7-C-i 

APPENDIX 7-C. LCC ENERGY USE CALCULATIONS

TABLE OF CONTENTS

7-C.1 INTRODUCTION ....................................................................................................... 7-C-3

7-C.2 CLOTHES DRYERS ................................................................................................... 7-C-3

7-C.2.1 Number of Cycles ...................................................................................... 7-C-3

7-C.2.2 Energy Use Calculation ............................................................................. 7-C-4

7-C.3 ROOM AIR CONDITIONERS ................................................................................... 7-C-7

7-C.3.1 General Approach ...................................................................................... 7-C-7

7-C.3.2 Operating Hours ......................................................................................... 7-C-8

7-C.3.2.1 Residential.................................................................................................. 7-C-8

7-C.3.2.2 Commercial .............................................................................................. 7-C-12

LIST OF TABLES

Table 7-C.2.1 Number of Loads Washed per Week Based on RECS Sample ................. 7-C-3

Table 7-C.2.2 RECS Sample Clothes Dryer Usage .......................................................... 7-C-3

Table 7-C.2.3 RECS Sample Clothes Dryers Utilization ................................................. 7-C-4

Table 7-C.3.1 RECS Vintage Bins for Room Air Conditioner ......................................... 7-C-9

Table 7-C.3.2 Fraction of Shipments of Room Air Conditioner by Product Class ........ 7-C-11

Table 7-C.3.3 Average Room Air Conditioner EER by Product Class and Year Sold .. 7-C-12

Table 7-C.3.4 Weather Stations Classified as Desert ..................................................... 7-C-17

Table 7-C.3.5 Regression Equations ............................................................................... 7-C-19

Table 7-C.3.6 Building Type and Abbreviation ............................................................. 7-C-20

Table 7-C.3.7 Building Schedules and Abbreviation ..................................................... 7-C-20

Table 7-C.3.8 Room Air Conditioner Operating Hour Equations By Building Type 

and Schedule ............................................................................................ 7-C-21

Table 7-C.3.9 Room Air Conditioner Operating Hour Equations By Building Type 

and Schedule (Desert) .............................................................................. 7-C-22

Table 7-C.3.10 CBECS 2003 Building Code Match to Room Air Conditioner 

Equation Building Type ........................................................................... 7-C-23

LIST OF FIGURES

Figure 7-C.3.1 1972–2008 Average Shipment Weighted EER for Room Air 

Conditioners ............................................................................................. 7-C-10

Figure 7-C.3.2 ANSI/SHRAE Standard 55-2004: Thermal Environmental Conditions 

for Human Occupancy ............................................................................. 7-C-13

Figure 7-C.3.3 National Solar Radiation Database (NSRDB) Stations ........................... 7-C-14

Figure 7-C.3.4 Hours Above Comfort Zone in Palm Springs (1991) .............................. 7-C-16

Figure 7-C.3.5 Hours Above the Standard 55 Comfort Zone Compared to CLDD......... 7-C-17

Figure 7-C.3.6 Hours Above the Standard 55 Comfort Zone versus CLDD with 

Different Regions Highlighted ................................................................. 7-C-18
7-C-ii

Figure 7-C.3.7 Hours Above ANSI/ASHRAE Standard 55-2004 as a Function of 

Cooling Degree-Days............................................................................... 7-C-19
7-C-3

APPENDIX 7-C. LCC ENERGY USE CALCULATIONS

7-C.1 INTRODUCTION

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

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

7-C.2 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.2.1 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.2.1 and 7-C.2.2. 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.2.1 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.2.2 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.2.3). 
7-C-4

Table 7-C.2.3 RECS Sample Clothes Dryers Utilization 

Product Class

Electric 

Standard Gas 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-C.2.2 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 (8.45 lbs for standard and 3 lbs for compact clothes 

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

 

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

( ) 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. 

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) directory 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 proposed clothes dryer procedure 

value.

 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. 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 1010 CEC directory.1

 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 proposed clothes dryer 

procedure value. 
7-C-6

 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: 

Standby Power CD Time ClothesDryerEnergyUse CD Cycles Standby _ 60

_ _8760 ∗



 



 



 



 −= ∗

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.

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 RECS2

 and the 2009 American Housing 

Survey (AHS)3, 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.4 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-C-7

7-C.3 ROOM AIR CONDITIONERS 

7-C.3.1 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 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)b

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

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

incorporates standby power. The CEER 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.

 

b 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-8

7-C.3.2 Operating Hours 

7-C.3.2.1 Residential

 DOE calculated the annual room air conditioner 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. 

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

analysis.c

 

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

used the building shell index factor from AEO2010 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. 

 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.d

 

c 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. 

 The reported field energy consumption refers to the 

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
7-C-9

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.

 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.3.1. 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.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

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.3.1). AHAM also 

provided average EER data by product class (capacity) for 2005–2007.5 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.
7-C-10

Figure 7-C.3.1 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.

5

6

7

8

9

10

11

1970 1975 1980 1985 1990 1995 2000 2005 2010

Year

Average Shipment Weighted 
7-C-11

Table 7-C.3.2 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.3.3 shows the AHAM data on total shipment-weighted average EER and the 

average EER estimated for the representative product classes. 
7-C-12

Table 7-C.3.3 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 AHAM5

** Years in which standards became effective

 

7-C.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 
7-C-13

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.3.2).6

 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.3.2 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.3.2 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-14

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 7081.117 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).7

 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.3.3). A total of 858 

sites have a complete 15-year period of record. 

Figure 7-C.3.3 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-15

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: 

)ln( 13 )ln( 3

12

2

109 11

8 TCTCTCTCC

T

C Pws ×+×+×+×++=

where:

 C8 = -5.8002206 E+03 

 C9 = 1.3914993 E+00 

C10 = -4.8640239 E-02 

C11 = 4.1764768 E-05 

C12 = -1.4452093 E-08 

C13 = 6.5459673 E+00 

Pws = saturation pressure, Pa 

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:

( ) P Pw

Pw W - 0.62198×=

 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.3.4 shows the hours (2281 hours) in 1991 that were above the comfort zone 

for Palm Springs.
7-C-16

Figure 7-C.3.4 Hours Above Comfort Zone in Palm Springs 

(1991) 

Figure 7-C.3.5 shows hours above the Standard 55 comfort zone compared to CLDD for 

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

Hours above comfort zone

Palm Springs, 1991

0

0.005

0.01

0.015

0.02

0.025

0.03

0 5 10 15 20 25 30 35 40 45 50

dry bulb temperature

humidity ratio

100%RH

90%RH

80%RH

70%RH

60%RH

50%RH

40%RH

30%RH

20%RH

10%RH
7-C-17

Figure 7-C.3.5 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.3.4 Weather Stations Classified as Desert

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

Room AC Operating Hours

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 500 1000 1500 2000 2500 3000 3500 4000

CLDD 65

hours above Std 55
7-C-18

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.3.6, the desert and tropical sites are shown. The uppermost points on the 

original chart (Figure 7-C.3.5) represent data from stations in Hawaii, Guam and the Caribbean. 

Figure 7-C.3.6 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.3.7 for all hours of the 

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

Room AC Operating Hours

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 500 1000 1500 2000 2500 3000 3500 4000

CLDD 65

hours above Std 55

all

HI & Guam

Caribbean

desert
7-C-19

Figure 7-C.3.7 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.3.5. 

Table 7-C.3.5 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.3.6 and 7-C.3.7. An assumption was made that if the occupancy rate was greater than 20% of 

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-C-20

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

the ASHRAE standard 55 comfort zone. 

Table 7-C.3.6 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.3.7 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.3.8. 
7-C-21

Table 7-C.3.8 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 M_F ROH55 = 1.974 x CLDD + 93.29 0.9458

OUT ALL ROH55 = 2.759 x CLDD + 127.99 0.9430

ASM M_F ROH55 = 0.751 x CLDD + 119.67 0.9458

ASM ALL ROH55 = 1.396 x CLDD + 169.18 0.9430

EDU M_F ROH55 = 1.001 x CLDD + 117.11 0.9412

EDU ALL ROH55 = 1.398 x CLDD + 163.52 0.9424

FDS M_F ROH55 = 1.243 x CLDD + 112.91 0.9354

FDS ALL ROH55 = 1.510 x CLDD + 166.44 0.9408

LOD M_F ROH55 = 1.471 x CLDD + 17.11 0.9428

LOD ALL ROH55 = 2.206 x CLDD + 40.94 0.9408

MED M_F ROH55 = 1.001 x CLDD + 128.06 0.9428

MED ALL ROH55 = 1.151 x CLDD + 148.72 0.9408

OFF M_F ROH55 = 0.918 x CLDD + 119.76 0.9428

OFF ALL ROH55 = 1.510 x CLDD + 166.44 0.9408

RET M_F ROH55 = 0.751 x CLDD + 119.67 0.9458

RET ALL ROH55 = 1.281 x CLDD + 170.57 0.9450

WHS M_F ROH55 = 0.836 x CLDD + 109.17 0.9422

WHS ALL ROH55 = 1.514 x CLDD + 178.06 0.9419

The 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.3.9. 
7-C-22

Table 7-C.3.9 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 M_F ROH55 = 1.974 x CLDD + 93.29 0.8353

OUT ALL ROH55 = 2.759 x CLDD + 127.99 0.8925

ASM M_F ROH55 = 0.289 x CLDD + 546.12 0.8353

ASM ALL ROH55 = 0.600 x CLDD + 721.20 0.8925

EDU M_F ROH55 = 0.409 x CLDD + 532.56 0.8723

EDU ALL ROH55 = 0.572 x CLDD + 741.06 0.8794

FDS M_F ROH55 = 0.553 x CLDD + 449.33 0.8914

FDS ALL ROH55 = 0.663 x CLDD + 690.02 0.8985

LOD M_F ROH55 = 0.642 x CLDD + 40.06 0.8260

LOD ALL ROH55 = 0.951 x CLDD + 157.74 0.8985

MED M_F ROH55 = 0.402 x CLDD + 603.12 0.8260

MED ALL ROH55 = 0.458 x CLDD + 706.19 0.8985

OFF M_F ROH55 = 0.353 x CLDD + 573.23 0.8260

OFF ALL ROH55 = 0.663 x CLDD + 690.02 0.8985

RET M_F ROH55 = 0.289 x CLDD + 546.12 0.8353

RET ALL ROH55 = 0.534 x CLDD + 749.00 0.8813

WHS M_F ROH55 = 0.317 x CLDD + 524.97 0.8087

WHS ALL ROH55 = 0.612 x CLDD + 837.58 0.8682

 To estimate the 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.3.10) 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-23

Table 7-C.3.10 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 115 year CDD average values, DOE decreased the estimated commercial 

sector operating hours by 2 percent on average. 
7-C-24

REFERENCES

1. California Energy Commission, California Energy Commission Appliance Efficiency 

Database, 2010. (Posted July) <http://www.energy.ca.gov/appliances/database/>

2. U.S. Department of Energy: Energy Information Administration, Residential Energy 

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

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

3. 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

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

differences in technology and ambient conditions, January 13, 2004. European 

Committee of Domestic Equipment Manufacturers (CECED). <http://www.aibdeutschland.de/das_institut/mitarbeiterinnen/dok/630.php?id=40&dokid=202&anzeige=d

et&ITitel1=&IAutor1=> 

5. Association of Home Appliance Manufacturers (AHAM), Trends in Energy Efficiency 

2008 

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

Conditions for Human Occupancy, 2004. 

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

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