Review of Survey

o 4 - u

E1JILDING •#4 tC; I ur

Data to Support

Revisions to DOE’s

Dishwasher Test

Procedure

U.S. Department of Energy

Energy Efficiency and

Renewable Energy

Office of Building Technology,

State and Community Programs

1000 Independence Avenue, SW

Washington, DC 20585

Date: November 29, 2001

Arthur D. Little, Inc.

Acorn Park

Cambridge, MA 02140
.3

Executive Summary

To support revisions to the Department of Energy’s test procedures for measures of energy and water

consumption in dishwashers various survey data on consumers’ dishwasher usage habits were

collected from a number ofsources including several dishwasher manufacturers, detergent

manufacturers, energy and consumer interest groups, independent researchers, and government

agencies.

The fmdings ofthe review of available data on consumers’ dishwasher usage habits show broad

support to defme:

• Consumers’ pretreatment methods,

• Distribution of households by the level ofsoil in a dishwasher load,

• Quantitative amount ofsoil on the dishware, and

• Frequency of households’ use of a dishwasher.

Drawing from these survey fmdings, the existing test method for dishwashers, and ANSIJAHAM

Standard DW- 1, a weighted, three-point test method using different numbers of soiled dishware is

recommended to measure the energy consumption ofsoil-sensing dishwashers. It is further

recommended that the number of average-use cycles per year be reduced to 203.

Background

The Department of Energy’s Dishwasher Test Procedure is in the process of being revised. The need

to revise the test procedure is driven by the development of advanced soil-sensing dishwashers.

The introduction in the mid- 1990’s of advanced dishwashers equipped with the ability to sense the

soil level in the dishwasher and in response to adjust the wash cycle created a challenge to the

Dishwasher Test Procedure. The current test procedure, designed for fixed cycle dishwashers,

measures energy consumption using a load of clean dishes. It has been well demonstrated that soilsensing dishwashers yield lower energy consumption when tested with the clean load of dishes, as

compared to when tested with soiled dishes. Therefore, current energy consumption results for soil

sensing dishwashers are not representative ofthe actual energy consumption of soil-sensing

dishwashers in use by consumers. This inaccuracy, created by the evolution oftechnology,

necessitates revision ofthe Dishwasher Test Procedure.

In addition to technology-driven change, consumers’ usage of dishwashers has also changed. The

most notable change in dishwasher usage is the frequency ofits use. As the number of occupants in

dishwasher-owning households has decreased, the occupants have grown older, and consumers eat

more prepared or carryout foods, the frequency of dishwasher usage has decreased significantly.

2
Overview of Current Dishwasher Test Procedure

The Department of Energy’s test procedures for measures of energy and water consumption (10 CFR

430.23(c)) call out measures for the energy factor (cycles per kilowatt-hour) and the estimated

annual operating cost (dollars per year) of dishwashers.

These measures reference the Department of Energy’s “Uniform Test Method for Measuring the

Energy Consumption of Dishwashers” (10 CFR 430 Subpt. B, App. C). The current test method uses

a test load of clean dishes. The test load consists of 8 place settings of dishware plus six serving

pieces as specified in the industry-recognized standard, AHAM Standard DW- 1. The total per-cycle

energy consumption of a dishwasher is based on the energy consumption measured during this test

with a load of clean dishes.

Dishwashers must meet or exceed a minimum energy factor (10 CFR 430.32 cf)). The energy factor

for dishwashers is the reciprocal ofthe total per-cycle energy consumption. Standard dishwashers

(currently equal to or greater than 22” in exterior width) must have an energy factor not less than 0.46

cycles/kWh. Compact dishwashers (currently, less than 22” in exterior width) must have an energy

factor not less than 0.62 cycles/kWh.

The estimated annual operating cost for a dishwasher is listed on a dishwasher’s Energy Guide label

to assist consumers in making purchasing decisions. The estimated annual operating cost for a

dishwasher is based on the total per-cycle energy consumption, the representative average-use cycles

per year, and the representative unit cost of energy.

Needed Test Procedure Revisions and Supporting Data Requirements

As mentioned previously, it has been well demonstrated that soil-sensing dishwashers can consume

more energy when tested with a load ofsoiled dishes, as compared to when tested with a load of

clean dishes. This indicates that the energy consumption of a soil-sensing dishwasher, as measured in

the current test method, does not likely represent the total per-cycle energy consumption of a soilsensing dishwasher in household use. Therefore, the measures derived from the total per-cycle

energy consumption — the energy factor and the estimated annual operating cost- do not represent a

soil-sensing dishwasher in household use.

Further, there is evidence that the representative average-use cycles per year is overstated. This

means that the estimated annual operating cost of a dishwasher — whether soil-sensing or non-soil

sensing — is overestimated. Therefore, the information on the Energy Guide label is not

representative and may be misleading to consumers. The Energy Guide label on a soil-sensing

dishwasher is particularly impacted as the estimated annual operating cost and the total per-cycle

energy consumption are not representative of household use.

The key questions to understand in defining an energy consumption test for soil-sensing dishwashers,

assuring that soil-sensing dishwashers have energy factors not less than the minimum energy

standard, and assuring that the information on the Energy Guide label is representative, are:

1. How soiled are the dishes in the dishwashers of U.S. households?,

— Quantity ofsoil?

— Type of soil?

3
2. How are the dishwashers loaded in U.S. households?

— Quantity of dishware?

— Type of dishware?

3. How to reflect that soiling in a modified energy consumption test method?, and

4. How often do U.S. households use a dishwasher?

The following sections present the review and analysis of a broad collection of data that lead to

answers for these questions and offer an approach to incorporate the fmdings ofthe data in a revised

energy consumption test procedure for dishwashers.

Data Sources

This report is based on: 1) review of existing industry and DOE dishwasher test standards; 2) review

and analysis ofsurvey information from eight individual sources including dishwasher and detergent

manufacturers, energy and consumer interest groups, independent researchers, and government

agencies; and 3) discussions with key personnel in industry, DOE, NIST, consumer groups and

Arthur D. Little. The surveys form the core ofthe information to address the key questions and to

guide revisions to the test procedure. They vary in size, breadth of information, and quality of

information pertaining to consumers’ dishwasher habits.

More than half ofthe surveys are nationally representative, cumulatively representing over 20,000

respondents, while the others are regional in scope. The surveys present information collected

between 1997 and 2001, however most ofthe surveys are from the 2000-2001 timeframe. Nationally

representative means that the study populations ofthese surveys were selected to match or was

judged to distribute similarly to the U.S. Census profile of households. The demographics considered

to make this selection or judgment included: market size, age of household, type of household,

household size, household income, type ofresidence, and ownership versus rental ofresidence.

A key requirement ofthis report is to maintain the confidentiality ofthe industry survey sources. To

this end no one industry source is referenced and the data presented is an aggregation ofthe survey

information. However, Table 1 gives an overview of each survey’s scope and size.

Table I — Overview of scope and size of surveys

Survey Number of Breadth of Quality of . Scope Identifier Households Information Information

Survey A Nationally Representative > 8,000 Wide High

Survey B Nationally Representative > 6,000 Wide High

Survey C Nationally Representative < 1,000 Wide High

Survey D Regional > 1,000 Limited Moderate

Survey E Regional < 250 Limited Low

Survey F Regional < 250 Moderate Moderate

Survey G Nationally Representative < 500 Moderate Moderate

Survey H Nationally Representative < 1,000 Moderate Moderate

4
1997 RECS Nationally Representative 5,900 Limited High

The aggregation ofthe various survey data has required some regrouping ofthe survey results. The

regrouping is necessitated because each survey may have a different number of categories or different

categories for a particular habit question. The following sections address how the survey data

addresses the data requirements outline above, and how the survey data was analyzed to address

those data requirements.

5
Detailed Findings

The fmdmgs ofthis review of available survey data on U.S. households’ dishwasher usage habits and

characteristics and of existing dishwasher test standards show broad support to address the key

questions above and to make revisions to the energy consumption test procedure for dishwashers.

The available surveys provide data on a number of habits and characteristics of households with

dishwashers, including:

• Households’ pretreatment methods,

• Distribution of households by level of soil in a dishwasher load,

• Quantitative amount of soil in a dishwasher load,

• Frequency of households’ usage of a dishwasher,

• Distribution of the type of dishware in a dishwasher load, and

• Size ofthe dishwasher load.

Existing dishwasher cleaning performance test standards provide much ofthe data on critical

elements for an energy consumption test procedure for soil-sensing dishwashers, including:

• Types of soil,

• “Worst case” amounts of soil,

• Application of soils to dishware,

• Types of dishware, and

• Amount of dishware.

A majority ofthe recommended revisions to the energy consumption test procedure draw primarily

from the survey data on the following habits and characteristics of households with dishwashers:

• Households’ pretreatment methods,

• Distribution of households by level of soil in a dishwasher load,

• Quantitative amounts of soil in a dishwasher load, and

• Frequency of households’ usage of a dishwasher.

Review of existing dishwasher test standards provided direction for test method elements that were

either not covered or not widely covered by the surveys. These test method elements include:

• Types of soil, and

• Type of dishware

The fmdings below on the habits and characteristics of consumers with dishwashers, coupled with

existing test methods, build to address the key questions in revising the dishwasher test procedure.

6
How soiled are the dishes in the dishwashers of U.S. households?

This section covers survey data and test method infonnation available to assess 1) the quantity of soil

on dishware in U.S. households and 2) the type of soil on the dishware. The quantity of soil is

derived from data on pretreatment methods and resultant soil levels on dishware, qualitative ranking

of soil level, and assessment of quantitative amounts associated with the qualitative ranking of soil

level.

Households’ Pretreatment Methods

Survey data from six ofthe eight sources (surveys A, C, E, F, G and H) provide information on

households’ pretreatment habits. Four ofthese surveys are nationally representative and

cumulatively represent over 10,000 U.S. households.

All six ofthe survey sources present their data in similar categories that make aggregation ofthe data

direct and simple. Aggregating these surveys and weighting the responses in each category by the

total number of respondents indicates that more than 70% ofU.S. households pretreats dishes with

water prior to placing them in the dishwasher. Figure 1 shows the aggregation ofthe surveys’

responses to questions on pretreatment habits. The simple import ofthis finding is that currently the

vast majority of U.S. households’ dishwasher loads are cleaner than they would be otherwise.

Ficiure I — U.S. Households’ Dishwasher Pretreatment Habits

50.0%

70.0%

Ca

a,

U,

CU

5o%

b

40.0% U,

0

30.0%

0

D

10.0%

00%

Pretreatment Method

60.0%

20.0%

Pre-rinse with Pre-wash, including Pre-soak the dish Scrape food Removed large Do nothing

water some scrubbing without water scraps

7
Distribution of Households by Level of Soil in a Dishwasher Load

Four surveys (surveys A, C, D, and F) provide a combination of qualitative and quantitative

information on the soil in a dishwasher load. The first consideration is the qualitative information on

the level of soil in the dishwasher loads of U.S. households.

Surveys A and C are both large, nationally representative surveys that cumulatively represent over

9,000 U.S. households. Both surveys present very similar data on the qualitative level of soil on

dishware in households’ dishwasher loads. The larger ofthese two asked households to rate the

overall level ofsoil in their dishwasher loads. The other ranked and categorized households’

description ofthe overall level ofsoil in their dishwasher loads.

Both ofthese two surveys distribute the level of soil in households’ dishwasher loads in three

categories:

• Light level ofsoil,

• Medium level ofsoil, and

• Heavy level ofsoil.

Surveys D and F are regional in scope and each present their data on the level of soil in households’

dishwasher loads in more than three categories. Both surveys asked households to rate the overall

level ofsoil in their dishwasher loads against the descriptions oftheir categories. Although each of

the two surveys has more than three categories for the level of soil, the defmitions oftheir categories

clearly allow the data to be regrouped into the light, medium and heavy categories for soil level.

Aggregating the two nationally representative sources and weighting the responses in each category

by the total number ofrespondents yields a distribution of households within these three categories

that follows approximately 62%, 33% and 5% from light to heavy, as shown below in the Figure 2.

Including the two regional surveys in the aggregation changes the distribution only slightly to

approximately 62%, 32%, and 6% from light to heavy. In either aggregation the result is nearly the

same and consistent with the fmding that most households rinse dishes before placing them in the

dishwasher.

8
Figure 2— Distribution of U.S. Households by the Level of Soil in Dishwasher Loads

70%

60%

U,

.2 50% U,

U,

U,

40%

U,

_______________

30% U,

U,

z

0

u 20%

D

10%

0%

Medium Heavy

Soil Level

As it has bearing on determining amounts of soils representative of each of the three soil levels, it is

important to note how these four surveys compare individually. Surveys A, C, and F individually

each display very nearly the same distribution ofthe level of soil in households’ dishwasher loads,

which is essentially the distribution presented in Figure 2. Survey D departs substantially from this

distribution showing rather a distribution of approximately 62%, 21%, and 17% from light to heavy.

The author(s) ofsurvey D noted concerns that some number oftheir respondents may not have been

properly instructed on this question skewing their response to the heavy soil level. Therefore, in the

later section relating amounts ofsoil to the soil levels, survey D is treated with substantial

discounting ofthe response in the heavy soil level.

Types of Soil

The available surveys provide only limited information on the types of soil on the dishware of U.S.

households. Similarly, broader industry experience has revealed the difficulty of inventorying soil

types on the dishware of U.S. households and representatively recreating those soils for the purpose

oftesting.

However, the Association of Home Appliance Manufacturers (AHAM) has spent considerable time

and effort to defme the industry-recognized, ‘worst case’ cleaning performance test, ANSL’AHAM

Standard DW-1-1992. DW-1 precisely defmes: 1) food soils that are representative ofthe types of

soils on the dishware of U.S. households; 2) amounts ofthose food soils, and 3) procedures to apply

the food soils and to prepare the dishware for testing. DW-1 meets industry requirements for test

repeatability.

62%

33%

Light

5%

9
ANSIJAHAM Standard DW- 1 includes 13 food soils that are intended to be representative ofthe

types of food soils on the dishware of U.S. households. These foods soils are not intended to mirror

exactly the food soils on the dishware of U.S. households. Table 2 is an excerpt from ANSIJAHAM

Standard DW-1 that lists the food soils, the amounts ofthe food sufficient to soil a ten place table

setting, and specific descriptions ofthe foods.

Table 2 — Soiling Ingredients from ANSIIAHAM Standard DW-1

Item Quantity Description

Corn 6 teaspoons (30 ml) Cream style

Eggs 4 (50 g) minimum weight Fresh, grade A, large

Coffee Grounds 1 1⁄4 teaspoons (6 ml) Folgers, decaffeinated drip grind

Round steak with all visible fat

removed. Mix together 75% round Ground Beef Mixture 5 teaspoons (25 ml) steak with 25% kidney suet; grind

together twice.

Fleischmans corn oil (6 g of fat per 14 Margarine 1 tablespoon (15 ml) g serving) not whipped

Milk 2/3 cup (160 ml) Carnation nofat dry

Quaker Oats instant regular flavor (12 Oatmeal 5 teaspoons (25 ml) individual packages)

Peanut Butter 2 1/2 teaspoons (13 ml) JIF Creamy

Potatoes 13 teaspoons (65 ml) Hungry Jack instant mashed

Preserves 10 teaspoons (50 ml) Smuckers red raspberry

Salt 1/4 teaspoon (1.25 ml) Morton iodized

Tomato Juice 1 cup (240 ml) Campbell’s

Tomato Paste 12 oz.can Contadina

10
Figure 3 shows an example of a place setting soiled with the foods specified in DW-l. However, the

food soils in Figure 1 are not applied as precisely as specified in DW-l.

Figure 3 — An example of a Place Setting Soiled with Food Soils from DW-1

Given the inherent difficulty of engineering soil types and the fact that a worst case soil types has

already been defmed by an industry standard, and that the current test method references part ofthat

standard, it is recommended in the best interst of DOE and the industry to use the dishware soiling

procedure in DW-1 in a revised energy consumption test method for soil-sensing dishwashers.

As described in the section below, surveys have probed consumers to defme the quantity ofsoil on

their dishes and often relate the quantity of soil in terms ofthe DW- 1 standard.

11
Quantitative Amount of Soil in a Dishwasher Load

This section defines quantitative amounts of soil for each ofthe three soil levels that characterize the

distribution ofsoil levels found in dishwasher loads of U.S. households. Surveys C, D, and F,

cumulatively representing over 2,000 U.S. households, provide text and/or graphic descriptions to

link their categories ofthe level of soil to the three soil levels — Light, Medium, Heavy- and to

quantitative amounts ofsoil for each level. Referencing ANSJJAHAM Standard DW- 1 for the types

of soil and, most importantly, the amounts of soil is essential in relating each ofthe three soil levels

to an amount ofsoil.

The relationship to the amounts ofsoil representative ofthe soil levels is derived differently for each

survey, but for each survey the relationship is made in terms ofthe number of place settings in the

DOE test load that are soiled according to ANSIJAHAM Standard DW- 1. The author(s) ofsurvey C

make the relation from the extensive descriptions in their survey data to an associated amount ofsoil

in terms of DW- 1 soiled place settings. For survey D the respondents directly make the link to an

amount of soil in terms of DW-l soiled place settings. For survey F, Arthur D. Little has made the

link from the survey’s description of its soil categories to an amount of soil in terms of DW- 1 place

settings.

Table 3 shows the range ofthe survey data on representative amounts ofsoil for each ofthe three soil

levels. For each survey the amounts ofsoil are expressed in terms ofthe number of place settings in

the DOE test load that are soiled according to ANSI/AHAM Standard DW-l.

Table 3 — Range of Survey Data on the Representative Amounts of Soil in the Three Soil Levels

Soil Amounts in terms of Place Settings Soiled Per DW-1

Light Medium Heavy

SurveyC %ofl 2 4-5

• Survey D 1-2 4-6 6-8

. SurveyF 1 4 8

Aggregating the survey data in Table 3 is not as straightforward as it was in previous sections. Only

survey C is nationally representative while surveys D and F are regional. Although this difference

alone is not necessarily a concern, this difference in combination with the differences in the

representative amounts ofsoil between the national and regionally representative surveys presents a

challenge. The depth, breadth, and national representation ofthe data available in survey C suggest

that its representative amounts of soil for the three soil levels alone could be taken to represent U.S.

households. However, including data from the narrower scopes ofsurveys D and F would yield more

conservative, that is greater, representative amounts of soil for the three soil levels.

Taking the more conservative path, surveys C, D, and F were aggregated to yield representative

amounts of soil for each ofthe three soil levels. However, before aggregating these surveys the data

from survey D corresponding to the heaviest amount of soil needed to be discounted. As noted

earlier, the author(s) ofsurvey D raised accuracy concerns and cast suspicion on some number of

their responses that may have skewed to greater amounts of soil due to lack of proper instruction.

12
The data from survey D was discounted in the following way to address this concern. The percentage

of responses in its heaviest soil category was reduced from 17% to 5% of its respondents making it

consistent with all ofthe other surveys. The responses displaced by this reduction were discarded, as

any attempt to redistribute them to lighter soil categories in survey D would only introduce

uncertainty.

Figure 4 show the distribution ofresponses from surveys C, D (modified), and F on representative

amounts of soil corresponding to the three soil levels — Light, Medium, and Heavy. Calculating the

weighted averages ofthe responses for each level ofsoil yields conservative values for the

representative amounts of soil in each ofthe three soil levels found in the dishwashers of U.S.

households. Table 4 shows these results.

Figure 4— Distribution of Survey Respondents on Representative Amounts of Soil in Each of the Three

Soil Levels

100% —

Light Soil Level

- 1 Soiled Place

Table 4— Representative Amounts of Soil in Each of the Three Soil Levels Found in Dishwashers of

U.S. households

Soil Amounts in terms of Place Settings Soiled Per DW-1

Weighted Average 1 3 6

Medium Soil Level

- 3 Soiled Place Settings

Heavy Soil Level

- 6 Soiled Place Settings

a

-J

0

Co

U

a

w

C

C

C

a

C

0

a.

‘5

a

a

Cl,

I

0

C

a

C)

a

a.

90%

80%

70%

60%

50%

40%

30%

20%

10%

0%

1/2 1 2 2 4 6

Number of Place Settings in the DOE Test Load Soiled According to DW-1

5 8

Light Medium Heavy

13
How are the dishwashers loaded in U.S. households?

This section considers the information available in surveys A and C to understand how many dishes

and what type of dishes should be in the test load(s) of DOE’s energy consumption test procedure.

Quantity of dishware

The available survey information clearly indicates that in the vast majority of households (> 80%)

dishwashers are run at full capacity. Given the directness ofthis fmding, it is recommended that the

eight place settings test load called for in the existing test method should be retained and applied to

any revisions to the test method for soil-sensing dishwashers.

It is interesting to note the implication ofthis fmding in conjunction with the fmding on the frequency

of use of a dishwasher found in a later section ofthis report. As most households only operate a

dishwasher once it is full, and dishwashers are run about once every other day, then the dishware,

pretreated and not, is accumulating over two days. The further implication is that some portion,

probably half, ofthe dishware in the load, pretreated and not, is air-drying for about a day.

The dishwasher industry is aware ofthe implication that dishware with varying amounts of soil is airdrying prior to running a cycle and that this can affect the cleaning performance of a dishwasher.

ANSIJAHAM Standard DW-l currently calls for a two hours of air-drying for soiled dishware prior

to running a test load. AHAM, its members, and others interested groups are reviewing the need to

revise the air-drying specification. It is recommended that any revisions to the air-drying

specification in ANSI/AHAM Standard DW- 1 should be automatically included in the revised test

method for soil-sensing dishwashers as it is an integral part of a soiling procedure dishware.

Type of dishware

The available survey information indicates, as might be expected, that there is a wide variety of

dishware used in U.S. households. However, survey A offers some information on the material type

of dishware. Survey A indicates that for more than half ofthe households surveyed plastic dishware

makes up a quarter or more ofthe dishwasher loads.

The impact of a portion ofthe test load being made up of plastic dishware is unknown. However, any

impact is likely to be ofsecondary importance to implementing a soil-based test method for soil

sensing dishwashers. Therefore, it is recommended that a revised test method for soil-sensing

dishwashers use the uniform set of ceramic dishware and glassware referenced in the current test

method. As a future effort the impact of plastic dishware may be assessed and considered in later

revisions to the test method.

14
How to reflect that soiling in a modified energy consumption test method?

This section presents an approach to modify the energy consumption test procedure for dishwashers

to consider soil-sensing dishwashers. The proposed approach follows directly from the above

findings.

Proposed Energy Consumption Test Method

This proposed revision to the energy consumption test method for dishwashers applies only to soilsensing dishwashers. The revision would create two paths in the test method. One path for non-soilsensing dishwashers would follow the existing test method. The other path for soil-sensing

dishwashers would follow the outline below for a revised test method.

The revised test method requires three energy consumption tests using different numbers ofsoiled

dishware. To cover the distribution of soil levels in the dishwasher loads of U.S. households, the

energy consumption of soil-sensing dishwashers needs to be measured at each ofthree soil levels —

Light, Medium, and Heavy- creating a three-point test method. The amount of soil at each ofthe soil

levels is defmed by the number of place settings out ofthe eight place settings in the existing test load

that are soiled in accordance with ANSIIAHAM Standard DW- 1. The number of soiled place

settings in the test load at each ofthe soil levels is shown in the test schedule in Table 5.

Table 5— Test Schedule for Soil-Sensing Dishwashers

Soiled Place Settings Clean Place Settings Test Soil Level per AHAM Standard per AHAM Standard Total Place Settings Number DW-1 DW-1

1 Light 1 7 8

2 Medium 3 5 8

3 Heavy 6 2 8

Note that the six serving pieces called for in the existing test method would be included clean.

The energy consumption for each ofthe three tests would be measured and calculated in the same

way as the existing test method. However, the energy factor for a soil-sensing dishwasher would be

based on a weighted average ofthe three energy consumption tests. The weighting factors are the

percentages for the distribution ofU.S. households in the three soil level categories — 62% Light level

ofsoil, 33% Medium, and 5% Heavy (see Figure 2).

Incorporating the weighting factors with the energy consumed in each test yields an energy factor for

soil-sensing dishwashers as defmed in Equation 1.

Equation I — Energy Factor for Soil-Sensing Dishwashers

EFsoii.sensing = 1I((.62*Test #1 Energy)+(.33*Test #2 Energy)+(.05*Test #3 Energy))

15
How often do U.S. households use a dishwasher?

Frequency of households’ usage of a dishwasher

Surveys from six ofthe eight sources present information on the frequency of households’ use of a

dishwasher. Five ofthe six surveys are nationally representative and cumulatively represent over

20,000 U.S. households.

One ofthese five surveys is the Energy Information Administration’s 1997 Residential Energy

Consumption Survey (1997 RECS). The 1997 RECS data on the usage of a dishwasher, as shown in

Figure 5, indicates that more than half of U. S. households with a dishwasher use it less than 4 times

per week. Therefore, the number ofrepresentative average use cycles per year for a dishwasher

should be in the vicinity of 208 cycles per year.

Although this is far fewer cycles per year than the 264 cycles per year recommended in an interim

rulemaking on dishwashers, it is not inconsistent with the steady decrease over the past 20 years in

the average use cycles for a dishwasher. ETA’s data is far more recent than the data available for the

interim rulemaking that recommends 264 cycles per year. The 264 cycles per year in the interim

rulemaking is based on an average of data gathered between 1985 and 1995.

Figure 5— 1997 RECS-Usage of a Dishwasher

60.0%

50.0%

a)

40.0%

30.0% U,

0

0

U)

20.0%

05

10.0%

0.0%

Less Than 4 Times 4 to 6 Times At Least Once Each Day

<1:5;’ <5>

However, calculating an average value for usage of a dishwasher from the RECS data is not

straightforward. To determine an average requires definition of a single value for each category that

is to be weighted by the percentage of responses in that category. The categories, “less than 4 times”

and “at least once each day”, do not defme a single value and therefore, make determining an average

somewhat arbitrary.

16
The issue in determining an average is not limited to the RECS data. Several ofthe other surveys

share the problem of defining a single value for a category, but to a much less extent than the RECS

data. Generally the other surveys minimize this issue by including more categories, by better

distributing categories, and by having more bounded categories.

To analyze the frequency of use data a consistent approach was used to define an average value for

categories. A low value, an average value, and a high value were defmed for each category found in

the surveys. For bounded categories, such as “3-4 times per week”, the low value was 3, the average

value was 3.5, and the high value was 4. For upper bounded categories, such as “once a month or

less”, the low value was taken as 1 per 6 weeks, the average value was taken as 1 per 5 weeks, and

the high value was taken as 1 per 4 weeks. For lower bounded categories, such as “at least once per

day”, the low value was taken as 7 per week, the average value was taken as 8 per week, and the high

value was taken as 9 per week.

The five nationally representative surveys, including the RECS data, were analyzed in this way and

treated in aggregate. Table 6 shows the range of average-use cycles calculated using the low,

average, and high values for each category. Table 6 also shows the medians and the means for those

ranges.

Table 6— Range of Average-Use Cycles I Year for a Dishwasher

Range of Average-Use Cycles Near for a Dishwasher

Lowest Highest M Median of

AveraQe Averaqe ean Averaqes

Low Category Values 153 225 181 162

Average Category Values 181 245 206 191

High Category Values 201 282 232 226

17
S S

/€ to S(Y2 riioC

- Median: half of the responses are at

3.53/week or less I.e. —184 cycles per year

or less.

-Average: in aggregate, the average is

3.91 cycles per week or —203 cycles per

vor

Taking the five nationally representative surveys in aggregate, the distribution of responses for the

categories ofthese surveys is shown in Figure 6. Calculating a weighted average ofthese categories

a representative average-use of a dishwasher of 203 cycles per year.

Fiqure 6 — Distribution of Freciuencv of Households’ Use of a Dishwasher

16%

14%

(0

12%

c0

0’ (0 10i

8%

6%

4%

2%

0% n ii fl [1

I I I

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Recommendations

The following is a summary ofArthur D. Little’s recommendations on revisions to the Department of

Energy’s test procedures for measures of energy and water consumption and their “Uniform Test

Method for Measuring Energy Consumption of Dishwashers”. Arthur D. Little’s recommendations

on revisions to the test procedure include:

• Creating a separate path in the test method for soil-sensing dishwashers and adopting the

three point test method for soil-sensing dishwashers outlined above, and

• Reducing the average-use cycles per year for dishwashers to 203 cycles per year.

In addition to these revisions to the test procedure, there are several other recommendations for future

actions to capture greater efficiency benefits with dishwashers and to maintain the test procedure for

dishwashers:

• Assessing the energy impact of pretreating dishes and the energy saving opportunities of

greater utilization of dishwashers,

• Supporting industry efforts to update and maintain the ANSIJAHAM Standard DW-l,

• Assessing the energy impact of plastic dishware in the test load, and

• Monitoring and updating the distribution of households with dishwashers by the level of

soil in the load through a follow-up assessment of households’ dishwasher usage habits

and characteristics.

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