-2004. On average, mechanical ventilation increases gas energy use, 

which is typically associated with heating, but actually reduces electrical energy consumption that is 

usually related to cooling. For example, for the 90.1-2004 gas energy consumption due to minimum 

mechanical ventilation increases by 20.3%, but reduces electrical energy consumption by 2.8%. These 

results do not apply to every building or to all climates. In some buildings for example, ventilation

reduces the overall energy consumption, because the benefits of economizing overcome any increase in 

heating energy. In this section we will further analyze our findings related to outside air, specifically in 

relation to mechanical ventilation and infiltration. We will also discuss the effects of mechanical 

equipment, including economizers and energy recovery devices. We make recommendations for each 

item about future actions that have the highest potential to reduce the energy impact of outside air. 

Ventilation has a significant effect on all vintages of construction. The effect decreases as the 

commercial building stock is reconstructed to comply with 90.1-2004, and it decreases even more if 

buildings are reconstructed using Max Tech. The diminished effect of outside air on newer buildings is 

primarily attributed to the fact that economizers and energy recovery devices are more commonly

installed in new buildings. 

The Max Tech Construction Group of this study applied economizers and energy recovery systems to 

every building in the commercial stock. Ventilation had a minimal impact on the overall energy 

consumption. From the aggregate sum, there seems to be little opportunity to improve the outside air 

management of advanced buildings, but the gas and electricity breakdowns lead us to a different 

conclusion. Ventilation increases the gas EUI for the Max Tech Construction Group by 8.9% and 

decreases the electricity EUI by 3.1%. The two outcomes somewhat offset each other, but individually 

they indicate room for improvement. 

Increases in gas energy, conventionally associated with heating more than cooling, suggest that further 

research into heat recovery systems would be beneficial. Despite the aggregate results, energy recovery 

could also more effectively reduce cooling energy in some situations. Current and future studies of

advanced heat transfer techniques might be applied to energy recovery devices to more effectively 

salvage energy from exhaust air. One feature that would increase the benefit of current generation energy 

recovery devices is a bypass that would reduce fan energy when the energy recovery device is not used. 

The simulations in this work did not model a bypass as it affects fan energy. Controls in the simulations 

did, however, disengage the thermodynamic effects of the energy recovery systems during economizing. 

In future work, advanced controls could be implemented to take into account the fan energy increase and 

enter bypass mode when the system cannot recover more energy than is consumed by the fan. In relation 

to energy recovery, this study took a rather brute force approach by applying energy recovery devices to 

all buildings in the Max Tech Construction Group. Applying these systems to all buildings is probably 

impractical for real buildings. Further studies that concentrate on energy recovery systems rather than 

outside air as a whole would help to isolate the best opportunities for energy recovery devices. 

The electrical energy savings that are provided by ventilation, even in buildings that have economizers, 

indicate that the economizers are not optimally controlled. Ideally, simulations would have perfect 

economizer control; therefore, buildings equipped with economizers would achieve no savings in cooling 

energy as a result of ventilation. In this study there are savings related to ventilation, even in buildings 

with economizers. We conclude that the control logic implemented in the simulations was less than 

optimal, and there are missed opportunities for economizing in the simulations. Future work could refine
39

the control logic in the simulations, but even with ideal models, less then optimal control is almost certain 

in the physical implementations of economizers in real buildings. We recommend further research into 

the economizer control logic as it is modeled in software and physically implemented.

Infiltration was given less emphasis, but it has a noticeable impact on the energy consumption of the 90.1-

2004 Construction Group (the only type of construction where it was analyzed). Perhaps not surprisingly, 

based on the average results form this study, a quantity of outside air due to infiltration was found to have 

a more significant impact on energy consumption than the same volume of air introduced by the 

mechanical ventilation system. The difference is attributed to the fact that mechanical ventilation systems 

can properly control and condition outside air while outside air from infiltration is introduced directly to 

the building. These results are relevant, but there are significant simplifications in the constant volume 

method used to model infiltration. A more thorough investigation of the effects of infiltration could be 

conducted by using a more detailed model that more thoroughly accounts for the physics governing air 

flow. EnergyPlus includes detailed air flow models; however, implementing this type of model on a 

national scale study would introduce significant challenges because of the many unique buildings. 

We tried to break the aggregate results down by climate zone and building type. For instance, the 

minimum mechanical ventilation increases the total energy consumption of the sector average by 5.4% to 

11.7% in climate zone 6B, but decreases the average by 2.6% to 0.6% in climate zone 2B. Colder

climates are generally more affected by ventilation. The results are also broken down by building type, 

but unfortunately the limited number of buildings provided by the CBECS data set in some categories 

severely degrades the quality of the results. A study based on a larger sample of buildings is one way to 

improve the accuracy of the detailed results. An alternative, and perhaps more efficient, approach to

improving the detailed results is to conduct a study based on a prototypical set of benchmark buildings for 

each climate zone and subsector. A much smaller number of models would be needed if a set of carefully 

crafted prototypical buildings were used. A study based on prototypical buildings would be less time 

consuming, and fewer models would make it feasible to give each model individual attention. 

It is not within the scope of this report to recommend changes to the minimum ventilation requirements 

for commercial buildings, but current technology offers alternative methods of providing healthy indoor

air. Advanced filters and ultraviolet light might help meet indoor air quality objectives with reduced 

ventilation. These options also have parasitic energy loss, and further research is necessary to objectively 

compare their energy use to conventional ventilation.

Finally, although much of this work focuses on a rather optimistic outlook where all buildings are tightly 

constructed and have energy recovery and properly controlled economizers, the real world is obviously 

far from realizing this picture. Indeed, many of our suggestions focus on improving on a scenario that is 

already far removed from the real world. Based on the results and on personal experience, we believe that 

the effects of outdoor air can be minimized by ensuring that the targets that we already have are achieved. 

More effective governance and validation are more important to achieving this goal than are new

technical achievements. 
40

5. References

ASHRAE. (2004). ANSI/ASHRAE Standard 62.1-2004: Ventilation for Acceptable Indoor Air Quality. 

Atlanta, GA: ASHRAE.

ASHRAE. (2004). ANSI/ASHRAE/IESNA Standard 90.1-2004: Energy Standard for Buildings except 

Low-Rise Residential Buildings. Atlanta, GA: ASHRAE.

Chan, W.R. (2006). Assessing the Effectiveness of Shelter-in-Place as an Emergency Response to LargeScale Outdoor Chemical Releases. Dissertation. Department of Civil and Environmental Engineering, 

University of California, Berkeley. LBNL-60184.

Colliver, D.G. (1995). Energy Requirements for Conditioning of Ventilating Air. AIVC Technical Note 

47. University of Warwick Science Park. Great Britain.

Energy Information Administration. (2006). Annual Energy Outlook 2006. Washington, DC: EIA. 

Available from http://www.eia.doe.gov/oiaf/aeo.

EIA. (2006a). Annual Energy Review 2006. Washington, DC: EIA. Available from 

www.eia.doe.gov/emeu/aer/consump.html.

EIA. (2006b). 2003 Commercial Buildings Energy Consumption Survey. Washington, DC: EIA. 

Available from www.eia.doe.gove/emeu/cbecs/cbecs2003/introduction.html.

Eto, M.; Meyer, C. (1988). “The HVAC Costs of Fresh Air Ventilation.” ASHRAE Transactions 

94(2):331-45. Atlanta, GA: ASHRAE. 

Emmerich, S.J.; McDowell, T.; Wagdy A. (2005). Investigation of the Impact of Commercial Building 

Envelope Airtightness on HVAC Energy Use. NISTIR 7238. National Institute of Standards and 

Technology. 

Fisk, W.J. (2000). Health and Productivity Gains from Better Indoor Environments and Their 

Implications for the U.S. Department of Energy. LBNL-47458. Berkeley, CA: Lawrence Berkeley 

National Laboratory. 

Griffith, B.; Long, N.; Torcellini, P.; Judkoff, R.; Crawley, D.; Ryan, J. (2007). Assessment of the 

Technical Potential for Achieving Net-Zero-Energy Buildings in the Commercial Sector. NREL/ TP-550-

41957. Golden, CO: National Renewable Energy Laboratory. 

Griffith, B.; Long; N.; Torcellini; P.; Judkoff; R.; Crawley; D.; Ryan, J. (2008). Methodology for 

Modeling Building Energy Performance across the Commercial Sector. NREL Report No. TP-550-

41956. Golden, CO: NREL. 

Harrje, D.T.; Duil, G.S.; Bohac, D.L.; Gadsby, K.J. (1985). “Documenting Air Movements and 

Infiltration in Multicell Buildings Using Various Tracer-Gas Techniques.” ASHRAE Transactions

91(2B):2012-27. Atlanta, GA: ASHRAE. 

Orme, M. (2001). “Estimates of the Energy Impact of Ventilation and Associated Financial 

Expenditures.” Energy and Buildings 33:199-205. Amsterdam: Elsevier Science.

Persily, A.K. (1998) “Airtightness of Commercial and Institutional Buildings: Blowing Holes in the 

Myth of Tight Buildings.” DOE, ASHRAE, ORNL Conference – Thermal Envelopes VII, Clearwater, 

FL. 

Turk, B.H.; Grimsrud, D.T.; Brown, J.T.; Geisling-Sobotka, K.L.; Harrison, J.; Prill, R.J. (1989). 

“Commercial Building Ventilation Rates and Particle Concentrations.” ASHRAE Transactions 95(1):422-

433. Atlanta, GA: ASHRAE. 
F1147-E(10/2008) 

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April 2009

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Technical Report

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4. TITLE AND SUBTITLE

Assessment of the Energy Impacts of Outside Air in the Commercial 

Sector

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DE-AC36-08-GO28308

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K. Benne, B. Griffith, N. Long, P. Torcellini, D. Crawley, and 

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NREL/TP-550-41955

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14. ABSTRACT (Maximum 200 Words)

The enormous quantity of energy consumed by U.S. commercial buildings places a significant burden on the energy 

supply and is a potential source of economic strain. To address this, the DOE Building Technologies Program has 

established the goal of developing market-viable zero energy buildings by 2025. This study focuses on the effects of 

outside air, and considers various outside air sources, types of building construction, building subsectors, and 

climates. Based on the information about energy consumption attributed to outside air, it identifies topics for further 

research that have the greatest potential to achieve energy savings.

15. SUBJECT TERMS

zero energy building; zeb; outside air; ventilation

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