A national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

National Renewable Energy Laboratory 

Innovation for Our Energy Future 

Method for Evaluating Energy 

Use of Dishwashers, Clothes 

Washers, and Clothes Dryers 

Preprint 

M. Eastment and R. Hendron 

To be presented at the 2006 ACEEE Summer Study on 

Energy Efficiency in Buildings 

Pacific Grove, California 

August 13–18, 2006 

Conference Paper 

NREL/CP-550-39769 

August 2006 

NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 
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Method for Evaluating Energy Use of Dishwashers, Clothes Washers, 

and Clothes Dryers1

 

Mark Eastment and Robert Hendron, National Renewable Energy Laboratory 

ABSTRACT 

Building America teams are now researching opportunities to improve whole house 

energy efficiency including more challenging end-uses, such as lighting (both fixed and 

occupant-provided), appliances (clothes washer, dishwasher, clothes dryer, refrigerator, and 

range), and MELs. These end uses are all heavily dependent on occupant behavior and product 

choices. Part of that research is evaluating the energy savings resulting from the specification of 

efficient appliances in energy-efficient homes. Using DOE test procedures, the method outlined 

in this paper presents a reasonable way to calculate energy savings for specific dishwashers, 

clothes washers, and clothes dryers. The information necessary to generate these inputs is 

available on Energy-Guide labels, the ENERGY-STAR® website, California Energy 

Commission’s Appliance website, and manufacturer’s literature. 

Introduction 

The U.S. Department of Energy’s (DOE) Buildings Technology Program, including such 

initiatives as Building America, has recently entered a new phase of research. The focus is on all 

residential energy uses since significant progress has already been made toward reducing spaceconditioning loads in new housing in most climates in the United States. Lighting (both fixed and 

occupant-provided), appliances (clothes washer, dishwasher, clothes dryer, refrigerator, and 

range), and miscellaneous electric loads are all heavily dependent on occupant behavior and 

product choices and have grown to be a much more significant fraction of total household 

energy. 

How do we estimate the effect of efficient appliances on whole-building energy 

consumption? Using Energy-Guide label information at face value for whole building 

simulations is problematic because the data is representative of test procedures designed to give 

consumers cost and performance data with the intent of making “apples to apples” comparisons. 

This type of information lacks the level of detail and location specific information necessary to 

be used with a whole building energy simulation. The reported annual energy consumption on 

Energy-Guide labels includes machine electrical energy consumption and a nominal amount of 

energy for water heating based on hot water volume consumed under DOE test conditions. 

NREL has developed a reasonable analytical method for crediting the use of efficient 

dishwashers, clothes washers, and clothes dryers when compared to the Building America 

Research Benchmark (referred to as the Benchmark, Hendron 2005) where previously Building 

America analysts had no standardized method for calculating energy savings related to the 

 

1

 **This work has been authored by an employee of the Midwest Research Institute under Contract No. 

DE-AC36-99GO10337 with the U.S. Department of Energy. The United States Government retains and the 

publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow 

others to do so, for United States Government purposes. 

1
specification of efficient appliances in research homes. This method allows the user to develop 

inputs to whole building energy simulation tools that are sensitive to location specific design 

conditions and are disaggregated appropriately for use in a whole building energy simulation. 

Dishwashers 

Estimating the Energy and Hot Water Use of Dishwashers 

Figure 1 shows the flowchart for the solution method used to determine the hot water 

consumption and machine electrical energy use for dishwashers. 

Figure 1. Solution Method Flowchart for Dishwashers 

The basic approach is to disaggregate detailed performance characteristics (machine 

electrical energy consumption and hot water consumption per cycle) from the overall energy use 

and cost data listed in the Energy-Guide label. These values are adjusted for location specific 

design information and Benchmark operating assumptions, which, in some cases, differ 

significantly from DOE test procedures. 

Machine Types. To begin solving for the machine electrical energy consumption and hot water 

volume consumption, it is necessary to understand basic dishwasher types. The following 

definitions are used here: 

• Type 1 dishwashers – do not heat water internally, hot water connection only 

• Type 2 dishwashers – have an electric element internal to the machine for the purpose of 

providing auxiliary water heating, hot water connection only 

2
• Type 3 dishwashers – have an electric element internal to the machine for the purpose of 

heating all of the water used to wash the dishes, cold water connection only. 

In order to estimate the energy consumption of dishwashers, it is necessary to understand the 

underlying energy use calculations found in the 10CFR Part 430, Subpt. B, App. C (DOE 1999). 

Dissagregation of Energy-Guide Label Data. These equations from DOE test procedures 

determine estimated operating expenses and estimated annual energy consumption as it appears 

on Energy-Guide labels: 

A) Annual Estimated Energy Cost for Gas Water-Heating (Type 1 & 2 dishwashers when 

gas or oil-heated water, DOE 1999): 

[ ] ( ) ( W * D M* DN EAOC ) g = e + w

2

B) Annual Energy Consumption Equation: 

⎟

⎠

⎞ ⎜

⎝

⎛ = + M e * 

Btu

kWh ann 0.000293 *W N E . 3

If (B) is solved for M and then is substituted into the (A), the result can be solved for 

energy required for water heating: 

Equation 1: ( ) ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

⎥

⎦

⎤ ⎢

⎣

⎡ ⎟

⎠

⎞ ⎜

⎝

⎛ −

− = cycle

Btu 

e*

Btu

kWh 0.000293*DDN

EAOC E*D

 W

ew

anneg .

Machine energy is then given by 

Equation 2: ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ ⎟

⎠

⎞ ⎜

⎝

⎛ ⎟

⎠

⎞ ⎜

⎝

⎛ = cycle

kWh e * 

Btu

kWh 0.000293 *W -

N

E M ann .

To estimate the hot water volume consumed: 

Equation 3: ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

∆ = cycle

gal 

T *K 

W GHW .

4

Equations 2 and 3 solve for machine electrical energy and hot water volume consumed 

per cycle in terms of known values. For Type 3 dishwashers, hot water volume is known to be 

zero. 

Clothes Washers 

Estimating the Energy and Water Use of Clothes Washers 

Figure 2 shows the flowchart for the solution method used to determine the hot water 

consumption and machine electrical energy use for clothes washers. 

 2

 EAOCg = Estimated Annual Operating Cost for Gas Water Heating ($) 

N = Number of Cycles 

De = Average unit cost of electrical energy ($/kWh) 

M = machine energy, Mn or 0.5*(Mn + Mt) (kWh/cycle)) 

Dw = average unit cost in dollars per Btu for gas or oil, as appropriate ($/Btu) 

W = Water heating energy, Wn or 0.5*(Wn + Wt) (Btu/cycle) 3

 Eann = Annual energy consumption, N*Et or N*0.5*(En + Et) (kWh) 

e = nominal gas or oil water heater recovery efficiency = 0.75 

4

 GHW = Gallons of hot water (gal/cycle) for Type 1 dishwashers ∆T = 90°F, for Type 2 dishwashers ∆T = 70°F, K 

= 0.00240 kWh/(gal-°F) 

3
Figure 2. Solution Method Flowchart for Clothes Washers 

Machine Types. To begin solving for the machine electrical energy consumption and hot water 

volume consumption, it is necessary to understand basic clothes washer types, the following 

definitions are used here: 

• Type 1 clothes washer – does not heat water internally, hot and cold water connections 

• Type 2 clothes washer – uses thermostatically controlled water inlet valves to vary the 

volume of hot and cold water added to the wash load 

• Type 3 clothes washer – has an electric element internal to the machine for the purpose of 

providing auxiliary heating, hot and cold water connections 

• Type 4 clothes washer – has an electric element internal to the machine for the purpose of 

heating all of the water used to wash clothes; cold water connection only. 

To estimate the energy consumption of clothes washers, it is necessary to understand 

energy-use calculations found in 10CFR Part 430, Subpt. B, Appendix J1 (DOE 1999). 

4
Disaggregation of Energy-Guide Label Data. Equations from DOE test procedures that 

determine estimated operating expenses and estimated annual energy consumption appearing on 

Energy-Guide labels are as follows: 

D) Annual Estimated Energy Cost for Gas Water Heating (for gas and oil heated water): 

[ ] ( ) ( ) g = ETe + w HE* D M* D *N EAOC TG

5

E) Annual Energy Equation (for gas and oil heated water): 

⎟

⎠

⎞ ⎜

⎝

⎛ ann = TG + ET M e * 

Btu

kWh 0.000293 * HEN E . 

If (E) is solved for MET and is then substituted into (D), the result can be solved for 

energy required to heat water: 

Equation 4: ( ) ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

⎥

⎦

⎤ ⎢

⎣

⎡ ⎟

⎠

⎞ ⎜

⎝

⎛ = cycle

Btu 

e*

Btu

kWh 0.000293*D-DN

E*D-EAOC

HE

ew

anneg

TG .

Weighted average machine energy is then given by: 

Equation 5: ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ ⎟

⎠

⎞ ⎜

⎝

⎛ = cycle

kWh e *

Btu

kWh 0.00293 * HEN

E

 M TG ann ET .

To estimate the hot water volume consumed: 

Equation 6: ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

∆ = cycle

gal

T *K 

H GHW ET t . 6

Equations 5 and 6 solve for machine electrical energy and hot water volume consumed 

per cycle in terms of know values. For Type 4 Clothes Washers, hot water volume is known to 

be zero. 

Clothes Dryers 

Estimating the Energy Use of Clothes Dryers 

Figure 3 shows the flowchart for the solution method used to determine the machine 

electrical energy use and gas use for clothes dryers. Energy-Guide labeling is not required for 

clothes dryers,; however, a DOE test procedure for clothes dryers does exist for the purpose of 

determining clothes dryer compliance with federal appliance minimum efficiency regulations. In 

addition, clothes dryer energy use is dependent on moisture content of the wash load. This 

method incorporates equations used to determine the Modified Energy Factor7

 (MEF) for clothes 

washers and equations from the DOE test procedure for clothes dryers in order to model any 

combination of clothes washer and clothes dryer in a coupled fashion. 

 5

 N = Number of cycles per year assumed (392 cycles/yr) 

MET = Total weighted per-cycle machine electrical energy consumption (kWh/cycle) 

HETG = HET * 1/e * (3412Btu/kWh), gas water-heating energy consumption (Btu/cycle) 6

 GHWt = weighted average gallons of hot water used under test conditions representative of temperature use factors 

found in section 5 of Appendix J1 (DOE 1999) (gal/cycle), ∆T = 75°F (Appendix J1) 7

 Modified Energy Factor for clothes washers includes a nominal dryer energy use, which is determined from tests 

that quantify the amount of water remaining in wash loads as a result of different clothes washer spin cycles. 

5
Figure 3. Solution Method Flowchart for Clothes Dryers 

Machine Types. For the purpose of defining clothes dryer machine types, there are two different 

basic machine types: conventional clothes dryers or heat pump (vapor compression) type clothes 

dryers that do not vent to the outside. However, the important distinction for dryers is the fuel 

type (all electric or gas-electric). To estimate the energy consumption of clothes dryers, it is 

necessary to understand the energy-use calculations in 10CFR Part 430, Subpt. B, App. D (DOE 

1999). 

Relevant Equations from DOE Test Procedure and Equation Derivation. The two equations 

of interest are as follows:

F) Clothes dryer efficiency: 

ce

d

E

TLW = EF , electric clothes dryers8

 8

 EF = Energy Factor (lbs-load dry weight/kWh/cycle) 

TLWd = Test load weight for clothes dryer (lbs, dry) 

Ece = Total per-cycle electric clothes dryer energy consumption (kWh/cycle) 

6
cg

d

E

TLW = EF , gas clothes dryers 9

G) Total dryer energy consumption: 

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ =

dw

tce W-W

66 * FU* E E , electric clothes dryers 10

kWh

Btu 3412

E

 E E g

gecg

⎟

⎟

⎟

⎟

⎠

⎞

⎜

⎜

⎜

⎜

⎝

⎛

⎟

⎠

⎞ ⎜

⎝

⎛ += , gas clothes dryers. 11

For electric clothes dryers the two equations are solved for Et: 

( )

( ) 66 * FU

W-W * 

EF

TLW

 E

dw

d

t

⎟

⎠

⎞ ⎜

⎝

⎛

= . 

Because moisture content of the test load is defined as the water weight over the dry-load 

weight, we can re-write Ww and Wd as follows: 

lbs

lbs TLW

lbs

 100 W

d

initialwater,

w ⎟

⎠

⎞ ⎜

⎝

⎛ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ = as expressed % 12

⎟

⎠

⎞ ⎜

⎝

⎛

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ = lbs

lbs

TLW

lbs

 100 W

d

finalwater,

d expressed as %. 13

Solving these two equations for Ww – Wd and substituting into the equation for Et: 

Equation 7: ⎟

⎟

⎠

⎞

⎜

⎜

⎝

∆ ⎛ = cyclekWh

66 * FU* EF

lbs * 100 E water t .

For gas dryers, we make an assumption about the fraction of total energy for a gas clothes 

dryer that is attributed to machine electrical energy consumption: 

= cg1ge (kWh E* f E ) 14 and, ⎟

⎠

⎞ ⎜

⎝

⎛ = kWh

Btu

g cg1 3412 * E* )f - (1 E . 

Solving the gas dryer equations for Ete and Etg: 

Equation 8: ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛∆ = cycle

kWh

66*FU*EF

lbs*100*f E 1 water te

Equation 9: 

( )

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ ⎟

⎠

⎞ ⎜

⎝

⎛ ∆

= cycle

ft GEF*66*FU*EF

kWh

Btu lbs*100*f-1 *3412

E

1 water 3

tg . 

 9

 Ecg = Total per-cycle gas clothes dryer energy consumption (kWh/cycle) 10 Et = Measured clothes dryer electrical energy consumption during test cycle (kWh) 

FU = Field use factor, 1.18 for time termination control system and 1.04 for automatic control systems. 

66 = experimentally established value for the percent reduction in the moisture content of the test load (%, 

DOE 1999) 

Ww = Moisture content of the wet test load (lbswater/lbsdry cloth) 

Wd = Moisture content of the test load after drying (lbswater/lbsdry cloth) 11 Ege = Ete * FU * (66/(Ww – Wd)), per-cycle gas clothes dryer electrical energy consumption (kWh/cycle)

Eg = Etg * FU * GEF * (66/(Ww – Wd)), per-cycle gas clothes dryer gas energy consumption (Btu/cycle) 12 lbswater,initial = water weight before drying (lbs) 13 lbswater,final = water weight after drying (lbs) 14 f1 = fraction of total gas clothes dryer energy attributed to machine electrical energy 

7
Equations 7, 8, and 9 solve for measured dryer energy consumption in terms of the 

change in weight of water during the drying cycle. We make the simplifying assumption that all 

of the water weight remaining in a load of wash after the clothes-washer final spin cycle is 

removed during the drying cycle. The water weight in a load of clothes can be calculated and 

substituted into equations 7, 8, and 9 to calculate the energy use of the clothes dryer as a function 

of the water weight remaining in the wash load. The water weight remaining in a wash load after 

the final clothes washer spin cycle can be estimated if the following values are known: 

• Clothes washer modified energy factor (MEF, ft3

/kWh) 

• Clothes washer drum capacity (ft3

) 

• Weight of water transferred from clothes washer to clothes dryer (lbs). 

The three equations of interest are as follows: 

H)

ETE D E

C MEF

+ = 15

I) 4% TLW*DUF*DEF*LAF

D RMC

w

E

+ = (%)16 

J) . Water weig = TLW * RMCht w

Using substitution we have: 

Equation 10: ( ) w

w

TE

TLW *0.04 

 TLW*DUF*DEF*LAF 

 EMEF

C

Water weig ht 

⎥

⎥

⎥

⎥

⎦

⎤

⎢

⎢

⎢

⎢

⎣

⎡

+

⎟

⎠

⎞ ⎜

⎝

⎛

= . 

Substituting equation 10 into equations 7, 8, and 9 for the clothes dryer: 

Equation 11: ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ ⎪

⎪

⎭

⎪

⎪

⎬

⎫

⎪

⎪

⎩

⎪

⎪

⎨

⎧

⎥

⎥

⎥

⎥

⎥

⎦

⎤

⎢

⎢

⎢

⎢

⎢

⎣

⎡

+

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

= cycle

kWh

66 * FU* EF

TLW*0.04

TLW*DUF*DEF*LAF

EMEF

C

100

E

dryer

w

w

TE

washer

newt, , electric dryer

Equation 12: ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ ⎪

⎪

⎭

⎪

⎪

⎬

⎫

⎪

⎪

⎩

⎪

⎪

⎨

⎧

⎥

⎥

⎥

⎥

⎥

⎦

⎤

⎢

⎢

⎢

⎢

⎢

⎣

⎡

+

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

= cycle

kWh

66 * FU* EF

TLW *0.04

TLW*DUF*DEF*LAF

EMEF

C

100*f

E

dryer

w

w

TE

washer

1

newte, , electrical energy 

consumed by a gas clothes dryer

 15 MEF = Modified Energy Factor (ft3

/kWh/cycle) 

C = W/d, Capacity (ft3

), W = Weight of water (lbs), d = Density of water (62.0 lbs/ft3 for 100 °F or 62.3 lbs/ft3 for 

60 °F) 

ETE = ME + HET, Total per-cycle energy consumption when electrically heated water is used (kWh/cycle) 

DE = Nominal dryer energy consumption for removal of remaining moisture content (kWh/cycle) 16 LAF = 0.52, load adjustment factor 

TLWw = Max value as shown in test load table, 10CFR Part 430, Subpt. B, App. J1, Table 5.1 (lbs/cycle) 

RMC = Remaining moisture content (lbswater/lbsdrycloth, expressed as %) 

DEF = 0.5 (kWh/lb), nominal energy factor for clothes dryer 

DUF = 0.84, clothes dryer use factorRMC = lbswater/lbsdrycloth (expressed as %) 

8
Equation 13: 

( )

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ ⎪

⎪

⎭

⎪

⎪

⎬

⎫

⎪

⎪

⎩

⎪

⎪

⎨

⎧

⎥

⎥

⎥

⎥

⎥

⎦

⎤

⎢

⎢

⎢

⎢

⎢

⎣

⎡

+

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

= cycle

ft

GEF*66*FU*EF

TLW *0.04

TLW*DUF*DEF*LAF

EMEF

C

100*f-1

E

3

dryer

w

w

TE

washer

1

newtg, , gas 

consumption of the dryer.

Equations 11, 12, and 13 solve for clothes-dryer energy use that is representative of the 

remaining water weight in the wash load as a result of the final clothes-washer spin cycle. This 

method assumes a linear relationship between water weight and the clothes dryer energy 

consumption based on data for a conventional clothes dryer tested by the National Institute of 

Standards and Technology (Kao 1998). 

Building America Application 

Building America Benchmark and Prototype 

The Benchmark represents a hypothetical residential building that varies its physical and 

energy-related features according to climate and prototype house design with the intent of 

representing typical 1990s construction. For appliances the Benchmark specifies daily hot water 

consumption, annual electrical and gas consumption, hourly usage patterns, DHW tank setpoint, 

and monthly incoming water-mains temperatures with the intent of modeling a whole building 

with an hourly annual building energy-simulation tool. The Benchmark assumes a 3-ft3

 clothes 

washer capacity, which corresponds to a 12.5-lb test load weight, and an 8-place-setting capacity 

dishwasher. The prototype home must be modeled using the same assumption for DHW tank 

setpoint and mains-water temperatures. The assumed number of cycles for the prototype 

appliances are defined in the Building America Performance Analysis Procedures (Hendron et al. 

2004). The equations below specify appliance cycles per year as a function of number of 

bedrooms for the prototype: 

Equation 14: ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

⎥

⎦

⎤ ⎢

⎣

⎡ ⎟

⎠

⎞ ⎜

⎝

⎛ +=

yr

cycles

TLW (lbs)

12.5lbs * 

6

N 1⁄2 *392 N

proto

br

CW proto

17

Equation 15: ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ = yr

cycles

CD proto CW proto DUF* N N 18

Equation 16: 

yr

cycles

capacity setting place actual

8 * 

6

N 1⁄2 * 215 N br

 DWproto ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ ⎥

⎦

⎤ ⎢

⎣

⎡ ⎟

⎠

⎞ ⎜

⎝

⎛ += . 19

For each of the appliances, the prototype cycles per year is multiplied by the adjusted 

machine electrical energy consumption and adjusted hot water volume consumed to give new 

annual totals. Outside of Building America, other users may wish to use different assumptions 

for the number of cycles per year that each appliance experiences. 

 17 Nproto CW = Prototype clothes washer annual operation frequency (cycles/yr) 

Nbr = # of Bedrooms 

TLWproto = prototype clothes washer test load weight, determined using Table 5.1 Appendix J1 (DOE 1999) 18 Nproto CD = Prototype clothes dryer annual operation frequency (cycles/yr) 

DUF = 0.84, from DOE test procedures 

19 Nproto DW = Prototype dishwasher cycles per year (cycles/yr) 

9
Effect of Mains Water Temperature and Hot Water Temperature 

The energy consumption of most dishwashers and clothes washers is affected by the 

mains or cold water inlet temperature and the domestic hot water temperature. The exception is 

Type 1 dishwashers and clothes washers, for which the energy consumption and hot water 

consumption of the machine will not vary from the measured values under DOE test conditions 

as a result of the lack of built in controls and assuming “generic” user behavior for comparison 

purposes. 

Thermostatic Control Valves. Type 2 clothes washers vary the amount of hot water the 

machine uses in order to attain a specific wash temperature by opening and closing hot and cold 

water valves during the fill portion of the cycle that utilizes both hot and cold water. We make 

the assumption that the mixed water temperature in a Type 2 clothes washer during cycles that 

draw hot and cold water is 92.5°F based a field test Colorado. In order to correct the hot and cold 

water volumes for this control type, a general derivation of the correction in hot water volume 

for a Type 2 clothes washer operating with water temperatures that differ from the test conditions 

is shown below. During machine sub cycles that use both hot and cold water the volume fraction 

of hot water is defined as follows: 

GWT

GHW X t = ,

20 where . t += GCW GHW GWT t

21

These equations are solved for GCWt and substituted into conservation of energy: 

HWI + CWIt t = mixed GWT *T GCW * T GHW * T . 22

Then solved for volume fraction to give: 

Equation 17: 

HWI CWI

mixed CWI

T-T

T -T = X .

The volume fraction of hot water is defined by the test condition temperatures and an 

assumed mixed temperature. In order to calculate the hot water used under actual conditions 

where the hot and cold water temperatures are different from the test conditions the conservation 

of energy equation is as follows: 

act hot, ( )( ) V GHWt T act,cold t V-GCW mixed ∗ Τ = ∆ Τ + ∆+ GWT . 23

Substituting GCWt and GWT terms and solving for ∆V: 

Equation 18: 

( ) ( )

⎟

⎟

⎟

⎟

⎠

⎞

⎜

⎜

⎜

⎜

⎝

⎛

Τ−Τ

Τ−Τ + −Τ 1

 =∆

act,hot act,cold

mixed act,cold act,hotact,cold

t

T

X GHW V . 

 20 GHWt = Volume of hot water used under test conditions(gal) 

GWT = Volume of water used during subcycles that using hot and cold water under test conditions (gal) 

X = Hot water volume fraction for machine subcycles that use hot and cold water (assumed 92.5oF mixed wash 

water temperature) 

21 GCWt = Volume of cold water used during subcycles using hot and cold water under test conditions (gal) 22 Tmixed = Mixed water temperature, current assumption is 92.5°F for Type 2 machines 

THWI = Hot water inlet temperature, 135°F for J1 test conditions 

TCWI = Cold water inlet temperature, 60°F for J1 test conditions 23 Thot, act = new hot water temperature, if different from test conditions (°F) 

Tcold, act = new cold water temperature, if different from test conditions (°F) 

∆V = increase in hot water volume and decrease in cold water volume (gal) 

10
∆V is known for any combination of hot and cold water inlet temperatures, and the 

quantity of hot water used by the clothes washer can be estimated under alternate conditions. 

Internal Electric Water Heaters. Type 2 and 3 dishwashers, as well as Type 3 and 4 clothes 

washers, have internal electric water-heating elements that adjust the water temperature. The 

general solution for each of these machines that will correct the machine electrical energy for 

alternate conditions is as follows:

Equation 19: ( ) . = final T-T * K * m Q initial

24

For dishwashers: (lbm GHW * d m ) = t . 25

For clothes washers: ( ) lbm 

X

GHW * d m T = . 

For Type 3 clothes washers: ( ) final = HWI + T * X-1 T * X T CWI

26

( ) initial = act hot, + T * X-1 T * X T act cold, . 27

Substituting Tinitial and Tfinal into ( ) = finalp T -T * C * m Q initial with simplifications gives us, 

Equation 20: [ ( ) ] = HWI CWI act hot, + act cold, + CWI T-T T T - T -TX * K * m Q act cold, .

Additional machine electrical energy for Type 3 clothes washers (supplemental internal 

electric heating element) for conditions that differ from the test procedure is heavily dependent 

on how the Type 3 clothes washer mixes hot and cold water (we assume that a 0.5 fixed-volume 

fraction is reasonable for calculation of Tinitial and Tfinal). 

Additional machine electrical energy for Type 4 clothes washers (cold water inlet only) is 

calculated by setting Tfinal to be 60°F and Tinitial is set to the cold water inlet temperature. 

Conclusion 

Using information available on Energy-Guide labels, the ENERGY-STAR website,28

California Energy Commission’s Appliance website,29 and manufacturer’s literature for 

dishwashers, clothes washers, and clothes dryers, the residential energy analyst will be able to 

generate inputs to whole building energy simulation tools that are specific to real appliance 

models. This methodology allows the analyst to do the following: 

• Disaggregate machine electrical energy and hot water consumption for a 

particular dishwasher or clothes washer model under DOE test conditions for 

basic appliance control strategies 

 24 Q = energy necessary to heat water (kWh) 

m = mass of water (lbm) 

Tfinal = final water temp = 140°F for Type 2 Dishwashers; = 50°F for Type 3 Dishwashers; = 60°F for Type 4 

Clothes Washers (°F) 

Tinitial = initial water temperature, Tinitial = hot water inlet temp for Type 2 Dishwashers; = cold water inlet temp for 

Type 3 Dishwashers and Type 4 Clothes Washers (°F) 

25 d = density (8.333lbm/gal) 

26 THWI = 135°F for Appendix J1 

TCWI = 60°F for Appendix J1 27 Thot, act = prototype domestic hot water temperature, 120°F in the Building America context 

Tcold, act = prototype cold water inlet temperature, monthly mains water temperature for Building America 28 www.energystar.gov/ia/products/prod_lists/ appliances_prod_list.xls 

29 www.energy.ca.gov/appliances/appliance/ excel_based_files/cook_wash/ 

11
• Account for variability in incoming water temperatures that may affect the energy 

and water use of dishwashers and clothes washers 

• Model the interaction of clothes washers and clothes dryers for any combination 

of these appliances 

• Account for a varying number of cycles per year that the appliance is used 

• Compare appliance models in greater detail than comparing energy and cost 

information presented on Energy-Guide labels or the Energy-Star website. 

The methodology does not account for occupant behavior, such as occupants who use only cold 

water only for clothes washing, hot water distribution system losses, dryer energy needed to heat 

a load of clothes to the point where moisture in the wash load begins to evaporate or a clothes 

dryer that is undersized relative to the clothes washer drum capacity. To assist residential energy 

efficiency research, NREL has the following spreadsheet tool to perform these calculations 

assuming Benchmark operating conditions 

(www.eere.energy.gov/buildings/building_america/pa_resources.html). 

Acknowledgements 

Credit for the initial equation derivation to separate machine energy and hot water volume used 

for dishwashers and clothes washers goes to Blaise Stoltenberg, a former NREL intern. The 

authors thank Ren Anderson and others in the NREL Buildings Group for their peer review of 

this work throughout the process. We also express our appreciation to Ed Pollock and George 

James of the U.S. Department of Energy for providing the necessary leadership and financial 

support for this research activity through Building America. 

References 

Building Science Corporation. 2004. 40-60% Prototype Performance Evaluation, Deliverable 

Report KAAX-3-32443-3.B.2, Westford, Mass.: Building Science Corporation. 

[DOE] Department of Energy. 1999. Code of Federal Regulations Title 10, Energy, Part 430, 

Subpart B, Appendicies C, D, J and J1, Washington, D.C.: U.S. Department of Energy. 

Hendron, Robert, Ren Anderson, Ron Judkoff, Craig Christensen, Mark Eastment, Paul Norton, 

Paul Reeves, and Ed Hancock. 2004. Building America Performance Analysis Procedures, 

Rev. 1. NREL/TP-550-35567. Golden, Colo: National Renewable Energy Laboratory. 

Hendron, Robert. 2005. Building America Research Benchmark Definition, Updated December 

29, 2004. NREL Report No. 37529. Golden, Colo: National Renewable Energy Laboratory. 

Kao, J. 1998. Energy Test Results of a Conventional Clothes Dryer and a Condenser Clothes 

Dryer, Gaithersburg, Md.: National Institute of Standards and Technology. 

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4. TITLE AND SUBTITLE

Method for Evaluating Energy Use of Dishwashers, Clothes 

Washers, and Clothes Dryers: Preprint 

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14. ABSTRACT (Maximum 200 Words)

Building America teams are researching opportunities to improve energy efficiency for some of the more challenging end-uses, 

such as lighting (both fixed and occupant-provided), appliances (clothes washer, dishwasher, clothes dryer, refrigerator, and 

range), and miscellaneous electric loads, which are all heavily dependent on occupant behavior and product choices. These enduses have grown to be a much more significant fraction of total household energy use (as much as 50% for very efficient homes) 

as energy efficient homes have become more commonplace through programs such as ENERGY STAR and Building America. As 

modern appliances become more sophisticated the residential energy analyst is faced with a daunting task in trying to calculate

the energy savings of high efficiency appliances. Unfortunately, most whole-building simulation tools do not allow the input of

detailed appliance specifications. Using DOE test procedures the method outlined in this paper presents a reasonable way to 

generate inputs for whole-building energy-simulation tools. The information necessary to generate these inputs is available on

Energy-Guide labels, the ENERGY-STAR website, California Energy Commission's Appliance website and manufacturer's 

literature. Building America has developed a standard method for analyzing the effect of high efficiency appliances on wholebuilding energy consumption when compared to the Building America's Research Benchmark building. 

15. SUBJECT TERMS

Building America; U.S. Department of Energy; energy efficient homes; miscellaneous electrical loads; MELs; 

appliances; DOE test procedures 

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