EE-RM-TP-99-500 COMMENT 25

OFFIC! or 

BUlL. tNG T£CH~OlOGY, ~"T A"1 ,{ ,.,N 0 C0l-l ,M.u ,N.I T "YP Jl 0 G ,R A J;I S 

Review of Survey 

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: December 18, 2001 

Arthur D. Little, Inc. 

Acorn Park 

Cambridge, MA 02140 
EE-RM-TP-99-500 COMMENT 25

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 of sources including several dishwasher manufacturers, detergent 

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

agencies. 

The findings of the review of available data on consumers' dishwasher usage habits show broad 

support to define: 

• Consumers' pretreatment methods, 

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

• Quantitative amount of soil on the dishware, and 

• Frequency of households' use of a dishwasher. 

Drawing from these survey findings, the existing test method for dishwashers, and ANSI! AHAM 

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

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

rt~com; nended that the number of average-use cycles per year be reduced into the range of 200 to 233 

cycles per year. 

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 soilsensing dishwashers are not representative of the actual energy consumption of soil-sensing 

dishwashers in use by consume:rs. This inaccuracy, created by the evolution of technology, 

necessitates revision of the 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 of its 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 
EE-RM-TP-99-500 COMMENT 25 -

'. 

Overview of Current Dishwasher Test Procedure 

The Department of Energy's test procedures for measures of energy and water consumption (l0 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 

operates a dishwasher on the cycle recommended by the manufacturer for a full load of normally 

soiled dishes, but 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, ANSI! AHAM 

Standard DW -1. The total per-cycle energy consumption of a dishwasher is based on the energy 

consumption measured during this test run on the normal cycle with a load of clean dishes. 

DishwashErs ml$t meet or exceed a minimum energy factor (10 CFR 430.32(f)). The energy factor 

for dishwa ;;hers is the reciprocal of the total per-cycle energy consumption. Standard dishwashers 

(currently (qual t~) or greater than 22" in exterior width) must have an energy factor not less than 0.46 

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

factor not les~, than 0.62 cycles/kWh. 

It should be noted that effective: June 17, 2002 that the definitions of standard and compact 

dishwashers will be based on place setting capacity. A standard dishwasher will be one having a 

capacity greater than or equal to 8 place settings plus 6 serving pieces as defined in ANSI! AHAM 

Standard DW -1. A compact dishwasher will be one having a capacity less than 8 place setting plus 6 

serving pieces. 

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 of soiled 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 householld 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-soilsensing - 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 in revising the test procedure for dishwashers to assure that soil-sensing 

dishwashers have energy factors not less than the minimum energy standard, and that the information 

on the Energy Guide label is representative, are: 

3 
EE-RM-TP-99-500 COMMENT 25 -", 

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

- Quantity of soil? 

- Type of soil? 

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

- Quantity of dishware? 

- Type of dishware? 

3. How to reflect 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 findings of the data in a revised 

energy consumption test procedure for dishwashers. 

Data Sources 

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

and analysis of survey infonnatio 1 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 fonn the core of the infonnation to address the key questions and to 

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

infonnation pertaining to consumers' dishwasher habits. 

More than half of the 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 of the surveys are from the 2000-2001 timeframe. Nationally 

representative means that the study populations of these 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 of residence, and ownership versus rental of residence. 

A key requirement of this 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 of the survey 

infonnation. However, Table :1 gives an overview of each survey's scope and size. 

Table 1 - Overview of scope and size of surveys 

Survey Scope Number of Breadth of Quality of 

Identifier Households Information Information 

Survey A Nationally Representative > 8,000 Wide High 

Survey B Nationally Representative > 11,000 Wide High 

Survey C Nationally Representative < 1,000 Wide High 

Survey 0 Regional > 1,000 Limited Moderate 

Survey E Regional < 250 Limited Low 

SurveyF Regional < 250 Moderate Moderate 

4 
EE-RM-TP-99-500 COMMENT 25

Survey G Nationally Representative < 500 Moderate Moderate 

Survey H Nationally Representative < 1,000 Moderate Moderate 

1997 RECS Nationally Representative 5,900 Limited High 

The aggregation of the various survey data has required some regrouping of the 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 outlined above, and how the survey data were analyzed to address 

those data requirements. 

5 
EE-RM-TP-99-500 COMMENT 25

Detailed Findings 

The findings of this 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 H dish\'vasher load, and 

• Size of the dishwasher load. 

Existing dishwasher cleaning performance test standards provide much of the 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 loaq, 

• 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 findings 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 
EE-RM-TP-99-500 COMMENT 25

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

This section covers survey data and test method information 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 of the eight sources (surveys A, C, E, F, G and H) provide information on 

households' pretreatment habits. Four of these surveys are nationally representative and 

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

All six of the survey sources present their data in similar categories that make aggregation of the 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.~:. households pretreat dishes with 

water prior to placing them in the dishwasher. Figure 1 shows the aggngation of the surveys' 

responses to questions on pretreatment habits. The simple import of thL.; finding is that currently the 

vast majority of U.S. households' dishwasher loads are cleaner than the.·) would be otherwise. 

Figure 1 - U.S. Households' Dishwasher Pretreatment Habits 

80.0% ,..-----------------.-----.----.-.--------.... -----------------.---.. ---., 

70.0% 

Over 70% of consumers pretreat dishes 

with water beforE~ loading into 

dishwasher. 

~ 60.0% (" -----------~-----------'\ .s::. 

U) 

~ 50.0% 

is 

:E 

~ 40.0% 

~ 

'0 

.s::. 

51 30.0% ::I 

o 

:I: 

~ 20.0% 

10.0% 

0.0% 

Pre-rinse with Pre-wash, including Pre-soak the dish Scrape food 

water some scrubbing without water 

Pretreatment Method 

Removed large 

scraps 

Do nothing 

7 
EE-RM-TP-99-500 COMMENT 25

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 of these two asked households to rate the 

overall level of soil in their dishwasher loads. The other ranked and categorized households' 

description of the overall level of soil in their dishwasher loads. 

Both of these two surveys distribute the level of soil in households' dishwasher loads in three 

categories: 

• Light level of soil, 

• Medium level of soil, and 

• Heavy level of soil. 

Surveys D and F are regional in scope and each present their data on the level \)f soil in households' 

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

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

the two surveys has more than three categories for the level of soil, the definitions of their categories 

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

Aggregating the two nationally representative sources (surveys A and C) and weighting the responses 

in each category by the total number of respondents yields a distribution of households within these 

three categories that follows approximately 62%, 33% and 5% from light to heavy, as shown below 

in 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 finding that most households rinse dishes before placing them 

in the dishwasher. 

8 
EE-RM-TP-99-500 COMMENT 25

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

70% 

60% 

I!! J! 50% III 

; 

s: 

III 

Q 40% s: 

:t:! 

~ 

III 

'tI 

:g 30% 

GI 

III 

:::J 

0 

:J: 

iii 20% 

::i 

10% 

0% 

62% 

Light 

33% 

Medium 

Soil Level 

Heavy 

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 each display 

very nearly the same distribution of the level of soil in households' dishwasher loads, which is 

essentially the distribution presented in Figure 2. Survey D also shows a similar trend. At the light 

level of soil survey D is consistent with Figure 2 showing approximately 62% of its respondents 

distribute in the light level of soil category. 

However, survey D departs from the other surveys at the medium and heavy levels of soil showing 

rather a distribution of approximately 21 % at the medium level and 17% at the heavy level. The 

author(s) of survey D noted concerns that some number of their respondents may not have been 

properly instructed on this question skewing their responses to heavier soil levels. Therefore, in the 

later section relating amounts of soil to the soil levels, survey D is treated with complete discounting 

of the responses at the heavy 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 

of testing. 

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

and effort to define the industry-recognized, 'worst case' cleaning performance test, ANSIIAHAM 

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

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

9 
EE-RM-TP-99-500 COMMENT 25

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

repeatability. 

ANSIIAHAM Standard DW-l includes 13 food soils that are intended to be representative of the 

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

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

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

setting, and specific descriptions of the foods. 

Table 2 - Soiling Ingredients from ANSI/AHAM 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 ~ teaspoons (6 ml) Folgers, decaffeinated drip grind 

Round steak with all visible fat 

Ground Beef Mixture 5 teaspoons (25 ml) removed. Mix together 75% round 

steak with 25% kidney suet; grind 

together twice. 

Margarine 1 tablespoon (15 ml) Fleischmans corn oil (6 g offat per 14 

l) serving) not whipped 

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

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

individual packages) 

Peanut Butter 2 'V2 teaspoons (13 ml) JIF Creamy 

Potatoes 1 ~~ teaspoons (65 ml) Hungry Jack instant mashed 

Preserves 1 () teaspoons (50 ml) Smuckers red raspberry 

Salt % teaspoon (1.25 ml) Morton iodized 

Tomato Juice 1 cup (240 ml) Campbell's 

Tomato Paste 12oz.can Contadina 

10 
EE-RM-TP-99-500 COMMENT 25

Figure 3 shows an example of a place setting soiled with the foods specified in DW -1. However, the 

food soils in Figure 3 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 worst case soil types have 

already been defined by an industry standard, and that the current test method references part of that 

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

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

As described in the section below, surveys have probed consumers to define the quantity of soil on 

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

11 
EE-RM-TP-99-500 COMMENT 25

.' 

Quantitative Amount of Soil in a Dishwasher Load 

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

distribution of soil 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 of the level of soil to the three soil levels - Light, Medium, Heavy- and to 

quantitative amounts of soil for each level. Referencing ANSI! AHAM Standard DW -1 for the types 

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

to an amount of soil. 

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

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

DOE test load that are soiled according to ANSIIAHAM Standard DW-l. The author(s) of survey C 

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

in tenns ofDW-l soiled place settings. For survey D the respondents directly make the link to an 

amount of soil in tenns of DW··1 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 of the survey data on representative amounts of soil for each of the three soil 

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

the DOE test load that are soiled according to ANSIIAHAM 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 

Survey C 1/2 2 5 

Survey D 1-2 4-6 8 

Survey F 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 of soil between the nationally and regionally representative surveys presents a 

challenge. The depth, breadth, and national representation of the 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 of surveys 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 of the three soil levels. However, before aggregating these surveys the data 

from survey D needs to be treated carefully. 

As discussed previously, survey D shows the same distribution of respondents as in surveys C and F 

(also survey A) for the light level of soil, which is approximately 62%. At the medium and heavy 

levels of soil survey D departs from the other surveys showing rather a distribution of approximately 

21 % at the medium level and 17% at the heavy level. The author(s) of survey D noted concerns that 

12 
EE-RM-TP-99-500 COMMENT 25

some number of their respondents were not properly instructed on this question and may have skewed 

their responses to the heavy soil level. 

The author( s) of survey D intended that respondents select one of several images that most closely 

represents the amount of soil typically found on each piece of dishware in their dishwashers. Some 

respondents did not receive clarification on this instruction and / or may have misinterpreted this 

instruction to mean "select one of the several images that most closely represents the total amount of 

soil on the dishware in their dishwashers." Certainly this misinterpretation would introduce an 

upward skew to any of the responses in survey D, not just those in the heavy soil level as the survey 

author(s) indicated. This means that its light soil level may be underestimated, its medium level may 

or may not be impacted, and the heavy level may be overestimated. 

Given that some number of respondents may have taken this interpretation, there is cause to question 

survey D in general. However, for the purpose of a conservative aggregation of surveys C, D, and F, 

survey D can be included without great concern for overestimation, if its responses in the heavy soil 

level are completely discounted. In the following aggregation survey D is included without its 

responses at the heavy soil level. 

Figure 4 show the distribution of responses 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 of soil yields conservative values for the 

representative amounts of soil in each of the 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% 1 

Gi 

90% { 

> f 

j 80% + 

·0 r 

en I 

.s::. 70% 1 u 

60% 1 CII 

w 

.5 

J!l 

c 

III 

"0 

c 50% 8. 

1/1 

~ 

F 

40% 

::l 

en 30% 

0 

.. 

c 

III 20% ~ III 

II.. 

10% 

0% 

1/2 2 2 4 6 5 8 

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

13 
EE-RM-TP-99-500 COMMENT 25

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

U.S. households 

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

Light Medium Heavy 

I Weighted Average 1 3 6 

14 
EE-RM-TP-99-500 COMMENT 25

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 of this finding, 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 finding in conjunction with the finding on the frequency 

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

dishwash;:r once it is full, and dishwashers are run about once every other day, then the dishware, 

pretreatec.' ancl r,ot, is accumulating over two days. The further implication is that some portion, 

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

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

ANSI! AHAM Standard D W -1 currently calls for a two hours of air-drying for soiled dishware prior 

to running a test load. AHAM, its members, and other 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 of the households surveyed, plastic dishware 

makes up a quarter or more of the dishwasher loads. 

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

impact is likely to be of secondary importance to implementing a soil-based test method for soilsensing 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. 

15 

i I 
EE-RM-TP-99-500 COMMENT 25

How to reflect 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 of soiled 

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

energy consumption of seil-sensing dishwashers needs to be measured at each of three soil levels -

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

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

that are soiled in accordance whh ANSI! AHAM Standard DW -1. The number of soiled place 

settings in the test load at eacr} \)fthe 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 

Number Soil Level per AHAM Standard per AHAM Standard Total Place Settings 

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 of the 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 of the three energy consumption tests. The weighting factors are the 

percentages for the distribution of U.S. households in the three soil level categories - 62% Light level 

of soil, 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 defined in Equation 1. 

Equation 1 - Energy Factor for Soil-Sensing Dishwashers 

EFsoll-sensing = 1/«.62*Test #1 Energy)+(.33*Test #2 Energy)+(.05*Test #3 Energy)) 

16 
EE-RM-TP-99-500 COMMENT 25

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

Frequency of households' usage of a dishwasher 

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

dishwasher. Five of the six surveys (surveys A, B, G, H, and 1997 RECS) are nationally 

representative and cumulatively represent over 20,000 U.S. households. 

One of these 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, indicate that more than half of U.S. households with a dishwasher use it less than 4 times 

per week. Therefore, the number of representative average-use cycles per year for a dishwasher 

should be in the vicinity of 208 cycles per year. 

Although this is far fewer cycle~s per year ~han the 264 cycles per year recommended in an interim 

rulemaking on dishwashers, it is not inco.'1~;istent with the steady decrease over the past 20 years in 

the average-use cycles for a dishwas.'1Ier. ElA's data are 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 gcthered between 1985 and 1995. 

Figure 5 - 1997 RECS-Usage of a Dishwasher 

60.0% r········ .. ·····•····························· .... ······· ...........•........•.... -•...................................................•.•....................................................................................................................................................................................................•....................................................................................... , 

... 

ell 

s:. 

III 

50.0% 

; 40.0% s:. 

III 

o 

C\I 

:e 

~ 30.0% III 

" 15 

s:. 

~ ~ 20.0% 

en 

::i 

10.0% 

0.0% +----

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

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 define a single value and therefore, make determining an average 

somewhat arbitrary. 

17 
EE-RM-TP-99-500 COMMENT 25

The issue in determining an average is not limited to the RECS data. Several of the 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 estimate values for the 

surveys' categories. A low value, an average value, and a high value were defined 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. 

Table 6 shows the range of average-use cycles caicula~ed using the low, average, and high values for 

the categories in each survey. On inspection ofTlble 6, it is clear that the surveys' data on average 

frequency of use falls roughly in two groups - less than L'06 cycles per year and greater than 206 

cycles per year. 

Table 6 - Range of Average-Use Cycles I Year for a Di!ihwa~.her 

Range of Average-Use Cycles I Year for a Dishwasher 

Low Category Values Average Category High Category Values Values 

Survey A 162 181 201 

Survey B 153 191 230 

Survey G 155 189 224 

Survey H 225 225 226 

1997 RECS 207 245 282 

Average of 180 206 233 Averages 

18 

-------------------------------! 
EE-RM-TP-99-500 COMMENT 25

Another approach to reduce the surveys' data to a value for the representative average-use cycles per 

year is to consider the distribution of responses for the categories of the five nationally representative 

surveys as shown in Figure 6. lin aggregate the five nationally representative surveys indicate that 

half of U.S. households with dishwashers use their dishwashers less than 170 times per year. 

Again calculating an average of these categories requires definition of a single value for each 

category. By applying the average value for each category, as in the above discussion, to the 

distribution in Figure 6 an average weighted by the number of respondents in the five nationally 

representative surveys can be calculated. This calculation yields a weighted average of 200 cycles 

per year. 

Figure 6 - Distribution of Frequency of Households' Use of a Dishwasher 

I!! 

GI 

.c 

20% 

18% 

16% 

j 14% 

i5 12% 

E 

~ 10% 

'C 

'0 

.c 8% 5l 

:::I 

o 

:x: 6% 

en 

::i 

4% 

2% 

0% 

•• uu ..... u_.u.u. ___ • __ ._. __ .. _·· __ ._. __ .. __________ •____ • __ ,, __ ._'._ 

" 

, 

. 

-m I iii " II ;' ~ "" , 

-

r--

- Median: half of the responses are at 

3.£8/week or less I.e. -170 cycles per year 

or le:ls 

- Average: in aggregate, the average is 3.86 

CYCleS per week or -200 cycles per year. 

9 

• 

In III . , i 

The previous discussions on the frequency of use of dishwashers in U.S. households suggest that the 

representative average-use cycles per year for a dishwasher should be at least 200. Additional data 

from the dishwasher detergent industry is being sought to refine further the number for the 

representative average-use cycles per year. This additional data is anticipated for late December 

2001 or early January 2002. Without regard for this additional data it is clear that a revised number 

for the representative average-use cycles per year should be substantially less than the 264 in the 

interim rulemaking, but not less than 200 cycles per year. 

19 
EE-RM-TP-99-500 COMMENT 25

Recommendations 

The following is a summary of Arthur 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 into the range of 200 to 233 

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 maint(l.in the test procedure for 

dishwashers: 

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

greater utilization of dishwashers, 

• Supporting industry efforts to update and maintain the ANSI! AHAM Standard DW -1, 

• 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. 

20