7B-i

APPENDIX 7B. ENERGY USE IN COMMERICAL APPLICATIONS

TABLE OF CONTENTS

7B-1 INTRODUCTION .........................................................................................................7B-1

7B-2 ANSI/ASHRAE STANDARD FOR THERMAL COMFORT.....................................7B-1

7B-3 NATIONAL SOLAR RADIATION DATA .................................................................7B-2

7B-4 EQUATIONS AND CALCULATIONS .......................................................................7B-8

LIST OF TABLES

Table 7B-3.1 Weather Stations Classified as Desert .........................................................7B-6

Table 7B-4.1 Regression Equations...................................................................................7B-9

Table 7B-4.2 Building Types and Abbreviations ............................................................7B-10

Table 7B-4.3 Building Schedules and Abbreviations......................................................7B-10

Table 7B-4.4 Equations for Portable AC Operating Hours by Building Type and 

Schedule, Non-Desert Locations ...............................................................7B-11

Table 7B-4.5 Equations for Portable AC Operating Hour by Building Type and 

Schedule, Desert Locations........................................................................7B-12

Table 7B-4.6 CBECS 2003 Building Codes Matched to Building Types in Portable 

AC Equations.............................................................................................7B-13

LIST OF FIGURES

Figure 7B-2.1 ANSI/SHRAE Standard 55-2004: Thermal Environmental Conditions 

for Human Occupancy .................................................................................7B-1

Figure 7B-3.1 National Solar Radiation Database Stations................................................7B-3

Figure 7B-3.2 Hours that Exceeded ASHRAE Standard 55 Comfort Zone in Palm 

Springs CA, 1991.........................................................................................7B-5

Figure 7B-3.3 Hours that Exceeded ASHRAE Standard 55Comfort Zone Compared 

to CLDD.......................................................................................................7B-6

Figure 7B-3.4 Hours that Exceeded ASHRAE Standard 55 Comfort Zone versus

CLDD Highlighting Various Regions .........................................................7B-8

Figure 7B-4.1 Hours that Exceeded ANSI/ASHRAE Standard 55 Comfort Zone as a 

Function of Cooling Degree-Days, Continental United States....................7B-9
7B-1

APPENDIX 7B. ENERGY USE IN COMMERICAL APPLICATIONS

7B-1 INTRODUCTION

This appendix describes the method the U.S. Department of Energy (DOE) used to 

calculate the energy use of portable air conditioners (ACs) installed in commercial applications. 

DOE applied data regarding local cooling degree-days to the commercial buildings it sampled 

from the Energy Information Administration's 2003 Commercial Buildings Energy Consumption 

Survey (CBECS).

1 DOE calculated the annual operating hours for portable ACs in each sampled 

commercial building by establishing a relationship between cooling degree-days and operating 

hours for various combinations of building type and building schedule. DOE focused on 

buildings that have no central air conditioning, as reported in the 2003 CBECS.

7B-2 ANSI/ASHRAE STANDARD FOR THERMAL COMFORT

DOE assumed that a portable AC is operated when outdoor air conditions exceed the 

comfort zone described by ANSI/ASHRAE Standard 55-2004, Thermal Environmental 

Conditions for Human Occupancy (see Figure 7B-2.1).

2

Figure 7B-2.1 ANSI/SHRAE Standard 55-2004: Thermal 

Environmental Conditions for Human 

Occupancy

ANSI/ASHRAE Standard 55 is based on the following assumptions.

 Metabolic rates of occupants are 1.1 met (occupants are engaged in near-sedentary 

physical activity).
7B-2

 Occupants are wearing 0.5 clo of clothing insulation, a level typical of clothing worn 

when the outdoor environment is warm.

 Air speeds are not greater than 0.20 m/s (40 ft/min).

 Humidity is at or near the upper recommended limit, and the humidity ratio is 0.012. 

The range of operative temperatures presented in Figure 7B-2.1 reflects an assumed 80-

percent rate of occupant acceptance. That percentage reflects a 10-percent dissatisfaction 

criterion for a general (whole-body) thermal comfort index based on a combination of two 

indexes. Predicted mean vote (PMV) is an index that predicts the mean value of the votes of a 

large group of persons on a seven-point thermal sensation scale. The predicted percentage of 

dissatisfied (PPD) index establishes a quantitative prediction of the percentage of people 

dissatisfied with the thermal environment determined from PMV. The overall index is termed the 

PMV-PPD index. An additional average 10-percent rate of dissatisfaction may occur from local 

(partial-body) thermal discomfort. A portable air conditioner is assumed to operate if outdoor 

conditions exceed the outdoor comfort zone, as defined by a W (humidity ratio) greater than 

0.012, or a T (temperature) that exceeds Tcomf for that humidity ratio. Tcomf is given by the 

following equation.

where W is the humidity ratio of outdoor conditions for a given hour.

To estimate how often outdoor conditions exceed ANSI/SHRAE Standard 55-2004

(OH55), DOE used the following equation.

OH55 = (a * CDD) + b

Where:

OH55 = average annual hours when outdoor air conditions exceed the ASHRAE 

Standard 55 comfort zone, 

CDD = the number of annual cooling degree-days (65 °F) for a given location, and

a and b = linear fit parameters.

7B-3 NATIONAL SOLAR RADIATION DATA 

To estimate portable air conditioner (AC) operation and energy use in buildings from the 

CBECS sample, DOE used data on cooling degree-days (CDDs) from the National Solar 

Radiation Database (NSRDB) for 1991–2005.

3 The 1991–2005 NSRDB, which is an update of 

the 1961–1990 NSRDB database, is an hourly ground-based database of solar and 

meteorological fields for 1,454 NSRDB stations. The data, which provide a complete 15-year 

period of record for 858 sites. The NSRDB stations are divided into three classes (see Figure 7B3.1).
7B-3

Figure 7B-3.1 National Solar Radiation Database Stations

NSRDB stations are assigned a U.S. Air Force class number as follows:

 Class I stations have a complete period of record for solar and key meteorological 

fields (all hours for 1991–2005) and have the highest-quality solar of modeled data 

(221 sites).

 Class II stations have a complete period of record but significant periods of 

interpolated, filled, or otherwise lower-quality input data for the solar models (637 

sites).

 Class III stations have some gaps in the period of record but at least 3 years of data 

that might be useful for some applications (596 sites).

The NSRDB database has complete fields for measured hourly dry bulb temperature, dew 

point temperature, relative humidity, and atmospheric pressure for all class I and class II stations. 

DOE used data from the dry bulb temperature, relative humidity, and atmospheric pressure fields 

to calculate the humidity ratio for each operating hour for every commercial building in DOE's 

sample. DOE calculated the humidity ratio (W) using procedures from ASHRAE's 2005

Handbook–Fundamentals.

a The process utilizes dry bulb temperature, relative humidity, and 

 

a Chapter 6 in the 2005 ASHRAE Handbook is titled Psychrometrics. Under the section on "Numerical Calculation 

of Moist Air Properties," Situation 3 describes the process for calculating humidity ratio (W) from dry bulb

temperature, relative humidity, and pressure.
7B-4

pressure. The saturation pressure for the dry bulb temperature is calculated using the following 

equation.

ln( ) 1 3 ln( )

3

1 2

2

9 1 0 1 1

8 C C T C T C T C T

T

C Pws          

Where:

C8 = -5.8002206 E+03,

C9 = 1.3914993 E+00,

C10 = -4.8640239 E-02,

C11 = 4.1764768 E-05,

C12 = -1.4452093 E-08,

C13 = 6.5459673 E+00,

Pws = saturation pressure, Pa, and

T = absolute temperature, K = °C + 273.15

The partial pressure (Pw) of the water vapor is the saturation pressure multiplied by the 

relative humidity:

Pw   Pws

The humidity ratio, W, is defined as the ratio of the mass of water vapor to the mass of 

dry air contained in a given air sample. The ratio can be calculated from the pressure and the 

partial pressure of the water vapor as:

P Pw

Pw W

-

 0.62198

By comparing the conditions for a given hour in a specific geographic location against 

the criteria established in ANSI/ASHRAE Standard 55-2004, we can determine whether a 

portable air conditioner would have operated during that hour. Figure 7B-3.2 shows the 2,281 

hours in 1991 that exceeded the comfort zone for Palm Springs, CA.
7B-5

Figure 7B-3.2 Hours that Exceeded ASHRAE Standard 55 

Comfort Zone in Palm Springs CA, 1991

Figure 7B-3.3 shows hours that exceeded the ANSI/ASHRAE Standard 55-2004 comfort 

zone compared to CLDD for 15 years (1991–2005) for all NSRDB class 1 and class II stations.

Hours above comfort zone

Palm Springs, 1991

0

0.005

0.01

0.015

0.02

0.025

0.03

0 5 10 15 20 25 30 35 40 45 50

dry bulb temperature humidity ratio

100%RH

90%RH

80%RH

70%RH

60%RH

50%RH

40%RH

30%RH

20%RH

10%RH
7B-6

Figure 7B-3.3 Hours that Exceeded ASHRAE Standard 

55Comfort Zone Compared to CLDD

The lower branch of data points (outlined in red in Figure 7B-3.3) reflects low-desert 

locations, where humidity is not a factor that affects comfort. After examining the data, DOE 

classified the following sites as desert.

Table 7B-3.1 Weather Stations Classified as Desert

Station State

Davis Monthan Air Force Base AZ

Deer Valley/Phoenix AZ

Douglas Bisbee-Douglas Int'l. Airport AZ

Kingman (AMOS*) AZ

Luke Air Force Base AZ

Phoenix Sky Harbor Int'l. Airport AZ

Scottsdale Muni Airport? AZ

Tucson Int'l. Airport AZ

Yuma Int'l. Airport AZ

Yuma Marine Corps Air Station AZ

Bakersfield Meadows Field CA

Blythe Riverside Co Airport CA

China Lake Naval Air Station CA

Daggett Barstow-Daggett Airport CA

Edwards Air Force Base CA

Imperial CA

Lancaster Gen. Wm. Fox Field CA

Room AC Operating Hours

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 500 1000 1500 2000 2500 3000 3500 4000

CLDD 65 hours above Std 55
7B-7

Station State

Needles Airport CA

Palm Springs Int'l. Airport CA

Palm Springs Thermal Airport CA

Palmdale Airport CA

Twentynine Palms CA

Carlsbad Cavern City Air Terminal NM

Deming Muni [Airport] NM

Holloman Air Force Base NM

Las Cruces Intl [Airport] NM

Roswell Industrial Air Park NM

Truth or Consequences Muni [Airport] NM

Las Vegas Mccarran Int'l. [Airport] NV

Mercury Desert Rock Airport [SURFRAD†] NV

Nellis Air Force Base NV

El Paso Int'l. [Airport] [UT

‡

] TX

Saint George (AWOS§) UT

*AMOS = Automated Meteorological Observing System

† SURFRAD = Surface Radiation Network

‡ UT = University of Texas??

§ AWOS = Automated Weather Observing System

Figure 7B-3.4 shows NSRDB data points highlighting desert and tropical sites. The 

uppermost points represent data from stations in Hawaii, Guam, and the Caribbean.
7B-8

Figure 7B-3.4 Hours that Exceeded ASHRAE Standard 55

Comfort Zone versus CLDD Highlighting Various

Regions

7B-4 EQUATIONS AND CALCULATIONS

DOE removed the sites in Hawaii, Guam, and the Caribbean islands from consideration 

because their conditions of high humidity likely would call for use of a portable dehumidifier 

rather than a portable AC. After removing the sites in Hawaii, Guam, and the Caribbean islands

from DOE's set of data for commercial buildings, DOE performed regressions to predict the 

hours per year that exceed ASHRAE Standard 55 from the number of cooling degree-days for 

each year. The data points and regression lines are shown in Figure 7B-4.1 for all hours of the 

year. The figure reflects 15 years' worth of data from 842 sites in the continental United States.

Room AC Operating Hours

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 500 1000 1500 2000 2500 3000 3500 4000

CLDD 65 hours above Std 55

all

HI & Guam

Caribbean

desert
7B-9

Figure 7B-4.1 Hours that Exceeded ANSI/ASHRAE Standard 55

Comfort Zone as a Function of Cooling DegreeDays, Continental United States 

The regression equations used to derive the average annual number of hours when 

outdoor air conditions exceed ASHRAE Standard 55 comfort zone (OH55) are shown in Table 

7B-4.1.

Table 7B-4.1 Regression Equations

Region Equation R2 No. of 

Sites

Non-desert OH55 = 2.759 x CLDD + 127.99 0.9224 809

Desert OH55 = 1.153 x CLDD + 574.04 0.8714 33

The number of annual hours that exceed the ASHRAE Standard 55 comfort zone in a 

given geographic location will differ depending on building schedule, which refers to the 

period(s) when a building is open. Thus, DOE performed the regression for various combinations 

of building type and schedule, yielding somewhat different equations for each combination. The 

building types included are: assembly, education, food service, office, retail, and warehouse. For 

each building type, DOE estimated operating hours for building schedules that included: (1) open 

24 hours a day and seven days a week; (2) open business hours Monday through Friday; (3) open 

business hours Monday through Saturday; (4) open business hours Monday through Friday and 

Sunday; (5) open business hours all week. The building types and schedule abbreviations are 

shown in Table 7B-4.2 and Table 7B-4.3. DOE assumed that if the occupancy rate was greater 

than 20 percent of full occupancy, a portable AC would operate when outdoor air conditions 

exceeded the ASHRAE standard 55 comfort zone. 

CLDD vs #hours > ASHRAE Std55 

all day, all year 1991-2005

y = 2.7592x + 127.99

R

2

 = 0.9224

y = 1.153x + 574.04

R

2

 = 0.8714

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 500 1000 1500 2000 2500 3000 3500

CLDD (base 65F)

hours/year above ASHRAE Std 55

non-desert

desert

Linear (non-desert)

Linear (desert)
7B-10

Table 7B-4.2 Building Types and Abbreviations

Building Type Abbreviation

Assembly ASM

Education EDU

Food service FDS

Lodging LOD

Medical MED

Office OFF

Outdoor OUT

Retail RET

Warehouse WHS

Table 7B-4.3 Building Schedules and Abbreviations

Building Schedule Abbreviation

24 hours per day, 7 days per week 247

Business hours, Monday–Friday M-F

Business hours, Monday–Friday and Saturday

and Sunday

ALL

The equations for predicting the hours per year a portable AC would operate for various 

commercial building types and schedules for non-desert locations are shown in Table 7B-4.4.
7B-11

Table 7B-4.4 Equations for Portable AC Operating Hours by Building Type and 

Schedule, Non-Desert Locations

Building 

Type

Times 

Open Equation R2

ALL 247 ROH55 = 2.759 x CLDD + 127.99 0.9224

OUT M_F ROH55 = 1.974 x CLDD + 93.29 0.9458

OUT ALL ROH55 = 2.759 x CLDD + 127.99 0.9430

ASM M_F ROH55 = 0.751 x CLDD + 119.67 0.9458

ASM ALL ROH55 = 1.396 x CLDD + 169.18 0.9430

EDU M_F ROH55 = 1.001 x CLDD + 117.11 0.9412

EDU ALL ROH55 = 1.398 x CLDD + 163.52 0.9424

FDS M_F ROH55 = 1.243 x CLDD + 112.91 0.9354

FDS ALL ROH55 = 1.510 x CLDD + 166.44 0.9408

LOD M_F ROH55 = 1.471 x CLDD + 17.11 0.9428

LOD ALL ROH55 = 2.206 x CLDD + 40.94 0.9408

MED M_F ROH55 = 1.001 x CLDD + 128.06 0.9428

MED ALL ROH55 = 1.151 x CLDD + 148.72 0.9408

OFF M_F ROH55 = 0.918 x CLDD + 119.76 0.9428

OFF ALL ROH55 = 1.510 x CLDD + 166.44 0.9408

RET M_F ROH55 = 0.751 x CLDD + 119.67 0.9458

RET ALL ROH55 = 1.281 x CLDD + 170.57 0.9450

WHS M_F ROH55 = 0.836 x CLDD + 109.17 0.9422

WHS ALL ROH55 = 1.514 x CLDD + 178.06 0.9419

[The top (highlighted) row of the table pertains to any building type that operate on a

24/7 schedule, because the occupancy rate will exceed 20 percent at all times. The analysis does 

not account for differences in building operation schedules on holidays.

The equations for predicting the hours per year a portable AC would operate for various 

building types and schedules for desert locations are shown in Table 7B-4.5.
7B-12

Table 7B-4.5 Equations for Portable AC Operating Hour by Building Type and 

Schedule, Desert Locations

Buildin

g Type

Times 

Open Equation R2

ALL 247 ROH55 = 1.153 x CLDD + 574.04 0.9224

OUT M_F ROH55 = 1.974 x CLDD + 93.29 0.8353

OUT ALL ROH55 = 2.759 x CLDD + 127.99 0.8925

ASM M_F ROH55 = 0.289 x CLDD + 546.12 0.8353

ASM ALL ROH55 = 0.600 x CLDD + 721.20 0.8925

EDU M_F ROH55 = 0.409 x CLDD + 532.56 0.8723

EDU ALL ROH55 = 0.572 x CLDD + 741.06 0.8794

FDS M_F ROH55 = 0.553 x CLDD + 449.33 0.8914

FDS ALL ROH55 = 0.663 x CLDD + 690.02 0.8985

LOD M_F ROH55 = 0.642 x CLDD + 40.06 0.8260

LOD ALL ROH55 = 0.951 x CLDD + 157.74 0.8985

MED M_F ROH55 = 0.402 x CLDD + 603.12 0.8260

MED ALL ROH55 = 0.458 x CLDD + 706.19 0.8985

OFF M_F ROH55 = 0.353 x CLDD + 573.23 0.8260

OFF ALL ROH55 = 0.663 x CLDD + 690.02 0.8985

RET M_F ROH55 = 0.289 x CLDD + 546.12 0.8353

RET ALL ROH55 = 0.534 x CLDD + 749.00 0.8813

WHS M_F ROH55 = 0.317 x CLDD + 524.97 0.8087

WHS ALL ROH55 = 0.612 x CLDD + 837.58 0.8682

To estimate the operating hours for portable ACs in each building

in the CBECS 2003 sample that has a portable AC, DOE identified the building type and 

schedule using information provided by CBECS, then applied the appropriate equation (nondesert or desert) combined with the number of cooling degree-days for the location of the 

building. DOE adjusted the results by applying a scaling factor to account for the difference 

between the number of building operating hours that were assumed when deriving the equations 

and the actual building operating hours reported by CBECS 2003. Table 7B-4.6 shows the 

CBECS building codes matched to the building types in the regression equations.
7B-13

Table 7B-4.6 CBECS 2003 Building Codes Matched to Building Types in Portable AC 

Equations

CBECS 

2003 PBA 

Code*

Definition Building Type 

Match

CBECS 2003 

Buildings with

Portable ACs %

1 Vacant Not Applicable

2 Office OFF 8.8

4 Laboratory MED 0.0

5 Nonrefrigerated warehouse WHS 14.3

6 Food sales RET 5.5

7 Public order and safety OFF 8.8

8 Outpatient health care MED 0.0

11 Refrigerated warehouse WHS 0.0

12 Religious worship ASM 7.7

13 Public assembly ASM 7.7

14 Education EDU 12.1

15 Food service FDS 2.2

16 Inpatient health care MED 0.0

17 Nursing MED 2.2

18 Lodging LOD 1.1

23 Strip shopping mall RET 0.0

24 Enclosed mall RET 0.0

25 Retail other than mall RET 1.1

26 Service RET 24.2

91 Other OFF 4.4

 * PBA = Principal building activity.

The approach described here provides a best guess of the operating hours for a portable

AC in a particular CBECS building. Operating hours are affected by some factors not included in 

the analysis, however, such as interior heat gains from equipment or people and solar gains. To 

develop a distribution of the number of operating hours for each sample building, DOE added an 

error band to the value derived using the regression equation. The error band includes values that 

are ±10 percent from the regression line for the appropriate building type and schedule 

combination.

The operating hours for portable ACs in commercial buildings were estimated based on 

the cooling climate in 2003. To match the 115-year average CDD values, DOE decreased the 

operating hours estimated for commercial applications by 2 percent on average.
7B-14

REFERENCES

 

1 U.S. Department of Energy–Energy Information Administration. Commercial Buildings 

Energy Consumption Survey. 2003. (Last accessed September 8, 2014.) 

<http://www.eia.gov/consumption/commercial/data/2003/>

2 American National Standards Institute and American Society of Heating, Refrigeration, 

and Air-Conditioning Engineers, Inc. ANSI/ASHRAE 55-2004 Thermal Environmental 

Conditions for Human Occupancy. 2004.

3 National Renewable Energy Laboratory. National Solar Radiation Database: 1991–2005 

Update: User’s Manual. May 2007. Technical Report NREL/TP-581-41364. (Last 

accessed September 12, 2014.) <http://www.nrel.gov/docs/fy07osti/41364.pdf>