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

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Contract No. DE-AC36-08GO28308

Energy Implications of 

Retrofitting Retail Sector 

Rooftop Units with SteppedSpeed and Variable-Speed 

Functionality

Daniel Studer, Rachel Romero, 

Lesley Herrmann, and Kyle Benne

Technical Report

NREL/TP-5500-51102

April 2012
NREL is a national laboratory of the U.S. Department of Energy, Office of Energy 

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

National Renewable Energy Laboratory

15013 Denver West Parkway

Golden, Colorado 80401

303-275-3000 • www.nrel.gov

Contract No. DE-AC36-08GO28308

Energy Implications of 

Retrofitting Retail Sector 

Rooftop Units With SteppedSpeed and Variable-Speed 

Functionality

Daniel Studer, Rachel Romero, 

Lesley Herrmann, Kyle Benne

Prepared under Task No. BEC7.1311

Technical Report

NREL/TP-5500-51102

April 2012
NOTICE

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iii

Acknowledgments

The authors would like to thank the U.S. Department of Energy (DOE) Building Technologies 

Program for its support. This report was prepared by the National Renewable Energy Laboratory

(NREL) Center for Electricity, Resources, and Building Systems Integration.

Many NREL colleagues provided valuable input and support. We are indebted to Eric Bonnema 

for his model development assistance and contributions to the post-processing of simulation 

results, to Ian Doebber for his insights on rooftop unit (RTU) design and fan flow controls, and 

to Brent Griffith for his extensive EnergyPlus support. We also thank Matt Leach, who provided 

information about energy management system controls for EnergyPlus and reviewed this report, 

as well as Michael Deru, Feitau Kung, William Livingood, Paul Torcellini, and Ron Judkoff who 

also reviewed this document. 

This project would not have been possible without the contributions of the 2011 Retailer Energy 

Alliance Heating, Ventilating, and Air-Conditioning (HVAC) Project Team. Thank you to the 

project team members, particularly Scott Williams from Target, David Sheets from Walmart, 

Paul Holliday from Lowe’s, and Kyle Wilkes from JCPenney. Their contributions improved the

representation of systems and controls.
iv

Executive Summary

Background

According to the 2003 Commercial Buildings Energy Consumption Survey (EIA 2008), 

approximately 2.7 billion ft2 of commercial retail floor space is served by packaged airconditioning units. Often, these rooftop units (RTUs) are oversized to meet extreme and 

infrequent thermal loads (Felts et al. 2000). Thus, RTU supply fans may provide air at rates that 

are much higher than those needed to meet most thermal loads, wasting the energy needed to 

move and heat or cool the excess air.

To address this issue, some U.S. retailers have started to upgrade existing RTUs, retrofitting their 

constant-speed motors with stepped- or variable-speed functionality. Such retrofits may be more 

cost effective than replacing an entire RTU, particularly if the unit is in the middle of its lifespan. 

Other U.S. retailers, however, are uncomfortable pursuing this measure, as there is a lack of 

supporting data detailing the climate zone-specific energy savings potential associated with this 

upgrade. Building and portfolio energy managers have thus been unable to present a compelling

business case for RTU fan motor upgrades.

This study uses whole-building energy simulation to estimate the energy impact of stepped- and 

variable-speed RTU fan motor retrofits in the retail environment, across 16 locations in all 15 

U.S. climate zones. The results allow retailers to estimate the building-level energy savings 

associated with this retrofit measure. This is a critical step in enabling retailers to determine 

whether a compelling business case can be made.

Development Process

EnergyPlus Version 6.0 (DOE 2010) was used to evaluate the whole-building energy savings 

associated with stepped- and variable-speed RTU fan motor retrofits as follows: 

1. Two prototype big-box retail EnergyPlus models were created: one with refrigeration 

systems and one without. 

2. Each prototype model was replicated across 16 locations, which encompassed all 15 U.S. 

climate zones, as defined by DOE (2005). 

3. Standard 90.1-2004 (ASHRAE 2004a) was applied to the building envelope to create 

climate-specific baseline models. 

4. Custom sizing and control logic was used to modify a subset of the baseline models with 

stepped- and variable-speed RTU fan motor controls. 

5. EnergyPlus was used to simulate the energy performance of all models to determine the 

energy savings associated with these retrofits.
v

Results

Table ES–1 through Table ES–3 present an overview of the simulation results1. Annual wholebuilding and electric energy savings were seen in all climate zones when switching to stepped- or 

variable-speed fan motor operation. Whole-building energy savings ranged from 0.7%–8.4%. 

Normalized annual electricity savings ranged from 0.50–1.67 kWh/ft2 (1.70–5.70 kBtu/ft2). 

Average electricity savings across all locations were 1.17 kWh/ft2 (3.98 kBtu/ft2) for the steppedspeed cases and 1.23 kWh/ft2 (4.40 kBtu/ft2

) for the variable-speed cases. The results suggest

that for certain building types, annual whole-building electricity savings of 200,000 kWh may be 

realized.

Heating energy increased in all climates, because less fan energy was imparted to the supply 

airstream during the heating season. On average, this increase was 0.0149 therm/ft2 for the 

stepped-speed cases and 0.0162 therm/ft2 for the variable-speed cases. (This increase was 

always more than offset by the electricity use reduction.)

Based on the average energy savings, if variable-speed retrofits were implemented across 10% of 

the 2.7 billion ft2 of retail space served by packaged RTUs (EIA 2008), retailers would save 

approximately 332 GWh/yr (1.13 × 1012 Btu/yr) of electricity and increase natural gas use by 4.4 

million therm/yr (4.34 × 1011 Btu/yr). Assuming typical utility rates of $0.10/kWh and 

$1.00/therm, this would equate to annual utility cost savings of $28.8 million.

This measure requires that a relatively small number of RTU fan motors be upgraded per 

building. Therefore, this report makes a case that such retrofits should be investigated in all 

climate zones to address the oftentimes dispersed energy loads in commercial buildings.

The energy savings values presented here depend on a number of assumptions, including the

cooling coil and fan flow rate sizing methodology, sequence of operations, space set points, and

hours of operation. In order to provide broadly applicable findings, values were used that reflect 

common practice. Appendix C provides instructions about how to use the results of this study to 

estimate high-level utility cost savings. A retailer can use such results to justify site-specific 

assessments of retrofit feasibility and determine if a compelling business case can be made.

 

1 Note that additional differences between the models with and without refrigeration, such as zoning layout and the 

fan flow rate sizing methodology, affect the energy consumption and savings values. Readers should exercise 

caution when comparing results between model types.
vi

Table ES–1 Annual Whole-Building Energy Savings for All Models (%)

Climate 

Zone Location

Models With Refrigeration Models Without Refrigeration

Stepped-Speed Variable-Speed Stepped-Speed Variable-Speed

1A Miami, FL 2.5 3.5 2.3 2.3

2A Houston, TX 3.2 4.0 3.6 3.6

2B Phoenix, AZ 3.5 4.7 4.1 5.2

3A Atlanta, GA 3.2 3.9 3.7 3.7

3B Los Angeles, CA 6.1 6.5 8.1 8.3

3B Las Vegas, NV 3.4 4.6 4.1 5.5

3C San Francisco, CA 5.8 5.9 8.3 8.4

4A Baltimore, MD 2.2 2.6 2.5 2.4

4B Albuquerque, NM 3.1 3.8 3.6 4.1

4C Seattle, WA 3.1 3.2 4.0 4.0

5A Chicago, IL 1.8 2.1 2.1 2.0

5B Boulder, CO 2.6 3.1 3.2 3.5

6A Minneapolis, MN 1.5 1.8 1.7 1.7

6B Helena, MT 1.8 2.1 2.3 2.4

7 Duluth, MN 1.1 1.2 1.4 1.3

8 Fairbanks, AK 0.7 0.7 0.9 0.9

Table ES–2 Annual Electricity Savings for All Models (kWh/ft2)

Climate 

Zone Location

Models With Refrigeration Models Without Refrigeration

Stepped-Speed Variable-Speed Stepped-Speed Variable-Speed

1A Miami, FL 0.66 0.94 0.50 0.51

2A Houston, TX 0.95 1.13 0.89 0.91

2B Phoenix, AZ 1.00 1.30 0.98 1.22

3A Atlanta, GA 1.14 1.30 1.11 1.13

3B Los Angeles, CA 1.31 1.40 1.38 1.41

3B Las Vegas, NV 1.11 1.39 1.13 1.41

3C San Francisco, CA 1.47 1.50 1.66 1.67

4A Baltimore, MD 1.19 1.31 1.16 1.24

4B Albuquerque, NM 1.24 1.43 1.23 1.40

4C Seattle, WA 1.41 1.44 1.55 1.57

5A Chicago, IL 1.22 1.32 1.14 1.27

5B Boulder, CO 1.30 1.42 1.29 1.44

6A Minneapolis, MN 1.18 1.28 1.06 1.20

6B Helena, MT 1.30 1.39 1.27 1.43

7 Duluth, MN 1.24 1.29 1.13 1.29

8 Fairbanks, AK 1.12 1.18 1.00 1.14
vii

Table ES–3 Annual Natural Gas Savings* for All Models (therm/ft2)

Climate 

Zone Location

Models With Refrigeration Models Without Refrigeration

Stepped-Speed Variable-Speed Stepped-Speed Variable-Speed

1A Miami, FL 0.000 0.000 0.000 0.000

2A Houston, TX –0.005 –0.005 –0.005 –0.005

2B Phoenix, AZ –0.004 –0.004 –0.005 –0.005

3A Atlanta, GA –0.012 –0.012 –0.012 –0.013

3B Los Angeles, CA –0.002 –0.002 –0.002 –0.002

3B Las Vegas, NV –0.009 –0.009 –0.010 –0.010

3C San Francisco, CA –0.009 –0.010 –0.011 –0.011

4A Baltimore, MD –0.020 –0.020 –0.020 –0.023

4B Albuquerque, NM –0.017 –0.017 –0.017 –0.019

4C Seattle, WA –0.023 –0.023 –0.025 –0.026

5A Chicago, IL –0.023 –0.024 –0.020 –0.025

5B Boulder, CO –0.021 –0.021 –0.019 –0.023

6A Minneapolis, MN –0.023 –0.023 –0.018 –0.023

6B Helena, MT –0.026 –0.026 –0.023 –0.027

7 Duluth, MN –0.029 –0.029 –0.023 –0.029

8 Fairbanks, AK –0.026 –0.028 –0.021 –0.025

*Negative values indicate that natural gas use increased.
viii

Nomenclature

ACH air changes per hour

ASHRAE American Society of Heating, Refrigerating and Air-Conditioning 

Engineers

c.i. continuous insulation

cfm cubic feet per minute

COP coefficient of performance

DOE U.S. Department of Energy

EPD equipment power density

EUI energy use intensity

ft foot, feet

ft2 square foot, square feet

HVAC heating, ventilating, and air conditioning

in. inch, inches

kBtu kilo-Btu

kW kilowatt, kilowatts

kWh kilowatt-hour, kilowatt-hours

LPD lighting power density

m meter, meters

m2 square meter, square meters

MJ megajoule, megajoules

NREL National Renewable Energy Laboratory

OA outside air

RH relative humidity

RTU rooftop unit

SAT supply air temperature

therm unit of heat energy equal to 100 kBtu

VAV variable air volume

w.c. water column
ix

Contents

Acknowledgments..........................................................................................................................iii

Executive Summary....................................................................................................................... iv

Background ................................................................................................................................ iv

Development Process................................................................................................................. iv

Results......................................................................................................................................... v

Nomenclature............................................................................................................................... viii

Figures and Tables......................................................................................................................... xi

Figures........................................................................................................................................ xi

Tables......................................................................................................................................... xi

1.0 Introduction.......................................................................................................................... 1

1.1 Objective .......................................................................................................................... 1

1.2 Scope ................................................................................................................................ 1

2.0 Building Energy Modeling Methodology............................................................................ 2

2.1 EnergyPlus ....................................................................................................................... 2

2.2 Climate Zones .................................................................................................................. 2

2.3 Modeling Process............................................................................................................. 3

3.0 Model Development............................................................................................................. 4

3.1 Form ................................................................................................................................. 4

3.2 Fabric................................................................................................................................ 6

3.2.1 Opaque Envelope.......................................................................................................... 6

3.2.2 Vertical Fenestration..................................................................................................... 7

3.3 Infiltration......................................................................................................................... 7

3.4 Internal Load Densities .................................................................................................... 8

3.4.1 Occupancy .................................................................................................................... 8

3.4.2 Plug and Process Loads................................................................................................ 9

3.4.3 Refrigeration Loads.................................................................................................... 10

3.5 Schedules........................................................................................................................ 10

3.6 Lighting .......................................................................................................................... 10

3.7 Heating, Ventilating, and Air Conditioning................................................................... 11

3.7.1 System Type ............................................................................................................... 11

3.7.2 Rooftop Unit Performance Properties ........................................................................ 11
x

3.7.3 Economizer................................................................................................................. 12

3.7.4 Sizing.......................................................................................................................... 12

3.7.5 Outdoor Air................................................................................................................. 13

3.7.6 Supply Fan.................................................................................................................. 13

3.7.7 Control Logic.............................................................................................................. 14

4.0 Results................................................................................................................................ 20

4.1 Fan Energy Savings........................................................................................................ 20

4.2 Whole-Building Energy Savings.................................................................................... 21

4.3 Electricity Consumption Savings................................................................................... 27

4.4 Natural Gas Consumption Savings ................................................................................ 28

4.5 Utility Cost Savings ....................................................................................................... 29

4.6 Relative Humidity .......................................................................................................... 30

5.0 Conclusions........................................................................................................................ 32

6.0 Next Steps.......................................................................................................................... 33

7.0 References.......................................................................................................................... 34

Appendix A Schedules............................................................................................................. 35

A.1 Occupancy, Lighting, and Equipment Schedules........................................................... 35

A.2 Heating and Cooling Set Point Schedules...................................................................... 36

Appendix B Additional Results Tables................................................................................... 38

B.1 Detailed Whole-Building Results .................................................................................. 38

B.2 Sizing.............................................................................................................................. 46

B.3 Fan Energy Savings (SI Units)....................................................................................... 52

B.4 Electricity Consumption Savings (SI Units).................................................................. 53

B.5 Natural Gas Consumption Savings (SI Units)................................................................ 54

Appendix C How to Calculate Preliminary Utility Cost Savings............................................ 56
xi

Figures and Tables

Figures

Figure 2–1 DOE climate zones and representative cities............................................................. 2

Figure 3–1 Rendering of models with refrigeration: view from the southeast ........................... 4

Figure 3–2 Floor plan for models with refrigeration.................................................................... 4

Figure 3–3 Rendering of models without refrigeration: view from the southeast ...................... 5

Figure 3–4 Floor plan for models without refrigeration............................................................... 5

Figure 4–1 Models with refrigeration: annual whole-building EUI by end use for steppedspeed cases .............................................................................................................. 23

Figure 4–2 Models with refrigeration: annual whole-building EUI by end use for variablespeed cases .............................................................................................................. 24

Figure 4–3 Models without refrigeration: annual whole-building EUI by end use for 

stepped-speed cases................................................................................................. 25

Figure 4–4 Models without refrigeration: annual whole-building EUI by end use for 

variable-speed cases................................................................................................ 26

Figure A–1 Occupancy, lighting, and equipment schedules....................................................... 36

Figure A–2 Heating and cooling set points................................................................................. 36

Tables

Table ES–1 Annual Whole-Building Energy Savings for All Models (%).................................. vi

Table ES–2 Annual Electricity Savings for All Models (kWh/ft2) .............................................. vi

Table ES–3 Annual Natural Gas Savings* for All Models (therm/ft2

)....................................... vii

Table 3–1 Space Type Details for Models With Refrigeration .................................................. 6

Table 3–2 Space Type Details for Models Without Refrigeration ............................................. 6

Table 3–3 Envelope Details........................................................................................................ 7

Table 3–4 Fenestration Details ................................................................................................... 7

Table 3–5 Peak Occupant Density for Models With Refrigeration............................................ 8

Table 3–6 Peak Occupant Density for Models Without Refrigeration....................................... 9

Table 3–7 EPDs for Models With Refrigeration ........................................................................ 9

Table 3–8 EPDs for Models Without Refrigeration ................................................................. 10

Table 3–9 LPDs for Models With Refrigeration ...................................................................... 11

Table 3–10 LPDs for Models Without Refrigeration ................................................................. 11

Table 3–11 HVAC System Performance Values........................................................................ 12
xii

Table 3–12 OA Rates for Models With Refrigeration................................................................ 13

Table 3–13 OA Rates for Models Without Refrigeration........................................................... 13

Table 4–1 Normalized Annual Fan Energy Consumption for Models With Refrigeration...... 20

Table 4–2 Normalized Annual Fan Energy Consumption for Models Without Refrigeration. 21

Table 4–3 Annual Whole-Building Energy Savings for All Models (%)................................. 22

Table 4–4 Normalized Annual Whole-Building Electricity Consumption for Models With 

Refrigeration............................................................................................................ 27

Table 4–5 Normalized Annual Whole-Building Electricity Consumption for Models 

Without Refrigeration ............................................................................................. 28

Table 4–6 Normalized Annual Whole-Building Natural Gas Consumption* for Models 

With Refrigeration................................................................................................... 29

Table 4–7 Normalized Annual Whole-Building Natural Gas Consumption* for Models 

Without Refrigeration ............................................................................................. 29

Table 4–8 Models With Refrigeration: 95th Percentile RH Values ......................................... 31

Table 4–9 Models Without Refrigeration: 95th Percentile RH Values.................................... 31

Table A–1 Occupancy, Lighting, and Equipment Schedules.................................................... 35

Table A–2 Heating and Cooling Set Points............................................................................... 37

Table B–1 Energy End Use Breakdown for Models With Refrigeration – IP Units................. 38

Table B–1 Energy End Use Breakdown for Models With Refrigeration – IP Units 

(Continued).............................................................................................................. 39

Table B–2 Energy End Use Breakdown for Models Without Refrigeration – IP Units............ 40

Table B–2 Energy End Use Breakdown for Models Without Refrigeration – IP Units 

(Continued).............................................................................................................. 41

Table B–3 Energy End Use Breakdown for Models With Refrigeration – SI Units................. 42

Table B–3 Energy End Use Breakdown for Models With Refrigeration – SI Units 

(Continued).............................................................................................................. 43

Table B–4 Energy End Use Breakdown for Models Without Refrigeration – SI Units............ 44

Table B–4 Energy End Use Breakdown for Models Without Refrigeration – SI Units 

(Continued).............................................................................................................. 45

Table B–5 Cooling Coil Sizing Results by Zone for Models With Refrigeration – tons.......... 46

Table B–6 Cooling Coil Sizing Results by Zone for Models With Refrigeration – ft2

/ton....... 46

Table B–7 Cooling Coil Sizing Results by Zone for Models With Refrigeration – kW........... 47

Table B–8 Cooling Coil Sizing Results by Zone for Models Without Refrigeration – tons..... 47

Table B–9 Cooling Coil Sizing Results by Zone for Models Without Refrigeration – ft2/ton . 48

Table B–10 Cooling Coil Sizing Results by Zone for Models Without Refrigeration – kW...... 48
xiii

Table B–11 Heating Coil Sizing Results by Zone for Models With Refrigeration – kBtu/h...... 49

Table B–12 Heating Coil Sizing Results by Zone for Models With Refrigeration – Btu/h∙ft2 ... 49

Table B–13 Heating Coil Sizing Results by Zone for Models With Refrigeration – kW........... 50

Table B–14 Heating Coil Sizing Results by Zone for Models Without Refrigeration – kBtu/h. 50

Table B–15 Heating Coil Sizing Results by Zone for Models Without Refrigeration –

Btu/h∙ft2 ................................................................................................................... 51

Table B–16 Heating Coil Sizing Results by Zone for Models Without Refrigeration – kW...... 51

Table B–17 Normalized Annual Fan Energy Consumption for Models With Refrigeration...... 52

Table B–18 Normalized Annual Fan Energy Consumption for Models Without Refrigeration. 52

Table B–19 Normalized Annual Whole-Building Electricity Consumption for Models With 

Refrigeration............................................................................................................ 53

Table B–20 Normalized Annual Whole-Building Electricity Consumption for Models 

Without Refrigeration ............................................................................................. 53

Table B–21 Normalized Annual Whole-Building Natural Gas Consumption* for Models 

With Refrigeration................................................................................................... 54

Table B–22 Normalized Annual Whole-Building Natural Gas Consumption* for Models 

Without Refrigeration ............................................................................................. 55

Table C–1 Annual Whole Building Energy Savings (%) for All Models................................. 56

Table C–2 High-Level Calculation Methodology ..................................................................... 56
1

1.0 Introduction

According to the 2003 Commercial Buildings Energy Consumption Survey (EIA 2008), 

approximately 2.7 billion ft2 of commercial retail floor space is served by packaged airconditioning units. Often, these rooftop units (RTUs) are oversized to meet extreme and 

infrequent thermal loads (Felts et al. 2000). Thus, RTU supply fans may provide air at rates that 

are much higher than those needed to meet most thermal loads, wasting the energy needed to 

move and heat or cool the excess air.

To enable more efficient RTU operation during normal operating conditions, some U.S. retailers 

have started to upgrade existing RTUs, retrofitting their constant-speed motors with stepped- or 

variable-speed functionality. Such retrofits may be more cost effective than replacing an entire 

RTU, particularly if the unit is in the middle of its lifespan. Other U.S. retailers, however, are 

uncomfortable pursuing this measure, as there is a lack of supporting data detailing the climate 

zone-specific energy savings potential associated with this upgrade. Building and portfolio

energy managers have thus been unable to present a compelling business case for RTU fan motor 

upgrades.

This study uses whole-building energy simulation to estimate the energy impact of stepped- and 

variable-speed RTU fan motor retrofits in the retail environment, across 16 locations in all 15 

U.S. climate zones. The results allow retailers to estimate the building-level energy savings 

associated with this retrofit measure. This is a critical step in enabling retailers to determine 

whether a compelling business case can be made.

1.1 Objective

Our objective was to use whole-building energy simulation to quantify the energy savings 

associated with stepped- and variable-speed RTU fan motor retrofits in a typical big-box retail 

environment.

1.2 Scope

This report provides normalized, simulation-based energy savings estimates for RTU fan motor 

retrofits. Because the big-box retail environment is diverse, we examined buildings with and 

without refrigeration systems (walk-in coolers and refrigerated cases).
2

2.0 Building Energy Modeling Methodology

2.1 EnergyPlus

EnergyPlus Version 6.0 (DOE 2010), a publicly available building energy simulation engine, 

was used for all analyses. EnergyPlus was selected because it is a detailed U.S. Department of 

Energy (DOE) simulation tool that computes building energy use based on the interactions 

between climate; building form and fabric; internal gains; heating, ventilating, and air 

conditioning (HVAC) systems; and renewable energy systems. All simulations were run on 

desktop computers at the National Renewable Energy Laboratory (NREL).

2.2 Climate Zones

The models used for this study were simulated in 16 locations, which represent all 15 U.S. 

climate zones. The eight climate zones and three subzones used to determine these locations are 

depicted in Figure 2–1. The zones are defined primarily by heating degree days and cooling 

degree days (Briggs et al. 2003). The climate zones range from hot (zone 1) to cold (zone 8). 

Subzones indicate varying moisture conditions. Humid subzones are designated by the letter A, 

dry subzones by B, and marine subzones by C.

Figure 2–1 DOE climate zones and representative cities

(Credit: DOE 2005)

Models were simulated for large cities only, as the weather data for such locations were directly

applicable to a large fraction of the total U.S. building floor area. Energy savings were 

determined by running the baseline and all retrofit simulations with the same Typical 
3

Meteorological Year 3 weather file (one set of simulations for each city) (Deru et al. 2011). The 

16 specific locations for which analyses were performed are listed below, are marked in Figure 

2–1, and are designated as being representative of their respective climate zones.

2

• Zone 1A Miami, Florida (hot, humid)

• Zone 2A Houston, Texas (hot, humid)

• Zone 2B Phoenix, Arizona (hot, dry)

• Zone 3A Atlanta, Georgia (hot, humid)

• Zone 3B Las Vegas, Nevada (hot, dry) and Los Angeles, California (warm, dry)

• Zone 3C San Francisco, California (marine)

• Zone 4A Baltimore, Maryland (mild, humid)

• Zone 4B Albuquerque, New Mexico (mild, dry)

• Zone 4C Seattle, Washington (marine)

• Zone 5A Chicago, Illinois (cold, humid)

• Zone 5B Boulder, Colorado (cold, dry)

• Zone 6A Minneapolis, Minnesota (cold, humid)

• Zone 6B Helena, Montana (cold, dry)

• Zone 7 Duluth, Minnesota (very cold)

• Zone 8 Fairbanks, Alaska (extremely cold)

2.3 Modeling Process

Two prototype big-box retail EnergyPlus models were created: one with refrigeration systems

(for food sales) and one without. Each prototype model was then replicated across 16 locations,

and Standard 90.1-2004 (ASHRAE 2004a) was applied to the building envelope to create 

climate-specific baseline models. Each of the 32 baseline models was then modified with 

stepped- and variable-speed RTU fan motor functionality, and the energy performance of all 96

models (32 constant-speed, 32 stepped-speed, and 32 variable-speed) was simulated using 

EnergyPlus to determine energy savings. 

 

2 This report contains numerous climate zone tables in which the states will be designated with their respective two-letter postal 

codes: Florida (FL), Texas (TX), Arizona (AZ), Georgia (GA), Nevada (NV), California (CA), Maryland (MD), New Mexico

(NM), Washington (WA), Illinois (IL), Colorado (CO), Minnesota (MN), Montana (MT), and Alaska (AK).
4 

3.0 Model Development

3.1 Form

The building form for each prototype model was based on floor plans supplied by a major U.S. 

retailer. The models with refrigeration included all space types in the models without 

refrigeration, plus a pharmacy, a grocery area, a walk-in freezer area, and a kitchen. The total 

floor area for the models with refrigeration was 133,275 ft2

 (12,382 m2). The total floor area for 

the models without refrigeration was 111,825 ft2

 (10,389 m2). Figure 3–1 through Figure 3–4 

and Table 3–1 and Table 3–2 provide additional details about the zone layout and space types 

assumed for both prototype models. 

Figure 3–1 Rendering of models with refrigeration: view from the southeast 

(Credit: Rachel Romero/NREL)

Figure 3–2 Floor plan for models with refrigeration

(Credit: Rachel Romero/NREL)
5 

Figure 3–3 Rendering of models without refrigeration: view from the southeast 

(Credit: Rachel Romero/NREL)

Figure 3–4 Floor plan for models without refrigeration

(Credit: Rachel Romero/NREL)
6

Table 3–1 Space Type Details for Models With Refrigeration

Zone Floor Area (ft2) Floor Area (m2) Total (%)

Grocery 16,250 1,510 12.2

Kitchen 1,800 167 1.4

Office 4,500 418 3.4

Pharmacy 1,950 181 1.5

Restroom 900 84 0.7

Sales 1 21,875 2,032 16.4

Sales 2 21,875 2,032 16.4

Sales 3 21,875 2,032 16.4

Sales 4 21,875 2,032 16.4

Stockroom 16,400 1,524 12.3

Vestibule 2,025 188 1.5

Walk-in freezer 1,950 181 1.5

Total 133,275 12,382 100.0

Table 3–2 Space Type Details for Models Without Refrigeration

Zone Floor Area (ft2) Floor Area (m2) Total (%)

Office 8,250 766 7.4

Restroom 900 84 0.8

Sales 1 21,875 2,032 19.6

Sales 2 21,875 2,032 19.6

Sales 3 21,875 2,032 19.6

Sales 4 21,875 2,032 19.6

Stockroom 13,150 1,222 11.8

Vestibule 2,025 188 1.8

Total 111,825 10,389 100.0

3.2 Fabric

3.2.1 Opaque Envelope

The thermal properties for opaque exterior surfaces in all models were taken from Standard 90.1-

2004 (ASHRAE 2004a). Wall insulation values were chosen assuming steel-framed 

construction. The roof insulation was assumed to be entirely above deck. Table 3–3 details the 

thermal resistance of the exterior walls and roofs for all models by climate zone.
7

Table 3–3 Envelope Details

Climate 

Zone Location

Exterior Wall Insulation

(ft2∙h∙°F/Btu)

Roof Insulation

(ft2∙h∙°F/Btu)

1A Miami, FL R-13 R-15 c.i.

2A Houston, TX R-13 R-15 c.i.

2B Phoenix, AZ R-13 R-15 c.i.

3A Atlanta, GA R-13 R-15 c.i.

3B Los Angeles, CA R-13 R-15 c.i.

3B Las Vegas, NV R-13 R-15 c.i.

3C San Francisco, CA R-13 R-15 c.i.

4A Baltimore, MD R-13 R-15 c.i.

4B Albuquerque, NM R-13 R-15 c.i.

4C Seattle, WA R-13 R-15 c.i.

5A Chicago, IL R-13 + R-3.8 c.i. R-15 c.i.

5B Boulder, CO R-13 + R-3.8 c.i. R-15 c.i.

6A Minneapolis, MN R-13 + R-3.8 c.i. R-15 c.i.

6B Helena, MT R-13 + R-3.8 c.i. R-15 c.i.

7 Duluth, MN R-13 + R-7.5 c.i. R-15 c.i.

8 Fairbanks, AK R-13 + R-7.5 c.i. R-20 c.i.

3.2.2 Vertical Fenestration

Window properties for all models were determined according to Standard 90.1-2004 (ASHRAE 

2004a) and are detailed in Table 3–4.

Table 3–4 Fenestration Details

Climate Zone

U-Factor 

(Btu/h∙ft2∙°F)

Solar Heat Gain 

Coefficient

Visible Light 

Transmittance

1A U-1.22 0.25 0.25

2 (A,B) U-1.22 0.25 0.25

3 (A,B) U-0.57 0.39 0.50

3C U-1.22 0.61 0.61

4 (A,B,C) U-0.57 0.39 0.50

5 (A,B) U-0.57 0.49 0.62

6 (A,B) U-0.57 0.49 0.62

7 U-0.57 0.49 0.49

8 U-0.46 0.45 0.45

3.3 Infiltration

The infiltration rate for all zones in all models was assumed to be 0.15 cfm/ft2 at 0.016 in. w.c. 

(0.76 L/s∙m

2 at 4 Pa) of above-grade envelope area (walls and roof). This value was chosen as it 

represented an acceptable middle ground between the infiltration rates used by Deru et al. (2011) 

for new construction and existing buildings. During occupied hours, when outdoor air (OA) was 

being brought in by the HVAC system, the building was assumed to be pressurized, and the 
8

infiltration rate was set to 50% of this design value. During unoccupied hours, the infiltration 

rate was reset to the design value.

Additional infiltration was added to the vestibule zone at a maximum flow rate of 2.22 cfm/ft2

(11.30 L/s∙m

2

) of floor area to account for infiltration associated with opening and closing of the 

main entry doors. This value was calculated using Equation 52 from Chapter 16 of the 2009 

ASHRAE Handbook—Fundamentals (ASHRAE 2009): 

Q = CA × A × Rp (3-1)

Where:

Q = airflow rate (cfm)

CA = airflow coefficient [cfm/ft2/(in. of water)0.5]

A = area of the door opening (ft2)

Rp = pressure factor [(in. of water)0.5]

The airflow coefficient and pressure factor were calculated using methodology presented by 

Yuill (1996). To determine the airflow coefficient, a maximum occupancy flow rate through the 

entry of 159 people per hour was assumed, a value based on measured data presented by Yuill 

(1996). The door opening was assumed to be equal to 42 ft2 (3.9 m2). Daily variations in 

vestibule infiltration were assumed to follow the occupancy schedule.

3.4 Internal Load Densities

3.4.1 Occupancy

Peak occupant density values were taken from Standard 62.1-2004 (ASHRAE 2004b). For the 

models with refrigeration, the average floor area per person was 76.5 ft2 (7.1 m

2

); for those

without refrigeration, it was 74.6 ft2 (6.9 m2

). Table 3–5 and Table 3–6 detail the peak occupant 

density by zone for both model types.

Table 3–5 Peak Occupant Density for Models With Refrigeration

Zone

Standard 62.1-2004 

Equivalent Zone

Occupancy Density 

(people/100 m2)

Area per Person

(ft2/person)

Area per Person 

(m2/person)

Grocery Supermarket 8.0 134.5 12.5

Kitchen Sales 15.0 71.8 6.7

Office Office 5.0 215.3 20.0

Pharmacy Pharmacy 10.0 107.6 10.0

Restroom Sales 15.0 71.8 6.7

Sales 1 Sales 15.0 71.8 6.7

Sales 2 Sales 15.0 71.8 6.7

Sales 3 Sales 15.0 71.8 6.7

Sales 4 Sales 15.0 71.8 6.7

Stockroom Shipping/receiving 0.0 0.0 0.0

Vestibule Main entry lobbies 10.0 107.6 10.0

Walk-in freezer Sales 15.0 71.8 6.7

Total 11.8 76.5 7.1
9

Table 3–6 Peak Occupant Density for Models Without Refrigeration

Zone

Standard 62.1-2004 

Equivalent Zone

Occupancy Density 

(people/100 m2)

Area per Person 

(ft2/person)

Area per Person 

(m2/person)

Office Office 5.0 215.3 20.0

Restroom Sales 15.0 71.8 6.7

Sales 1 Sales 15.0 71.8 6.7

Sales 2 Sales 15.0 71.8 6.7

Sales 3 Sales 15.0 71.8 6.7

Sales 4 Sales 15.0 71.8 6.7

Stockroom Shipping/receiving 0.0 0.0 0.0

Vestibule Main entry lobbies 10.0 107.6 10.0

Total 12.4 74.6 6.9

3.4.2 Plug and Process Loads

The equipment data detailed in Table 3–7 and Table 3–8 were adapted from metered values

obtained from a big-box retailer. The total equipment power density (EPD) for the models with 

refrigeration was 0.65 W/ft2 (7.0 W/m2

); those without refrigeration had an EPD of 0.56 W/ft2

(6.0 W/m2). This difference is due mainly to the lack of a “kitchen” zone in the models without 

refrigeration.

Table 3–7 EPDs for Models With Refrigeration

Zone

EPD

(W/ft2)

EPD

(W/m2)

Grocery 0.00 0.00

Kitchen 14.08 151.59

Office 1.00 10.72

Pharmacy 0.35 3.75

Restroom 0.00 0.00

Sales 1 0.55 5.91

Sales 2 0.55 5.91

Sales 3 0.55 5.91

Sales 4 0.55 5.91

Stockroom 0.50 5.34

Vestibule 0.00 0.00

Walk-in freezer 0.00 0.00

Total 0.65 7.00
10

Table 3–8 EPDs for Models Without Refrigeration

Zone

EPD

(W/ft2)

EPD

(W/m2)

Office 1.00 10.72

Restroom 0.00 0.00

Sales 1 0.55 5.91

Sales 2 0.55 5.91

Sales 3 0.55 5.91

Sales 4 0.55 5.91

Stockroom 0.50 5.34

Vestibule 0.00 0.00

Total 0.56 6.04

3.4.3 Refrigeration Loads

For the models with refrigeration, refrigerated cases were assumed to be present in the grocery, 

kitchen, and walk-in freezer zones. The grocery zone contained single-deck ice cream cases, 

vertical door freezer cases for frozen foods, and multideck cases for dairy and deli items, for a 

total of 415 linear feet (126.5 m) of refrigerated cases. The kitchen zone contained 20 linear feet 

(6.1 m) of multideck cases for dairy and deli items. The walk-in freezer zone contained 1,779 ft2

(165.3 m

2

) of walk-in freezers. 

3.5 Schedules

All models assumed that the buildings were open to customers from 8:00 a.m. to 10:00 p.m., 

seven days per week; however, because store employees had to be in the space before and after 

sales hours, occupied hours were assumed to be from 7:00 a.m. to 11:00 p.m., seven days per

week. Occupancy, lighting, equipment, and set point schedules are presented in Appendix A.

3.6 Lighting

Lighting power density (LPD) values for all models were taken from Standard 90.1-2004 Table 

9.6.1 (ASHRAE 2004a). The total building LPD for the models with refrigeration was 1.53 

W/ft2 (16.5 W/m2). The building LPD for the models without refrigeration was 1.52 W/ft2 (16.4 

W/m2

). The LPDs for each model type and zone and the associated Standard 90.1-2004

(ASHRAE 2004a) space type are listed in Table 3–9 and Table 3–10.

All models were assumed to have 3,014 W of exterior lighting. This value was adapted from 

data obtained from a big-box retailer. The exterior lighting system was controlled by an ambient 

light sensor, ensuring that the lights were on from dusk until dawn. Exterior lighting was 

modeled to more accurately determine building peak electrical demand. It had no impact on the 

results of this study.
11

Table 3–9 LPDs for Models With Refrigeration

Zone Standard 90.1-2004 Space Type

LPD

(W/ft2)

LPD

(W/m2)

Grocery Retail-sales area 1.7 18.3

Kitchen Food preparation 1.2 12.9

Office Office 1.1 11.8

Pharmacy Hospital-pharmacy 1.2 12.9

Restroom Restrooms 0.9 9.7

Sales 1 Retail-sales area 1.7 18.3

Sales 2 Retail-sales area 1.7 18.3

Sales 3 Retail-sales area 1.7 18.3

Sales 4 Retail-sales area 1.7 18.3

Stockroom Active storage 0.8 8.6

Vestibule Atrium 0.6 6.5

Walk-in freezer Retail-sales area 1.7 18.3

Total 1.53 16.5

Table 3–10 LPDs for Models Without Refrigeration

Zone Standard 90.1-2004 Space Type

LPD

(W/ft2)

LPD

(W/m2)

Office Office 1.1 11.8

Restroom Restrooms 0.9 9.7

Sales 1 Retail-sales area 1.7 18.3

Sales 2 Retail-sales area 1.7 18.3

Sales 3 Retail-sales area 1.7 18.3

Sales 4 Retail-sales area 1.7 18.3

Stockroom Active storage 0.8 8.6

Vestibule Atrium 0.6 6.5

Total 1.52 16.4

3.7 Heating, Ventilating, and Air Conditioning

3.7.1 System Type

Each zone was assumed to be conditioned by a packaged RTU. Each RTU model consisted of a 

fan, a two-stage direct expansion cooling coil, a single-stage gas-fired heat exchanger, and an 

OA mixer.

3.7.2 Rooftop Unit Performance Properties

Performance properties for all RTUs are shown in Table 3–11. The energy efficiency ratio was 

taken from Standard 90.1-2004 Table 6.8.1A (ASHRAE 2004a). The heating efficiency, heating 

fuel type, and economizer control type were taken from previous RTU-related work (Hale et al. 

2009). Additional assumptions included an internal static pressure drop of 0.42 in. w.c. (105 Pa), 

an external static pressure drop of 0.70 in. w.c. (174 Pa), and a total fan efficiency of 35%. 

These assumptions were based on previous engineering experience. Combined coefficients of 

performance (COPs) for the compressor and condenser were calculated for the models with 
12

refrigeration and the models without refrigeration based on their respective design fan flow rates

(see Section 3.7.4) and the above values for energy efficiency ratio, fan efficiency, and fan static 

pressure drop. Because of the differences in design fan flow rate (see Section 3.7.4) between the 

models with and without refrigeration, separate COP values for each model type were calculated 

and used to ensure that the overall RTU energy efficiency ratio met that specified by Standard 

90.1-2004 Table 6.8.1A (ASHRAE 2004a). For further information, see the methodology 

detailed in Hale et al.

Table 3–11 HVAC System Performance Values

HVAC Input Modeled Value

RTU energy efficiency ratio 10.1

Compressor/condenser combined COP for models with refrigeration 3.45

Compressor/condenser combined COP for models without refrigeration 3.36

Heating efficiency 80%

Heating fuel Natural gas

Fan static pressure 1.12 in. w.c. (279 Pa)

Fan mechanical efficiency: power gained by the air/power input to the fan 

motor 35%

Combined fan motor and belt efficiency 77%

Economizer control Differential dry-bulb

Five empirically derived curve fits were used to model the performance map of the direct 

expansion equipment. These described the unit’s cooling capacity and efficiency as functions of 

the cooling coil inlet air conditions, cooling coil airflow rate, and the condenser inlet air dry-bulb

temperature. The specific performance curves used for this study were derived from measured 

values obtained through laboratory testing of a 10-ton RTU (Kozubal et al. 2010).

3.7.3 Economizer

Differential dry-bulb economizers were included in all models and across all climate zones. The 

OA damper was modeled as having full modulating capability.

3.7.4 Sizing

EnergyPlus Runtime Language was used to size the cooling coil capacity and fan flow rate for 

each RTU. Cooling coil capacities for all models were sized to provide one ton of cooling for 

every 375 ft2 served (100.9 W/m2). Fan sizes, in terms of maximum volumetric flow rate, were

set to 1.2 cfm/ft2 (6.1 L/s∙m2

) of zone floor area for the models with refrigeration and to 1.0

cfm/ft2 (5.1 L/s∙m2) of zone floor area for the models without refrigeration. These values were 

based on engineering judgment and are meant to represent the typical RTU fan over sizing

observed in the retail sector. The heating coils were “autosized” using EnergyPlus’ built-in 

sizing algorithms.

We assumed that only 10-ton RTUs were used to condition the building. For example, if a zone 

required 20 tons of cooling, a single 20-ton RTU was simulated using 10-ton unit performance 

properties, thereby mimicking the performance of two, 10-ton units operating together to serve 

that zone.
13

3.7.5 Outdoor Air

OA supply flow rates for each zone were calculated in accordance with Standard 62.1-2004

(ASHRAE 2004b). Table 3–12 and Table 3–13 detail the OA design flow rates for both 

prototype models.

Table 3–12 OA Rates for Models With Refrigeration

Zone

Standard 62.1-2004

Equivalent Zone

OA per 

Area 

(cfm/ft2)

OA per 

Area 

(L/s∙m2)

OA per 

Person 

(cfm/person)

OA per 

Person 

(L/s∙person)

Total

OA

(cfm)

Total 

OA

(L/s)

Grocery Supermarket 0.06 0.305 7.5 3.540 1,881 888

Kitchen Sales 0.12 0.610 7.5 3.540 404 191

Office Office 0.06 0.305 5.0 2.360 375 177

Pharmacy Pharmacy 0.18 0.914 5.0 2.360 442 208

Restroom Sales 0.12 0.610 7.5 3.540 202 95

Sales 1 Sales 0.12 0.610 7.5 3.540 4,911 2,318

Sales 2 Sales 0.12 0.610 7.5 3.540 4,911 2,318

Sales 3 Sales 0.12 0.610 7.5 3.540 4,911 2,318

Sales 4 Sales 0.12 0.610 7.5 3.540 4,911 2,318

Stockroom Shipping/receiving 0.12 0.610 0.0 0.000 1,968 929

Vestibule Main entry lobbies 0.06 0.305 5.0 2.360 216 102

Walk-in freezer Sales 0.12 0.610 7.5 3.540 438 207

Total 0.11 0.562 6.4 3.029 25,569 12,068

Table 3–13 OA Rates for Models Without Refrigeration

Zone

Standard 62.1-2004

Equivalent Zone

OA per 

Area 

(cfm/ft2)

OA per 

Area 

(L/s∙m2)

OA per 

Person 

(cfm/person)

OA per 

Person 

(L/s∙person)

Total

OA

(cfm)

Total 

OA

(L/s)

Office Office 0.06 0.305 5.0 2.360 375 177

Restroom Sales 0.12 0.610 7.5 3.540 202 95

Sales 1 Sales 0.12 0.610 7.5 3.540 4,911 2,318

Sales 2 Sales 0.12 0.610 7.5 3.540 4,911 2,318

Sales 3 Sales 0.12 0.610 7.5 3.540 4,911 2,318

Sales 4 Sales 0.12 0.610 7.5 3.540 4,911 2,318

Stockroom Shipping/receiving 0.12 0.610 0.0 0.000 1,968 929

Vestibule Main entry lobbies 0.06 0.305 5.0 2.360 216 102

Total 0.11 0.582 6.4 3.015 22,405 10,574

3.7.6 Supply Fan

Each RTU supply fan was hard-sized to provide a maximum volumetric flow rate of 1.2 cfm/ft2

(6.1 L/s∙m

2

) of zone floor area for the models with refrigeration and 1.0 cfm/ft2 (5.1 L/s∙m

2

) of 

zone floor area for the models without refrigeration. The fan power at part-load was modeled 

according to ASHRAE 90.1-2004 Appendix G Table G3.1.3.15 Method 2 for the Part-Load Fan 

Power Equation (ASHRAE 2004a): 

Pfan = 0.0013 + 0.1470 × PLRfan + 0.9506 × (PLRfan)

2 - 0.0998 × (PLRfan)3 (3-2)
14

Where:

Pfan = fraction of full-load fan power

PLRfan = fan part-load ratio (current cfm/design cfm)

For all models with refrigeration, the RTU fan minimum flow rate was 0.7 cfm/ft2 (3.7 L/s∙m

2

) of 

zone floor area, a value equivalent to 60% of the design flow rate. The minimum RTU fan flow 

rate for the models without refrigeration was 0.4 cfm/ft2 (2.0 L/s∙m

2

) of zone floor area, a value 

equivalent to 40% of the design flow rate. The RTU fan minimum flow rate was kept higher in 

the models with refrigeration to prevent microclimates that the refrigerated cases would 

otherwise have created.

3.7.7 Control Logic

Typically, EnergyPlus models are run with simulation time steps set between 10 and 15 minutes, 

which is longer than the time the HVAC system normally takes to respond to changing building 

conditions. At the beginning of each time step, EnergyPlus’ traditional controls predict the exact 

amount of heating or cooling that will be needed for each thermal zone to reach the space set 

point. EnergyPlus then compares this value to the HVAC system capacity and runs the system at 

an artificial heating or cooling part-load ratio—taking into account coil cycling losses—to ensure 

that at the end of the time step, the zone temperature meets the space set point.

The downside to this type of control is that the fan is locked into a single, average operational 

flow rate during each 10- to 15-minute time step. Although this control scheme will accurately 

predict annual fan energy use, it cannot be used to compare the effects of certain dynamic fan 

operation strategies, as EnergyPlus limits the types of available fan control schemes.

To resolve this issue, custom EnergyPlus Runtime Language code was written to control RTU 

fan motor and coil operation, which enabled the study of stepped- and variable-speed RTU 

operation. The simulation time steps used for this study were set equal to 1 minute. Smaller 

time steps allowed us to more realistically reflect real-world stepped- and variable-speed RTU 

operation, where fan flow rates are adjusted on minute timescales in response to changing 

indoor, outdoor, and coil conditions.

The following subsections describe the EnergyPlus Runtime Language code that was used to 

control each RTU fan motor type. This code was adapted from real-world control logic to

characterize the energy performance of the investigated strategies across a broad array of 

building types and climates. As such, the control logic provided here was not tailored to a 

particular application; changes to the control logic for a particular installation may provide even 

greater energy savings than those presented in this report.

3.7.7.1 Constant-Speed Case

For the baseline case (constant-speed), the RTU fan speed was fixed at the design fan speed 

during occupied hours for all operating modes. The control logic narrative for the constantspeed fan motor case follows.

1. Deadband

a. During occupied hours, when the system was not in heating, economizing, or 

cooling mode, deadband mode was active.

i. The OA dampers were set to the minimum ventilation position.

ii. The heating and cooling coils were turned off.
15

b. During unoccupied hours, when the system was not in heating, economizing, or 

cooling mode, the RTU fan was turned off.

2. Heating

a. The heating coil was engaged when the zone temperature was below the heating 

set point (Tzone < Tset,heat).

i. During occupied hours, the OA dampers were set to the minimum 

ventilation position.

ii. During unoccupied hours, the OA dampers were closed.

iii. The RTU continued to heat the zone until the zone temperature was at 

least 1°F above the heating set point [Tzone ≥ (Tset,heat + 1°F)].

3. Economizing

a. If (1) the OA temperature was less than 65°F and greater than 50°F (50°F < TOA < 

65°F), and (2) the zone temperature was above the cooling set point by no more 

than 1°F [Tset,cool < Tzone ≤ (Tset,cool + 1°F)], economizing was engaged.

i. The OA dampers were set to 100% open.

ii. The cooling coils remained off.

iii. The RTU operated in economizer mode until either:

1. The OA temperature was less than or equal to 50°F (TOA ≤ 50°F), 

at which point the RTU entered Stage 1 cooling mode.

2. The OA temperature was greater than or equal to 65°F (TOA ≥ 

65°F), at which point the RTU entered Stage 1 cooling mode.

3. The zone temperature was at least 1°F below the cooling set point

[Tzone ≤ (Tset,cool – 1°F)], at which point the RTU entered deadband

mode.

4. The zone temperature was greater than 1°F above the cooling set 

point [Tzone > (Tset,cool + 1°F)], at which point the RTU entered 

Stage 2 cooling mode.

4. Cooling

a. Stage 1 cooling was engaged when the zone temperature rose above the cooling 

set point by no more than 1°F [Tset,cool < Tzone ≤ (Tset,cool + 1°F)] and the OA 

temperature was not between 50°F and 65°F (economizing condition).

i. The first compressor was engaged.

ii. The RTU remained in Stage 1 cooling until either:

1. The zone temperature was at least 1°F below the cooling set point

[Tzone ≤ (Tset,cool – 1°F)], at which point the RTU entered deadband

mode.

2. The zone temperature was greater than 1°F above the cooling set 

point [Tzone > (Tset,cool + 1°F)], at which point the RTU entered 

Stage 2 cooling mode. 

iii. During unoccupied hours, the OA dampers were closed.

b. Stage 2 cooling was engaged when the zone temperature was greater than 1°F

above the cooling set point [Tzone > (Tset,cool + 1°F)].

i. Both compressors were engaged.

ii. The RTU remained in Stage 2 cooling until the zone temperature was at 

least 1°F below the cooling set point [Tzone ≤ (Tset,cool – 1°F)], at which 

point the RTU entered deadband mode.
16

iii. During unoccupied hours, the OA dampers were closed, unless the OA 

temperature was less than 65°F and greater than 50°F (50°F < TOA < 

65°F), in which case the OA dampers were set to the minimum ventilation 

position.

c. During occupied hours, the OA dampers were set to the minimum ventilation 

position.

3.7.7.2 Stepped-Speed Case

For the stepped-speed case, the RTU fan was modeled with four fan speed steps: off, minimum

flow rate, reduced flow rate, and full flow rate. Minimum flow rate was used when the zone was 

in deadband operation, meaning that its HVAC system was not heating, cooling, or economizing. 

The minimum flow rates for both prototype models are detailed in Section 3.7.6. During Stage 1

cooling, the fan operated at a reduced flow rate equal to 80% of the design fan flow rate. This

equated to 1.0 cfm/ft2 (4.9 L/s∙m2) for the models with refrigeration and 0.8 cfm/ft2 (4.1 L/s∙m2) 

for those without refrigeration. Full flow rate was used when the RTU was in heating, 

economizing, or Stage 2 cooling mode. The control logic narrative for the stepped-speed fan 

motor case follows.

1. Deadband

a. During occupied hours, when the system was not in heating, economizing, or 

cooling mode, deadband mode was active.

i. The fan flow rate was set to minimum. If this flow rate proved 

insufficient to maintain a supply air temperature (SAT) of at least 50°F, 

the fan flow rate was increased to 80% of the design fan flow rate. If this 

flow rate was still insufficient, the fan flow rate was increased to 100% of 

the design fan flow rate.

ii. The OA dampers were modulated as appropriate to supply minimum 

ventilation.

iii. The heating and cooling coils were turned off.

b. During unoccupied hours, when the system was not in heating, economizing, or 

cooling mode, the RTU fan was turned off.

2. Heating

a. The heating coil was engaged when the zone temperature was below the heating 

set point [Tzone < Tset,heat].

i. The RTU fan flow rate was set equal to the design fan flow rate.

ii. During occupied hours, the OA dampers were set to the minimum 

ventilation position.

iii. During unoccupied hours, the OA dampers were closed.

iv. The RTU continued to heat the zone until the zone temperature was at 

least 1°F above the heating set point [Tzone ≥ (Tset,heat + 1°F)].

3. Economizing

a. If (1) the OA temperature was less than 65°F and greater than 50°F (50°F < TOA < 

65°F), and (2) the zone temperature was above the cooling set point by no more 

than 1°F [Tset,cool < Tzone ≤ (Tset,cool + 1°F)], economizing was engaged.

i. The RTU fan flow rate was set equal to the design fan flow rate.

ii. The OA dampers were set to 100% open.

iii. The cooling coils remained off.
17

iv. The RTU operated in economizer mode until either:

1. The OA temperature was less than or equal to 50°F (TOA ≤ 50°F), 

at which point the RTU entered Stage 1 cooling mode.

2. The OA temperature was greater than or equal to 65°F (TOA ≥ 

65°F), at which point the RTU entered Stage 1 cooling mode.

3. The zone temperature was at least 1°F below the cooling set point

[Tzone ≤ (Tset,cool – 1°F)], at which point the RTU entered deadband

mode.

4. The zone temperature was greater than 1°F above the cooling set 

point [Tzone > (Tset,cool + 1°F)], at which point the RTU entered 

Stage 2 cooling mode.

4. Cooling

a. Stage 1 cooling was engaged when the zone temperature rose above the cooling 

set point by no more than 1°F [Tset,cool < Tzone ≤ (Tset,cool + 1°F)] and the OA 

temperature was not between 50°F and 65°F (economizing condition).

i. The RTU fan flow rate was set equal to 80% of the design fan flow rate.

ii. The first compressor was engaged.

iii. The RTU remained in Stage 1 cooling until either:

1. The zone temperature was at least 1°F below the cooling set point

[Tzone ≤ (Tset,cool – 1°F)], at which point the RTU entered deadband

mode.

2. The zone temperature was greater than 1°F above the cooling set 

point [Tzone > (Tset,cool + 1°F)], at which point the RTU entered 

Stage 2 cooling mode.

iv. During unoccupied hours, the OA dampers were closed.

b. Stage 2 cooling was engaged when the zone temperature was greater than 1°F 

above the cooling set point [Tzone > (Tset,cool + 1°F)].

i. The RTU fan flow rate was set equal to the design fan flow rate.

ii. Both compressors were engaged.

iii. The RTU remained in Stage 2 cooling until the zone temperature was at 

least 1°F below the cooling set point [Tzone ≤ (Tset,cool – 1°F)], at which 

point the RTU entered deadband mode.

iv. During unoccupied hours, the OA dampers were closed, unless the OA 

temperature was less than 65°F and greater than 50°F (50°F < TOA < 

65°F), in which case the OA dampers were set to the minimum ventilation 

position.

c. During occupied hours, the OA dampers were modulated to supply minimum 

ventilation.

3.7.7.3 Variable-Speed Case

For the variable-speed case, the fan flow rate was continuously varied, as opposed to being 

operated in discrete steps. Minimum flow rate was used when the zone was in deadband 

operation, meaning that its HVAC system was not heating, cooling, or economizing. The 

minimum flow rates for both model types are detailed in Section 3.7.6. During Stage 1 cooling, 

the fan flow rate was varied in order to hold the SAT at 55°F. Full flow rate was used when the 

RTU was in heating, economizing, or Stage 2 cooling mode. The control logic narrative for the 

variable-speed case follows.
18

1. Deadband

a. During occupied hours, when the system was not in heating, economizing, or 

cooling mode, deadband mode was active.

i. The fan flow rate was set to minimum. If this flow rate proved 

insufficient to maintain a SAT of at least 50°F, the RTU fan flow rate was 

varied between minimum and maximum flow to raise the SAT to 50°F.

ii. The OA dampers were modulated as appropriate to supply minimum 

ventilation.

iii. The heating and cooling coils were turned off.

b. During unoccupied hours, when the system was not in heating, economizing, or 

cooling mode, the RTU fan was turned off.

2. Heating

a. The heating coil was engaged when the zone temperature was below the heating 

set point [Tzone < Tset,heat].

i. The RTU fan flow rate was set equal to the design fan flow rate.

ii. During occupied hours, the OA dampers were set to the minimum 

ventilation position.

iii. During unoccupied hours, the OA dampers were closed.

iv. The RTU continued to heat the zone until the zone temperature was at 

least 1°F above the heating set point [Tzone ≥ (Tset,heat + 1°F)].

3. Economizing

a. If (1) the OA temperature was less than 65°F and greater than 50°F (50°F < TOA < 

65°F), and (2) the zone temperature was above the cooling set point by no more 

than 1°F [Tset,cool < Tzone ≤ (Tset,cool + 1°F)], economizing was engaged.

i. The RTU fan flow rate was set equal to the design fan flow rate.

ii. The OA dampers were set to 100% open.

iii. The cooling coils remained off.

iv. The RTU operated in economizer mode until either:

1. The OA temperature was less than or equal to 50°F (TOA ≤ 50°F), 

at which point the RTU entered Stage 1 cooling mode.

2. The OA temperature was greater than or equal to 65°F (TOA ≥ 

65°F), at which point the RTU entered Stage 1 cooling mode.

3. The zone temperature was at least 1°F below the cooling set point

[Tzone ≤ (Tset,cool – 1°F)], at which point the RTU entered deadband

mode.

4. The zone temperature was greater than 1°F above the cooling set 

point [Tzone > (Tset,cool + 1°F)], at which point the RTU entered 

Stage 2 cooling mode.

4. Cooling

a. Stage 1 cooling was engaged when the zone temperature rose above the cooling 

set point by no more than 1°F [Tset,cool < Tzone ≤ (Tset,cool + 1°F)] and the OA 

temperature was not between 50°F and 65°F (economizing condition).

i. The RTU fan flow rate was modulated between minimum and maximum 

flow, such that the SAT was equal to 55°F.

ii. The first compressor was engaged.

iii. The RTU remained in Stage 1 cooling until either:
19

1. The zone temperature was at least 1°F below the cooling set point

[Tzone ≤ (Tset,cool – 1°F)], at which point the RTU entered deadband

mode.

2. The zone temperature was greater than 1°F above the cooling set 

point [Tzone > (Tset,cool + 1°F)], at which point the RTU entered 

Stage 2 cooling mode.

iv. During unoccupied hours, the OA dampers were closed.

b. Stage 2 cooling was engaged when the zone temperature was greater than 1°F 

above the cooling set point [Tzone > (Tset,cool + 1°F)].

i. The RTU fan flow rate was set equal to the design fan flow rate.

ii. Both compressors were engaged.

iii. The RTU remained in Stage 2 cooling until the zone temperature was at 

least 1°F below the cooling set point [Tzone ≤ (Tset,cool – 1°F)], at which 

point the RTU entered deadband mode.

iv. During unoccupied hours, the OA dampers were closed, unless the OA 

temperature was less than 65°F and greater than 50°F (50°F < TOA < 

65°F), in which case the OA dampers were set to the minimum ventilation 

position.

c. During occupied hours, the OA dampers were modulated to supply minimum 

ventilation.
20

4.0 Results

This section describes the simulation results3, including fan energy use, whole-building energy

use, electricity consumption, natural gas consumption, utility cost savings, and observed relative 

humidity (RH) values.

4.1 Fan Energy Savings

Table 4–1 and Table 4–2 detail the predicted fan energy savings by climate zone, using total fan 

energy use intensity (EUI) as the basis for the savings calculations. As expected, the steppedspeed cases show significant energy savings over the constant-speed cases; the variable-speed

cases show even greater savings in all climates.

Baseline fan energy use is constant across climate zones, because the supply fans were hardsized using a climate-independent methodology to represent typical RTU fan over sizing (see 

Section 3.7.4). 

Table 4–1 Normalized Annual Fan Energy Consumption for Models With Refrigeration

Climate 

Zone Location

Constant-Speed Fan Stepped-Speed Fan Variable-Speed Fan

Fan EUI 

(kBtu/ft2)

Fan EUI 

(kBtu/ft2)

Savings 

(%)

Fan EUI 

(kBtu/ft2)

Savings 

(%)

1A Miami, FL 9.0 6.4 28.9 5.0 44.3

2A Houston, TX 9.0 5.6 37.3 4.7 47.7

2B Phoenix, AZ 9.0 5.6 37.5 4.7 48.0

3A Atlanta, GA 9.0 5.0 44.4 4.2 53.1

3B Los Angeles, CA 9.0 4.6 49.0 4.1 54.6

3B Las Vegas, NV 9.0 5.3 41.4 4.5 50.4

3C San Francisco, CA 9.0 4.0 55.1 3.9 56.2

4A Baltimore, MD 9.0 4.9 45.7 4.3 51.9

4B Albuquerque, NM 9.0 4.8 46.6 4.2 53.7

4C Seattle, WA 9.0 4.2 52.9 4.1 54.5

5A Chicago, IL 9.0 4.8 46.6 4.3 51.9

5B Boulder, CO 9.0 4.6 48.3 4.2 52.7

6A Minneapolis, MN 9.0 4.9 44.9 4.5 49.9

6B Helena, MT 9.0 4.6 48.4 4.4 51.4

7 Duluth, MN 9.0 4.8 46.7 4.6 48.9

8 Fairbanks, AK 9.0 5.3 41.6 5.1 43.8

 

3 Note that additional differences between the models with and without refrigeration, such as zoning layout and the 

fan flow rate sizing methodology, affect the energy consumption and savings values. Readers should exercise 

caution when comparing results between model types.
21

Table 4–2 Normalized Annual Fan Energy Consumption for Models Without Refrigeration

Climate 

Zone Location

Constant-Speed Fan Stepped-Speed Fan Variable-Speed Fan

Fan EUI 

(kBtu/ft2)

Fan EUI 

(kBtu/ft2)

Savings 

(%)

Fan EUI 

(kBtu/ft2)

Savings 

(%)

1A Miami, FL 7.5 5.2 31.0 3.6 52.2

2A Houston, TX 7.5 4.1 44.6 3.0 59.7

2B Phoenix, AZ 7.5 4.1 45.6 3.1 58.8

3A Atlanta, GA 7.5 3.4 54.1 2.5 66.7

3B Los Angeles, CA 7.5 2.7 63.2 2.3 69.4

3B Las Vegas, NV 7.5 3.6 51.5 2.8 63.1

3C San Francisco, CA 7.5 1.9 74.3 1.9 75.0

4A Baltimore, MD 7.5 3.4 54.6 2.5 65.9

4B Albuquerque, NM 7.5 3.3 56.3 2.7 64.1

4C Seattle, WA 7.5 2.3 69.7 2.1 71.7

5A Chicago, IL 7.5 3.5 53.0 2.6 65.0

5B Boulder, CO 7.5 3.2 57.6 2.6 64.7

6A Minneapolis, MN 7.5 3.8 49.3 3.0 60.4

6B Helena, MT 7.5 3.2 56.7 2.7 63.7

7 Duluth, MN 7.5 3.7 51.2 3.0 59.9

8 Fairbanks, AK 7.5 4.2 44.5 3.7 50.7

4.2 Whole-Building Energy Savings

Figure 4–1 through Figure 4–4 provide whole-building energy consumption comparisons for the

stepped- and variable-speed cases, using total building EUI as the basis for the savings 

calculations. The figures also provide a breakdown of EUI by end use. Appendix B.1 includes

tables detailing these data. Annual whole-building energy savings ranged from 0.7%–8.4% and 

were seen in all climate zones when switching to stepped- or variable-speed fan motor

functionality.

Stepped- or variable-speed fan motor functionality decreased fan energy use in all climates, but

also increased heating energy use. This outcome is attributed to the need to make up for 

beneficial fan heat that is no longer imparted to the supply airstream during the heating season. 

For the stepped- and variable-speed cases, the fans are operated at full flow rate during heating 

mode, so this heat is lost primarily when the systems are in deadband operation and the fans are 

operating at their minimum flow rate.

Cooling energy does not uniformly increase or decrease as a result of switching to stepped- or 

variable-speed fan motor functionality; however, there is a strong correlation between an 

increase in cooling energy and a decrease in average space RH (see Section 4.6). This is to be 

expected. As the cooling coil face velocity is decreased because of a reduction in flow rate 

during Stage 1 cooling for the stepped- and variable-speed cases, the cooling coils have more

time to remove moisture from the airstream. This improvement in moisture removal 

effectiveness means more latent heat is removed from the airstream and subsequently more 

cooling energy is required to meet the zone temperature set point. For all locations, however, 

any increase in heating and cooling energy is always more than offset by the reduction in fan 

energy.
22

As shown in Table 4–3, whole-building energy savings vary from climate zone to climate zone

when switching to stepped- or variable-speed fan motor functionality. Table 4–3 also shows 

that, when comparing the stepped- and the variable-speed cases, whole-building energy savings 

do not vary in a similar manner. For example, the whole-building energy savings observed in 

Seattle, WA, for the stepped- and variable speed models without refrigeration are almost 

identical, whereas there is a very large energy savings difference between these two models in 

Phoenix, AZ.

These trends are attributable to two factors: (1) climatic differences and (2) differences in the 

fan control logic implemented in each case. For example, in Seattle, WA, both models would be 

expected to operate in deadband or economizing mode the majority of the year. In deadband 

mode, the RTU supply fans operate at their minimum flow rates in both the stepped- and 

variable-speed cases. In economizing mode, the fans in both cases operate at their design flow 

rates. Because the fans in both models would be expected to operate in an identical manner for 

the majority of the year, the magnitude of the whole-building energy savings would be expected 

to be similar.

In contrast, for Phoenix, AZ, the models would likely spend much of their time in Stage 1

cooling. Because the fan flow rates are reduced in both the stepped- and variable-speed cases 

during Stage 1 cooling, energy savings would be expected in both cases. However, because the 

variable-speed control logic allows a greater possible reduction in fan flow rate, the wholebuilding energy savings for the variable-speed model would be expected to be greater than the

savings for the stepped-speed model.

Examination of climate and associated impacts on RTU fan operation, as dictated by the casespecific control logic, can be used to explain the energy savings differences observed between 

the stepped- and variable-speed cases for the remaining climate zones.

Table 4–3 Annual Whole-Building Energy Savings for All Models (%)

Climate 

Zone Location

Models With Refrigeration Models Without Refrigeration

Stepped-Speed Variable-Speed Stepped-Speed Variable-Speed

1A Miami, FL 2.5 3.5 2.3 2.3

2A Houston, TX 3.2 4.0 3.6 3.6

2B Phoenix, AZ 3.5 4.7 4.1 5.2

3A Atlanta, GA 3.2 3.9 3.7 3.7

3B Los Angeles, CA 6.1 6.5 8.1 8.3

3B Las Vegas, NV 3.4 4.6 4.1 5.5

3C San Francisco, CA 5.8 5.9 8.3 8.4

4A Baltimore, MD 2.2 2.6 2.5 2.4

4B Albuquerque, NM 3.1 3.8 3.6 4.1

4C Seattle, WA 3.1 3.2 4.0 4.0

5A Chicago, IL 1.8 2.1 2.1 2.0

5B Boulder, CO 2.6 3.1 3.2 3.5

6A Minneapolis, MN 1.5 1.8 1.7 1.7

6B Helena, MT 1.8 2.1 2.3 2.4

7 Duluth, MN 1.1 1.2 1.4 1.3

8 Fairbanks, AK 0.7 0.7 0.9 0.9
23 

Figure 4–1 Models with refrigeration: annual whole-building EUI by end use for stepped-speed 

(Credit: Lesley Herrmann/NREL) 

2.5%

3.2%

3.5%

3.2%

6.1%

3.4%

5.8%

2.2%

3.1%

3.1%

1.8%

2.6%

1.5%

1.8%

1.1%

0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Annual Energy End Use Intensity (kBtu/ft2)

Case

Int Equip (elec) Int Light (elec) Ext Light (elec) Refrig (elec) Cooling (elec) Heating (gas) Fans (e
24

Figure 4–2 Models with refrigeration: annual whole-building EUI by end use for variable-speed cases

(Credit: Lesley Herrmann/NREL)

3.5%

4.0%

4.7%

3.9%

6.5%

4.6%

5.9%

2.6%

3.8%

3.2%

2.1%

3.1%

1.8%

2.1%

1.2%

0.7%

1A

2A

2B

3A

3B:CA

3B

3C

4A

4B

4C

5A

5B

6A

6B

7

8

0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Climate Zone

Annual Energy End Use Intensity (kBtu/ft2)

Case

Int Equip (elec) Int Light (elec) Ext Light (elec) Refrig (elec) Cooling (elec) Heating (gas) Fans (elec) Savings
25

Figure 4–3 Models without refrigeration: annual whole-building EUI by end use for stepped-speed cases

(Credit: Lesley Herrmann/NREL)

2.3%

3.6%

4.1%

3.7%

8.1%

4.1%

8.3%

2.5%

3.6%

4.0%

2.1%

3.2%

1.7%

2.3%

1.4%

0.9%

1A

2A

2B

3A

3B:CA

3B

3C

4A

4B

4C

5A

5B

6A

6B

7

8

0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Baseline

Stepped

Climate Zone

Annual Energy End Use Intensity (kBtu/ft2)

Case

Int Equip (elec) Int Light (elec) Ext Light (elec) Cooling (elec) Heating (gas) Fans (elec) Savings
26

Figure 4–4 Models without refrigeration: annual whole-building EUI by end use for variable-speed cases

(Credit: Lesley Herrmann/NREL)

2.3%

3.6%

5.2%

3.7%

8.3%

5.5%

8.4%

2.4%

4.1%

4.0%

2.0%

3.5%

1.7%

2.4%

1.3%

0.9%

1A

2A

2B

3A

3B:CA

3B

3C

4A

4B

4C

5A

5B

6A

6B

7

8

0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Baseline

Variable

Climate Zone

Annual Energy End Use Intensity (kBtu/ft2)

Case

Int Equip (elec) Int Light (elec) Ext Light (elec) Cooling (elec) Heating (gas) Fans (elec) Savings
27

4.3 Electricity Consumption Savings

Table 4–4 and Table 4–5 detail annual whole-building electricity consumption, normalized by 

floor area, for all models. The stepped- and variable-speed cases show less electricity 

consumption than do the constant-speed fan motor cases; the variable-speed cases outperform the 

stepped-speed cases in every location.

The electricity savings presented in Table 4–4 and Table 4–5 appear to be small when 

normalized by area, but whole-building electricity savings may be substantial given the size of 

commercial buildings. Annual electricity savings can be estimated for a specific building by 

multiplying the normalized electricity savings by the building floor area. Annual electricity 

savings of up to 200,000 kWh are predicted for the models used in this study.

Sector-wide savings potential can be approximated by averaging the savings estimates from the 

16 locations. For stepped-speed retrofits, the average savings was 1.17 kWh/ft2; for variablespeed retrofits, it was 1.23 kWh/ft2

. If these savings were realized across 10% of the 2.7 billion 

ft2 of retail space served by packaged RTUs (EIA 2008), retailers would save 316–332 GWh/yr 

(1.08–1.13 × 1012 Btu/yr).

Table 4–4 Normalized Annual Whole-Building Electricity Consumption for Models With 

Refrigeration

Climate 

Zone Location

Constant-Speed Fan Stepped-Speed Fan Variable-Speed Fan

Use

(kWh/ft2)

Use 

(kWh/ft2)

Savings 

(kWh/ft2)

Use 

(kWh/ft2)

Savings 

(kWh/ft2)

1A Miami, FL 26.51 25.85 0.66 25.57 0.94

2A Houston, TX 24.28 23.33 0.95 23.15 1.13

2B Phoenix, AZ 24.62 23.62 1.00 23.32 1.30

3A Atlanta, GA 21.96 20.82 1.14 20.66 1.30

3B Los Angeles, CA 20.55 19.24 1.31 19.15 1.40

3B Las Vegas, NV 23.08 21.97 1.11 21.69 1.39

3C San Francisco, CA 19.35 17.87 1.47 17.85 1.50

4A Baltimore, MD 21.10 19.90 1.19 19.79 1.31

4B Albuquerque, NM 20.86 19.62 1.24 19.43 1.43

4C Seattle, WA 19.35 17.94 1.41 17.91 1.44

5A Chicago, IL 20.38 19.16 1.22 19.06 1.32

5B Boulder, CO 19.98 18.67 1.30 18.55 1.42

6A Minneapolis, MN 20.13 18.95 1.18 18.85 1.28

6B Helena, MT 19.41 18.11 1.30 18.03 1.39

7 Duluth, MN 19.12 17.88 1.24 17.84 1.29

8 Fairbanks, AK 18.73 17.61 1.12 17.55 1.18
28

Table 4–5 Normalized Annual Whole-Building Electricity Consumption for Models Without 

Refrigeration

Climate 

Zone Location

Constant-Speed Fan Stepped-Speed Fan Variable-Speed Fan

Use

(kWh/ft2)

Use 

(kWh/ft2)

Savings 

(kWh/ft2)

Use 

(kWh/ft2)

Savings 

(kWh/ft2)

1A Miami, FL 21.95 21.45 0.50 21.44 0.51

2A Houston, TX 19.83 18.94 0.89 18.93 0.91

2B Phoenix, AZ 20.49 19.51 0.98 19.28 1.22

3A Atlanta, GA 17.65 16.53 1.11 16.51 1.13

3B Los Angeles, CA 16.13 14.74 1.38 14.72 1.41

3B Las Vegas, NV 19.16 18.03 1.13 17.75 1.41

3C San Francisco, CA 15.09 13.43 1.66 13.42 1.67

4A Baltimore, MD 16.95 15.79 1.16 15.71 1.24

4B Albuquerque, NM 16.91 15.68 1.23 15.51 1.40

4C Seattle, WA 15.23 13.68 1.55 13.66 1.57

5A Chicago, IL 16.31 15.18 1.14 15.04 1.27

5B Boulder, CO 16.08 14.79 1.29 14.64 1.44

6A Minneapolis, MN 16.11 15.05 1.06 14.91 1.20

6B Helena, MT 15.57 14.30 1.27 14.15 1.43

7 Duluth, MN 15.23 14.10 1.13 13.95 1.29

8 Fairbanks, AK 14.98 13.97 1.00 13.84 1.14

4.4 Natural Gas Consumption Savings

Table 4–6 and Table 4–7 detail whole-building natural gas consumption, normalized by floor

area, for all models. Negative values indicate an increase in natural gas use. Because of the 

decrease in fan energy in the stepped- and variable-speed cases, the heating energy requirement 

increased, leading to an increase in natural gas use in all models. 

Annual natural gas savings can be estimated for a specific building by multiplying the 

normalized natural gas savings contained in Table 4–6 and Table 4–7 by the building floor area. 

We performed this calculation and predict that the worst-case increase in natural gas use would

be 3,900 therm/yr for the models used in this study.

On average, annual natural gas use increased by 0.0149 therm/ft2 for the stepped-speed cases and 

by 0.0162 therm/ft2 for the variable-speed cases. If these savings were realized across 10% of 

the 2.7 billion ft2 of retail space served by packaged RTUs (EIA 2008), retailers would increase 

natural gas use by 4.0–4.4 million therm/yr (4.02–4.34 × 1011 Btu/yr).
29

Table 4–6 Normalized Annual Whole-Building Natural Gas Consumption* for Models With 

Refrigeration

Climate 

Zone Location

Constant-Speed Fan Stepped-Speed Fan Variable-Speed Fan

Use 

(therm/ft2)

Use 

(therm/ft2)

Savings 

(therm/ft2)

Use 

(therm/ft2)

Savings 

(therm/ft2)

1A Miami, FL 0.000 0.000 0.000 0.000 0.000

2A Houston, TX 0.030 0.034 –0.005 0.034 –0.005

2B Phoenix, AZ 0.018 0.022 –0.004 0.022 –0.004

3A Atlanta, GA 0.094 0.105 –0.012 0.105 –0.012

3B Los Angeles, CA 0.005 0.006 –0.002 0.006 –0.002

3B Las Vegas, NV 0.046 0.055 –0.009 0.055 –0.009

3C San Francisco, CA 0.040 0.049 –0.009 0.049 –0.010

4A Baltimore, MD 0.222 0.241 –0.020 0.242 –0.020

4B Albuquerque, NM 0.128 0.145 –0.017 0.145 –0.017

4C Seattle, WA 0.161 0.184 –0.023 0.184 –0.023

5A Chicago, IL 0.331 0.355 –0.023 0.355 –0.024

5B Boulder, CO 0.213 0.234 –0.021 0.234 –0.021

6A Minneapolis, MN 0.473 0.496 –0.023 0.496 –0.023

6B Helena, MT 0.361 0.387 –0.026 0.388 –0.026

7 Duluth, MN 0.591 0.620 –0.029 0.621 –0.029

8 Fairbanks, AK 1.017 1.043 –0.026 1.045 –0.028

*Negative values indicate that natural gas use increased.

Table 4–7 Normalized Annual Whole-Building Natural Gas Consumption* for Models Without 

Refrigeration

Climate 

Zone Location

Constant-Speed Fan Stepped-Speed Fan Variable-Speed Fan

Use 

(therm/ft2)

Use 

(therm/ft2)

Savings 

(therm/ft2)

Use 

(therm/ft2)

Savings 

(therm/ft2)

1A Miami, FL 0.000 0.000 0.000 0.000 0.000

2A Houston, TX 0.031 0.036 -0.005 0.037 -0.005

2B Phoenix, AZ 0.018 0.022 -0.005 0.022 -0.005

3A Atlanta, GA 0.097 0.109 -0.012 0.110 -0.013

3B Los Angeles, CA 0.006 0.007 -0.002 0.007 -0.002

3B Las Vegas, NV 0.045 0.055 -0.010 0.055 -0.010

3C San Francisco, CA 0.041 0.052 -0.011 0.052 -0.011

4A Baltimore, MD 0.229 0.249 -0.020 0.252 -0.023

4B Albuquerque, NM 0.130 0.147 -0.017 0.149 -0.019

4C Seattle, WA 0.167 0.193 -0.025 0.193 -0.026

5A Chicago, IL 0.344 0.364 -0.020 0.369 -0.025

5B Boulder, CO 0.218 0.237 -0.019 0.240 -0.023

6A Minneapolis, MN 0.491 0.509 -0.018 0.514 -0.023

6B Helena, MT 0.373 0.396 -0.023 0.400 -0.027

7 Duluth, MN 0.614 0.637 -0.023 0.643 -0.029

8 Fairbanks, AK 1.056 1.077 -0.021 1.081 -0.025

*Negative values indicate that natural gas use increased.

4.5 Utility Cost Savings

The energy savings values presented here depend on a number of assumptions, including the 

cooling coil and fan flow rate sizing methodology, sequence of operations, space set points, and
30

hours of operation. In order to provide broadly applicable findings, values were used that reflect 

common practice.

Appendix C provides instructions about how to use the results of this study to estimate high-level 

utility cost savings. A retailer can use such results to justify site-specific assessments of retrofit

feasibility and determine if a compelling business case can be made.

Assuming typical utility rates of $0.10/kWh and $1.00/therm, if average savings were realized

across 10% of the 2.7 billion ft2 of retail space served by packaged RTUs (EIA 2008), retailers 

would save $27.6 million annually with stepped-speed retrofits, or $28.8 million with variablespeed retrofits.

4.6 Relative Humidity

Table 4–8 and Table 4–9 detail the 95th percentile RH values for all models. These values were

chosen to exclude extreme outliers, but still provide an understanding of space maximum RH. 

RH values are reported for the “grocery” zone for the models with refrigeration and for the “sales 

1” zone for the models without refrigeration, as these represented the critical zones for each 

building type.

Active zone RH control was outside the scope of this study, and the lack of such control explains 

the high RH values observed in most models, particularly those seen in the humid “A” climate 

subzones. The models captured the effect on space RH caused by moisture condensing on the 

cooling coil surface as the coil met the zone sensible load. The models did not, however,

account for the re-entrainment of moisture into the airstream, which would have occurred in 

practice when the cooling coil was shut off and condensation on the cooling coil evaporated back 

into the airstream. Thus, the negative impact on space RH caused by frequent cooling coil 

cycling (and conversely, the RH benefit of switching to stepped- or variable-speed fan motor

functionality) was not fully captured. Therefore, RH improvements observed in most climate 

zones would likely be even greater in practice.

The reported RH values for the stepped- and variable-speed cases increase minimally in climate 

zones 3C and 8. These increases are negligible and are due to very slight differences in the zone

dry-bulb temperatures between cases.
31

Table 4–8 Models With Refrigeration: 95th Percentile RH Values

Climate 

Zone Location

Constant-Speed Fan 

RH (%)

Stepped-Speed Fan 

RH (%)

Variable-Speed Fan 

RH (%)

1A Miami, FL 72.5 71.9 70.2

2A Houston, TX 71.8 71.2 69.9

2B Phoenix, AZ 56.2 55.5 53.8

3A Atlanta, GA 66.7 66.2 64.5

3B Los Angeles, CA 59.2 58.9 58.0

3B Las Vegas, NV 42.2 42.0 42.0

3C San Francisco, CA 49.4 49.6 49.5

4A Baltimore, MD 67.8 67.3 65.6

4B Albuquerque, NM 48.3 47.9 46.7

4C Seattle, WA 50.8 50.9 50.3

5A Chicago, IL 63.1 62.7 61.1

5B Boulder, CO 46.8 46.5 45.8

6A Minneapolis, MN 63.0 62.7 61.0

6B Helena, MT 40.1 40.1 40.1

7 Duluth, MN 56.9 56.5 55.8

8 Fairbanks, AK 45.5 45.8 45.8

Table 4–9 Models Without Refrigeration: 95th Percentile RH Values

Climate 

Zone Location

Constant-Speed Fan 

RH (%)

Stepped-Speed Fan 

RH (%)

Variable-Speed Fan 

RH (%)

1A Miami, FL 73.2 72.4 69.5

2A Houston, TX 72.9 72.4 69.7

2B Phoenix, AZ 56.3 55.4 53.1

3A Atlanta, GA 69.2 68.0 63.7

3B Los Angeles, CA 63.2 62.6 60.7

3B Las Vegas, NV 45.8 45.7 45.3

3C San Francisco, CA 54.2 54.5 54.2

4A Baltimore, MD 70.1 69.2 65.5

4B Albuquerque, NM 51.7 51.0 49.7

4C Seattle, WA 55.6 55.5 54.8

5A Chicago, IL 66.4 65.5 61.3

5B Boulder, CO 49.8 49.3 48.7

6A Minneapolis, MN 67.1 65.9 62.0

6B Helena, MT 44.3 44.2 44.2

7 Duluth, MN 62.1 61.7 59.0

8 Fairbanks, AK 50.2 50.4 50.3
32

5.0 Conclusions

Our simulations showed annual whole-building and electric energy savings in all climate zones 

when constant-speed RTU fan motors were upgraded with stepped- or variable-speed 

functionality. Whole-building energy savings ranged from 0.7%–8.4%.

Normalized electricity savings ranged from 0.50–1.67 kWh/ft2 (1.70–5.70 kBtu/ft2

). Average 

annual electricity savings across all locations were 1.17 kWh/ft2 (3.98 kBtu/ft2) for the steppedspeed cases and 1.23 kWh/ft2 (4.40 kBtu/ft2

) for the variable-speed cases. The results suggest

that for certain building types, annual whole-building electricity savings of 200,000 kWh may be 

realized.

Heating energy increased in all climates, because less fan energy was imparted to the supply 

airstream during the heating season. On average, this increase was 0.0149 therm/ft2 for the 

stepped-speed cases and 0.0162 therm/ft2 for the variable-speed cases. (This increase was 

always more than offset by the electricity use reduction.)

Based on the average energy savings, if variable-speed retrofits were implemented across 10% of 

the 2.7 billion ft2 of retail space served by packaged RTUs (EIA 2008), retailers would save 

approximately 332 GWh/yr (1.13 × 1012 Btu/yr) of electricity and increase natural gas use by 4.4 

million therm/yr (4.34 × 1011 Btu/yr). Assuming typical utility rates of $0.10/kWh and 

$1.00/therm, this would equate to annual utility cost savings of $28.8 million.

This measure requires that a relatively small number of RTU fan motors be upgraded per 

building. Therefore, this report makes a case that such retrofits should be investigated in all 

climate zones to address the oftentimes dispersed energy loads in commercial buildings.
33

6.0 Next Steps

The energy savings values presented here depend on a number of assumptions, including the 

cooling coil and fan flow rate sizing methodology, sequence of operations, space set points, and

hours of operation. In order to provide broadly applicable findings, values were used that reflect 

common practice. 

Appendix C provides instructions about how to use the results of this study to estimate high-level 

utility cost savings. A retailer can use such results to justify site-specific assessments of retrofit 

feasibility and determine if a compelling business case can be made.

Indirect benefits may be sufficient to motivate retailers to pursue constant-speed RTU fan motor 

retrofits, especially for those who own or operate buildings in humid regions. Because moisture 

problems are largely attributed to short-cycling of oversized HVAC equipment, future work 

could focus on enhancing the EnergyPlus whole-building energy models to predict the effects of 

stepped- and variable-speed fan motor retrofits on moisture re-entrainment. For a retail building 

with moisture control issues, such modeling could yield recommendations about whether fan 

motor retrofits would significantly improve moisture control. Simulation would enable this 

analysis to span a range of climates and building types.

Physical testing could also improve the assessment of associated benefits. Whereas simulation 

can examine retrofit impacts over a wide range of conditions, carefully designed experimental 

testing could uncover important real-world considerations. Testing results could also be used to 

validate and improve the numerical models used for this study. By retrofitting a constant-speed 

RTU with variable-speed functionality, stepped- and variable-speed performance could be 

determined empirically to complement or refine this analysis. Using such techniques to capture 

moisture control advantages, component-specific impacts, and other drivers may accelerate

large-scale retailer investment in energy-saving RTU fan motor retrofits.

The development of an application guide to help retailers effectively execute stepped- and 

variable-speed RTU fan motor retrofits would also help to accelerate adoption of this technology. 

Ideally, such a guide would provide high-level implementation advice and be paired with 

manufacturer-created retrofit packages that would facilitate retrofit installation while maintaining 

the original equipment warranty. The development of such a solution would require involvement 

from RTU manufacturers, private sector retailers, and research and development organizations. 

While the level of collaboration required to successfully execute these tasks is significant, the 

potential benefits associated with this kind of a documentation/product solution pair warrant a 

closer examination of this path.
34

7.0 References

ASHRAE. (2004a). ANSI/ASHRAE/IESNA Standard 90.1-2004 Energy Standard for 

Buildings Except Low-Rise Residential Buildings. Atlanta, GA: American Society of Heating, 

Refrigerating and Air-Conditioning Engineers, Inc.

ASHRAE. (2004b). ASHRAE Standard 62.1-2004 Ventilation for Acceptable Indoor Air 

Quality. Atlanta, GA: American Society of Heating, Refrigerating and Air-Conditioning 

Engineers, Inc.

ASHRAE. (2009). 2009 ASHRAE Handbook—Fundamentals. Atlanta, GA: American Society 

of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

Briggs, R.S.; Lucas, R.G.; Taylor, Z.T. (2003). Climate Classification for Building Energy 

Codes and Standards: Part 1- Development Process. Richland, WA.

Deru, M.; Field, K.; Studer, D.; Benne, K.; Griffith, B.; Torcellini, P.; Liu, B.; Halverson, M.;

Winiarski, D.; Rosenberg, M.; Yazdanian, M.; Huang, J.; Crawley, D. (2011). U.S. Department 

of Energy Commercial Reference Building Models of the National Building Stock. Golden, CO: 

National Renewable Energy Laboratory. NREL/TP-5500-46861. 

DOE (2005). Map of DOE’s Proposed Climate Zones. Available at www.energycodes.gov/

implement/pdfs/color_map_climate_zones_Mar03. Last accessed July 2010.

DOE (2010). EnergyPlus Energy Simulation Software, Version 6.0. 

www.eere.energy.gov/buildings/energyplus/. Washington, D.C.: U.S. Department of Energy. 

EIA. (2008). 2003 Commercial Buildings Energy Consumption Survey Table B41. 

Washington, DC: Energy Information Administration. Available at www.eia.gov/emeu/cbecs/ 

cbecs2003/detailed_tables_2003/detailed_tables_2003.html. Last accessed September 2011.

Felts, Don R., Bailey, Patrick. (2000). The State of Affairs – Packaged Cooling Equipment in 

California. 2000 American Council for an Energy Efficient Economy Summer Study on Energy 

Efficiency in Buildings. Available at http://eec.ucdavis.edu/ACEEE/2000/PDFS/

PANEL03/233.pdf. Last accessed November 15, 2011.

Hale, E.; Leach, M.; Hirsch, A.; Torcellini, P. (2009). General Merchandise 50% Energy 

Savings: Technical Support Document. Golden, CO, National Renewable Energy Laboratory. 

NREL/TP-550-46100.

Kozubal, E.; Doebber, I.; Deru, M.; Page, J. (2010). Performance Mapping of Commercial 

Rooftop Units. Presentation given at the ASHRAE Winter Conference, January 24, 2010, 

Orlando, FL.

Yuill, G.K. (1996). Impact of High Use Automatic Doors on Infiltration. Project 763-TRP. 

Atlanta, GA: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.
35

Appendix A Schedules

A.1 Occupancy, Lighting, and Equipment Schedules

Occupancy, lighting, and equipment schedules are presented in Table A–1 and Figure A–1.

Table A–1 Occupancy, Lighting, and Equipment Schedules

Hour

Occupancy

(Percent of Peak)

Lighting

(Percent of Peak)

Plug Loads

(Percent of Peak)

1 0 5 40

2 0 5 40

3 0 5 40

4 0 5 40

5 0 5 40

6 0 5 40

7 0 5 40

8 30 25 95

9 50 100 95

10 70 100 95

11 90 100 95

12 90 100 95

13 90 100 95

14 70 100 95

15 70 100 95

16 70 100 95

17 90 100 95

18 90 100 95

19 70 100 95

20 70 100 95

21 50 100 95

22 50 100 95

23 30 100 95

24 0 25 40
36

Figure A–1 Occupancy, lighting, and equipment schedules

(Credit: Rachel Romero/NREL)

A.2 Heating and Cooling Set Point Schedules

Figure A–2 and Table A–2 detail the heating and cooling set point values for each hour of the 

day. Set point temperatures during occupied hours were 68°F (heating) and 74°F (cooling). 

During unoccupied hours, the set point temperatures were 59°F (heating) and 81°F (cooling). 

These set point schedules were applied seven days per week, year-round. 

Figure A–2 Heating and cooling set points

(Credit: Rachel Romero/NREL)

0%

20%

40%

60%

80%

100%

0 2 4 6 8 10 12 14 16 18 20 22 24

Percent of Peak Value

Hour

Occupancy

Lighting

Equipment

50

55

60

65

70

75

80

85

0 2 4 6 8 10 12 14 16 18 20 22 24

Temperature (°F)

Hour

Heating

Cooling
37

Table A–2 Heating and Cooling Set Points

Hour

Heating

(°F)

Heating

(°C)

Cooling

(°F)

Cooling

(°C)

1 59.0 15.0 81.0 27.2

2 59.0 15.0 81.0 27.2

3 59.0 15.0 81.0 27.2

4 59.0 15.0 81.0 27.2

5 59.0 15.0 81.0 27.2

6 59.0 15.0 81.0 27.2

7 59.0 15.0 81.0 27.2

8 68.0 20.0 74.0 23.3

9 68.0 20.0 74.0 23.3

10 68.0 20.0 74.0 23.3

11 68.0 20.0 74.0 23.3

12 68.0 20.0 74.0 23.3

13 68.0 20.0 74.0 23.3

14 68.0 20.0 74.0 23.3

15 68.0 20.0 74.0 23.3

16 68.0 20.0 74.0 23.3

17 68.0 20.0 74.0 23.3

18 68.0 20.0 74.0 23.3

19 68.0 20.0 74.0 23.3

20 68.0 20.0 74.0 23.3

21 68.0 20.0 74.0 23.3

22 68.0 20.0 74.0 23.3

23 59.0 15.0 81.0 27.2

24 59.0 15.0 81.0 27.2
38 

Appendix B Additional Results Tables

B.1 Detailed Whole-Building Results

Table B–1 Energy End Use Breakdown for Models With Refrigeration – IP Units

Climate 

Zone Location Model

Gas 

(kBtu/ft2∙yr) Electricity (kBtu/ft2∙yr)

Total 

(kBtu/ft2∙yr)

Savings 

Heating Cooling Fans (%)

Interior 

Lights

Exterior 

Lights Equipment Refrigeration

1A Miami, 

FL

Constant 0.0 23.7 9.0 30.2 0.1 14.9 12.6 90.5 –

Stepped 0.0 24.0 6.4 30.2 0.1 14.9 12.6 88.2 2.5

Variable 0.0 24.5 5.0 30.2 0.1 14.9 12.6 87.3 3.5

2A Houston, 

TX

Constant 3.0 16.8 9.0 30.2 0.1 14.9 11.9 85.8 –

Stepped 3.4 16.9 5.6 30.2 0.1 14.9 11.9 83.1 3.2

Variable 3.4 17.2 4.7 30.2 0.1 14.9 11.9 82.4 4.0

2B Phoenix, 

AZ

Constant 1.8 18.9 9.0 30.2 0.1 14.9 10.9 85.8 –

Stepped 2.2 18.9 5.6 30.2 0.1 14.9 10.9 82.7 3.5

Variable 2.2 18.8 4.7 30.2 0.1 14.9 10.9 81.7 4.7

3A Atlanta, 

GA

Constant 9.4 9.8 9.0 30.2 0.1 14.9 11.0 84.3 –

Stepped 10.5 9.9 5.0 30.2 0.1 14.9 11.0 81.6 3.2

Variable 10.5 10.2 4.2 30.2 0.1 14.9 10.9 81.0 3.9

3B Los Angeles, 

CA

Constant 0.5 4.8 9.0 30.2 0.1 14.9 11.1 70.6 –

Stepped 0.6 4.8 4.6 30.2 0.1 14.9 11.1 66.3 6.1

Variable 0.6 5.0 4.1 30.2 0.1 14.9 11.1 66.0 6.5

3B Las Vegas, 

NV

Constant 4.6 14.5 9.0 30.2 0.1 14.9 10.1 83.3 –

Stepped 5.5 14.5 5.3 30.2 0.1 14.9 10.1 80.5 3.4

Variable 5.5 14.3 4.5 30.2 0.1 14.9 10.1 79.5 4.6

3C San Francisco, 

CA

Constant 4.0 1.5 9.0 30.2 0.1 14.9 10.4 70.0 –

Stepped 4.9 1.4 4.0 30.2 0.1 14.9 10.4 65.9 5.8

Variable 4.9 1.4 3.9 30.2 0.1 14.9 10.4 65.8 5.9

4A Baltimore, 

MD

Constant 22.2 7.5 9.0 30.2 0.1 14.9 10.4 94.2 –

Stepped 24.1 7.5 4.9 30.2 0.1 14.9 10.4 92.1 2.2

Variable 24.2 7.7 4.3 30.2 0.1 14.9 10.4 91.7 2.6
39 

Table B–1 Energy End Use Breakdown for Models With Refrigeration – IP Units (Continued)

Climate 

Zone Location Model

Gas 

(kBtu/ft2∙yr) Electricity (kBtu/ft2∙yr)

Total 

(kBtu/ft2∙yr)

Savings 

Heating Cooling Fans (%)

Interior 

Lights

Exterior 

Lights Equipment Refrigeration

4B Albuquerque, 

NM

Constant 12.8 7.3 9.0 30.2 0.1 14.9 9.7 84.0 –

Stepped 14.5 7.3 4.8 30.2 0.1 14.9 9.7 81.4 3.1

Variable 14.5 7.3 4.2 30.2 0.1 14.9 9.7 80.8 3.8

4C Seattle, 

WA

Constant 16.1 1.9 9.0 30.2 0.1 14.9 10.0 82.1 –

Stepped 18.4 1.8 4.2 30.2 0.1 14.9 10.0 79.6 3.1

Variable 18.4 1.9 4.1 30.2 0.1 14.9 10.0 79.5 3.2

5A Chicago, 

IL

Constant 33.1 5.4 9.0 30.2 0.1 14.9 10.0 102.7 –

Stepped 35.5 5.4 4.8 30.2 0.1 14.9 10.0 100.8 1.8

Variable 35.5 5.5 4.3 30.2 0.1 14.9 10.0 100.5 2.1

5B Boulder, 

CO

Constant 21.3 4.6 9.0 30.2 0.1 14.9 9.4 89.5 –

Stepped 23.4 4.5 4.6 30.2 0.1 14.9 9.4 87.2 2.6

Variable 23.4 4.5 4.2 30.2 0.1 14.9 9.4 86.7 3.1

6A Minneapolis, 

MN

Constant 47.3 4.7 9.0 30.2 0.1 14.9 9.9 116.0 –

Stepped 49.6 4.7 4.9 30.2 0.1 14.9 9.9 114.2 1.5

Variable 49.6 4.8 4.5 30.2 0.1 14.9 9.9 113.9 1.8

6B Helena, 

MT

Constant 36.1 2.9 9.0 30.2 0.1 14.9 9.2 102.4 –

Stepped 38.7 2.8 4.6 30.2 0.1 14.9 9.2 100.5 1.8

Variable 38.8 2.8 4.4 30.2 0.1 14.9 9.2 100.3 2.1

7A Duluth, 

MN

Constant 59.1 1.8 9.0 30.2 0.1 14.9 9.3 124.4 –

Stepped 62.0 1.7 4.8 30.2 0.1 14.9 9.3 123.0 1.1

Variable 62.1 1.8 4.6 30.2 0.1 14.9 9.3 122.9 1.2

8A Fairbanks, 

AK

Constant 101.7 0.8 9.0 30.2 0.1 14.9 8.9 165.6 –

Stepped 104.3 0.8 5.3 30.2 0.1 14.9 8.9 164.4 0.7

Variable 104.5 0.8 5.1 30.2 0.1 14.9 8.9 164.4 0.7
40 

Table B–2 Energy End Use Breakdown for Models Without Refrigeration – IP Units

Climate 

Zone Location Model

Gas 

(kBtu/ft2∙yr) Electricity (kBtu/ft2∙yr)

Total 

(kBtu/ft2∙yr)

Savings 

Heating Cooling Fans (%)

Interior 

Lights

Exterior 

Lights Equipment

1A Miami, 

FL

Constant 0.0 24.5 7.5 30.0 0.2 12.8 74.9 –

Stepped 0.0 25.1 5.2 30.0 0.2 12.8 73.2 2.3

Variable 0.0 26.6 3.6 30.0 0.2 12.8 73.2 2.3

2A Houston, 

TX

Constant 3.1 17.3 7.5 30.0 0.2 12.8 70.8 –

Stepped 3.6 17.5 4.1 30.0 0.2 12.8 68.2 3.6

Variable 3.7 18.6 3.0 30.0 0.2 12.8 68.3 3.6

2B Phoenix, 

AZ

Constant 1.8 19.5 7.5 30.0 0.2 12.8 71.7 –

Stepped 2.2 19.6 4.1 30.0 0.2 12.8 68.8 4.1

Variable 2.2 19.8 3.1 30.0 0.2 12.8 68.0 5.2

3A Atlanta, 

GA

Constant 9.7 9.8 7.5 30.0 0.2 12.8 69.9 –

Stepped 10.9 10.0 3.4 30.0 0.2 12.8 67.3 3.7

Variable 11.0 10.9 2.5 30.0 0.2 12.8 67.3 3.7

3B Los Angeles, 

CA

Constant 0.6 4.6 7.5 30.0 0.2 12.8 55.6 –

Stepped 0.7 4.6 2.7 30.0 0.2 12.8 51.1 8.1

Variable 0.7 5.0 2.3 30.0 0.2 12.8 51.0 8.3

3B Las Vegas, 

NV

Constant 4.5 14.9 7.5 30.0 0.2 12.8 69.9 –

Stepped 5.5 14.9 3.6 30.0 0.2 12.8 67.1 4.1

Variable 5.5 14.8 2.8 30.0 0.2 12.8 66.1 5.5

3C San Francisco, 

CA

Constant 4.1 1.1 7.5 30.0 0.2 12.8 55.6 –

Stepped 5.2 0.9 1.9 30.0 0.2 12.8 51.0 8.3

Variable 5.2 1.0 1.9 30.0 0.2 12.8 51.0 8.4

4A Baltimore, 

MD

Constant 22.9 7.4 7.5 30.0 0.2 12.8 80.7 –

Stepped 24.9 7.5 3.4 30.0 0.2 12.8 78.8 2.5

Variable 25.2 8.1 2.5 30.0 0.2 12.8 78.8 2.4
41 

Table B–2 Energy End Use Breakdown for Models Without Refrigeration – IP Units (Continu

Climate 

Zone Location Model 

Gas 

(kBtu/ft2·yr) Electricity (kBtu/ft2·yr) 

Heating Cooling Fans 

Interior Lights Exterior Lights Equipment 

4B Albuquerque, NM 

Constant 13.0 7.3 7.5 30.0 0.2 12.8 

Stepped 14.7 7.3 3.3 30.0 0.2 12.8 Variable 14.9 7.3 2.7 30.0 0.2 12.8 

4C Seattle, WA 

Constant 16.7 1.5 7.5 30.0 0.2 12.8 

Stepped 19.3 1.5 2.3 30.0 0.2 12.8 Variable 19.3 1.5 2.1 30.0 0.2 12.8 

5A Chicago, IL 

Constant 34.4 5.2 7.5 30.0 0.2 12.8 

Stepped 36.4 5.3 3.5 30.0 0.2 12.8 Variable 36.9 5.7 2.6 30.0 0.2 12.8 

5B Boulder, CO 

Constant 21.8 4.4 7.5 30.0 0.2 12.8 

Stepped 23.7 4.3 3.2 30.0 0.2 12.8 Variable 24.0 4.3 2.6 30.0 0.2 12.8 

6A Minneapolis, MN 

Constant 49.1 4.5 7.5 30.0 0.2 12.8 

Stepped 50.9 4.6 3.8 30.0 0.2 12.8 Variable 51.4 5.0 3.0 30.0 0.2 12.8 

6B Helena, MT 

Constant 37.3 2.7 7.5 30.0 0.2 12.8 

Stepped 39.6 2.6 3.2 30.0 0.2 12.8 Variable 40.0 2.6 2.7 30.0 0.2 12.8 

7A Duluth, MN 

Constant 61.4 1.5 7.5 30.0 0.2 12.8 

Stepped 63.7 1.5 3.7 30.0 0.2 12.8 Variable 64.3 1.6 3.0 30.0 0.2 12.8 

8A Fairbanks, AK 

Constant 105.6 0.6 7.5 30.0 0.2 12.8 

Stepped 107.7 0.5 4.2 30.0 0.2 12.8 Variable 108.1 0.6 3.7 30.0 0.2 12.8 
42 

Table B–3 Energy End Use Breakdown for Models With Refrigeration – SI Units

Climate 

Zone Location Model

Gas 

(MJ/m2∙yr) Electricity (MJ/m2∙yr)

Total 

(MJ/m2∙yr)

Savings 

Heating Cooling Fans (%)

Interior 

Lights

Exterior 

Lights Equipment Refrigeration

1A Miami, 

FL

Constant 0.2 269.7 102.7 343.6 1.5 169.3 143.9 1,031.0 –

Stepped 0.3 273.6 73.1 343.6 1.5 169.3 143.9 1,005.2 2.5

Variable 0.3 279.0 57.2 343.6 1.5 169.3 143.6 994.5 3.5

2A Houston, 

TX

Constant 33.9 191.6 102.5 343.6 1.5 169.3 135.5 977.9 –

Stepped 39.1 193.0 64.3 343.6 1.5 169.3 135.5 946.3 3.2

Variable 39.2 196.5 53.7 343.6 1.5 169.3 135.4 939.1 4.0

2B Phoenix, 

AZ

Constant 20.0 215.8 102.5 343.6 1.5 169.3 124.3 977.1 –

Stepped 24.5 215.4 64.1 343.6 1.5 169.3 124.3 942.8 3.5

Variable 24.6 214.6 53.3 343.6 1.5 169.3 124.2 931.1 4.7

3A Atlanta, 

GA

Constant 106.7 111.9 102.4 343.6 1.4 169.3 124.9 960.3 –

Stepped 120.0 113.1 57.0 343.6 1.4 169.3 124.9 929.3 3.2

Variable 120.1 115.9 48.1 343.6 1.4 169.3 124.7 923.2 3.9

3B Los Angeles, 

CA

Constant 5.4 55.2 102.3 343.6 1.6 169.3 126.7 804.2 –

Stepped 7.3 54.5 52.2 343.6 1.6 169.3 126.7 755.3 6.1

Variable 7.3 56.8 46.5 343.6 1.6 169.3 126.6 751.7 6.5

3B Las Vegas, 

NV

Constant 52.1 165.4 102.5 343.6 1.7 169.3 114.6 949.2 –

Stepped 62.8 164.8 60.0 343.6 1.7 169.3 114.6 916.7 3.4

Variable 62.7 163.2 50.9 343.6 1.7 169.3 114.6 905.9 4.6

3C San Francisco, 

CA

Constant 45.2 16.8 102.1 343.6 1.6 169.3 118.8 797.4 –

Stepped 56.0 15.6 45.9 343.6 1.6 169.3 118.9 750.9 5.8

Variable 56.0 15.9 44.8 343.6 1.6 169.3 118.9 750.1 5.9

4A Baltimore, 

MD

Constant 252.5 84.9 102.3 343.6 1.6 169.3 118.5 1,072.7 –

Stepped 275.1 85.3 55.6 343.6 1.6 169.3 118.5 1,048.9 2.2

Variable 275.5 87.2 49.2 343.6 1.6 169.3 118.3 1,044.7 2.6
43 

Table B–3 Energy End Use Breakdown for Models With Refrigeration – SI Units (Continued)

Climate 

Zone Location Model

Gas 

(MJ/m2∙yr) Electricity (MJ/m2∙yr)

Total 

(MJ/m2∙yr)

Savings 

Heating Cooling Fans (%)

Interior 

Lights

Exterior 

Lights Equipment Refrigeration

4B Albuquerque, 

NM

Constant 145.8 83.4 102.3 343.6 1.6 169.3 110.7 956.7 –

Stepped 164.8 82.8 54.6 343.6 1.6 169.3 110.7 927.4 3.1

Variable 165.1 82.9 47.3 343.6 1.6 169.3 110.6 920.4 3.8

4C Seattle, 

WA

Constant 183.4 21.6 102.1 343.6 1.6 169.3 114.0 935.6 –

Stepped 209.3 20.7 48.2 343.6 1.6 169.3 114.0 906.7 3.1

Variable 209.5 21.2 46.4 343.6 1.6 169.3 114.0 905.6 3.2

5A Chicago, 

IL

Constant 377.4 61.1 102.3 343.6 1.6 169.3 114.5 1,169.9 –

Stepped 404.1 61.2 54.7 343.6 1.6 169.3 114.5 1,149.0 1.8

Variable 404.4 62.9 49.2 343.6 1.6 169.3 114.4 1,145.4 2.1

5B Boulder, 

CO

Constant 243.0 52.5 102.3 343.6 1.6 169.3 107.4 1,019.6 –

Stepped 267.0 51.3 52.9 343.6 1.6 169.3 107.4 993.1 2.6

Variable 266.6 51.2 48.3 343.6 1.6 169.3 107.3 988.0 3.1

6A Minneapolis, 

MN

Constant 538.8 53.3 102.4 343.6 1.5 169.3 112.5 1,321.4 –

Stepped 564.9 53.2 56.4 343.6 1.5 169.3 112.5 1,301.5 1.5

Variable 565.1 54.8 51.3 343.6 1.5 169.3 112.4 1,298.0 1.8

6B Helena, 

MT

Constant 411.7 33.4 102.3 343.6 1.5 169.3 104.7 1,166.5 –

Stepped 441.1 32.4 52.8 343.6 1.5 169.3 104.7 1,145.4 1.8

Variable 441.6 32.1 49.7 343.6 1.5 169.3 104.7 1,142.5 2.1

7A Duluth, 

MN

Constant 673.8 20.3 102.3 343.6 1.6 169.3 106.3 1,417.3 –

Stepped 706.3 19.8 54.6 343.6 1.6 169.3 106.3 1,401.5 1.1

Variable 707.3 20.4 52.2 343.6 1.6 169.3 106.3 1,400.7 1.2

8A Fairbanks, 

AK

Constant 1,158.9 9.6 102.6 343.6 1.5 169.3 101.5 1,887.0 –

Stepped 1,188.3 8.8 59.9 343.6 1.5 169.3 101.5 1,873.0 0.7

Variable 1,191.2 8.8 57.7 343.6 1.5 169.3 101.5 1,873.6 0.7
44 

Table B–4 Energy End Use Breakdown for Models Without Refrigeration – SI Units

Climate 

Zone Location Model

Gas 

(MJ/m2∙yr) Electricity (MJ/m2∙yr)

Total 

(MJ/m2∙yr)

Savings 

Heating Cooling Fans (%)

Interior 

Lights

Exterior 

Lights Equipment

1A Miami, 

FL

Constant 0.3 278.8 85.1 341.6 1.8 146.1 853.7 –

Stepped 0.4 285.9 58.7 341.6 1.8 146.1 834.4 2.3

Variable 0.4 303.4 40.6 341.6 1.8 146.1 833.8 2.3

2A Houston, 

TX

Constant 35.7 196.6 85.1 341.6 1.8 146.1 806.8 –

Stepped 41.2 199.8 47.1 341.6 1.8 146.1 777.6 3.6

Variable 41.7 212.2 34.3 341.6 1.8 146.1 777.6 3.6

2B Phoenix, 

AZ

Constant 20.1 222.2 85.1 341.6 1.8 146.1 816.9 –

Stepped 25.3 222.8 46.3 341.6 1.8 146.1 783.8 4.1

Variable 25.3 225.0 35.1 341.6 1.8 146.1 774.8 5.2

3A Atlanta, 

GA

Constant 110.2 111.5 85.1 341.6 1.7 146.1 796.2 –

Stepped 123.6 114.4 39.1 341.6 1.7 146.1 766.5 3.7

Variable 124.9 124.2 28.3 341.6 1.7 146.1 766.9 3.7

3B Los Angeles, 

CA

Constant 6.3 52.3 85.1 341.6 1.9 146.1 633.3 –

Stepped 8.4 52.3 31.3 341.6 1.9 146.1 581.7 8.1

Variable 8.4 56.6 26.0 341.6 1.9 146.1 580.7 8.3

3B Las Vegas,

NV

Constant 51.7 170.3 85.1 341.6 2.0 146.1 796.7 –

Stepped 63.0 170.1 41.2 341.6 2.0 146.1 764.0 4.1

Variable 63.2 168.9 31.4 341.6 2.0 146.1 753.3 5.5

3C San Francisco, 

CA

Constant 47.1 12.1 85.1 341.6 1.9 146.1 633.8 –

Stepped 59.1 10.7 21.9 341.6 1.9 146.1 581.2 8.3

Variable 59.1 10.9 21.2 341.6 1.9 146.1 580.8 8.4

4A Baltimore, 

MD

Constant 261.1 84.3 85.1 341.6 1.9 146.1 920.0 –

Stepped 283.4 85.8 38.7 341.6 1.9 146.1 897.4 2.5

Variable 286.8 92.2 29.1 341.6 1.9 146.1 897.7 2.4
45 

Table B–4 Energy End Use Breakdown for Models Without Refrigeration – SI Units (Continued)

Climate 

Zone Location Model

Gas 

(MJ/m2∙yr) Electricity (MJ/m2∙yr)

Total 

(MJ/m2∙yr)

Savings 

Heating Cooling Fans (%)

Interior 

Lights

Exterior 

Lights Equipment

4B Albuquerque, 

NM

Constant 147.9 82.8 85.1 341.6 1.9 146.1 805.3 –

Stepped 167.0 82.8 37.1 341.6 1.9 146.1 776.5 3.6

Variable 169.3 83.0 30.6 341.6 1.9 146.1 772.5 4.1

4C Seattle, 

WA

Constant 190.7 17.5 85.1 341.6 1.9 146.1 782.8 –

Stepped 219.7 16.6 25.8 341.6 1.9 146.1 751.6 4.0

Variable 220.4 17.4 24.1 341.6 1.9 146.1 751.4 4.0

5A Chicago, 

IL

Constant 391.7 59.5 85.1 341.6 1.9 146.1 1,025.9 –

Stepped 414.7 60.4 40.0 341.6 1.9 146.1 1,004.7 2.1

Variable 420.1 65.4 29.8 341.6 1.9 146.1 1,004.9 2.0

5B Boulder, 

CO

Constant 248.1 50.4 85.1 341.6 1.9 146.1 873.2 –

Stepped 270.0 49.4 36.1 341.6 1.9 146.1 845.1 3.2

Variable 273.9 49.5 30.0 341.6 1.9 146.1 843.0 3.5

6A Minneapolis, 

MN

Constant 559.2 51.6 85.2 341.6 1.8 146.1 1,185.5 –

Stepped 579.8 52.3 43.2 341.6 1.8 146.1 1,164.8 1.7

Variable 585.6 56.5 33.7 341.6 1.8 146.1 1,165.3 1.7

6B Helena, 

MT

Constant 425.1 30.8 85.2 341.6 1.8 146.1 1,030.5 –

Stepped 450.9 29.7 36.9 341.6 1.8 146.1 1,007.0 2.3

Variable 456.1 29.6 30.9 341.6 1.8 146.1 1,006.1 2.4

7A Duluth, 

MN

Constant 699.5 17.5 85.3 341.6 1.9 146.1 1,291.8 –

Stepped 725.5 17.0 41.6 341.6 1.9 146.1 1,273.7 1.4

Variable 732.2 18.5 34.2 341.6 1.9 146.1 1,274.4 1.3

8A Fairbanks, 

AK

Constant 1,203.1 7.2 85.6 341.6 1.8 146.1 1,785.4 –

Stepped 1,226.6 6.2 47.5 341.6 1.8 146.1 1,769.9 0.9

Variable 1,232.0 6.3 42.2 341.6 1.8 146.1 1,770.0 0.9
46

B.2 Sizing

Table B–5 Cooling Coil Sizing Results by Zone for Models With Refrigeration – tons

Zone

Climate Zone

1A 2A 2B 3A 3BCA 3BNV 3C 4A 4B 4C 5A 5B 6A 6B 7 8

Grocery 43.3 43.3 43.3 43.3 43.3 43.3 43.3 43.3 43.3 43.3 43.3 43.3 43.3 43.3 43.3 43.3

Kitchen 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.8

Office 12.0 12.0 12.0 12.0 12.0 12.0 12.0 12.0 12.0 12.0 12.0 12.0 12.0 12.0 12.0 12.0

Pharmacy 5.2 5.2 5.2 5.2 5.2 5.2 5.2 5.2 5.2 5.2 5.2 5.2 5.2 5.2 5.2 5.2

Restroom 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4

Sales 1 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3

Sales 2 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3

Sales 3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3

Sales 4 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3

Stockroom 43.7 43.7 43.7 43.7 43.7 43.7 43.7 43.7 43.7 43.7 43.7 43.7 43.7 43.7 43.7 43.7

Vestibule 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4

Walk-in freezer 5.2 5.2 5.2 5.2 5.2 5.2 5.2 5.2 5.2 5.2 5.2 5.2 5.2 5.2 5.2 5.2

Table B–6 Cooling Coil Sizing Results by Zone for Models With Refrigeration – ft2/ton

Zone

Climate Zone

1A 2A 2B 3A 3BCA 3BNV 3C 4A 4B 4C 5A 5B 6A 6B 7 8

Grocery 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375

Kitchen 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375

Office 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375

Pharmacy 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375

Restroom 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375

Sales 1 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375

Sales 2 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375

Sales 3 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375

Sales 4 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375

Stockroom 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375

Vestibule 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375

Walk-in freezer 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375
47

Table B–7 Cooling Coil Sizing Results by Zone for Models With Refrigeration – kW

Zone

Climate Zone

1A 2A 2B 3A 3BCA 3BNV 3C 4A 4B 4C 5A 5B 6A 6B 7 8

Grocery 152 152 152 152 152 152 152 152 152 152 152 152 152 152 152 152

Kitchen 17 17 17 17 17 17 17 17 17 17 17 17 17 17 17 17

Office 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42

Pharmacy 18 18 18 18 18 18 18 18 18 18 18 18 18 18 18 18

Restroom 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8

Sales 1 205 205 205 205 205 205 205 205 205 205 205 205 205 205 205 205

Sales 2 205 205 205 205 205 205 205 205 205 205 205 205 205 205 205 205

Sales 3 205 205 205 205 205 205 205 205 205 205 205 205 205 205 205 205

Sales 4 205 205 205 205 205 205 205 205 205 205 205 205 205 205 205 205

Stockroom 154 154 154 154 154 154 154 154 154 154 154 154 154 154 154 154

Vestibule 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19

Walk-in freezer 18 18 18 18 18 18 18 18 18 18 18 18 18 18 18 18

Table B–8 Cooling Coil Sizing Results by Zone for Models Without Refrigeration – tons

Zone

Climate Zone

1A 2A 2B 3A 3BCA 3BNV 3C 4A 4B 4C 5A 5B 6A 6B 7 8

Office 22.0 22.0 22.0 22.0 22.0 22.0 22.0 22.0 22.0 22.0 22.0 22.0 22.0 22.0 22.0 22.0

Restroom 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4

Sales 1 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3

Sales 2 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3

Sales 3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3

Sales 4 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3 58.3

Stockroom 35.1 35.1 35.1 35.1 35.1 35.1 35.1 35.1 35.1 35.1 35.1 35.1 35.1 35.1 35.1 35.1

Vestibule 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4
48

Table B–9 Cooling Coil Sizing Results by Zone for Models Without Refrigeration – ft2/ton

Zone

Climate Zone

1A 2A 2B 3A 3BCA 3BNV 3C 4A 4B 4C 5A 5B 6A 6B 7 8

Office 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375

Restroom 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375

Sales 1 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375

Sales 2 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375

Sales 3 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375

Sales 4 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375

Stockroom 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375

Vestibule 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375 375

Table B–10 Cooling Coil Sizing Results by Zone for Models Without Refrigeration – kW

Zone

Climate Zone

1A 2A 2B 3A 3BCA 3BNV 3C 4A 4B 4C 5A 5B 6A 6B 7 8

Office 77 77 77 77 77 77 77 77 77 77 77 77 77 77 77 77

Restroom 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8

Sales 1 205 205 205 205 205 205 205 205 205 205 205 205 205 205 205 205

Sales 2 205 205 205 205 205 205 205 205 205 205 205 205 205 205 205 205

Sales 3 205 205 205 205 205 205 205 205 205 205 205 205 205 205 205 205

Sales 4 205 205 205 205 205 205 205 205 205 205 205 205 205 205 205 205

Stockroom 123 123 123 123 123 123 123 123 123 123 123 123 123 123 123 123

Vestibule 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19
49

Table B–11 Heating Coil Sizing Results by Zone for Models With Refrigeration – kBtu/h

Zone

Climate Zone

1A 2A 2B 3A 3BCA 3BNV 3C 4A 4B 4C 5A 5B 6A 6B 7 8

Grocery 804 839 790 828 806 776 821 869 712 838 889 740 901 809 893 973

Kitchen 94 101 94 102 94 94 97 108 88 102 114 94 117 105 117 131

Office 219 226 214 222 219 209 223 232 191 225 235 196 237 212 234 252

Pharmacy 101 110 102 110 102 101 106 117 96 111 123 102 127 114 127 143

Restroom 47 51 47 51 47 47 49 54 44 51 57 47 58 53 58 66

Sales 1 1,138 1,233 1,140 1,237 1,147 1,137 1,183 1,313 1,070 1,240 1,380 1,143 1,420 1,280 1,417 1,595

Sales 2 1,138 1,233 1,140 1,237 1,147 1,137 1,183 1,313 1,070 1,240 1,380 1,143 1,420 1,280 1,417 1,595

Sales 3 1,138 1,233 1,140 1,237 1,147 1,137 1,183 1,313 1,070 1,240 1,380 1,143 1,420 1,280 1,417 1,595

Sales 4 1,138 1,233 1,140 1,237 1,147 1,137 1,183 1,313 1,070 1,240 1,380 1,143 1,420 1,280 1,417 1,595

Stockroom 813 850 800 840 815 785 831 881 722 849 902 751 915 822 907 991

Vestibule 100 104 98 102 100 96 102 107 88 104 109 91 111 99 110 119

Walk-in freezer 101 110 102 110 102 101 105 117 95 111 123 102 127 114 126 142

Table B–12 Heating Coil Sizing Results by Zone for Models With Refrigeration – Btu/h∙ft2

Zone

Climate Zone

1A 2A 2B 3A 3BCA 3BNV 3C 4A 4B 4C 5A 5B 6A 6B 7 8

Grocery 49.5 51.6 48.6 51.0 49.6 47.7 50.5 53.5 43.8 51.5 54.7 45.5 55.4 49.8 54.9 59.9

Kitchen 52.0 56.4 52.1 56.6 52.4 52.0 54.1 60.0 48.9 56.7 63.1 52.3 64.9 58.5 64.8 72.9

Office 48.7 50.2 47.6 49.3 48.8 46.5 49.5 51.5 42.3 50.0 52.2 43.5 52.6 47.2 52.0 56.0

Pharmacy 52.1 56.4 52.2 56.7 52.5 52.0 54.1 60.1 49.0 56.8 63.2 52.4 65.1 58.6 65.0 73.1

Restroom 52.0 56.4 52.1 56.6 52.4 52.0 54.1 60.0 48.9 56.7 63.1 52.3 64.9 58.5 64.8 72.9

Sales 1 52.0 56.4 52.1 56.6 52.4 52.0 54.1 60.0 48.9 56.7 63.1 52.3 64.9 58.5 64.8 72.9

Sales 2 52.0 56.4 52.1 56.6 52.4 52.0 54.1 60.0 48.9 56.7 63.1 52.3 64.9 58.5 64.8 72.9

Sales 3 52.0 56.4 52.1 56.6 52.4 52.0 54.1 60.0 48.9 56.7 63.1 52.3 64.9 58.5 64.8 72.9

Sales 4 52.0 56.4 52.1 56.6 52.4 52.0 54.1 60.0 48.9 56.7 63.1 52.3 64.9 58.5 64.8 72.9

Stockroom 49.6 51.8 48.8 51.2 49.7 47.9 50.7 53.7 44.0 51.7 55.0 45.8 55.8 50.1 55.3 60.4

Vestibule 49.3 51.2 48.3 50.5 49.4 47.4 50.2 52.9 43.4 51.1 54.0 45.0 54.7 49.1 54.1 58.8

Walk-in freezer 52.0 56.4 52.1 56.6 52.4 52.0 54.1 60.0 48.9 56.7 63.1 52.3 64.9 58.5 64.8 72.9
50

Table B–13 Heating Coil Sizing Results by Zone for Models With Refrigeration – kW

Zone

Climate Zone

1A 2A 2B 3A 3BCA 3BNV 3C 4A 4B 4C 5A 5B 6A 6B 7 8

Grocery 236 246 232 243 236 227 241 255 209 245 260 217 264 237 262 285

Kitchen 27 30 27 30 28 27 29 32 26 30 33 28 34 31 34 38

Office 64 66 63 65 64 61 65 68 56 66 69 57 69 62 69 74

Pharmacy 30 32 30 32 30 30 31 34 28 32 36 30 37 34 37 42

Restroom 14 15 14 15 14 14 14 16 13 15 17 14 17 15 17 19

Sales 1 333 361 334 363 336 333 347 385 314 363 405 335 416 375 415 468

Sales 2 333 361 334 363 336 333 347 385 314 363 405 335 416 375 415 468

Sales 3 333 361 334 363 336 333 347 385 314 363 405 335 416 375 415 468

Sales 4 333 361 334 363 336 333 347 385 314 363 405 335 416 375 415 468

Stockroom 238 249 234 246 239 230 244 258 212 249 264 220 268 241 266 290

Vestibule 29 30 29 30 29 28 30 31 26 30 32 27 32 29 32 35

Walk-in freezer 30 32 30 32 30 30 31 34 28 32 36 30 37 33 37 42

Table B–14 Heating Coil Sizing Results by Zone for Models Without Refrigeration – kBtu/h

Zone

Climate Zone

1A 2A 2B 3A 3BCA 3BNV 3C 4A 4B 4C 5A 5B 6A 6B 7 8

Office 338 350 331 345 338 324 344 361 296 349 368 306 372 334 368 399

Restroom 40 44 40 44 40 40 42 47 38 44 50 41 52 47 52 59

Sales 1 967 1063 976 1073 977 979 1013 1143 929 1072 1214 1003 1254 1132 1255 1427

Sales 2 967 1063 976 1073 977 979 1013 1143 929 1072 1214 1003 1254 1132 1255 1427

Sales 3 967 1063 976 1073 977 979 1013 1143 929 1072 1214 1003 1254 1132 1255 1427

Sales 4 967 1063 976 1073 977 979 1013 1143 929 1072 1214 1003 1254 1132 1255 1427

Stockroom 549 579 543 575 552 535 564 605 495 579 623 518 635 571 630 693

Vestibule 84 88 83 87 84 81 86 91 75 88 94 78 95 86 95 104
51

Table B–15 Heating Coil Sizing Results by Zone for Models Without Refrigeration – Btu/h∙ft2

Zone

Climate Zone

1A 2A 2B 3A 3BCA 3BNV 3C 4A 4B 4C 5A 5B 6A 6B 7 8

Office 40.9 42.4 40.1 41.8 41.0 39.3 41.7 43.8 35.9 42.3 44.5 37.1 45.1 40.4 44.6 48.3

Restroom 44.2 48.6 44.6 49.1 44.7 44.8 46.3 52.3 42.5 49.0 55.5 45.9 57.3 51.7 57.4 65.3

Sales 1 44.2 48.6 44.6 49.1 44.7 44.8 46.3 52.3 42.5 49.0 55.5 45.9 57.3 51.7 57.4 65.3

Sales 2 44.2 48.6 44.6 49.1 44.7 44.8 46.3 52.3 42.5 49.0 55.5 45.9 57.3 51.7 57.4 65.3

Sales 3 44.2 48.6 44.6 49.1 44.7 44.8 46.3 52.3 42.5 49.0 55.5 45.9 57.3 51.7 57.4 65.3

Sales 4 44.2 48.6 44.6 49.1 44.7 44.8 46.3 52.3 42.5 49.0 55.5 45.9 57.3 51.7 57.4 65.3

Stockroom 41.8 44.0 41.3 43.7 42.0 40.7 42.9 46.0 37.6 44.1 47.4 39.4 48.3 43.4 47.9 52.7

Vestibule 41.5 43.5 40.8 43.0 41.6 40.2 42.4 45.2 37.0 43.4 46.4 38.6 47.1 42.3 46.7 51.1

Table B–16 Heating Coil Sizing Results by Zone for Models Without Refrigeration – kW

Zone

Climate Zone

1A 2A 2B 3A 3BCA 3BNV 3C 4A 4B 4C 5A 5B 6A 6B 7 8

Office 99 103 97 101 99 95 101 106 87 102 108 90 109 98 108 117

Restroom 12 13 12 13 12 12 12 14 11 13 15 12 15 14 15 17

Sales 1 283 312 286 314 286 287 297 335 272 314 356 294 368 332 368 418

Sales 2 283 312 286 314 286 287 297 335 272 314 356 294 368 332 368 418

Sales 3 283 312 286 314 286 287 297 335 272 314 356 294 368 332 368 418

Sales 4 283 312 286 314 286 287 297 335 272 314 356 294 368 332 368 418

Stockroom 161 170 159 168 162 157 165 177 145 170 183 152 186 167 185 203

Vestibule 25 26 24 26 25 24 25 27 22 26 28 23 28 25 28 30
52

B.3 Fan Energy Savings (SI Units)

Table B–17 Normalized Annual Fan Energy Consumption for Models With Refrigeration

Climate 

Zones Cities

Constant-Speed Fan Stepped-Speed Fan Variable-Speed Fan

Fan EUI

(MJ/m2)

Fan EUI 

(MJ/m2)

Savings

(%)

Fan EUI 

(MJ/m2)

Savings

(%)

1A Miami, FL 102.3 72.8 28.9 57.0 44.3

2A Houston, TX 102.1 64.0 37.3 53.5 47.7

2B Phoenix, AZ 102.2 63.9 37.5 53.1 48.0

3A Atlanta, GA 102.0 56.8 44.4 47.9 53.1

3B Los Angeles, CA 102.0 52.0 49.0 46.3 54.6

3B Las Vegas, NV 102.1 59.8 41.4 50.7 50.4

3C San Francisco, CA 101.8 45.8 55.1 44.6 56.2

4A Baltimore, MD 101.9 55.4 45.7 49.0 51.9

4B Albuquerque, NM 102.0 54.4 46.6 47.2 53.7

4C Seattle, WA 101.8 48.0 52.9 46.3 54.5

5A Chicago, IL 101.9 54.5 46.6 49.0 51.9

5B Boulder, CO 101.9 52.7 48.3 48.2 52.7

6A Minneapolis, MN 102.0 56.2 44.9 51.1 49.9

6B Helena, MT 101.9 52.6 48.4 49.5 51.4

7 Duluth, MN 101.9 54.4 46.7 52.1 48.9

8 Fairbanks, AK 102.2 59.7 41.6 57.5 43.8

Table B–18 Normalized Annual Fan Energy Consumption for Models Without Refrigeration

Climate 

Zones Cities

Constant-Speed Fan Stepped-Speed Fan Variable-Speed Fan

Fan EUI

(MJ/m2)

Fan EUI 

(MJ/m2)

Savings

(%)

Fan EUI 

(MJ/m2)

Savings

(%)

1A Miami, FL 84.8 58.5 31.0 40.5 52.2

2A Houston, TX 84.8 46.9 44.6 34.2 59.7

2B Phoenix, AZ 84.8 46.1 45.6 34.9 58.8

3A Atlanta, GA 84.8 38.9 54.1 28.2 66.7

3B Los Angeles, CA 84.8 31.2 63.2 25.9 69.4

3B Las Vegas, NV 84.8 41.1 51.5 31.3 63.1

3C San Francisco, CA 84.8 21.8 74.3 21.2 75.0

4A Baltimore, MD 84.8 38.5 54.6 29.0 65.9

4B Albuquerque, NM 84.8 37.0 56.3 30.5 64.1

4C Seattle, WA 84.8 25.7 69.7 24.0 71.7

5A Chicago, IL 84.8 39.9 53.0 29.7 65.0

5B Boulder, CO 84.8 36.0 57.6 29.9 64.7

6A Minneapolis, MN 84.9 43.1 49.3 33.6 60.4

6B Helena, MT 84.9 36.8 56.7 30.8 63.7

7 Duluth, MN 85.0 41.5 51.2 34.1 59.9

8 Fairbanks, AK 85.3 47.3 44.5 42.1 50.7
53

B.4 Electricity Consumption Savings (SI Units)

Table B–19 Normalized Annual Whole-Building Electricity Consumption for Models With 

Refrigeration

Climate 

Zones Cities

Constant-Speed Fan Stepped-Speed Fan Variable-Speed Fan

Use

(kWh/m2)

Use 

(kWh/m2)

Savings 

(kWh/m2)

Use 

(kWh/m2)

Savings 

(kWh/m2)

1A Miami, FL 285.4 278.2 7.1 275.3 10.1

2A Houston, TX 261.4 251.2 10.2 249.2 12.2

2B Phoenix, AZ 265.0 254.2 10.7 251.0 14.0

3A Atlanta, GA 236.3 224.1 12.3 222.3 14.0

3B Los Angeles, CA 221.2 207.1 14.1 206.1 15.1

3B Las Vegas, NV 248.4 236.4 11.9 233.5 14.9

3C San Francisco, CA 208.3 192.4 15.9 192.2 16.1

4A Baltimore, MD 227.1 214.2 12.8 213.0 14.1

4B Albuquerque, NM 224.5 211.1 13.4 209.1 15.4

4C Seattle, WA 208.3 193.1 15.2 192.7 15.5

5A Chicago, IL 219.4 206.2 13.2 205.2 14.2

5B Boulder, CO 215.0 201.0 14.0 199.7 15.3

6A Minneapolis, MN 216.7 203.9 12.7 202.9 13.7

6B Helena, MT 209.0 195.0 14.0 194.1 14.9

7 Duluth, MN 205.8 192.5 13.4 192.0 13.9

8 Fairbanks, AK 201.6 189.6 12.0 189.0 12.6

Table B–20 Normalized Annual Whole-Building Electricity Consumption for Models Without 

Refrigeration

Climate 

Zones Cities

Constant-Speed Fan Stepped-Speed Fan Variable-Speed Fan

Use

(kWh/m2)

Use 

(kWh/m2)

Savings 

(kWh/m2)

Use

(kWh/m2)

Savings 

(kWh/m2)

1A Miami, FL 236.3 230.9 5.4 230.8 5.5

2A Houston, TX 213.5 203.9 9.6 203.7 9.8

2B Phoenix, AZ 220.6 210.0 10.6 207.5 13.1

3A Atlanta, GA 189.9 178.0 12.0 177.7 12.2

3B Los Angeles, CA 173.6 158.7 14.9 158.4 15.2

3B Las Vegas, NV 206.3 194.1 12.2 191.0 15.2

3C San Francisco, CA 162.4 144.5 17.9 144.4 18.0

4A Baltimore, MD 182.4 170.0 12.5 169.1 13.3

4B Albuquerque, NM 182.0 168.7 13.3 167.0 15.0

4C Seattle, WA 163.9 147.3 16.6 147.0 16.9

5A Chicago, IL 175.6 163.4 12.2 161.9 13.7

5B Boulder, CO 173.1 159.2 13.8 157.6 15.5

6A Minneapolis, MN 173.4 162.0 11.4 160.5 12.9

6B Helena, MT 167.6 154.0 13.7 152.3 15.3

7 Duluth, MN 164.0 151.8 12.2 150.1 13.9

8 Fairbanks, AK 161.2 150.4 10.8 148.9 12.3
54

B.5 Natural Gas Consumption Savings (SI Units)

Table B–21 Normalized Annual Whole-Building Natural Gas Consumption* for Models With 

Refrigeration

Climate 

Zones Cities

Constant-Speed Fan Stepped-Speed Fan Variable-Speed Fan

Use

(MJ/m2)

Use

(MJ/m2)

Savings

(MJ/m2) Use (MJ/m2)

Savings 

(MJ/m2)

1A Miami, FL 0.2 0.3 0.0 0.3 0.0

2A Houston, TX 33.9 39.1 –5.3 39.2 –5.3

2B Phoenix, AZ 20.0 24.5 –4.6 24.6 –4.6

3A Atlanta, GA 106.7 120.0 –13.3 120.1 –13.4

3B Los Angeles, CA 5.4 7.3 –2.0 7.3 –2.0

3B Las Vegas, NV 52.1 62.8 –10.7 62.7 –10.7

3C San Francisco, CA 45.2 56.0 –10.8 56.0 –10.8

4A Baltimore, MD 252.5 275.1 –22.5 275.5 –22.9

4B Albuquerque, NM 145.8 164.8 –19.0 165.1 –19.3

4C Seattle, WA 183.4 209.3 –26.0 209.5 –26.1

5A Chicago, IL 377.4 404.1 –26.7 404.4 –26.9

5B Boulder, CO 243.0 267.0 –24.1 266.6 –23.7

6A Minneapolis, MN 538.8 564.9 –26.1 565.1 –26.3

6B Helena, MT 411.7 441.1 –29.5 441.6 –29.9

7 Duluth, MN 673.8 706.3 –32.5 707.3 –33.5

8 Fairbanks, AK 1,158.9 1,188.3 –29.4 1,191.2 –32.3

*Negative values indicate that natural gas use increased.
55

Table B–22 Normalized Annual Whole-Building Natural Gas Consumption* for Models Without 

Refrigeration

Climate 

Zones Cities

Constant-Speed Fan Stepped-Speed Fan Variable-Speed Fan

Use

(MJ/m2)

Use

(MJ/m2)

Savings

(MJ/m2)

Use

(MJ/m2)

Savings 

(MJ/m2)

1A Miami, FL 0.3 0.4 0.0 0.4 0.0

2A Houston, TX 35.7 41.2 –5.5 41.7 –6.0

2B Phoenix, AZ 20.1 25.3 –5.1 25.3 –5.2

3A Atlanta, GA 110.2 123.6 –13.4 124.9 –14.8

3B Los Angeles, CA 6.3 8.4 –2.1 8.4 –2.1

3B Las Vegas, NV 51.7 63.0 –11.3 63.2 –11.5

3C San Francisco, CA 47.1 59.1 –12.0 59.1 –12.0

4A Baltimore, MD 261.1 283.4 –22.3 286.8 –25.8

4B Albuquerque, NM 147.9 167.0 –19.1 169.3 –21.4

4C Seattle, WA 190.7 219.7 –29.0 220.4 –29.7

5A Chicago, IL 391.7 414.7 –22.9 420.1 –28.4

5B Boulder, CO 248.1 270.0 –21.8 273.9 –25.8

6A Minneapolis, MN 559.2 579.8 –20.7 585.6 –26.5

6B Helena, MT 425.1 450.9 –25.8 456.1 –31.0

7 Duluth, MN 699.5 725.5 –26.0 732.2 –32.7

8 Fairbanks, AK 1,203.1 1,226.6 –23.5 1,232.0 –28.9

*Negative values indicate that natural gas use increased.
56

Appendix C How to Calculate Preliminary Utility Cost Savings

Retail building managers and engineers can use this appendix to calculate preliminary utility cost 

savings associated with stepped- and variable-speed RTU fan motor retrofits. These high-level 

results are approximate, but can be used to justify site-specific assessments of retrofit feasibility. 

They may also help to present a compelling business case for fan motor upgrades.

Use Table C–1 and the following steps to estimate the annual whole-building utility cost savings 

for your buildings.

Table C–1 Annual Whole Building Energy Savings (%) for All Models

Climate 

Zone Location

Models With Refrigeration Models Without Refrigeration

Stepped-Speed Variable-Speed Stepped-Speed Variable-Speed

1A Miami, FL 2.5 3.5 2.3 2.3

2A Houston, TX 3.2 4.0 3.6 3.6

2B Phoenix, AZ 3.5 4.7 4.1 5.2

3A Atlanta, GA 3.2 3.9 3.7 3.7

3B Los Angeles, CA 6.1 6.5 8.1 8.3

3B Las Vegas, NV 3.4 4.6 4.1 5.5

3C San Francisco, CA 5.8 5.9 8.3 8.4

4A Baltimore, MD 2.2 2.6 2.5 2.4

4B Albuquerque, NM 3.1 3.8 3.6 4.1

4C Seattle, WA 3.1 3.2 4.0 4.0

5A Chicago, IL 1.8 2.1 2.1 2.0

5B Boulder, CO 2.6 3.1 3.2 3.5

6A Minneapolis, MN 1.5 1.8 1.7 1.7

6B Helena, MT 1.8 2.1 2.3 2.4

7 Duluth, MN 1.1 1.2 1.4 1.3

8 Fairbanks, AK 0.7 0.7 0.9 0.9

Step 1: Select the climate zone that best matches your building location. 

Step 2: If your building has significant refrigeration loads, choose values from the columns 

labeled “Models With Refrigeration.” Otherwise, choose values from the columns 

labeled “Models Without Refrigeration.”

Step 3: Select the fan motor functionality for which you are interested in estimating savings. 

Then identify the whole-building annual energy savings value for that case from Table 

C–1. 

Step 4: Use Table C–2 to calculate the utility cost savings for your building.

Table C–2 High-Level Calculation Methodology

Annual Building Energy 

Costs 

($/year)

Whole-Building Annual 

Energy Savings 

(%)

Annual Energy Cost 

Savings 

($/year)

X =