7-i

CHAPTER 7. ENERGY USE ANALYSIS

TABLE OF CONTENTS

7.1 INTRODUCTION ........................................................................................................... 7-1

7.2 CONSUMER SAMPLES ................................................................................................ 7-2

7.2.1 Clothes Dryer Household Sample.................................................................................... 7-2

7.2.2 Room Air Conditioners.................................................................................................... 7-3

7.2.2.1 Residential Sample......................................................................................... 7-3

7.2.2.2 Commercial Building Sample........................................................................ 7-3

7.3 CLOTHES DRYERS....................................................................................................... 7-4

7.3.1 Number of Cycles............................................................................................................ 7-4

7.3.2 Energy Use Calculation ................................................................................................... 7-5

7.3.3 Variability of Annual Energy Consumption.................................................................... 7-8

7.3.4 Average Annual Energy Consumption by Efficiency Level ......................................... 7-12

7.4 ROOM AIR CONDITIONERS..................................................................................... 7-14

7.4.1 General Approach .......................................................................................................... 7-14

7.4.2 Operating Hours............................................................................................................. 7-15

7.4.2.1 Residential.................................................................................................... 7-15

7.4.2.2 Commercial.................................................................................................. 7-18

7.4.3 Variability of Room Air Conditioner Annual Energy Consumption............................. 7-20

7.4.4 Average Annual Energy Consumption by Efficiency Level ......................................... 7-27

7.4.5 Estimating Room Air Conditioner Energy Use by Month............................................. 7-29

LIST OF TABLES

Table 7.2.1 Selection of RECS 2005 Records for Clothes Dryer Sample .............................. 7-2

Table 7.2.2 Selection of RECS 2005 Records for Residential Room Air Conditioner 

Samples................................................................................................................ 7-3

Table 7.2.3 Selection of CBECS 2003 Records for Commercial Room Air Conditioner 

Samples................................................................................................................ 7-4

Table 7.3.1 Number of Loads Washed per Week Based on RECS 2005 Sample .................. 7-5

Table 7.3.2 RECS 2005 Sample Clothes Dryer Usage ........................................................... 7-5

Table 7.3.3 Average Clothes Dryers Utilization Derived from RECS 2005 Sample ............. 7-5

Table 7.3.4 Electric Standard and Gas Clothes Dryer: Average Annual Energy 

Consumption by Efficiency Level ..................................................................... 7-13

Table 7.3.5 Electric Compact Vented Dryer: Average Annual Energy Consumption by 

Efficiency Level................................................................................................. 7-13

Table 7.3.6 Electric Compact Vent-less Dryer and Combination Washer/Dryer: 

Average Annual Energy Consumption by Efficiency Level ............................. 7-14

Table 7.4.1 RECS Vintage Bins for Room Air Conditioner................................................. 7-16

Table 7.4.2 Average Room Air Conditioner EER by Product Class and Year Sold ............ 7-17

Table 7.4.3 Regression Equations......................................................................................... 7-19

Table 7.4.4 Room Air Conditioner, Without Reverse Cycle and with Louvers, less 

than 6,000 Btu/h: Average Annual Energy Use................................................. 7-27
7-ii

Table 7.4.5 Room Air Conditioner, Without Reverse Cycle and with Louvers, 8,000–

13,999 Btu/h: Average Annual Energy Use ...................................................... 7-27

Table 7.4.6 Room Air Conditioner, Without Reverse Cycle and with Louvers, 20,000-

24,999 Btu/h: Average Annual Energy Use ...................................................... 7-28

Table 7.4.7 Room Air Conditioner, Without Reverse Cycle and with Louvers, greater 

than 25,000 Btu/h: Average Annual Energy Use............................................... 7-28

Table 7.4.8 Room Air Conditioner, Without Reverse Cycle and with Louvers, greater 

than 25,000 Btu/h: Average Annual Energy Use............................................... 7-28

Table 7.4.9 Room Air Conditioner, Without Reverse Cycle and with Louvers, greater 

than 25,000 Btu/h: Average Annual Energy Use............................................... 7-29

LIST OF FIGURES

Figure 7.3.1 Range of Annual Energy Use for Vented Electric Standard Clothes Dryers ...... 7-9

Figure 7.3.2 Range of Annual Energy Use for Vented Electric Compact 120V Clothes 

Dryers................................................................................................................... 7-9

Figure 7.3.3 Range of Annual Energy Use for Vented Electric Compact 240V Clothes 

Dryers................................................................................................................. 7-10

Figure 7.3.4 Range of Annual Gas Use for Vented Gas Clothes Dryers............................... 7-10

Figure 7.3.5 Range of Annual Electricity Use for Vented Gas Clothes Dryers..................... 7-11

Figure 7.3.6 Range of Annual Energy Use for Vent-less 240V Clothes Dryers.................... 7-11

Figure 7.3.7 Range of Annual Energy Use for Vent-less Combination Washer/Dryers........ 7-12

Figure 7.4.1 Hours Above ANSI/ASHRAE Standard 55-2004 as a Function of Cooling 

Degree-Days ...................................................................................................... 7-19

Figure 7.4.2 Range of Annual Energy Use for Residential Room Air Conditioners 

without Reverse Cycle and with Louvers, less than 6,000 Btu/h ...................... 7-21

Figure 7.4.3 Range of Annual Energy Use for Residential Room Air Conditioners 

without Reverse Cycle and with Louvers, 8,000–13,999 Btu/h ........................ 7-21

Figure 7.4.4 Range of Annual Energy Use for Residential Room Air Conditioners 

without Reverse Cycle and with Louvers, 20,000–24,999 Btu/h ...................... 7-22

Figure 7.4.5 Range of Annual Energy Use for Residential Room Air Conditioners 

without Reverse Cycle and with Louvers, greater than 25,000 Btu/h ............... 7-22

Figure 7.4.6 Range of Annual Energy Use for Residential Room Air Conditioners 

without Reverse Cycle and without Louvers, 8,000–10,999 Btu/h ................... 7-23

Figure 7.4.7 Range of Annual Energy Use for Residential Room Air Conditioners 

without Reverse Cycle and without Louvers, greater than 11,000 Btu/h .......... 7-23

Figure 7.4.8 Range of Annual Energy Use for Commercial Room Air Conditioners 

without Reverse Cycle and with Louvers, Less than 6,000 Btu/h..................... 7-24

Figure 7.4.9 Range of Annual Energy Use for Commercial Room Air Conditioners 

without Reverse Cycle and with Louvers, 8,000–13,999 Btu/h ........................ 7-24

Figure 7.4.10 Range of Annual Energy Use for Commercial Room Air Conditioners 

without Reverse Cycle and with Louvers, 20,000–24,999 Btu/h ...................... 7-25

Figure 7.4.11 Range of Annual Energy Use for Commercial Room Air Conditioners 

without Reverse Cycle and with Louvers, greater than 25,000 Btu/h ............... 7-25
7-iii

Figure 7.4.12 Range of Annual Energy Use for Commercial Room Air Conditioners 

without Reverse Cycle and without Louvers, 8,000–10,999 Btu/h ................... 7-26

Figure 7.4.13 Range of Annual Energy Use for Commercial Room Air Conditioners 

without Reverse Cycle and without Louvers, greater than 11,000 Btu/h .......... 7-26
7-1

CHAPTER 7. ENERGY USE ANALYSIS

7.1 INTRODUCTION

To carry out the life-cycle cost (LCC) and payback period (PBP) analyses described in 

chapter 8, DOE must determine the operating cost savings to consumers from more efficient 

products. This chapter describes how DOE determined the annual energy consumption of room 

air conditioners and clothes dryers for use in the LCC and PBP analyses.

The engineering analysis described in chapter 5 reports energy use based on the DOE test 

procedure. This test provides standardized results that serve as the basis for comparing the

performance of different appliances used under the same conditions. Actual usage in the field 

varies depending on the conditions in which the appliances are operated.a

 

To establish a reasonable range of energy consumption in the field for room air 

conditioners and clothes dryers in residential applications, DOE primarily used data from the 

Energy Information Administration (EIA)’s 2005 Residential Energy Consumption Survey 

(RECS 2005).1 RECS is a national sample survey of housing units that collects statistical 

information on the consumption of and expenditures for energy in housing units along with data 

on energy-related characteristics of the housing units and occupants. RECS 2005 collected data 

on 4,381 housing units and was constructed by EIA to be a national representation of the 

household population in the United States.

Room air conditioners are predominantly used in homes, but they are also used in some 

commercial buildings. To determine the energy use patterns of room air conditioners in 

commercial applications, DOE used EIA’s 2003 Commercial Building Energy Consumption 

Survey (CBECS)

2 to develop a representative sample of commercial buildings using room air 

conditioners. CBECS 2003 collected energy-related data for 5,215 buildings and was constructed 

by EIA to be a national representation of the commercial building stock in the United States.

The details of each building sample are described in the following section.

 

a DOE assembled estimates of the average annual energy use of room air conditioners from several studies and 

sources. Unfortunately, none of the studies is based on metered data. The studies rely on power measurements and 

assumptions regarding usage to derive the annual energy consumption values.
7-2

7.2 CONSUMER SAMPLES

7.2.1 Clothes Dryer Household Sample

The subset of RECS 2005 records used for the clothes dryer sample met all of the 

following criteria:

• The household had a clothes dryer.

• The household had and used a clothes washer.

• Clothes dryer fuel was electricity, natural gas, or LPG.

• Clothes dryer use was greater than zero.

Table 7.2.1 shows how the sample was divided into three sub-samples to match to the 

product classes analyzed. For compact electric dryers, DOE developed a sub-sample consisting 

of households with an electric dryer in multifamily buildings, manufactured homes, and singlefamily homes with less than 1,000 square feet and no garage or basement, since DOE reasoned 

that these products are most likely to be found in these housing types. 

Table 7.2.1 Selection of RECS 2005 Records for Clothes Dryer Sample 

Product Class Selection Criterion No. of 

Records

No. of U.S. 

Households 

Represented 

(million)

Electric Standard 

Dryer

Has Dryer = Yes

Fuel Type = Electricity

Use of Dryer > 0

2655 67.0

Electric Compact 

Vented Dryer and 

Vent-less Dryer

Has Dryer = Yes

Fuel Type = Electricity

Use of Dryer > 0

Type of Housing = Mobile home, 

multifamily, or single family 

(≤1000 sq. ft., no attached garage, 

no basement)

570 14.4

Gas Dryer

Has Dryer = Yes

Fuel Type = Natural Gas or LPG

Use of Dryer > 0

756 20.3
7-3

7.2.2 Room Air Conditioners

7.2.2.1 Residential Sample

The subset of RECS 2005 records used for the room air conditioner sample met all of the 

following criteria:

• A room air conditioner was present in the household.

• Room air conditioner energy consumption was greater than zero.

Households were assigned to the sub-samples based on the average adjusted capacity of 

the unit needed for the household. The average adjusted capacity was calculated based on 

ENERGY STAR sizing guidelines for room air conditionersb combined with household 

characteristics such as shading, insulation, window and glass type, number of household 

members, and ceiling type. See appendix 7-A for more details. Table 7.2.2 shows the number of 

RECS records in each sub-sample and the selection criteria. DOE used EIA’s weightings for 

each RECS 2005 household. The weightings indicate how commonly each household 

configuration occurs in the general population.

Table 7.2.2 Selection of RECS 2005 Records for Residential Room Air Conditioner 

Samples

Product Class Selection Criterion No. of 

Records

No. of U.S.

Households 

Represented 

(million)

No. of U.S. 

RAC Units

Represented 

(million)

Total sample 1222 28.2 50.6

1 Average adjusted capacity ≤ 6,000 

Btu/h 266 9.2 16.9

3 and 8 Average adjusted capacity > 6,000 

Btu/h and ≤ 14,000 Btu/h 890 38.9 97.1

5 Average adjusted capacity ≥ 18,000 

Btu/h 66 2.5 5.4

7.2.2.2 Commercial Building Sample

The subset of CBECS 2003 records used for the commercial-sector room air conditioner 

sample met all of the following criteria:

 

b http://www.energystar.gov/index.cfm?c=roomac.pr_properly_sized
7-4

• A room air conditioner served as a source of air conditioning.c

• Building is not vacant.

• A room air conditioner is used as the primary equipment to cool at least a portion 

of the building.

The sample was divided into sub-samples to match to the product classes analyzed. 

CBECS 2003 provides the total cooling square footage and the fraction of cooling by the room 

air conditioner for each building record, but it does not provide the number of room air 

conditioners used by the building, so the total room air conditioner cooling square footage is 

used to determine the subsamples. Table 7.2.3 shows the number of CBECS records in each subsample. DOE used EIA’s weightings for each CBECS 2003 building. The weightings indicate 

how commonly each building configuration occurs in the general population.

Table 7.2.3 Selection of CBECS 2003 Records for Commercial Room Air Conditioner 

Samples

Product Class Selection Criterion No. of 

Records

No. of U.S. 

Buildings

Represented 

(million)

Total sample 440 0.4

>6,000 Btu/h Total RAC Cooling sq. ft. 

> 0

440 0.4

8,000 to 13,999 Btu /h Total RAC Cooling sq. ft. 

> 300

400 0.3

≥ 20,000 Btu /h Total RAC Cooling sq. ft. 

> 900

352 0.3

7.3 CLOTHES DRYERS

DOE determined the annual energy consumption of clothes dryers by multiplying the

number of cycles per year by the energy use per cycle.

7.3.1 Number of Cycles

DOE estimated the number of clothes dryer cycles per year for each sample household 

using data given by RECS 2005 on the number of laundry loads washed (clothes washer cycles) 

per week and the frequency of clothes dryer use. The responses in RECS 2005 fall into one of 

the bins shown in Tables 7.3.1 and 7.3.2. For each question, DOE assumed a uniform 

 

c PTAC systems could also be listed as room air conditioners, so DOE tried to select buildings with only room air 

conditioners. A building was selected as having a room air conditioner if it did not have a PTAC type heating 

system.
7-5

distribution within the boundaries of each bin and randomly assigned a value from within the 

appropriate range to each sample household. 

Table 7.3.1 Number of Loads Washed per Week Based on RECS 2005 Sample

Bin Loads per Week Derived Loads per Year*

Min Max

1 1 load or less 0 78

2 2 to 4 loads 78 234

3 5 to 9 loads 234 494

4 10 to 15 loads 494 806

5 More than 15 loads 806 1118

* The ranges reflect the inclusion of values in between the given bin boundaries.

Table 7.3.2 RECS 2005 Sample Clothes Dryer Usage 

Bin Description

Fraction of Washer Cycles 

When Dryer is used

Min Max

1 Use it every time wash clothes 1 1

2 Use it for some, but not all, loads of 

wash 0.50 1

3 Use it infrequently 0.00 0.50

The responses to the above questions vary among sample households using different 

clothes dryer products, so they yield somewhat different values for the average annual number of 

clothes dryer cycles for each product class (see Table 7.3.3).

Table 7.3.3 Average Clothes Dryers Utilization Derived from RECS 2005 Sample 

Electric 

Standard Gas

Electric 

Compact and 

Vent-less

Washer loads 

per year

301 292 268

Clothes dryer 

frequency* 0.95 0.93 0.94

Clothes dryer 

loads per year 283 274 251

* Fraction of washer loads

** Accounts for fraction of households that have a clothes washer, but no clothes dryer

7.3.2 Energy Use Calculation

For each considered efficiency level, DOE derived the field energy use by separately 

estimating the active mode and standby mode energy use and then adding them together. The 
7-6

DOE clothes dryer test procedure3 calculates active mode energy consumption by dividing the 

weight (lbs) of clothes dried per cycle (8.45 lbs for standard and 3 lbs for compact clothes 

dryers) by the Combined Energy Factor (CEF) (lbs/kWh) and subtracting standby power.

d DOE 

adjusted the test procedure energy use to reflect field conditions by making an adjustment for 

clothes dryer load weight and moisture removal factor.

For each household, DOE determined the per-cycle test procedure clothes dryer energy 

use during active mode by using the following formula:

TP TP TP

TP

Active CD Cycles Stby CD Cycles Stby hrs

CEF

avgLoadWeight TP / _ 1000

* _ _ * 



 



 



 



  −



 



 =

Where:

avgLoadWeightTP = average load weight in the test procedure, lbs,

CEF = efficiency of the clothes dryer during active mode, lbs per kWh, 

CD_CyclesTP = test procedure clothes dryer cycles per year,

Stby_hrsTP = test procedure standby hours, and, 

Stby = clothes dryers standby power usage, watts.

For each household, DOE determined the field adjustment for clothes dryer energy use 

during active mode by using the following formula:

( ) RMC CD Cycles RMC RMC

RMC RMC

avgLoadWeight

avgLoadWeight EnergyUse TP RMC Adj

TP TP End

Field Field Enc

TP

Field

Active Active adj _

,

, ∗

















+















−

− ∗













 = − ∗

Where:

TPActive = test procedure energy use per cycle, kWh per cycle,

RMCadj = RMC adjustment factor for the fixed energy use, kWh per cycle,

avgLoadWeightTP = average load weight in the test procedure, lbs,

avgLoadWeightField = average load weight for each household, lbs, 

RMCTP = remaining moisture content in the test procedure, 57.5 percent,

RMCTP,Enc = remaining moisture content at the end of the cycle in the test 

procedure, 5 percent,

RMCField = remaining moisture content for the household, percent,

RMCField,End = remaining moisture content at the end of the cycle for the 

household, percent,

CD_Cycles = clothes dryer cycles per year.

 

d See chapter 5 for more information on how to convert from CEF to EF. 
7-7

DOE assigned a fixed energy use adjustment (RMCadj) equal to 0.25 kWh/cycle to 

account for energy required to heat the clothes dryer cabinet.

To assign a field average load weight (avgLoadWeightField) for each household, DOE 

developed a distribution of load weights by matching the listed tub sizes for models in the July 

2010 California Energy Commission (CEC) directory4 with the correlations between tub size and 

average pounds in the DOE test procedure. To account for a wider distribution of households that 

do not wash the average pounds in the DOE test procedure, DOE added a ±25 percent 

adjustment factor. The average load weights for standard-size units range from 3.8 lbs. to 13.7

lbs., with a mean value of 8.45 lbs, which matches DOE’s clothes dryer procedure value.

3

To assign a field remaining moisture content (RMCField) value for each household, DOE 

used the 2008 shipment weighted values provided by AHAM for front loader and top loader 

washers.5 The shipment weighted value is 38.1 percent for front loaders and 51 percent for top 

loaders, with an overall shipment weighted RMC value of 47 percent. In 2008, front loaders 

represented 31 percent of shipments, while top loaders represented the remaining 69 percent, so 

the overall RMS shipment weighted value is 47-percent. This shipment weighted average RMC 

value in the AHAM data is based on the clothes washer RMC which uses a correction factor to 

normalize testing results from different lots of test cloth. As a result, DOE determined that an 

initial clothes dryer RMC of 57.5 percent more accurately represents the moisture content of 

current laundry loads after a wash cycle and therefore adjusted the shipment weighted value for 

front loaders and top loaders accordingly. In order to get a distribution of values, DOE used the 

number of models listed at each unadjusted RMC in the July 2010 CEC directory.4 The adjusted 

RMC values used in the analysis range from 36 percent to 64 percent for front loaders, with an 

average of 47 percent, and from 42 percent to 75 percent for front loaders, with an average of 62 

percent. The overall average value of 57.5 percent matches DOE’s clothes dryer procedure 

value.

To assign a field remaining moisture content at the end of the cycle (RMCField,End) value 

for each household, DOE used a uniform distribution of 0 to 5 percent. In comparison, the DOE 

test procedure uses 5 percent.

Using the above approach, DOE calculated a unique value for the clothes dryer annual 

active mode energy consumption for each sample household with an electric clothes dryer using 

the number of dryer cycles specified for that household. For gas clothes dryers, DOE used a 

similar approach as for electric clothes dryers, but added an estimate of the energy use of the 

electric components. An estimate of 0.107 kWh per cycle, which was derived from tests done by 

DOE, was applied for all efficiency levels except for the max-tech level. For the latter, which has 

a more efficient motor, the tests found a value of 0.091 kWh.

For each household, DOE determined the field-adjusted clothes dryer energy use during 

standby mode by using the following formula:
7-8

ClothesDryerEnergyUseStandby 



 



 



 



 = − ∗

60

_ 8760 _ CD Time CD Cycles * Standby_Power

Where:

8760 = number of hours in one year, hrs,

CD_Time = clothes dryer time to complete one cycle, min/cycle, 

60 = number of minutes in one hour, min/hr,

Standby_Power = standby power, kW, and

CD_Cycles = clothes dryer cycles per year.

DOE assumed that clothes dryers take 60 minutes on average to complete a cycle.6, 7, 8

Standby power varies by efficiency level as discussed in chapter 5.

DOE also considered the impact of clothes dryer operation on home heating and cooling 

loads. A clothes dryer releases heat to the surrounding environment. If the dryer is located 

indoors, its use will tend to slightly reduce the heating load during the heating season and 

slightly increase the cooling load during the cooling season. To calculate this impact, DOE first 

estimated whether the clothes dryer in a RECS sample home is located in conditioned space 

(referred to as indoors) or in unconditioned space (such as garages, unconditioned basements, 

outdoor utility closets, or attics). Based on the 2005 RECS9 and the 2009 American Housing 

Survey (AHS)10, DOE assumed that 50 percent of vented standard electric and gas dryers are 

located indoors, while 100 percent of compact and ventless clothes dryers are located indoors. 

For these installations, DOE utilized the results from a European Union study about the impacts 

of clothes dryers on home heating and cooling loads to determine a the appropriate factor to 

apply to the total clothes dryer energy use.11 This study reported that for vented dryers there is a 

factor of negative 3 to 9 percent (average 6 percent) and for ventless dryers there is a factor of 

positive 7 to 15 percent (average 11 percent). DOE believes that this effect is the same for all of 

the considered efficiency levels because the amount of air passing through the clothes dryer does 

not vary.

7.3.3 Variability of Annual Energy Consumption

Figures 7.3.1 to 7.3.7 show the range of average annual energy consumption (active and 

standby mode) for clothes dryers in the household sample for each product class.
7-9

Figure 7.3.1 Range of Annual Energy Use for Vented Electric 

Standard Clothes Dryers

Figure 7.3.2 Range of Annual Energy Use for Vented Electric 

Compact 120V Clothes Dryers

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Level 0 Level 1 Level 2 Level 3 Level 4 Level 5 Level 6

Annual Energy Use (kWh)

Efficiency Level

Electric Standard Average Annual Energy Use

Average; Median; Box 25%-75%; Whisker 5%-95%

median

average

0

100

200

300

400

500

600

700

800

Level 0 Level 1 Level 2 Level 3 Level 4 Level 5 Level 6

Annual Energy Use (kWh)

Efficiency Level

Electric Compact 120V Average Annual Energy Use

Average; Median; Box 25%-75%; Whisker 5%-95%

median

average
7-10

Figure 7.3.3 Range of Annual Energy Use for Vented Electric 

Compact 240V Clothes Dryers

Figure 7.3.4 Range of Annual Gas Use for Vented Gas Clothes 

Dryers

0

100

200

300

400

500

600

700

800

900

Level 0 Level 1 Level 2 Level 3 Level 4 Level 5 Level 6

Annual Energy Use (kWh)

Efficiency Level

Electric Compact 240V Average Annual Energy Use

Average; Median; Box 25%-75%; Whisker 5%-95%

median

average

0

1

2

3

4

5

6

7

Level 0 Level 1 Level 2 Level 3 Level 4 Level 5

Annual Gas Use (MMBtu)

Efficiency Level

Gas Average Annual Gas Use

Average; Median; Box 25%-75%; Whisker 5%-95%

median

average
7-11

Figure 7.3.5 Range of Annual Electricity Use for Vented Gas 

Clothes Dryers

Figure 7.3.6 Range of Annual Energy Use for Vent-less 240V 

Clothes Dryers

0

10

20

30

40

50

60

70

80

90

100

Level 0 Level 1 Level 2 Level 3 Level 4 Level 5

Annual Energy Use (kWh)

Efficiency Level

Gas Average Annual Electricity Use

Average; Median; Box 25%-75%; Whisker 5%-95%

median

average

0

100

200

300

400

500

600

700

800

900

1000

Level 0 Level 1 Level 2 Level 3 Level 4 Level 5

Annual Energy Use (kWh)

Efficiency Level

Ventless 240V Average Annual Energy Use

Average; Median; Box 25%-75%; Whisker 5%-95%

median

average
7-12

Figure 7.3.7 Range of Annual Energy Use for Vent-less 

Combination Washer/Dryers

7.3.4 Average Annual Energy Consumption by Efficiency Level

Tables 7.3.4 through 7.3.6 present the average annual energy consumption by efficiency 

level for each considered clothes dryer product class. 

0

200

400

600

800

1000

1200

Level 0 Level 1 Level 2 Level 3 Level 4 Level 5

Annual Energy Use (kWh)

Efficiency Level

Ventless Combination Average Annual Energy Use

Average; Median; Box 25%-75%; Whisker 5%-95%

median

average
7-13

Table 7.3.4 Electric Standard and Gas Clothes Dryer: Average Annual Energy 

Consumption by Efficiency Level

Electric Gas

CEF

(lb/kWh) kWh/year CEF(lb/kWh)

MMBtu/ 

year kWh/year

3.55 718 3.14 2.53 42.2

3.56 716 3.16 2.53 39.0

3.61 707 3.20 2.53 29.8

3.73 684 3.30 2.45 29.8

3.81 670 3.41 2.37 29.8

4.08 627 3.61 2.25 25.5

5.42 476 -- -- --

Table 7.3.5 Electric Compact Vented Dryer: Average Annual Energy Consumption by 

Efficiency Level

120V 240V

CEF

(lb/kWh) kWh/year CEF(lb/kWh) kWh/year

3.43 317 3.12 353

3.48 314 3.16 349

3.61 305 3.27 340

3.72 295 3.36 331

3.80 289 3.48 319

4.08 268 3.60 308

5.41 198 4.89 223
7-14

Table 7.3.6 Electric Compact Vent-less Dryer and Combination Washer/Dryer: Average 

Annual Energy Consumption by Efficiency Level

Compact Vent-less Dryer (240V) Combination Washer-Dryer

CEF

(lb/kWh) kWh/year CEF(lb/kWh) kWh/year

2.55 372 2.08 463

2.59 366 2.35 399

2.69 354 2.38 394

2.71 351 2.46 383

2.80 337 2.56 365

4.03 210 3.69 226

7.4 ROOM AIR CONDITIONERS

7.4.1 General Approach

DOE calculated the annual energy consumption of a room air conditioner using the 

following equation:

IEER

Capacity OH RACENERGY

∗ =

Where:

RACENERGY = room air conditioner annual energy consumption (kWh/year),

Capacity = rated capacity in Btu/h,

OH = operating hours per year,

CEER = Combined Energy Efficiency Ratio in Btu/h/W.

DOE began with the data reported by RECS 2005 on the annual energy consumption 

(field energy consumption) for room air conditioning, referred to as FEC(all)RECS. The reported

end-use quantities were not based on metering of individual appliances; rather, EIA used a 

regression technique to estimate how much of the total annual electricity consumption for each 

household can be attributed to each end-use category.e

 

e The desire to use a large number of independent variables without using a large number of interaction terms and 

the desire to adapt the regression procedures to account for heteroscedastic error terms led to the use of a nonlinear 

regression technique. For more information, see: http://www.eia.doe.gov/pub/consumption/residential/append_c.pdf

The reported field energy consumption 

refers to the consumption of all of the room air conditioners in a home. 
7-15

RECS 2005 also reports the number of room air conditioners in the home. Of all homes 

that use a room air conditioner, 35 percent have two room air conditioners and 14 percent have

three or more room air conditioners. To estimate the energy consumption of a single room air 

conditioner, referred to as FECRECS, DOE divided FEC(all)RECS by the reported number of room 

air conditioners. For houses with both central air conditioning and room air conditioning, DOE 

scaled FEC(all)RECS using a relative use factor. For more information on the relative use factor 

used, see appendix 7-C. Although in reality the utilization of each of the room air conditioners in 

a home may vary, DOE has no way to estimate such variation.

For commercial-sector room air conditioners, CBECS does not report annual energy 

consumption for room air conditioning, so DOE estimated the energy consumption using 

variables specific to each building in the sample and data on cooling degree-days.

In conducting the analysis of energy use by products that would meet some future 

standard, DOE effectively substituted the room air conditioners in the sample residential and 

commercial buildings with a new product of identical product class (capacity) but with different 

energy efficiency. In order for the estimate of new room air conditioner energy consumption to 

reflect field conditions, DOE needed to estimate the number of room air conditioner operating 

hours for each household or commercial building in the samples.

7.4.2 Operating Hours

7.4.2.1 Residential

DOE calculated the annual room air conditioner active mode operating hours for each 

residential sample unit using the following formula:

BldgShellAdj CDDAdj Capacity

FEC EER OH RECS RECS * *

∗ =

Where:

OH = operating hours per year,

FECRECS = field energy consumption for a room air conditioner,

EERRECS = the estimated EER of the room air conditioner in the sample home,

Capacity = the room air conditioner capacity in Btu/h,

BldgShellAdj = adjustment to building shell efficiency in 2014, precent,

CDDAdj = cooling degree days (CDD) adjustment in Btu/h.

The derivation of FECRECS was discussed above. The capacity is given by the product 

class; DOE used the same representative capacities for each class as it did in the engineering 

analysis. 
7-16

To ensure that the estimated operating hours are representative of future conditions, DOE 

used the building shell index factor from Annual Energy Outlook (AEO) 2010 in 2014 for space 

cooling in all homes of 0.96 and 115 year historical average CDD by census division. The 

building shell index factor decreased energy use by 4 percent, while the CDD adjustment factor 

decreased energy use by 10 percent on average. 

DOE estimated the EER of the room air conditioner in each sample household by 

matching the age of the room air conditioner given by RECS with the average EER for the 

specific product class in the year of its vintage. In RECS, the age of a room air conditioner is 

given in one of the five bins shown in Table 7.4.1. DOE assumed a uniform distribution within 

each vintage bin and assigned an age to the room air conditioner in each sample household. 

Table 7.4.1 RECS Vintage Bins for Room Air Conditioner

Bin Age of unit

1 Less than 2 years old

2 2 to 4 years old

3 5 to 9 years old

4 10 to 19 years old

5 20 years or older

Once the vintage year was determined, DOE assigned an EER to the unit equal to the 

average EER for the appropriate capacity for that year. To derive a time series of average EER 

by capacity, DOE began with data from AHAM on total shipment-weighted average EER for 

1972–2007.

12 AHAM also provided average EER data by product class (capacity) for 2005–

2007.

12 To develop the EER values by product class (capacity) for earlier years, DOE first 

assumed that all of the products shipped in each product class had the minimum efficiency 

required by the standard in each particular year. DOE then estimated the shares of total 

shipments by product class in each year using data for 1990, 1993 and 2005–2007, and 

calculated a total shipment-weighted EER. DOE then calculated scalars for each year from the 

ratio of the actual total shipment-weighted EER to the calculated EER, and then applied the 

scalars to the minimum efficiency required for each product class in each year. Table 7.4.2 

shows the AHAM data on total shipment-weighted average EER and the average EER estimated 

for the representative product classes. 
7-17

Table 7.4.2 Average Room Air Conditioner EER by Product Class and Year Sold

Year Shipment 

Weighted EER

Derived Average EER*

< 6000 

Btu/h

8000-

13,999 

Btu/hr

(PC 3)

≥ 20,000 

Btu/hr

8000-

13,999 

Btu/hr

(PC 8)

2007 9.81 9.80 10.10 9.10 9.50

2006 10.02 9.80 10.40 9.20 9.50

2005 9.95 9.80 10.10 9.10 9.40

2004 9.71 9.70 9.86 8.83 9.15

2003 9.75 9.70 9.92 8.89 9.21

2002 9.75 9.70 9.92 8.88 9.21

2001 9.63 9.70 9.80 8.50 8.73

2000** 9.3 9.03 9.70 8.50 8.73

1999 9.07 8.56 9.63 8.50 8.73

1998 NA 8.56 9.63 8.50 8.73

1997 9.09 8.57 9.64 8.50 8.73

1996 9.08 8.55 9.62 8.50 8.73

1995 9.03 8.49 9.55 8.50 8.73

1994 8.97 8.42 9.47 8.50 8.73

1993 9.05 8.50 9.56 8.50 8.73

1992 8.88 8.31 9.35 8.50 8.73

1991 8.8 8.24 9.27 8.45 8.73

1990** 8.73 8.18 9.20 8.39 8.69

1989 8.48 7.95 8.95 8.15 8.45

1988 8.23 7.72 8.68 7.91 8.20

1987 8.06 7.56 8.51 7.75 8.03

1986 7.8 7.32 8.23 7.50 7.77

1985 7.7 7.22 8.13 7.40 7.67

1984 7.48 7.02 7.89 7.19 7.45

1983 7.29 6.84 7.69 7.01 7.27

1982 7.14 6.70 7.53 6.86 7.12

1981 7.06 6.62 7.45 6.79 7.04

1980 7.02 6.58 7.41 6.75 7.00

1978 6.72 6.44 7.25 6.60 6.85

1972 5.98 6.30 7.09 6.46 6.70

* Shaded area values were provided by AHAM12

** Years in which standards became effective

The estimated mean number of operating hours for the residential room air conditioner 

sample is 756 hours for the <6,000 Btu/h product class, 611 hours for 8,000 to 13,999 Btu/h 

product classes, and 175 hours for the ≥ 20,000 Btu/h product classes. For comparison, the DOE 

test procedure uses 750 hours per year for all room air conditioners.

3
7-18

7.4.2.2 Commercial

DOE calculated the annual operating hours for each sample commercial-sector room air 

conditioner by establishing a relationship between cooling degree-days and operating hours for a 

number of building type and building schedule combinations. DOE assumed that a room air 

conditioner is operated when the outdoor air conditions are above the comfort zone described by 

ANSI/ASHRAE Standard 55-2004 Thermal Environmental Conditions for Human Occupancy.13

To estimate how often this occurs, DOE used the following general equation:

OH55 = (a * CDD) + b

Where:

OH55 = average annual hours when the outdoor air conditions are above the

ASHRAE Standard 55 comfort zone,

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

a and b are linear fit parameters.

DOE used data on cooling degree-days from the National Solar Radiation Database

(NSRDB).

14 The 1991–2005 NSRDB is an update of the 1961–1990 NSRDB. This updated 

NSRDB dataset is an hourly ground-based data set of solar and meteorological fields for 1,454 

stations. A total of 858 sites have a complete 15-year period of record. 

After removing the sites in Hawaii, Guam, and the Caribbean islands, regressions were 

done to predict the hours per year above Standard 55 from the number of cooling degree-days for 

each year. The data points and regression lines are shown in Figure 7.4.1 for all hours of the 

year. The data represent 842 sites for 15 years each in the continental United States.
7-19

Figure 7.4.1 Hours Above ANSI/ASHRAE Standard 55-2004 as 

a Function of Cooling Degree-Days

As can be seen in the graph above, the data patterns are different for desert locations,

where humidity is not a present factor affecting comfort. The regression equations developed 

from the data are shown in Table 7.4.3.

Table 7.4.3 Regression Equations

Region Equation R2 # sites

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

Desert OH55 = 1.153 x CLDD + 574.04 0.8714 33

For a given location, the number of annual hours above the ASHRAE Standard 55 

comfort zone varies by schedule, which refers to the time that a building is open. Thus, DOE 

performed the regression for a number of combinations of building type and building 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 the following building schedules: (1) open 24 hours a day 

and seven days a week (24/7); (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. Each of these schedules yields a variation of the 

above equations.

CLDD vs #hours > ASHRAE Std55 

all day, all year 1991-2005

y = 2.7592x + 127.99

R2

 = 0.9224

y = 1.153x + 574.04

R2

 = 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)
7-20

To estimate the room air conditioner operating hours for each of the buildings in the 

CBECS room air conditioner sample, DOE identified the building type and the building schedule 

using information provided by CBECS, and used the appropriate equation (non-desert or desert) 

combined with the number of cooling degree-days for the location of the building. It adjusted 

the results with a scaling factor to account for the difference between the number of building

operating hours assumed to derive the equations and the actual building operating hours reported 

by CBECS.

The above approach provides a ‘best guess’ of the room air conditioner operating hours

for a particular CBECS building. However, operating hours are affected by some factors not 

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

develop a range for 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% from the regression line for the appropriate building type/schedule combination.

The estimated mean number of operating hours is 1,142 hours for the < 6,000 Btu/hr

product class, 1,054 hours for the 8,000 to 13,999 Btu/hr product classes, and 1,113 hours for the 

greater than 20,000 Btu/hr product classes.

The commercial sector operating hours were estimated based on the cooling climate in 

2003. To match the 115 year CDD average values, DOE decreased the estimated commercial 

sector operating hours by 2 percent on average.

7.4.3 Variability of Room Air Conditioner Annual Energy Consumption

Figures 7.4.2 to 7.4.13 show the range of average annual energy consumption by 

efficiency level within the residential and commercial samples for each representative product 

class. The higher utilization of room air conditioners in the commercial sector is evident in the 

figures.
7-21

Figure 7.4.2 Range of Annual Energy Use for Residential Room 

Air Conditioners without Reverse Cycle and with 

Louvers, less than 6,000 Btu/h

Figure 7.4.3 Range of Annual Energy Use for Residential Room 

Air Conditioners without Reverse Cycle and with 

Louvers, 8,000–13,999 Btu/h

0

200

400

600

800

1000

1200

Level 0 Level 1 Level 2 Level 3 Level 4 Level 5

Annual Energy Use (kWh)

Efficiency Level

Residential <6,000 Btu/h, with Louvers, Average Annual Energy Use

Average; Median; Box 25%-75%; Whisker 5%-95%

median

average

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Level 0 Level 1 Level 2 Level 3 Level 4 Level 5

Annual Energy Use (kWh)

Efficiency Level

Residential 8,000-13,999, with Louvers, Average Annual Energy Use

Average; Median; Box 25%-75%; Whisker 5%-95%

median

average
7-22

Figure 7.4.4 Range of Annual Energy Use for Residential Room 

Air Conditioners without Reverse Cycle and with 

Louvers, 20,000–24,999 Btu/h

Figure 7.4.5 Range of Annual Energy Use for Residential Room 

Air Conditioners without Reverse Cycle and with 

Louvers, greater than 25,000 Btu/h

0

200

400

600

800

1000

1200

1400

1600

Level 0 Level 1 Level 2 Level 3 Level 4

Annual Energy Use (kWh)

Efficiency Level

Residential 20,000-24,999 Btu/h, with Louvers, Average Annual Energy Use

Average; Median; Box 25%-75%; Whisker 5%-95%

median

average

0

200

400

600

800

1000

1200

1400

1600

1800

Level 0 Level 1 Level 2 Level 3

Annual Energy Use (kWh)

Efficiency Level

Residential >25,000 Btu/h, with Louvers, Average Annual Energy Use

Average; Median; Box 25%-75%; Whisker 5%-95%

median

average
7-23

Figure 7.4.6 Range of Annual Energy Use for Residential Room 

Air Conditioners without Reverse Cycle and without 

Louvers, 8,000–10,999 Btu/h

Figure 7.4.7 Range of Annual Energy Use for Residential Room 

Air Conditioners without Reverse Cycle and without 

Louvers, greater than 11,000 Btu/h

0

200

400

600

800

1000

1200

1400

1600

Level 0 Level 1 Level 2 Level 3 Level 4

Annual Energy Use (kWh)

Efficiency Level

Residential 8,000-10,999 Btu/h, without Louvers, Average Annual Energy Use

Average; Median; Box 25%-75%; Whisker 5%-95%

median

average

0

500

1000

1500

2000

2500

Level 0 Level 1 Level 2 Level 3 Level 4

Annual Energy Use (kWh)

Efficiency Level

Residential >11,000 Btu/h, without Louvers, Average Annual Energy Use

Average; Median; Box 25%-75%; Whisker 5%-95%

median

average
7-24

Figure 7.4.8 Range of Annual Energy Use for Commercial Room 

Air Conditioners without Reverse Cycle and with 

Louvers, Less than 6,000 Btu/h

Figure 7.4.9 Range of Annual Energy Use for Commercial Room 

Air Conditioners without Reverse Cycle and with 

Louvers, 8,000–13,999 Btu/h

0

200

400

600

800

1000

1200

1400

1600

1800

Level 0 Level 1 Level 2 Level 3 Level 4 Level 5

Annual Energy Use (kWh)

Efficiency Level

Commercial <6,000 Btu/h, with Louvers, Average Annual Energy Use

Average; Median; Box 25%-75%; Whisker 5%-95%

median

average

0

500

1000

1500

2000

2500

3000

Level 0 Level 1 Level 2 Level 3 Level 4 Level 5

Annual Energy Use (kWh)

Efficiency Level

Commercial 8,000-13,999 Btu/h, with Louvers, Average Annual Energy Use

Average; Median; Box 25%-75%; Whisker 5%-95%

median

average
7-25

Figure 7.4.10 Range of Annual Energy Use for Commercial Room 

Air Conditioners without Reverse Cycle and with 

Louvers, 20,000–24,999 Btu/h

Figure 7.4.11 Range of Annual Energy Use for Commercial Room 

Air Conditioners without Reverse Cycle and with 

Louvers, greater than 25,000 Btu/h

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

Level 0 Level 1 Level 2 Level 3 Level 4

Annual Energy Use (kWh)

Efficiency Level

Commercial 20,000-24,999 Btu/h, with Louvers, Average Annual Energy Use

Average; Median; Box 25%-75%; Whisker 5%-95%

median

average

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

Level 0 Level 1 Level 2 Level 3

Annual Energy Use (kWh)

Efficiency Level

Commercial >25,000 Btu/h, with Louvers, Average Annual Energy Use

Average; Median; Box 25%-75%; Whisker 5%-95%

median

average
7-26

Figure 7.4.12 Range of Annual Energy Use for Commercial Room 

Air Conditioners without Reverse Cycle and without 

Louvers, 8,000–10,999 Btu/h

Figure 7.4.13 Range of Annual Energy Use for Commercial Room 

Air Conditioners without Reverse Cycle and without 

Louvers, greater than 11,000 Btu/h

0

500

1000

1500

2000

2500

3000

3500

Level 0 Level 1 Level 2 Level 3 Level 4

Annual Energy Use (kWh)

Efficiency Level

Commercial 8,000-10,999 Btu/h, without Louvers, Average Annual Energy Use

Average; Median; Box 25%-75%; Whisker 5%-95%

median

average

0

500

1000

1500

2000

2500

3000

3500

4000

Level 0 Level 1 Level 2 Level 3 Level 4

Annual Energy Use (kWh)

Efficiency Level

Commercial >11,000 Btu/h, without Louvers, Average Annual Energy Use

Average; Median; Box 25%-75%; Whisker 5%-95%

median

average
7-27

7.4.4 Average Annual Energy Consumption by Efficiency Level

Tables 7.4.4 through 7.4.9 show the considered efficiency levels and corresponding 

calculated average annual energy consumption for each product class when the product is used in 

the residential or commercial sector. 

Table 7.4.4 Room Air Conditioner, Without Reverse Cycle and with Louvers, less than 

6,000 Btu/h: Average Annual Energy Use 

Efficiency

(CEER)

Residential

(kWh)

Commercial

(kWh)

9.52 401 599

10.1 376 565

10.6 358 539

11.1 342 514

11.4 334 502

11.7 326 489

Table 7.4.5 Room Air Conditioner, Without Reverse Cycle and with Louvers, 8,000–

13,999 Btu/h: Average Annual Energy Use 

Efficiency

(CEER)

Residential

(kWh)

Commercial

(kWh)

9.69 636 1088

10.2 604 1035

10.7 576 987

10.9 565 969

11.5 535 918

12.0 514 883
7-28

Table 7.4.6 Room Air Conditioner, Without Reverse Cycle and with Louvers, 20,000-

24,999 Btu/h: Average Annual Energy Use 

Efficiency

(CEER)

Residential

(kWh)

Commercial

(kWh)

8.47 506 3153

9.0 477 2968

9.4 452 2841

9.8 434 2726

10.2 419 2630

Table 7.4.7 Room Air Conditioner, Without Reverse Cycle and with Louvers, greater 

than 25,000 Btu/h: Average Annual Energy Use

Efficiency

(CEER)

Residential

(kWh)

Commercial

(kWh)

8.48 589 3153

9.0 555 2969

9.4 526 2842

9.8 505 2726

Table 7.4.8 Room Air Conditioner, Without Reverse Cycle and with Louvers, greater 

than 25,000 Btu/h: Average Annual Energy Use

Efficiency

(CEER)

Residential

(kWh)

Commercial

(kWh)

8.41 523 1252

9.3 474 1133

9.6 459 1098

10.0 438 1055

10.4 423 1018
7-29

Table 7.4.9 Room Air Conditioner, Without Reverse Cycle and with Louvers, greater 

than 25,000 Btu/h: Average Annual Energy Use

Efficiency

(CEER)

Residential

(kWh)

Commercial

(kWh)

8.44 779 1498

9.3 707 1360

9.5 693 1332

9.8 668 1291

10.0 654 1262

7.4.5 Estimating Room Air Conditioner Energy Use by Month

Room air conditioner use is concentrated in the warm parts of the year. In conducting the 

LCC analysis for room air conditioners (see chapter 8), DOE used monthly electricity prices 

because electricity tariffs show seasonal variation in many parts of the country. Therefore, to 

properly calculate room air conditioner operating costs, DOE needed to estimate how the annual 

room air conditioner electricity use for each sample household is apportioned over the year.

To estimate electricity use by month, DOE utilized data on seasonal climate variation, as 

measured by cooling degree-days. RECS 2005 provides data on yearly heating and cooling 

degree-days for each household in the sample, but does not break this information down by 

month. To estimate monthly cooling degree days for the households in the RECS sample, DOE 

developed an approach to match each household with a corresponding NOAA weather station. 

After matching the household to a weather station location, DOE utilized the monthly coolingdegree day data from the corresponding weather station to estimate the percentage of household 

energy use per month. See appendix 7-D for more details.
7-30

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Consumption Survey: 2005 Public Use Data Files, 2005.

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2. U.S. Department of Energy - Energy Information Administration, Commercial Buildings 

Energy Consumption Survey, 2003. <http://www.eia.doe.gov/emeu/cbecs/>

3. Department Of Energy, 10 CFR Part 430 Energy Conservation Program for Consumer 

Products: Test Procedures for Clothes Dryers and Room Air Conditioners; Final Rule.

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Consumption Survey: 2005 Public Use Data Files. 2008: Washington, DC. 

http://www.eia.doe.gov/emeu/recs/recspubuse05/pubuse05.html

10. U.S. Census Bureau: Housing and Household Economic Statistics Division, American 

Housing Survey National Data. 2009, HUD. 

http://www.huduser.org/portal/datasets/ahs/ahsdata09.html

11. Rüdenauer, I. and C.-O. Gensch, Energy demand of tumble dryers with respect to 

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et&ITitel1=&IAutor1=>

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