APPENDIX 7-C. LCC ENERGY USE CALCULATIONS
 

TABLE OF CONTENTS
 

7-C.1 INTRODUCTION ....................................................................................................... 7-C-2 

7-C.2 ROOM AIR CONDITIONERS ................................................................................... 7-C-2 

7-C.2.1 General Approach ...................................................................................... 7-C-2 

7-C.2.2 Operating Hours......................................................................................... 7-C-3 

7-C.2.2.1 Residential.................................................................................................. 7-C-3 

7-C.2.2.2 Commercial................................................................................................ 7-C-7 

7-C.3 CLOTHES DRYERS................................................................................................. 7-C-17 

7-C.3.1 Number of Cycles .................................................................................... 7-C-18 

7-C.3.2 Energy Use Calculation ........................................................................... 7-C-19 

LIST OF TABLES 

Table 7-C.2.1 RECS Vintage Bins for Room Air Conditioner......................................... 7-C-4 

Table 7-C.2.2 Fraction of Shipments of Room Air Conditioner by Product Class .......... 7-C-6 

Table 7-C.2.3 Average Room Air Conditioner EER by Product Class and Year Sold .... 7-C-7 

Table 7-C.2.4 Average Room Air Conditioner EER by Product Class and Year Sold .. 7-C-12 

Table 7-C.2.5 Regression Equations............................................................................... 7-C-14 

Table 7-C.2.6 Building Type and Abbreviation ............................................................. 7-C-15 

Table 7-C.2.7 Building Schedules and Abbreviation ..................................................... 7-C-15 

Table 7-C.2.8 Room Air Conditioner Operating Hour Equations By Building Type 

and Schedule ............................................................................................ 7-C-15 

Table 7-C.2.9 Room Air Conditioner Operating Hour Equations By Building Type 

and Schedule (Desert).............................................................................. 7-C-16 

Table 7-C.2.10 CBECS 2003 Building Code Match to Room Air Conditioner 

Equation Building Type........................................................................... 7-C-17
 

Table 7-C.3.1 Number of Loads Washed per Week Based on RECS Sample ............... 7-C-18
 

Table 7-C.3.2 RECS Sample Clothes Dryer Usage........................................................ 7-C-18
 

Table 7-C.3.3 RECS Sample Clothes Dryers Utilization ............................................... 7-C-19
 

LIST OF FIGURES 

Figure 7-C.2.1 1972–2008 Average Shipment Weighted EER for Room Air 

Conditioners............................................................................................... 7-C-5 

Figure 7-C.2.2 ANSI/SHRAE Standard 55-2004: Thermal Environmental Conditions 

for Human Occupancy ............................................................................... 7-C-8
 

Figure 7-C.2.3 National Solar Radiation Database (NSRDB) Stations ............................. 7-C-9
 

Figure 7-C.2.4 Hours Above Comfort Zone in Palm Springs (1991) .............................. 7-C-11
 

Figure 7-C.2.5 Hours Above the Standard 55 Comfort Zone Compared to CLDD......... 7-C-12
 

Figure 7-C.2.6 Hours Above the Standard 55 Comfort Zone versus CLDD with
 

Different Regions Highlighted................................................................. 7-C-13 

Figure 7-C.2.7 Hours Above ANSI/ASHRAE Standard 55-2004 as a Function of 

Cooling Degree-Days............................................................................... 7-C-14
 

7-C-i 

EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

APPENDIX 7-C. LCC ENERGY USE CALCULATIONS
 

7-C.1 INTRODUCTION
 

This appendix contains the calculation methodology for calculating the energy use of 

room air conditioners (RAC) and clothes dryers in the life-cycle cost (LCC) analysis. 

7-C.2 ROOM AIR CONDITIONERS 

7-C.2.1 General Approach 

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

following equation: 

Capacity ∗OH RACENERGY = IEER 

Where:
 

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

Capacity = rated capacity in Btu/h,
 

OH = operating hours per year,
 

IEER = Integrated Energy Efficiency Ratio in Btu/h/W.
 

DOE used the same representative capacities for each product class (PC) as it did in the 

engineering analysis: 5 kBtu/h for < 6000 Btu/h product classes (PC 3 and 8), 8 and 12 kBtu/h 

for 8000–13,999 Btu/hr product class (PC 1)a

, and 24 kBtu/h product class (PC 5). The IEER is 

also determined in the engineering analysis and is a new energy factor descriptor that 

incorporates standby power. The IEER is calculated as capacity times active mode hours (equal 

to 750) divided by the sum of active mode annual energy use and inactive mode annual energy 

use. The number of hours associated with this standby mode for room air conditioners is 5,115 

hours per year. See chapter 5 for details. 

For residential room air conditioners, the operating hours of the RAC are determined 

using the data reported by RECS 2005 on the annual energy consumption (field energy 

consumption) for room air conditioning, as well as assumed EER and capacity values for the 

existing room air conditioner. 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 degreedays. The following section provides a detailed explanation of the methodology for estimating 

the number of room air conditioner operating hours for each household or commercial building 

in the samples. 

a The fraction of 8 and 12 kBtu/h units was assumed to be equal, so each are assigned to a specific household 50 

percent of the time. 

7-C-2 

EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

7-C.2.2 Operating Hours 

7-C.2.2.1 Residential 

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

sample unit using the following formula: 

FEC ∗ EER RECS RECS OH = Capacity 

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.
 

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

analysis.b 

To estimate the energy consumption of a single room air conditioner, referred to as 

FECRECS, DOE divided the RECS 2005 reported annual energy consumption (field energy 

consumption) for room air conditioning, referred to as 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. The reported RECS 2005 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.c 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. 

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 

b 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) that the household or building owner would purchase if their room air conditioner 

failed. 

c 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 

7-C-3 

EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

includes a forecast of CDD that shows an increasing trend from 2010 to 2020.d The climate in 

2005 is close to the average in the AEO the climate forecast. 

In RECS 2005, some households are identified as having purchased ENERGY STAR air 

conditioners in the last 4 years. For these households, DOE applied the appropriate ENERGY 

STAR EER. For the rest of the sample, DOE estimated the EER of the existing 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-C.2.1. DOE 

assumed a uniform distribution within each vintage bin and assigned an age to the room air 

conditioner in each sample household. 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. 

Table 7-C.2.1 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 

To derive a time series of average EER by capacity, DOE began with data from AHAM 

on total shipment-weighted average EER for 1972–2008 (See Figure 7-C.2.1). AHAM also 

provided average EER data by product class (capacity) for 2005–2007.1 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. 

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

7-C-4 

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

 

 

 

 

 

 

 

10 

11 

Average Shipment Weighted 

9 

8 

7 

1990 1995 2000 2005 2010 

Year 

Figure 7-C.2.1	 1972–2008 Average Shipment Weighted EER for 

Room Air Conditioners 

DOE then estimated the shares of total shipments by product class in each year using data 

for 1989, 1992, and 2005–2007, and calculated a total shipment-weighted EER (See Table 7­

C.2.2). DOE then calculated scalars for each year from the ratio of the actual total shipmentweighted EER to the calculated EER, and then applied the scalars to the minimum efficiency 

required for each product class in each year. 

6 

5 

1970 1975 1980 1985 

7-C-5 

EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 7-C.2.2 Fraction of Shipments of Room Air Conditioner by Product Class
 

Product Class 2007 2006 2005 1992 1989 

1 

Without reverse 

cycle and with 

louvered sides 

Less than 6,000 Btu/h 32.0% 23.0% 37.0% 26.7% 27.7% 

2 6,000 to 7,999 Btu/h 16.0% 19.0% 19.0% 14.4% 17.7% 

3 8,000 to 13,999 Btu/h 36.0% 34.0% 30.0% 32.8% 29.7% 

4 14,000 to 19,999 Btu/h 6.0% 5.5% 3.0% 13.1% 13.2% 

5 20,000 Btu/h and more 2.6% 3.9% 2.0% 6.3% 7.0% 

6 

Without reverse 

cycle and without 

louvered sides 

Less than 6,000 Btu/h 

7.0% 12.0% 7.0% 

7 6,000 to 7,999 Btu/h 2.1% 3.2% 

8 8,000 to 13,999 Btu/h 2.1% 

9 14,000 to 19,999 Btu/h 

10 20,000 Btu/h and more 

11 With reverse 

cycle and with 

louvered sides 

Less than 20,000 Btu/h ** 

1.0% 

0.7% 

2.1% 1.5% 

12 20,000 Btu/h and more 0.1% 

13 With reverse 

cycle and without 

louvered sides 

Less than 14,000 Btu/h ** 

0.6% 0.4% 0.5% 

14 14,000 Btu/h and more 

15 Casement Casement Only 0.4% 0.6% 0.4% 

16 Casement Slider 

Table 7-C.2.3 shows the AHAM data on total shipment-weighted average EER and the 

average EER estimated for the representative product classes. 

7-C-6 

EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 7-C.2.3 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 AHAM1 

** Years in which standards became effective 

7-C.2.2.2 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 

7-C-7 

EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

number of building type and building schedule combinations. DOE assumed that the 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 

(see figure 7-C.2.2).2 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. 

Figure 7-C.2.2	 ANSI/SHRAE Standard 55-2004: Thermal 

Environmental Conditions for Human Occupancy 

ANSI/ASHRAE Standard 55 assumes that metabolic rates of 1.1 met, (engaged in near 

sedentary physical activity), 0.5 clo of clothing insulation, insulation levels typical of clothing 

worn when the outdoor environment is warm, air speeds are not greater than 0.20 m/s (40 

ft/min), upper recommended humidity limit, and 0.012 humidity ratio. The range of operative 

temperatures presented in Figure 7-C.2.2 are for 80 percent occupant acceptability. This is based 

on a 10 percent dissatisfaction criteria for general (whole body) thermal comfort based on the 

PMV-PPD index, plus an additional 10 percent dissatisfaction that may occur on average from 

local (partial body) thermal discomfort. Predicted mean vote (PMV) index is an index that 

predicts the mean value of the votes of a large group of persons on the seven point thermal 

7-C-8 

EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

sensation scale. The predicted percentage of dissatisfied (PPD) index is an index that establishes 

a quantitative prediction of the percentage of thermally dissatisfied people determined from 

PMV. The room air conditioner is assumed to operate if the outdoor conditions are outside 

comfort zone if W (humidity ratio)>0.012 or T>Tcomf for that humidity ratio. Tcomf is given by 

the following equation: Tcomf = −117.7081 ×W + 28.25491422 , where W is the humidity ratio 

at the outdoor conditions for that hour. 

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

(NSRDB).3 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 1454 

stations, which are subdivided into three classes of stations (see figure 7-C.2.3). A total of 858 

sites have a complete 15-year period of record. 

Figure 7-C.2.3	 National Solar Radiation Database (NSRDB) 

Stations 

Stations are identified with a USAF number as follows: 

•	 Class I Stations have a complete period of record (all hours 1991–2005) for solar and key 

meteorological fields and have the highest-quality solar modeled data (221 sites). 

•	 Class II Stations have a complete period of record but significant periods of interpolated, 

filled, or otherwise lower-quality input data for the solar models (637 sites). 

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

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

7-C-9 

EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The NSRDB has complete measured hourly Dry Bulb Temperature, Dew Point 

Temperature, Relative Humidity, and Atmospheric Pressure for all Class I & Class II Stations. 

The Dry Bulb Temperature, Relative Humidity, and Atmospheric Pressure fields were used to 

calculate the humidity ratio for each hour. The humidity ratio was calculated using procedures 

from the 2005 ASHRAE Handbook-Fundamentals, Chapter 6 Psychrometrics. Under the section 

on Numerical Calculation of Moist Air Properties, Situation 3 describes the process to calculate 

humidity ratio (W) from Dry Bulb Temperature, Relative humidity, and Pressure. The saturation 

pressure for the dry bulb temperature is calculated using the following equation: 

C8 2 3 ln( Pws ) = + C9 + C10 ×T + C11 ×T + C12 ×T + C13 × ln( T ) T 

where: 

C8 = -5.8002206 E+03 

C9 = 1.3914993 E+00 

C10 = -4.8640239 E-02 

C11 = 4.1764768 E-05 

C12 = -1.4452093 E-08 

C13 = 6.5459673 E+00 

Pws = saturation pressure, Pa 

T = absolute temperature, K = °C + 273.15 

The water vapor partial pressure is the saturation pressure multiplied by the relative 

humidity. 

Pw = φ × Pws 

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

dry air contained in the sample. It can be calculated from the pressure and the water vapor 

partial pressure as: 

Pw W = 0.62198× (P - Pw)

The testing the conditions for that hour against the criteria from Std 55, we can determine 

if the room air conditioner would have operated during that hour. 

Figure 7-C.2.4 shows the hours (2281 hours) in 1991 that were above the comfort zone 

for Palm Springs. 

7-C-10 

EERE-2007-BT-STD-0010 COMMENT 20.3
Hours above comfort zone
 

Palm Springs, 1991
 

0.03 

0.025 

humidity ratio 

100%RH 0.02 90%RH 

80%RH 

70%RH 

60%RH 0.015 50%RH 

40%RH 

30%RH 

0.01 20%RH 

10%RH

0.005 

0 

0 5 10 15 20 25 30 35 40 45 50 

dry bulb temperature 

Figure 7-C.2.4 Hours Above Comfort Zone in Palm Springs 

(1991) 

 Figure 7-C.2.5 shows hours above the Standard 55 comfort zone compared to CLDD for 

15 years (1991-2005) for all Class 1 & II weather stations. 

Room AC Operating Hours
 

10000
 

9000
 

8000
 

7000
 

hours above Std 55

6000 

5000 

4000 

3000 

2000 

1000 

0 

0 500 1000 1500 2000 2500 3000 3500 4000 

CLDD 65 

7-C-11

EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 7-C.2.5	 Hours Above the Standard 55 Comfort Zone 

Compared to CLDD 

The lower ‘branch’ in the ‘hours above Std 55’ vs ‘CLDD 65’ is from low desert
 

locations. After examining the data, the following sites were classified as desert.
 

Table 7-C.2.4 Average Room Air Conditioner EER by Product Class and Year Sold 

STATION ST 

DAVIS MONTHAN AFB AZ 

DEER VALLEY/PHOENIX AZ 

DOUGLAS BISBEE-DOUGLAS INTL A AZ 

KINGMAN (AMOS) AZ 

LUKE AFB AZ 

PHOENIX SKY HARBOR INTL AP AZ 

SCOTTSDALE MUNI AZ 

TUCSON INTERNATIONAL AP AZ 

YUMA INTL ARPT AZ 

YUMA MCAS AZ 

BAKERSFIELD MEADOWS FIELD CA 

BLYTHE RIVERSIDE CO ARPT CA 

CHINA LAKE NAF CA 

DAGGETT BARSTOW-DAGGETT AP CA 

EDWARDS AFB CA 

IMPERIAL CA 

LANCASTER GEN WM FOX FIELD CA 

NEEDLES AIRPORT CA 

PALM SPRINGS INTL CA 

PALM SPRINGS THERMAL AP CA 

PALMDALE AIRPORT CA 

TWENTYNINE PALMS CA 

CARLSBAD CAVERN CITY AIR TERM NM 

DEMING MUNI NM 

HOLLOMAN AFB NM 

LAS CRUCES INTL NM 

ROSWELL INDUSTRIAL AIR PARK NM 

TRUTH OR CONSEQUENCES MUNI AP NM 

LAS VEGAS MCCARRAN INTL AP NV 

MERCURY DESERT ROCK AP [SURFRAD] NV 

NELLIS AFB NV 

EL PASO INTERNATIONAL AP [UT] TX 

SAINT GEORGE (AWOS) UT 

In Figure 7-C.2.6, the desert and tropical sites are shown. The uppermost points on the 

original chart (Figure 7-C.2.5) represent data from stations in Hawaii, Guam and the Caribbean. 

7-C-12 

EERE-2007-BT-STD-0010 COMMENT 20.3
Room AC Operating Hours 

hours above Std 55 10000 

9000 

8000 

7000 

6000 

all 

HI & Guam 5000 Caribbean 

desert

4000 

3000 

2000 

1000 

0 

0 500 1000 1500 2000 2500 3000 3500 4000 

CLDD 65 

Figure 7-C.2.6 Hours Above the Standard 55 Comfort Zone 

versus CLDD with Different Regions Highlighted 

 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-C.2.7 for all hours of the 

year. This represents 842 sites for 15 years each in the continental United States. 

7-C-13

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
 2 R = 0.9224 

8000 

7000 

6000
 

non-desert
 

desert
 5000 Linear (non-desert)
 

Linear (desert)


4000
 

3000 

y = 1.153x + 574.04
 

2000
 2 R = 0.8714 

1000 

0 

0 500 1000 1500 2000 2500 3000 3500 

CLDD (base 65F) 

Figure 7-C.2.7 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 used to derive 

the average annual hours when the outdoor air conditions are above the ASHRAE Standard 55 

comfort zone (OH55) are shown in Table 7-C.2.5. 

Table 7-C.2.5 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 

 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 each of 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. The building types and schedule abbreviations are shown in table 7­

C.2.6 and 7-C.2.7. An assumption was made that if the occupancy rate was greater than 20% of 

full occupancy, the room air-conditioner would operate if the outdoor air conditions were above 

the ASHRAE standard 55 comfort zone. 

7-C-14

EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 7-C.2.6 Building Type and Abbreviation
 

Building Type Abbreviation 

Assembly ASM 

Education EDU 

Food Service FDS 

Lodging LOD 

Medical MED 

Office OFF 

Outdoor OUT 

Retail RET 

Warehouse WHS 

Table 7-C.2.7 Building Schedules and Abbreviation
 

Building Schedules Abbreviation 

24/7 hours 247 

Monday-Friday M-F 

Monday - Friday and Saturday and Sunday ALL 

The equations to predict the hours per year the outdoor air conditions are above the 

ASHRAE Standard 55 comfort zone for various building types and schedules for non-desert 

locations are shown table 7-C.2.8. 

Table 7-C.2.8	 Room Air Conditioner Operating Hour Equations By Building Type and 

Schedule 

building 

type 

open 

schedule 

equation R2 

ALL 247 ROH55 = 2.759 x CLDD + 127.99 0.9224 

OUT 

OUT 

M_F 

ALL 

ROH55 = 1.974 x CLDD + 93.29 

ROH55 = 2.759 x CLDD + 127.99 

0.9458 

0.9430 

ASM 

ASM 

M_F 

ALL 

ROH55 = 0.751 x CLDD + 119.67 

ROH55 = 1.396 x CLDD + 169.18 

0.9458 

0.9430 

EDU 

EDU 

M_F 

ALL 

ROH55 = 1.001 x CLDD + 117.11 

ROH55 = 1.398 x CLDD + 163.52 

0.9412 

0.9424 

FDS 

FDS 

M_F 

ALL 

ROH55 = 1.243 x CLDD + 112.91 

ROH55 = 1.510 x CLDD + 166.44 

0.9354 

0.9408 

LOD 

LOD 

M_F 

ALL 

ROH55 = 1.471 x CLDD + 17.11 

ROH55 = 2.206 x CLDD + 40.94 

0.9428 

0.9408 

MED 

MED 

M_F 

ALL 

ROH55 = 1.001 x CLDD + 128.06 

ROH55 = 1.151 x CLDD + 148.72 

0.9428 

0.9408 

OFF 

OFF 

M_F 

ALL 

ROH55 = 0.918 x CLDD + 119.76 

ROH55 = 1.510 x CLDD + 166.44 

0.9428 

0.9408 

RET 

RET 

M_F 

ALL 

ROH55 = 0.751 x CLDD + 119.67 

ROH55 = 1.281 x CLDD + 170.57 

0.9458 

0.9450 

WHS 

WHS 

M_F 

ALL 

ROH55 = 0.836 x CLDD + 109.17 

ROH55 = 1.514 x CLDD + 178.06 

0.9422 

0.9419 

7-C-15 

EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The highlighted rows are the same. This is because the occupancy rates were above 20 

percent for 24 hours per day for all building types operating under the 24/7 schedule. The 

analysis does not account for differences in building operation schedules due to holidays. 

The equations to predict the hours per year the outdoor air conditions are above the 

ASHRAE Standard 55 comfort zone for various building types and schedules for desert locations 

are shown table 7-C.2.9. 

Table 7-C.2.9	 Room Air Conditioner Operating Hour Equations By Building Type and 

Schedule (Desert) 

building 

type 

open 

schedule 

equation R2 

ALL 247 ROH55 = 1.153 x CLDD + 574.04 0.9224 

OUT 

OUT 

M_F 

ALL 

ROH55 = 1.974 x CLDD + 93.29 

ROH55 = 2.759 x CLDD + 127.99 

0.8353 

0.8925 

ASM 

ASM 

M_F 

ALL 

ROH55 = 0.289 x CLDD + 546.12 

ROH55 = 0.600 x CLDD + 721.20 

0.8353 

0.8925 

EDU 

EDU 

M_F 

ALL 

ROH55 = 0.409 x CLDD + 532.56 

ROH55 = 0.572 x CLDD + 741.06 

0.8723 

0.8794 

FDS 

FDS 

M_F 

ALL 

ROH55 = 0.553 x CLDD + 449.33 

ROH55 = 0.663 x CLDD + 690.02 

0.8914 

0.8985 

LOD 

LOD 

M_F 

ALL 

ROH55 = 0.642 x CLDD + 40.06 

ROH55 = 0.951 x CLDD + 157.74 

0.8260 

0.8985 

MED 

MED 

M_F 

ALL 

ROH55 = 0.402 x CLDD + 603.12 

ROH55 = 0.458 x CLDD + 706.19 

0.8260 

0.8985 

OFF 

OFF 

M_F 

ALL 

ROH55 = 0.353 x CLDD + 573.23 

ROH55 = 0.663 x CLDD + 690.02 

0.8260 

0.8985 

RET 

RET 

M_F 

ALL 

ROH55 = 0.289 x CLDD + 546.12 

ROH55 = 0.534 x CLDD + 749.00 

0.8353 

0.8813 

WHS 

WHS 

M_F 

ALL 

ROH55 = 0.317 x CLDD + 524.97 

ROH55 = 0.612 x CLDD + 837.58 

0.8087 

0.8682 

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

CBECS 2003 room air conditioner sample, DOE identified the building type (see Table 7­

C.2.10) 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. 

7-C-16 

EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 7-C.2.10 CBECS 2003 Building Code Match to Room Air Conditioner Equation 

Building Type 

CBECS 

2003 PBA 

Code Definition Building Type Match 

Fraction of 

CBECS 2003 

RAC Sample 

1 Vacant Not Applicable 

2 Office OFF 18.3% 

4 Laboratory MED 0.2% 

5 Nonrefrigerated warehouse WHS 5.9% 

6 Food sales RET 2.9% 

7 Public order and safety OFF 4.1% 

8 Outpatient health care MED 0.6% 

11 Refrigerated warehouse WHS 0.0% 

12 Religious worship ASM 8.7% 

13 Public assembly ASM 5.5% 

14 Education EDU 12.7% 

15 Food service FDS 4.5% 

16 Inpatient health care MED 0.2% 

17 Nursing MED 1.4% 

18 Lodging LOD 3.5% 

23 Strip shopping mall RET 0.0% 

24 Enclosed mall RET 0.0% 

25 Retail other than mall RET 11.8% 

26 Service RET 17.3% 

91 Other OFF 2.3% 

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

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

are ± 10% from the regression line for the appropriate building type/schedule combination. 

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-C.3 CLOTHES DRYERS 

DOE determined the annual energy consumption by-products that would meet a potential 

future standard by multiplying the number of cycles per year by the energy use per cycle. 

7-C-17 

EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

7-C.3.1 Number of Cycles 

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

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

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

Tables 7-C.3.1 and 7-C.3.2. 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. 

Table 7-C.3.1 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-C.3.2 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-C.3.3). 

7-C-18 

EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 7-C.3.3 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-C.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 

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

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

Energy Factor (EF) (lbs/kWh).e 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: 

⎛ ⎛⎞⎟

⎠

⎟ ∗

⎞

⎟

⎠

⎟ ∗ avgLoadWeight TP ∗ avgLoadWeight
 Field RMC
 Field CD EnergyUse
 = ⎜ CD Cycles
 ⎜

⎝

⎜

⎜

⎝

_ ActiveMode _ EF
 avgLoadWeight
 TP RMC
 TP 

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.
 

e 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. 

7-C-19 

EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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: 

ClothesDryerEnergyUse
S tan dby =
 

⎡

⎢

⎣

8760 − CD _ Cycles ∗
 

⎛

⎜

⎝

⎞

⎟

⎠

CD _ Time
 ⎤

∗ S tan dby _ Power
 ⎥ 60
 ⎦

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. 

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-C-20 

EERE-2007-BT-STD-0010 COMMENT 20.3
 

 

 

 

 

 

REFERENCES
 

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

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

Conditions for Human Occupancy, 2004. 

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

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

7-C-21 

EERE-2007-BT-STD-0010 COMMENT 20.3