CHAPTER 7. ENERGY USE CHARACTERIZATION 

TABLE OF CONTENTS 

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


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


7.2.1 Room Air Conditioners.................................................................................................... 7-2 


7.2.1.1 Residential Sample......................................................................................... 7-2 


7.2.1.2 Commercial Building Sample........................................................................ 7-3 


7.2.2 Clothes Dryer Household Sample.................................................................................... 7-3 


7.3 ROOM AIR CONDITIONERS ....................................................................................... 7-4 


7.3.1 General Approach ............................................................................................................ 7-4 


7.3.2 Operating Hours............................................................................................................... 7-5 


7.3.2.1 Residential...................................................................................................... 7-5 


7.3.2.2 Commercial.................................................................................................... 7-8 


7.3.3 Variability of Room Air Conditioner Annual Energy Consumption............................. 7-10 


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


7.3.5 Estimating Room Air Conditioner Energy Use by Month............................................. 7-16 


7.4 CLOTHES DRYERS..................................................................................................... 7-16 


7.4.1 Number of Cycles .......................................................................................................... 7-16 


7.4.2 Energy Use Calculation ................................................................................................. 7-17 


7.4.3 Variability of Annual Energy Consumption.................................................................. 7-19 


7.4.4 Average Annual Energy Consumption by Efficiency Level ......................................... 7-23 


LIST OF TABLES 

Table 7.2.1 Selection of RECS 2005 Records for Residential Room Air Conditioner 

Samples................................................................................................................ 7-2 


Table 7.2.2 Selection of CBECS 2003 Records for Commercial Room Air Conditioner 


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


Table 7.2.3 Selection of RECS 2005 Records for Clothes Dryer Sample .............................. 7-4 


Table 7.3.1 RECS Vintage Bins for Room Air Conditioner................................................... 7-6 


Table 7.3.2 Average Room Air Conditioner EER by Product Class and Year Sold .............. 7-7 


Table 7.3.3 Regression Equations........................................................................................... 7-9 


Table 7.3.4 Room Air Conditioner, Without Reverse Cycle and with Louvers, Less 


than 6,000 Btu/h: Average Annual Energy Use................................................. 7-15 


Table 7.3.5 Room Air Conditioner, Without Reverse Cycle and with Louvers, 8,000–
 

13,999 Btu/h: Average Annual Energy Use ...................................................... 7-15 


Table 7.3.6 Room Air Conditioner, Without Reverse Cycle and with Louvers, 20,000 


Btu/h or more: Average Annual Energy Use..................................................... 7-15 


Table 7.3.7 Room Air Conditioner, Without Reverse Cycle and without Louvers, 


8,000–13,999 Btu/h: Average Annual Energy Use ........................................... 7-16 


Table 7.4.1 Number of Loads Washed per Week Based on RECS Sample ......................... 7-17 


Table 7.4.2 RECS Sample Clothes Dryer Usage .................................................................. 7-17 


Table 7.4.3 RECS Sample Clothes Dryers Utilization ......................................................... 7-17 


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EERE-2007-BT-STD-0010 COMMENT 20.3
Table 7.4.4 Electric Standard and Gas Clothes Dryer: Average Annual Energy 

Consumption by Efficiency Level ..................................................................... 7-23 


Table 7.4.5 Electric Compact Vented Dryer: Average Annual Energy Consumption by
 

Efficiency Level................................................................................................. 7-24 


Table 7.4.6 Electric Compact Vent-less Dryer and Combination Washer/Dryer:
 

Average Annual Energy Consumption by Efficiency Level ............................. 7-24 


LIST OF FIGURES 

Figure 7.3.1 Hours Above ANSI/ASHRAE Standard 55-2004 as a Function of Cooling 

Degree-Days ........................................................................................................ 7-9 


Figure 7.3.2 Range of Annual Energy Use for Residential Room Air Conditioners 


Without Reverse Cycle and with Louvers, Less than 6,000 Btu/h .................... 7-11 


Figure 7.3.3 Range of Annual Energy Use for Residential Room Air Conditioners 


Without Reverse Cycle and with Louvers, 8,000–13,999 Btu/h ....................... 7-11 


Figure 7.3.4 Range of Annual Energy Use for Residential Room Air Conditioners 


Without Reverse Cycle and with Louvers, 20,000 Btu/h or more..................... 7-12 


Figure 7.3.5 Range of Annual Energy Use for Residential Room Air Conditioners 


Without Reverse Cycle and without Louvers, 8,000–13,999 Btu/h .................. 7-12 


Figure 7.3.6 Range of Annual Energy Use for Commercial Room Air Conditioners 


Without Reverse Cycle and with Louvers, Less than 6,000 Btu/h .................... 7-13 


Figure 7.3.7 Range of Annual Energy Use for Commercial Room Air Conditioners 


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


Figure 7.3.8 Range of Annual Energy Use for Commercial Room Air Conditioners 


Without Reverse Cycle and with Louvers, 20,000 Btu/h or more..................... 7-14 


Figure 7.3.9 Range of Annual Energy Use for Commercial Room Air Conditioners 


Without Reverse Cycle and without Louvers, 8,000–13,999 Btu/h .................. 7-14 


Figure 7.4.1 Range of Annual Energy Use for Vented Electric Standard Clothes Dryers .... 7-20 


Figure 7.4.2 Range of Annual Energy Use for Vented Electric Compact 120V Clothes 


Dryers................................................................................................................. 7-20 


Figure 7.4.3 Range of Annual Energy Use for Vented Electric Compact 240V Clothes 


Dryers................................................................................................................. 7-21 


Figure 7.4.4 Range of Annual Gas Use for Vented Gas Clothes Dryers ............................... 7-21 


Figure 7.4.5 Range of Annual Electricity Use for Vented Gas Clothes Dryers..................... 7-22 


Figure 7.4.6 Range of Annual Energy Use for Vent-less 240V Clothes Dryers.................... 7-22 


Figure 7.4.7 Range of Annual Energy Use for Vent-less Combination Washer/Dryers........ 7-23 


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CHAPTER 7. ENERGY USE CHARACTERIZATION 


7.1 INTRODUCTION 


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

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

products. The LCC and PBP analyses require data on annual energy use because, along with 

energy prices, DOE uses these data to establish the most significant component of consumer 

operating costs. Maintenance and repair costs are the other contributors to operating cost. This 

chapter describes how DOE determined the annual energy consumption of room air conditioners 

(RAC) 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, 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. 

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EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

7.2 CONSUMER SAMPLES
 

7.2.1 Room Air Conditioners 

7.2.1.1 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 served as the primary source of air conditioning. 

• There were at most 3 room air conditioners reported. 

• Room air conditioner energy consumption was greater than zero. 

Households were assigned to the sub-samples based on the amount of cooling area 

(square footage as given by RECS) per room air conditioner in the home. DOE reasoned that 

homes with relatively more cooling area per unit have room air conditioners with higher cooling 

capacity. The correspondence between cooling area per unit and capacity was based on 

ENERGY STAR sizing guidelines for room air conditioners.b

 See appendix 7-A for more details. 

Table 7.2.1 shows the number of RECS records in each sub-sample. DOE used EIA’s weightings 

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

configuration occurs in the general population. 

Table 7.2.1	 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 1096 25.2 40.9 

> 6000 Btu/h Cooling sq. ft. per unit < 250 374 13.3 23.7 

8,000 to 13,999 

Btu/h 

Cooling sq. ft. per unit between 250 

and 650 635 24.6 49.8 

2 20,000 Btu/h Cooling sq. ft. per unit 2 650 or 

energy use per unit > 10 MMBtu/yr 108 3.7 6.7 

b

 http://www.energystar.gov/index.cfm?c=roomac.pr_properly_sized 

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EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

7.2.1.2 Commercial Building Sample 

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

sample met all of the following criteria: 

•	 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 7.2.2 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 7.2.2	 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 

2 20,000 Btu /h Total RAC Cooling sq. ft. 

> 900 

352 0.3 

7.2.2	 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. 

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

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. 

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EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

 

• Clothes dryer use was greater than zero. 

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

(Table 7.2.3). 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 7.2.3 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. and no garage or 

basement) 

570 14.4 

Gas Dryer Has Dryer = Yes 

Fuel Type = Natural Gas or LPG 

Use of Dryer > 0 

756 20.3 

7.3 ROOM AIR CONDITIONERS 

7.3.1 General Approach 

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

following equation: 

RACENERGY = (Capacity * OH)/EER 

Where:
 

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


Capacity = rated capacity in Btu/h,
 

OH = operating hours per year,
 

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EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

 

 

 

EER = Energy Efficiency Ratio in Btu/h/W. 

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

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

 The reported field energy consumption refers to the 

consumption of all of the room air conditioners in a home. 

RECS 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. 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. 

7.3.2 Operating Hours 

7.3.2.1 Residential 

DOE calculated the annual room air conditioner operating hours for each residential 

sample unit using the following formula: 

OH = (FECRECS * EERRECS)/Capacity 

Where: 

OH = operating hours per year,
 

FECRECS = field energy consumption for a room air conditioner, 


d

 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 

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EERE-2007-BT-STD-0010 COMMENT 20.3
EERRECS = the estimated EER of the room air conditioner in the sample home, 

Capacity = the room air conditioner capacity 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. 

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 7.3.1. DOE assumed a uniform distribution within 

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

Table 7.3.1 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 

1972–2007.3

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

2007.3 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 7.3.2 

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

for the representative product classes. 

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EERE-2007-BT-STD-0010 COMMENT 20.3
Table 7.3.2 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) 

2 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 AHAM3 

** Years in which standards became effective 

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

sample is 1,310 hr for the >6,000 Btu/h product class, 678 hr for 8,000 to 13,999 Btu/h product 

classes, and 394 hr for the 2 20,000 Btu/h product class. For comparison, the DOE test procedure 

uses 750 hours per year for all room air conditioners. 

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EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

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

investigated whether the 2005 heating season covered by RECS reflects representative climate. 

DOE found that the number of cooling degree-days (CDD) in 2005 was 12 percent higher than 

the 30-year average (1971–2000). DOE believes, however, that this year is a reasonable proxy 

for climate over the forecast period beginning in 2014. The AEO2008 includes a forecast of CDD 

that shows an increasing trend from 2010 to 2020.e

 The climate in 2005 is close to the average in 

the AEO climate forecast. 

7.3.2.2 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.4 

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).5

 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 7.3.1 for all hours of the 

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

e

 http://www.eia.doe.gov/oiaf/archive/aeo08/issues.html 

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EERE-2007-BT-STD-0010 COMMENT 20.3
hours/year above ASHRAE Std 55

CLDD vs #hours > ASHRAE Std55 

all day, all year 1991-2005 

10000 

y = 2.7592x + 127.99
 

9000
 R2

 = 0.9224 

8000 

7000 

6000
 

non-desert
 

desert
 5000 

Linear (non-desert)
 

Linear (desert)


4000
 

3000 

y = 1.153x + 574.04
 

2000
 R2

 = 0.8714 

1000 

0 

0 500 1000 1500 2000 2500 3000 3500 

CLDD (base 65F) 

Figure 7.3.1 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 7.3.3. 

Table 7.3.3 Regression Equations 

R2 Region Equation # 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. 

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EERE-2007-BT-STD-0010 COMMENT 20.3
 

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 1,219 hours for the greater than 6,000 

Btu/hr product class, 1,144 hours for the 8,000 to 13,999 Btu/hr product classes, and 1,180 hours 

for the greater than 20,000 Btu/hr product class. 

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

2003. To match the residential analysis, which was based on 2005 climate, DOE increased the 

estimated commercial sector operating hours by 8 percent, as given by the ratio of CDD between 

2005 and 2003. 

7.3.3 Variability of Room Air Conditioner Annual Energy Consumption 

Figures 7.3.2 to 7.3.9 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. 

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EERE-2007-BT-STD-0010 COMMENT 20.3
Figure 7.3.2	 Range of Annual Energy Use for Residential Room 

Air Conditioners Without Reverse Cycle and with 

Louvers, Less than 6,000 Btu/h 

Figure 7.3.3	 Range of Annual Energy Use for Residential Room 

Air Conditioners Without Reverse Cycle and with 

Louvers, 8,000–13,999 Btu/h 

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EERE-2007-BT-STD-0010 COMMENT 20.3
Figure 7.3.4	 Range of Annual Energy Use for Residential Room 

Air Conditioners Without Reverse Cycle and with 

Louvers, 20,000 Btu/h or more 

Figure 7.3.5	 Range of Annual Energy Use for Residential Room 

Air Conditioners Without Reverse Cycle and 

without Louvers, 8,000–13,999 Btu/h 

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EERE-2007-BT-STD-0010 COMMENT 20.3
Figure 7.3.6	 Range of Annual Energy Use for Commercial Room 

Air Conditioners Without Reverse Cycle and with 

Louvers, Less than 6,000 Btu/h 

Figure 7.3.7	 Range of Annual Energy Use for Commercial Room 

Air Conditioners Without Reverse Cycle and with 

Louvers, 8,000–13,999 Btu/h 

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EERE-2007-BT-STD-0010 COMMENT 20.3
Figure 7.3.8	 Range of Annual Energy Use for Commercial Room 

Air Conditioners Without Reverse Cycle and with 

Louvers, 20,000 Btu/h or more 

Figure 7.3.9	 Range of Annual Energy Use for Commercial Room 

Air Conditioners Without Reverse Cycle and 

without Louvers, 8,000–13,999 Btu/h 

7.3.4 Average Annual Energy Consumption by Efficiency Level 

Tables 7.3.4 through 7.3.7 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. 

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Table 7.3.4 Room Air Conditioner, Without Reverse Cycle and with Louvers, Less than 

6,000 Btu/h: Average Annual Energy Use 

Efficiency 

(IEER) 

Residential 

(kWh) 

Commercial 

(kWh) 

9.52 688 640 

10.1 648 604 

10.6 618 575 

11.1 590 549 

11.6 565 526 

12.0 546 508 

Table 7.3.5 Room Air Conditioner, Without Reverse Cycle and with Louvers, 8,000– 

13,999 Btu/h: Average Annual Energy Use 

Efficiency 

(IEER) 

Residential 

(kWh) 

Commercial 

(kWh) 

9.71 672 1181 

10.3 632 1110 

10.8 602 1059 

11.3 576 1012 

11.5 566 994 

Table 7.3.6 Room Air Conditioner, Without Reverse Cycle and with Louvers, 20,000 

Btu/h or more: Average Annual Energy Use 

Efficiency 

(IEER) 

Residential 

(kWh) 

Commercial 

(kWh) 

8.47 1118 3343 

9.0 1052 3146 

9.4 1007 3012 

9.8 966 2889 

10.0 947 2832 

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EERE-2007-BT-STD-0010 COMMENT 20.3
 

Table 7.3.7 Room Air Conditioner, Without Reverse Cycle and without Louvers, 

8,000–13,999 Btu/h: Average Annual Energy Use 

Efficiency 

(IEER) 

Residential 

(kWh) 

Commercial 

(kWh) 

8.43 712 1359 

8.9 673 1285 

9.3 644 1230 

9.8 611 1167 

7.3.5 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. 

7.4 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. 

7.4.1 Number of Cycles 

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

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

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

shown in Tables 7.4.1 and 7.4.2. For each question, DOE assumed a uniform distribution within 

the boundaries of each bin and randomly assigned a value from within the appropriate range to 

each sample household. 

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EERE-2007-BT-STD-0010 COMMENT 20.3
Table 7.4.1 Number of Loads Washed per Week Based on RECS 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 7.4.2 RECS 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 7.4.3). 

Table 7.4.3 RECS Sample Clothes Dryers Utilization 

Product Class 

Electric 

Standard Gas Ventless 

Clothes Dryer DOE 

Test Procedure 

Assumption 

Clothes Washer DOE 

Test Procedure 

Assumption 

Washer loads 

per year 

301 292 268 NA 392 

Clothes dryer 

frequency* 0.95 0.93 0.94 NA 0.84** 

Clothes dryer 

loads per year 285 271 252 416 329 

* Fraction of washer loads 

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

7.4.2 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 

DOE test procedure calculates active mode energy consumption by dividing the weight (lbs) of 

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EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

clothes dried per cycle (7 lbs for standard and 3 lbs for compact clothes dryers) and by the 

Energy Factor (EF) (lbs/kWh).f

 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 field adjustment for clothes dryer energy use 

during active mode by using the following formula: 

avgLoadWeightTP avgLoadWeight RMC Field Field CD _ EnergyUse = ∗( J ∗( J ∗CD _ Cycles ActiveMode ( J ( J EF avgLoadWeight TP RMCTP 

Where: 

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, percent, 

RMCField = remaining moisture content for the household, percent, 

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

CD_Cycles = clothes dryer cycles per year. 

To assign an average load weight for each household, DOE developed a distribution of 

load weights by matching the listed tub sizes for models in the Dec. 22, 2008 California Energy 

Commission (CEC) directory with the correlations between tub size and average pounds in the 

DOE test procedure. The average load weights for standard-size units range from 5.1 lbs. to 10 

lbs., with a mean value of 8.1 lbs. For comparison, the DOE test procedure uses a weight of 7 lbs 

for standard-size units. 

To assign a RMC value for each household, DOE used a distribution of values based on 

the number of models listed at each RMC in the Dec. 22, 2008 CEC directory. The RMC values 

range from 30 percent to 61 percent, with an average of 46 percent. The remaining moisture 

content (RMC) in the test procedure is 70 percent. 

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

active mode energy consumption for each sample household with 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 electric 

components. An estimate of 200 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 187 kWh. 

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

standby mode by using the following formula: 

f

 See chapter 5 for more information on how to convert from IEF to EF. IEF assumes 416 cycles, 8156 hours of 

standby, and a standby power that varies by efficiency level. 

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EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

 

 

 

 

 

CD Time
 ClothesDryerEnergyUseStandby =
 −
 CD Cycles
 * Standby_Power
 _ 

60
 

8760 _ ∗( J

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. 

For vent-less clothes dryers, DOE considered the impact of the dryer on the home’s 

heating and cooling loads. A vent-less dryer releases heat to the surrounding environment. If the 

dryer is located indoors, dryer use will tend to slightly reduce the heating load during the heating 

season and slightly increase the cooling load during the cooling season. DOE believes that the 

effect is the same for all of the considered efficiency levels, and thus it did not include this factor 

in its analysis. 

 

 

[

7.4.3 Variability of Annual Energy Consumption 

 Figures 7.4.1 to 7.4.7 show the range of average annual energy consumption (active and 

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

 

 

:

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EERE-2007-BT-STD-0010 COMMENT 20.3
Electric Standard Average Annual Energy Use 

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

0 

200 

400 

600 

800 

1000 

1200 

1400 

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

Efficiency Level 

Annual Energy Use (kWh) 

median 

Average 

Figure 7.4.1 Range of Annual Energy Use for Vented Electric 

Standard Clothes Dryers 

Electric Compact 120V Average Annual Energy Use 

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

0 

100 

200 

300 

400 

500 

600 

700 

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

Efficiency Level 

Annual Energy Use (kWh) 

median 

Average 

Figure 7.4.2 Range of Annual Energy Use for Vented Electric 

Compact 120V Clothes Dryers 

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EERE-2007-BT-STD-0010 COMMENT 20.3
0 

100 

200 

300 

400 

500 

600 

700 

800 

Level 0 

Annual Energy Use (kWh) 

Electric Compact 240V Average Annual Energy Use 

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

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

Efficiency Level 

median 

Average 

Figure 7.4.3 Range of Annual Energy Use for Vented Electric 

Compact 240V Clothes Dryers 

0 

1 

1 

2 

2 

3 

3 

4 

4 

5 

5 

Level 0 

Annual Gas Use (MMBtu) 

Gas Average Annual Gas Use 

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

Level 1 Level 2 Level 3 Level 4 Level 5 

Efficiency Level 

median 

Average 

Figure 7.4.4 Range of Annual Gas Use for Vented Gas Clothes 

Dryers 

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EERE-2007-BT-STD-0010 COMMENT 20.3
Gas Average Annual Electricity Use 

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

0 

1 

1 

2 

2 

3 

3 

4 

4 

5 

5 

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

Efficiency Level 

Annual Electricity Use (kWh) 

median 

Average 

Figure 7.4.5 Range of Annual Electricity Use for Vented Gas 

Clothes Dryers 

Ventless 240V Average Annual Energy Use 

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

0 

100 

200 

300 

400 

500 

600 

700 

800 

900 

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

Efficiency Level 

Annual Energy Use (kWh) 

median 

Average 

Figure 7.4.6 Range of Annual Energy Use for Vent-less 240V 

Clothes Dryers 

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EERE-2007-BT-STD-0010 COMMENT 20.3
Ventless Combination Average Annual Energy Use 

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

0 

200 

400 

600 

800 

1000 

1200 

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

Efficiency Level 

Annual Energy Use (kWh) 

median 

Average 

Figure 7.4.7	 Range of Annual Energy Use for Vent-less 

Combination Washer/Dryers 

7.4.4 Average Annual Energy Consumption by Efficiency Level 

Tables 7.4.4 through 7.4.6 present the average annual energy consumption by efficiency 

level for each considered clothes dryer product class. 

Table 7.4.4	 Electric Standard and Gas Clothes Dryer: Average Annual Energy 

Consumption by Efficiency Level 

Electric Gas 

Integrated 

Energy Factor 

(lb/kWh) 

kWh/year 

Integrated 

Energy Factor 

(lb/kWh) 

MMBtu/ 

year kWh/year 

2.96 519 2.63 1.65 71.4 

3.04 504 2.71 1.60 71.4 

3.10 495 2.80 1.53 71.4 

3.33 461 2.97 1.45 67.9 

3.35 457 2.98 1.45 63.6 

3.40 445 3.02 1.45 51.6 

4.52 335 -- -- --

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EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

 

Table 7.4.5 Electric Compact Vented Dryer: Average Annual Energy Consumption by 

Efficiency Level 

120V 240V 

Integrated 

Energy Factor 

(lb/kWh) 

kWh/year 

Integrated 

Energy Factor 

(lb/kWh) 

kWh/year 

3.00 270 2.79 290 

3.08 263 2.86 283 

3.15 258 2.96 274 

3.37 241 3.06 265 

3.41 237 3.10 260 

3.53 225 3.19 248 

4.69 169 4.34 183 

Table 7.4.6 Electric Compact Vent-less Dryer and Combination Washer/Dryer: Average 

Annual Energy Consumption by Efficiency Level 

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

Integrated 

Energy Factor 

(lb/kWh) 

kWh/year 

Integrated 

Energy Factor 

(lb/kWh) 

kWh/year 

2.29 351 1.90 424 

2.31 347 2.15 375 

2.37 335 2.34 344 

2.39 332 2.36 340 

2.59 307 2.42 328 

3.54 224 3.31 239 

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REFERENCES 

1. 	 U.S. Department of Energy - Energy Information Administration, Residential Energy 

Consumption Survey: 2005 Public Use Data Files, 2005. 

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

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

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

3. 	 Association of Home Appliance Manufacturers, Trends in Energy Efficiency 2008 2008 

4. 	 American National Standards Institute & American Society of Heating, R., and AirConditioning Engineers, Inc.,, ANSI/ASHRAE 55-2004 Thermal Environmental 

Conditions for Human Occupancy, 2004. 

5. 	 National Renewable Energy Laboratory, National Solar Radiation Database 1991–2005 

Update: User’s Manual, 2007. <http://www.nrel.gov/docs/fy07osti/41364.pdf> 

6. 	 Pescatore, P. and P. Carbone, High Efficiency, High Performance Clothes Dryer, March 

31, 2005. TIAX. Report No. D0040. <http://www.osti.gov/bridge/servlets/purl/888669­

2VIDn8/888669.pdf> 

7. 	 Hekmat, D. and W. J. Fisk, IMPROVING THE ENERGY PERFORMANCE OF 

RESIDENTIAL CLOTHES DRYERS, February, 1984. LBNL. Report No. LBL-17501. 

<http://escholarship.org/uc/item/2f3347r8> 

8. 	PricewaterhouseCoopers, Ecodesign of Laundry Dryers, Preparatory studies for 

Ecodesign requirements of Energy-using-Products (EuP) – Lot 16, June 30, 2008. 

CODDE. <http://www.ecodryers.org/> 

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