A11100

NBS

PUBLICATIONS

NBSIR 80-2173

Water Usage Characteristics of

Household Appliances and the

Potential for Water Savings

Robert L. Palia

Center for Consumer Product Technology

National Engineering Laboratory

U.S. Department of Commerce

National Bureau of Standards

Washington, DC 20234

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80-2173

1980

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Department of Housing and Urban Development

Washington, DC 20410

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NBSIR 80-2173

WATER USAGE CHARACTERISTICS OF

HOUSEHOLD APPLIANCES AND THE

POTENTIAL FOR WATER SAVINGS

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Robert L. Palla

Center for Consumer Product Technology

National Engineering Laboratory

U.S. Department of Commerce

National Bureau of Standards

Washington, DC 20234

December 1980

Prepared for: Office of Policy Development and Research

Department of Housing and Urban Development

Washington, DC 20410

1981

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U.S. DEPARTMENT OF COMMERCE, Malcolm Saldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

i

PREFACE

This report is one of a group documenting National Bureau of Standards

(NBS) research and analysis efforts in developing water conservation test

methods, models for technical and economic analysis, and strategies for

implementation and acceptance of practices. This work is sponsored by the

Department of Housing and Urban Development, Office of Policy Development

and Research, Energy, Building Technology and Standards Division, under

Interagency Agreement H-48-78.
11

ABSTRACT

A study has been undertaken to quantify appliance water consumption and the

effectiveness of various consumer usage techniques and manufacturer design

modifications for saving water. Appliances considered are clothes washers and

dishwashers. Through a comparison of estimated water savings, the study

indicates that the most significant means of saving water are those which are already commercially available — front-loading machines and suds-saver options

for clothes washers, and short-cycle setting? for dishwashers. Water savings ot

about 20 to 30 percent are estimated with these features, or about 10 ga_lons

for clothes washers and 3 gallons for dishwashers.

Several appliance design modifications are also evaluated but do not offer

the same level of savings. Water usage characteristics such as supply and

discharge flow rates and the effect of supply pressure and cycle selection are

presented.
Xll

Table of Contents

Page

Preface i

Abstract. . ii

List of Tables v

List of Figures v

1. Introduction 1

2. Laboratory Test Appliances 1

3. Appliance Water Consumption, and Supply/

Discharge Characteristics 2

3.1 Clothes Washers 2

3.1.1 Water Consumption 2

3.1.2 Supply and Discharge Characteristics. . . 3

3.2 Dishwashers 3

3.2.1 Water Consumption 3

3.2.2 Supply and Discharge Characteristics. . . 4

4. Effects of Various Parameters on Water Consumption. . 4

4.1 Clothes Washers 4

4.1.1. Load Size/Water Level Setting 4

4.1.2 Cycle Selection 4

4.1.3 Supply Pressure 5

4.1.4 Temperature Selection 5

4.2 Dishwashers 5

4.2.1 Cycle Selection 5

4.2.2

Supply Pressure 6
iv

Page

5. Options and Design Modifications for Appliance

Water Conservation . f . . 7

5.1 Water Conservation Options for Clothes Washers. . ,

5.1.1 Front-Loading Machines 7

5.1.2 Suds-Saver Devices .... f

. 7

5.1.3 Better Use of Existing Water Levels Controls 8

5.2 Water Conservation Design Modifications for Clothes

Washers 8

5.2.1 Reduce Tub Volume 8

5.2.2 Reduce Clearance Between Inner and Outer Tubs 9

5.2.3 Develop Automatic Water Level Control. ... 9

5.3 Water Conservation Options and Design Modifications

for Dishwashers 9

5.3.1 Reduce the Number of Water Changes 9

5.3.2 Reduce the Quantity of Water Used Per Water

Change 10

6. Summary and Conclusions 10

7. References 12
V

Table 1 -

Table 2 -

Table 3 -

Table 4

Table 5 -

Table 6 -

Table 7 -

Table 8 -

Table 9 -

Table 10 -

Table 11 -

Table 12 -

Figure 1 -

Figure 2 -

Figure 3 -

List of Tables

Typical Wash/Rinse Phasing for Clothes Washers

Clothes Washer Water Consumption Breakdown for

Various Fill Levels

Some Reported Values for Clothes Washer Water

Consumption

Clothes Washer Supply and Discharge Flow Rates

Dishwasher Cycle Phasing, Water Consumption, and

Washing Index

Manufacturers' Estimates of Dishwasher Water

Consumption at Various Cycle Settings

Dishwasher Supply and Discharge Flow Rates

Typical Weights of Clothes Loads Washed

Increase in Clothes Washer Tub Volume in Recent

Years

Water Savings Attainable at Maximum Fill Levels by

Reducing Inner- to-Outer Tub Clearance to 0.5 Inches

Water Conservation Design Options and Estimated

Water Savings for Clothes Washers

Water Conservation Design Options and Estimated

Water Savings for Dishwashers

List of Figures

Schematic of a Typical Top-Loading Clothes Washer

Distribution of Static Water Pressure Found in a Survey of Residences Throughout the United States

Effect of Water Supply Pressure on Dishwasher Water

Consumption

1 . INTRODUCTION

Water-consuming appliances, namely clothes washers and dishwashers, account

for approximately 20 percent of all water used within a typical household [l ].*

As residential water usage accounts for roughly 40 percent of all potable fresh

water consumption (excluding irrigation) [l], the contribution of appliances to

total national water use is appreciable. In addition, and perhaps even more

significant, is the energy used to heat this water. Water heating accounts for

14 percent of residential energy consumption [2]. Appliances use about onethird of all hot water—an amount equivalent to 1 percent of national energy

use. Also, the demands appliances place on residential water supply and

drainage systems, for example, high discharge rates, may preclude water

conservation efforts involving the down-sizing of plumbing components.

As we approach an era in which wiser use of our resources is a necessity,

an examination of appliance water usage characteristics and the potential for

water savings is in order. Such an examination was conducted by the Center for

Consumer Product Technology (CCPT) at the National Bureau of Standards (NES).

This study was part of a comprehensive water conservation program sponsored by

the Department of Housing and Urban Development (HUD) through the Center for

Building Technology (CBT). The three primary objectives for the CCPT study were

to:

o determine typical clothes washer and dishwasher water consumption, and

supply/discharge characteristics,

o assess the effects of various parameters, such as cycle selection and

water pressure, on water consumption, and

o evaluate techniques for appliance water conservation and estimate the

corresponding water and energy savings potential.

The purpose of this study was to identify appliance parameters, usage

techniques, and options available to manufacturers and consumers, which offer

the most substantial water savings. Information and data developed through this

effort was to serve as an input to other portions of the CBT program, and as a

basis for HUD consumer information publications and HUD policy regarding minimum

performance standards for rehabilitative housing.

Results of the study indicate that substantial water savings are attainable

through several means, involving altering consumer habits and modifying

appliance design. By changing consumer habits alone, appliance water usage can

be reduced by about one third. This corresponds to a 7 percent reduction in

residential water usage. However, water savings are not always obtained without

trade-offs since reductions in water consumption may affect appliance

performance. As performance encompasses many often subjective factors, such as "gentleness of action" and "tangle free action" for clothes 'washers, the effect

of water conservation on performance has not been evaluated here. Rather, it is

felt that performance would best be dealt with by appliance manufacturers, with

performance and 'water conservation features bein.v traded off in the normal

workings of the marketplace.

*1lumbers in brackets refer to references on paee 12.
- 2 -

2. LABORATORY

- TEST APPLIANCES

The evaluation of effects of various parameters on appliance water usage

characteristics was based on NBS laboratory testing and on existing studies.

Five different model clothes washers and seven different model dishwashers were selected for laboratory tests. These units were purchased between 1970 and 1976

for use in the appliance energy efficiency program within COPT. Because no significant changes in appliance water consumption have occurred over the past

few years in the industry [3], these units remain representative of currently

available models in this respect. Throughout this report, values for parameters

such as water consumption and supply flow rate are presented for test units as well as other model appliances. When the values presented are based on NBS

laboratory tests, the appliance model is referred to as a "test unit" and is

denoted by the symbol CW or DW for clothes washers and dishwashers,

respectively.

3- APPLIANCE WATER CONSUMPTION AND SUPPLY/DISCHARG-E CHARACTERISTICS

3*1 Clothes Washers

The purpose of a clothes washer is to remove soil from garments and

fabrics. Various wash cycles are available for performing this function. A

typical wash cycle, usually termed the "normal" cycle, consists of a wash, spray

rinse, and deep rinse, sometimes followed by another spray rinse. (These parts

of a complete cycle are referred to as subcycles in this report). In contrast,

the "permanent press" cycle generally consists cf a wash followed by several

partial rinses and a deep rinse. Typical wash/rinse phasing for the "normal,"

"permanent press," and "soak" cycle settings is shown in Table 1. It should be

pointed out, however, that phasing and water consumption on these as well as other wash cycles may vary among clothes washer models. Several other wash

cycles such as "heavy-soil" and "knits" are also available on many machines.

These cycles differ in the number and order of washes and rinses, and in some cases, agitation speeds.

3-1*1 Water Consumption

The wash and deep rinse subcycles of conventional large-capacity, toploading machines use about 23 gallons of water each at the maximum fill level

settings, and and 12 gallons each at the minimum fill level setting. (Most

machines are equipped with a variable water level control which permits this

adjustment). The spray rinse subcycle uses three to five gallons, bringing the

water consumption for a complete normal cycle to about 50 gallons at the maximur.

fill level setting. A breakdown of water consumption for several test units is

presented in Table 2. Additional estimates of total water consumption obtained

from the literature are presented in Table 3 for various manufacturers models.

The temperature of the water used in the wash and deep rinse subcycles

('hot, warm, or cold) may be selected independently, but the spray rinse

temperature cannot. It is usually dependent on wash and deep rinse temperature

selection and may vary from one machine to the next, for example, a warm

wash/cold rinse temperature selection might give a warm spray rinse on one machine but a cold spray rinse on another.
- 3 -

3.1.2 Supply and Discharge Characteristics

While the volume of water consumed hy appliances is of primary interest

here, the rate at which it is supplied to and discharged from appliances can

ultimately determine the feasibility of other water conservation options

involving the downsizing of residential supply and drainage piping systems. The

supply and discharge flow rates for several model clothes washers were therefore

measured as part of this study.

Supply and discharge flow rates for five machines tested are presented in

Table 4. At a given pressure, these rates are essentially constant due to the

fixed orifice in the fill valve and constant discharge pump capacity. It can be

observed from the data presented that both supply and discharge flow rates

differ substantially between machines. Supply flow rates ranged from a low of

about 4 gallons per minute to a high of about 9 gallons per minute. Discharge

flow rates ranged from about 9 gallons per minute to 16 gallons per minute.

3-2 Dishwashers

The automatic dishwasher is a kitchen appliance for washing food

preparation utensils and dining dishes and flatware. Several dishwashing cycles

are generally available for performing this function. Most common are the

"normal," "rinse-hold", and "short wash" cycles, but "super wash," "energy

saver," and other special cycles are also available on many machines. All of

these cycles use only hot water.

Dishwasher operation and water consumption are dependent on the wash cycle

selected. The "normal" cycle typically consists of a wash, a rinse, a second

wash, and two or three rinses, with water changes occurring between each of

these subcycles. The phasing and number of wash and rinse cycles is not uniform

among dishwashers though, even on the "normal" cycle. As data presented in

Table 5 indicates, the phasing as well as water consumption and washing

performance differs substantially.

The "short wash" cycle, useful for lightly soiled dishes requiring less

washing action, is essentially the same as the "normal" cycle with the first

wash and first rinse eliminated.

3-2.1 Water Consumption

The volume of water consumed in each water change of the dishwashing cycle

is usally two to three gallons, with the water consumption for the entire normal

wash cycle (all hot 'water) being between 13 and 15 gallons. Water fills are

timed, however, making water consumption somewhat pressure-dependent. (Pressure

effects are discussed later in Section 4-2.2). Measured values of total water

consumption are presented in Table 5 for several dishwashers on the normal

cycle. Some manufacturers' estimates of water consumption on this and various

other cycle settings are presented in Table 6 for 1979 model appliances. These

values indicate a slight reduction in water consumption over the 1975 and 1976

models tested in this laboratory.
3-

2.2 Supply and Discharges Characteristics

Supply and discharge flow rates for seven different model dishwashers are

presented in Table 7- It can be noted that maximum supply and discharge flewrates for these dishwashers, typically about 2.5 gallons per minute and 6

gallons per minute, respectively, are substantially less than for the clothes

tested (Table 4)-

4. EFFECTS OF VARIOUS PARAMETERS OR WATER CONSUMPTION

The effects of several parameters on appliance water consumption were

evaluated based on laboratory testing and on review of existing studies.

Parameters considered were those use conditions which vary with installation,

and consumer usage patterns. These included supply pressure, cycle selection,

and load size.

4-

1 Clothes Washers

Several factors affect clothes washer water consumption. Primary factors

include fill level and cycle selection. Supply pressure and temperature

selection affect water consumption to a lesser degree.

4-1.1 Load Size/Water Level Setting

The larger the load size, the greater the volume of water required for the

washing operation. As a rough estimate, every round of clothes requires betwee*

1.5 to 3-0 gallons of water for washing. Bonk [4] reports that small 10-12

pound capacity machines use 23 to 39 gallons, medium 14 pound capacity machines

use 16* to 49 gallons and large 18 pound capacity machines use 27 to 54 gallons.

Measurements of total clothes washer water consumption, Tables 2 and 3, are in

good agreement with these estimates. For a given capacity machine, the large

range of water consumption values reflects the variation in per cycle water

consumption at the minimum and maximum fill level settings present on most

machines.

4-1-2 Cycle Selection

Different garments and fabrics may require special care in washing. Thus,

several wash cycles are provided on most machines. Common cycles include:

o normal cycle

0 permanent press cycle

0 delicate cycle

0 soak cycle

A breakdown of usage for each of these cycles is not currently available, but a survey of washer owners conducted between 1968 and 1970 indicates that the

normal cycle is used 89 percent of the time while the permanent press gentle,

and other cycles account for 11 percent of all usage [5]- With the increased

availability of synthetic and synthetic-natural fiber fabrics in recent years,

current usa^e of the normal cycle may be expected to be somewhat reduced.

*The value of 16 gallons is for front-loading machines. Conventional top-load ir machines would have a lower limit of about 25 gallons.
- 5 -

Water consumption differs substantially among cycles due to the wide range

of appliance designs. As shown in Table 3, water consumption for some machines

may be as much as 18 gallons higher on the permanent press cycle setting than on the normal cycle. Water usage on other cycles has not been investigated

.

4.1*3 Supply Pressure

Pill volume for the wash and deep rinse subcycles is, in most models,

controlled by a diaphragm-type pressure switch located between the inner and

outer tubs (see Figure l) . This switch senses the depth of water in the tub,

hence, the volume of the fill is independent of supply pressure. The spray

rinse subcycle is usually timed, however, so the actual volume used in this

subcycle is somewhat dependent on supply pressure. As was shown in Table 2, the

spray rinse contribution to total water consumption is small. Pressure effects

on this contribution are even smaller; typically an increase of 15 psi in the

pressure, increases total consumption by about 1 gallon.

4.1.4 Temperature Selection

In general, hot and cold water which is supplied to automatic clothes

washers enters a dual gate solenoid valve within the machine (see Figure l)

.

This valve controls the water flow and provides cold, warm, or hot water for the

various subcycles. Cold water is obtained by actuating the cold water side of

the valve, hot water by actuating the hot water side, and warm water by

actuating both sides simultaneously. Mixing ratios for 50/50 hot/cold water are

commonly used for warm water, but 60/40 and 40/60 ratios are also used in some

machines.

Temperature selection does not affect water usage for the fill and deep

rinse subcycles because, as previously mentioned, water consumption for these

subcycles depends only on the the water level control setting and therefore the

depth of water in the tub. However, temperature selection does affect water

consumption on the spray rinse subcycles, which are timed. This is because the

supply flow rate is higher for warm water spray rinses (both sides of the

solenoid valve open) than for cold or hot water rinses (one side of the solenoid

valve open). Although water usage is higher for warm spray rinse cycles, the

difference is minimal — typically about 1 gallon per cycle.

In summary, fill level influences clothes washer water consumption most

strongly, followed by cycle selection. Both supply pressure and temperature

selection affect only the water consumption of the spray rinse subcycle and are

relatively unimportant.

4-2 Dishwashers

Several factors affect dishwasher water consumption; these include cycle

selection and supply pressure.

4.2.1 Cycle Selection

Most dishwashers are equipped with a variety of wash cycles and special

features. Typical wash cycles include:
- 6 -

o super wash

o normal wash

o short wash

o rinse/hold

Some manufacturers' estimates of water consumption on these cycles are presented

in Table 6 for 1979 appliance models. Inspection of the estimates reveals that

water savings of about 2 to 5 gallons per cycle are possible by using either the

short wash cycle more frequently or the super wash cycle less frequently.

Adequate washing performance on the water-conserving cycles is necessary

however, in order for these savings to be realized.

4-2.2 Supply Pressure

As shown in Figure 2, static water supply pressure in the United States

ranges between 20 and 130 psig. Residential plumbing system designs and water

usage patterns add to the variation, and affect the pressure at which water is

delivered to points of use within the home. The net result is a wide range of

supply pressures under which appliances must satisfactorily operate.

The fill cycles for all current dishwashers are timed events. Supply

pressure, which affects incoming water flow rates, therefore plays an important

part in determining total dishwasher water consumption. Higher water supply

pressures generally result in greater incoming water flow rates and thus greater

dishwasher water consumption (the fill time remains constant and the water fills

to a higher level in the sump). The supply pressure versus water consumption

profile shown in Figure 3-Case 1 illustrates this fact. For this machine, which

is equipped with a fixed-orifice fill valve, water consumption is 2 gallons per

cycle greater at 60 psig supply pressure than at 20 psig. If the machine is

designed to give satisfactory performance using the quantity of water consumed

at a supply pressure of 20 psig, this additional 2 gallons is unnecessary.

Pressure-compensating fill valves are commonly used to reduce excessive

water use and to provide a more uniform incoming water flow rate over the wide

range of pressures encountered in the field. These valves utilize a flexible,

variable-orifice flow disc similar to that used in low-flow faucets and

showerheads. Inspection of the water consumption versus supply pressure profile

for a machine equipped with the pressure-compensating disc, Figure 3-Case 2,

illustrates the effectiveness of these devices. The water consumption of the

machine varied by less than 1 gallon per cycle over the entire pressure range.

It should be noted here that while the water consumption of machines not

equipped with pressure-compensating devices is reduced by decreasing water

supply pressure, the same may not always be true for machines equipped with the

devices. The tendency towards greater water consumption at low supply pressures

shown in Figure 3-Case 2, precludes any general statements regarding pressure

reduction as a means of saving water.

In summary, dishwasher water consumption can be reduced by about 2 to 5

gallons per cycle by using the normal and short wash cycles instead of the super

and normal cycles respectively. Smaller water savings — about 1 to 2 gallons
- 7 -

per cycle — are possible for machines not equipped with pressure-compensating

flow discs, by reducing the supply pressure.

5. OPTIONS AND DESIGN MODIFICATIONS FOR APPLIANCE WATER CONSERVATION

Several options and design modifications to decrease appliance water

consumption are possible. For clothes washers these involve using front-loading

type machines, reusing wash water for clothes washing, and reducing the volume

of water which is not actually needed for washing. For dishwashers they involve

reducing the number of water changes or fills in a cycle and reducing the volume

of water use per fill. Additional machine modifications, such as increased wash

or rinse cycle time, may be required simultaneously to insure that performance

is not degraded by the water-conserving changes.

Of the design modifications discussed herein, many have been implemented on various appliance models; others are still in the development stages in industry

or have not yet become commercially available. For the latter case, water

savings equivalent to those offered by the modification, for example, automatic

water level control, are usually attainable by merely altering appliance usage

habits.

5-1 Water Conservation Options for Clothes Washers

5*1.1 Front Loading Machines

The most commonly suggested and perhaps the most effective means of

reducing water consumption for clothes washing is through use of commercially

available front-loading type washers. Compared to conventional top-loading

machines, front loaders require 50 to 50 percent less water (about 20 gallons)

and 50 percent less detergent to wash equivalent loads (see Tables 2 and 5)*

Front loading machines are more expensive, however, and have a load capacity

about 50 percent less than top-loaders. (Full-size top-loading machines range

in capacity from 14 to 18 pounds of clothing. The front-loader capacity is

rated at 14 pounds, but would more realistically wash about 12 pounds of

clothes). The smaller load capacity of the front loader is not a significant

disadvantage because, as data in Table 8 indicates, loads exceeding the capacity

of the front-loader are seldom washed.

5*1.2 Suds-Saver Devices

Use of suds-saver devices for top-loading machines is a second means of

reducing water consumption. The suds-saver feature, available as an option from

several manufacturers, permits the reuse of wash water for subsequent w?ish

loads. No water savings are obtained on the initial cycle with the suds-saver,

but savings of about 20 gallons per cycle are generally realized on subsequent

wash cycles for which the suds-saver is utilized. No substantial performance

penalties are incurred with the suds-saver [6] but laundry practices, such as the order in which clothes are washed, must frequently be modified to

accommodate the use of suds-saver.

Sales of sud -saver equipped clothes washers have decreased consistently

over past years. Reasons cited for this sales decline include (l) elimination
- 8 -

of laundry tubs (required for storing wash water) in many newer homes (2)

increased connections to public sewer systems (eliminating septic tank problems

which the suds-saver reduced) and (3) public disfavor over washing clothes in

"dirty" water. Sales of suds-savers is still strong in many areas of the

country however, particularly where sewer connections are not available. A

consumer education program emphasizing water, energy, and detergent savings is

perhaps a good first step towards reviving this water saving option.

5.1.3 Better Use of Existing Water Level Controls

Most clothes washers currently in use are equipped with a water level

selection control. Manual adjustment of the water fill level with this control

to compensate for various load sizes and fabrics can result in minimum water

usage. As indicated in Table 8, however, the control is generally not used to

full advantage. Although typical dry wash loads weigh about 5-4 pounds capacity

washers and 5*9 pounds for 18 pounds capacity machines, the maximum fill level

setting is selected by consumers 79 and 60 percent of the time, respectively

[5]. This anomaly is perhaps due in part to the user's concept of a full load,

and to poor laundering habits—setting the control to maximum fill and leaving

it there.

Inspection of Table 2 or 3 indicates that water savings with the level • selection control would be as high as 25 gallons per cycle for cases in which

the maximum fill setting is used when the minimum setting would suffice. Also,

use cf the level selection control eliminates the need to defer washing until a "full" load is available, as "partial" loads may be washed with the minimum

amount of water necessary by adjusting the fill level.

5 • 2 Water Conservation Design Modifications for Clothes Washers

Water savings in addition to those offered by the front-loader and sudssaver are possible by reducing the volume of water used to the minimum which is

actually needed for satisfactory performance. Several design modifications have

been suggested as a means to this end [7,8]. Some of these include:

o reducing tub volume

o reducing clearance between inner and outer tubs

0 developing automatic water level control

A discussion of the rationale and expected water savings for each of these

modifications follows.

5-2.1 Reduce Tub Volume

Clothes washer tub-volume has increased gradually over recent years (see

Table 9)- Data presented in Table 8 indicate that the additional capacity is

utilized for less than 2 percent of all wash loads. If fill level controls are not adjusted frequently and accurately by the consumer, it would appear that a

reduction in tub volume to 1972 sizes would result in water savings of about 4

gallons per cycle — without much of a loss in utility. It should be pointed

out however, that these savings will not be fully realized if the number of wash
- 9 -

cycles needed to launder the same amount of clothing increases proportionally

with the smaller machine.

5-2.2 Reduce Clearance Between Inner and Outer Tubs

The clearance and hence enclosed volume between the inner and outer tubs of

some top-loading machines is much greater than on others. This enclosed volume,

while tending to dilute the concentration of suspended soil, is not involved

directly in the washing process. Its reduction, if performance requirements can still be satisfied, can result in water savings. Clothes washers with reduced

clearances of about 0.5 inch are already commercially available. As shown in

Table 10, reducing the clearances of other machines to 0.5 inch offer water

savings of as much as 2 gallons per cycle.

5.2.5 Develop Automatic Water Level Control

A device which could achieve substantial water savings is an automatic

water level control. This device would respond to the amount and type of

fabrics loaded into the machine, and would adjust the water level to the minimum

required for proper laundering. By eliminating the need for user judgement, the

automatic water level control would offer water savings equivalent to those

obtained through optimum use of the current, manual water level control. The

automatic water level control has been in development by manufacturers for

several years, but has not yet reached a marketable stage [ 5 ].

5*5 Water Conservation Options and Design Modifications for Dishwashers

Water conservation changes for dishwashers basically involve reductions in

the number of water changes in the wash cycle or reductions in the quantity of

water used per water change.

5-3-1 Reduce the Number of Water Changes

The number and phasing of dishwasher subcycles or water changes differs

among various appliance models, as does the total water consumption and washing

performance. As shown in Table 5, with the exception of a slight trend towards

higher washing indices at greater water consumption levels, there appears to be

little correlation between any of the aforementioned parameters. It can also be

noted from Table 5, that the washing index of some models is substantially

greater than others; a range of 66 percent to 92 percent was measured.

Elimination of the first wash and rinse subcycles for lightly soi.l.ed

dishes, or the final rinse for most wash loads has been suggested as a means of

reducing water and energy consumption [7,8]. Based on the test results of Table

5, these changes appear feasible for well-designed machines. Adequate

performance on the shorter cycles will of course, be dependent on the extent of

soil, and dishwasher design. Several manufacturers currently offer machines

with such short cycle options. Consumer use of these cycles can result in water

savings of about 2 to 5 gallons per cycle.
- 10 -

5-3*2 Reduce the Quantity of Water Used Per Water Change

The quantity of water used per water change or fill can be reduced in three

ways: (1) reducing water supply pressure (keeping fill time constant), (2)

improving the fill level control, and (3) changing the geometry of the washing

chamber.

As was discussed in Section 4.2.2, for machines not equipped with a

pressure-compensating fill valve, a reduction in water supply pressure results

in a reduction in fill rate and water savings of about 1 gallon per cycle for

pressure reductions of about 20 psi. Pressure reductions will be limited to the

point at which the water level in the sump falls below the level of the

immersion heater or circulating pump inlet during the cycle.

Provided the dishwasher circulating pump and immersion heater is kept

supplied with water, the effect of fill volume reduction will be confined to a slight increase in the soil concentration of the wash water. The relation

between soil concentration and washing performance has not been investigated,

but should be determined if this modification is to be recommended.

An alternative to supply pressure reduction is the use of a pressureindependent filling arrangement such as that used on clothes washers (see

Section 4-1.3)- Water savings with such a system would aJso be about 1 gallon

per cycle.

The third means of reducing water consumption involves altering the

geometiy of the dishwasher sump region so that a smaller volume of water is

required to keep the circulating pump primed. This typically involves

increasing the slope of the washing chamber floor toward the pump water inlet,

and recessing the pump water inlet. This modification, which offers water

savings of about 1 to 2 gallons per cycle, has already been incorporated by

several manufacturers.

6. SUMMARY AND CONCLUSIONS

Total water consumption for a typical top-loading clothes washer is about

50 gallons for a normal cycle at maximum fill level — 23 gallons each for the

wash and deep rinse subcycles and 3 gallons for the spray rinse. Water

consumption is strongly dependent on fill level and cycle selection, but is only

slightly influenced by water supply pressure or temperature selection. Supply

and discharge rates are generally about 4 to 9 gallons per minute and 9 to 16

gallons per minute respectively.

Clothes washer water consumption may be reduced by several means. A

summary of various water conservation options and design modifications are given

in Table 11, along with estimated water savings for each. It should be noted

that the most significant of these options — front-loading machines and sudssaver devices — are already commercially available. Others, such as automatic

water level control, can be duplicated by the consumer developing better

laundering practices.
For a large percentage of the dishwashers in use, average water consumption

is about 14 to 15 gallons for a normal cycle, which generally consists of from

5 to 7 wash and rinse subcycles. Newer models have reduced this average to

about 12 to 13 gallons. Water consumption is about 2 to 5 gallons lower on short cycle settings and about 2 gallons higher on super-wash cycles as compared

to normal cycles. Supply and discharge rates for the seven models tested ranged

from about 1 to 2.5 gallons per minute and from 5 to 6 gallons per minute

respectively.

A summary of water conservation design options for dishwashers is presented

in Table 12 along with estimated water savings. Again, it' should be noted that

the most effective water saving option — reduced number of water changes — is

possible with some machines currently on the market. Consumer use of the

shorter cycles is essential in saving water.
- 12 -

7

.

REFERENCES

1. Palla, R. L. , "The Potential for Energy Savings with Water Conservation

Devices", NBSIR 79-1770, National Bureau of Standards, Washington, D. C.

,

July 1979.

2. Muller, J. 0. , "The Potential for Energy Savings Through Reductions Through

the Use of Plow Reducing Devices and Other Conservation Methods", in Water

Conservation With Water Saving Devices, T. B. Shelton, ed. , Proceedings of

a Conference, Rutgers University, New Brunswick, New 'Jersey, November 30,

1976.

3* Personal Communication with Raymond M. Goodman, Whirlpool Corporation.

4. Bonk, M. J. , "Water Consumption of Automatic Dishwashers and Water

Consumption of Automatic Clothes Washers," Cabin John Water-Saving Test

Program, Washington Suburban Sanitary Commission, Hyattsville, Maryland,

1973.

5. "Laundry practices of normal and large capacity automatic washer owners,"

The Proctor and Gamble Company, 1970.

6. Goodman, R. M. , "Reduced Energy Consumption of Automatic Washers - Benefits

and Penalties," Proceedings of the Conference on Major Home Appliance

Technology for Energy Conservation, Purdue University, West Lafayette,

Indiana, February 27 - March 1, 1978.

7- Booz, Allen, and Hamilton, Inc. "Development of Appliance Energy Efficiency

Targpts and Consumer Costs," report prepared for The Federal Energy

Administration under contract no. CR-04-60487-00 , June 1976.

8. Science Applications, Inc. "Energy Efficiency Program for Clothes Washers,

Clothes Dryers, and Dishwashers," report prepared for the Department of

Energy under contract no. CR-04-60706-00, November 1977-

9. Consumer Union, "Washing Machines," Consumer Reports, Mt. Vernon, New York,

October 1978, and similar articles in 1977, 1975, 1974, 1973, and 1972.

10. California Department of Water Resources, Water Conservation Information

Bulletin, February 1977*

11. Washington Suburban Sanitary Commission, "Fixture List," Hyattsville,

Maryland, January 1975*

12. General Electric Field Survey Data, 1970.

13- Davies, A. D. , et al., "Household Appliance Usage Data", NBSIR 80-1994,

National Bureau of Standards, Washington, D.C., February 1980.
13

Table 1 - Typical Wash/Rinse Phasing For Clothes Washers f7

D

Regular cycle

Suds return (if machine is so equipped)

Fill

Wash (time variable to over 15 minutes)

Spin and drain (to suds saver, if so equipped)

Spray rinse and spin

Spin and drain

Fill for rinse

Stop

Permanent press cycle

Fill for wash

Wash

Spin and partial drain

Fill for cool rinse

Spin and partial drain

Fill for cool rinse

- Agitate

- Spin and drain

Fill for rinse

Agitate

Spin and drain

Soak cycle

Fill for soak

- Agitate

Soak (approximately 4 minutes)

Spin and drain

Step

Fill for regular cycle

r
Table 2-

Clothes

Washer

Water

Consumption

Breakdown

for

Various

Fill

Levels

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15

Table 3 - Some Reported Values for Clothes Washer Water Consumption

Refer enc e Consumer Reports [ 9 |* dwrUoI** wssc Hi]**

Manuf ac tur er Water Consumption per Cycle , gallons —

and Model flyr.lp Setting Fill Level, Normal Cvcle

Normal (Perm-Press) Min-Max Min -Max

Manufacturer 1 14 lb 20-43 27-49

18 lb 51 (47) 23-47 27-53

Manufacturer 2

14 lb — — 16-43 26-36

18 lb 47 (50) 16-47 27-53

Manufacturer 3

Large Capacity 41 (52) 20-40 2 0-40

Manufacturer 4

Top Loader 53 (53) 33-51 4 9 (max)

Front Loader -- 20-31 33(max)

Manufacturer 5 18 lb 51 (69) 27-53

ormal Cycle, maximum fill level, 40 psig supply pressure,

3 lb load. lumbers in parenthesis indicate water consumption

on permanent press cycle.

** Normal Cycle, minimjm-maximum fill level.
Table 4 - Clothes Washer Supply and Discharge Flow Rates

Flow Rate, GPM

Test

Unit Supply* Discharge

CW1 4.9 10.3

CW3 4.2 14.3

CW4 3.8 16.1

CW8 8.7 9.1

CW10 5.6 15.2

*Warm temperature setting, supply pressure = 35 psig flowing
17

Table 5 - Dishwasher Cycle Phasing, Water Consumption, and Washing Index

Test

Water Consumption* , gallons

Subcycle**

*Supply pressure = 35 psig flowing

**W = Wash, R = Rinse

***Measured in accordance with ANSI A 197.5 (AHAM DW-1)

Washing

Unit Total Inde:

R W R R R

DW1 2.6 3.1 3.1 3.1 3.3 15.2 75%

W R W R R

DW2 2.4 2.0 2.0 2.1 2.1 10.6 66

R W R W R R

DW3 2.1 2.2 2.7 2.2 2.2 2.3 13.7 91

W R W R R R

DW6 2.2 2.2 2.2 2.2 2.2 2.2 13.2 87

W R R W R R R

DW7 2.7 1.8 1.8 2.7 2.7 1.8 2.7 16.2 70

W R W R R R

DW8 2.4 2.7 2.7 2.7 2.7 1.5 14.7 92

W R R W R R

DW10 2.4 2.4 2.4 2.4 2.4 2.4 14.4 88
Table 6 - Manufacturers' Estimates of Dishwasher Water

Consumption at Various Cycle Settings

Manufacturer

and Model*

Water Consumption Per

Super Wash Normal Wash

Cycle, gallons

Short Wash Rinse & Hold

• A1 14 .

3

- 10.2 4.2

A2 13.5 10.3 9.0 3.9

Bl 15.0 13.5 7.5 2.3

B2 15.2 12.9 8.4 2.2

Cl 16.5 13.8 8 .

3

2.8

Dl 13.9 - 9.3 4.6

El 13.8 9.2 — 2.3

*1979 Models - -

Table 7 - Dishwasher Supply and Discharge Flow Rates

Flow Rate, GPM

Test

Unit Supply* Discharge

DW1 1.3 4.0

DW2 1.4 5.0

DW3 2.5 6.1

DW6 2.5 6.0

DW7 1.7 5.1

DW8 1.4 4.1

DW10 1.2 4.6

^Supply pressure = 35 psig flowing
19

Table 8 - Typical Weights of Clothes Loads Washed [5]

Normal Large

Load Size Capacity Capacity

Over 12 Pounds 1% 2%

Over 10 Pounds 3 5

Over 8 Pounds 7 14

Over 6 Pounds 34 45

Over 4 Pounds 59 48

Over 2 Pounds 93 93

Less Than 2 Pounds 7 7

All Loads

Average 5.4 Pounds 5.9 Pounds

Median 5.0 Pounds 5 . 5 Pounds

Table 9 - Increase in Clothes Washer Tub Volume Over Recent Years [9]

Gallons of Water Required for Single Fill*

1972 1973

Model Year

1974 1975 1977 1978

Number of Washer

Tested 12 16 14 15 14 14

Greatest Volume 27 25 25 26 25 26

Average Volume 20.3 22.0 22.4 23.3 22.9 23.1

Smallest Volume 12 15 16 19 19 10

*Two fills are used in most wash cycles
- zu -

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21 -

Table 11 - Water Conservation Design Options and Estimated Water Savings for

Clothes Washers

Design Option Estimated Water Savings Per Cycle

Gallons Percent*

Front Loader Design** 20 40

Suds-Saver*** 10 20

Reduced Tub Volume** 4 8

Reduced Clearance Between

Inner & Outer Tubs** 2 5

Automatic Water Level Control 25 50

*Water Consumption of Typical Wash Cycle Taken to be 50 Gallons

**Incorporated on Some Machines

**Based on One Reuse of Wash Water (Savings Shown are an Average

for the Regular and the Reuse Cycle)
22 -

Table 12 - Water Conservation Design Options and Estimated Water

Savings for Dishwashers

Design Option Estimated Water Savings Per Cycle

Gallons Percent *

Reduce Number of Water Changes

Eliminate First Wash and Rinse**

(Short Cycle) 5 33

Eliminate Final Rinse** 2.5 16

Reduce Quantity of Water Per Fill

Develop a More Accurate Fill

Control 1 5 Change Geometry of**

Washing Chamber 1.5 10

*Water Consumption of Standard Dishwasher Taken to be 15 Gal/Cycle

** Incorporated on Some Machines

i
23

Figure 1 - Schematic of a Typical Top-Loading Clothes Washer [8]
- 24 -

00

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- 25 -

Figure

3

-

Effect

of

Water

Supply

Pressure

on

Dishwasher

Water

Consumption

H8S-114A (REV. 9-78)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 80-2173

4. TITLE AND SUBTITLE

Water Usage Characteristics of Household Appliances and the

Potential for Water Savings

5. Publication Date December 1979

7. AUTHOR(S)

Robert L. Palla, Jr.

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, state, ZIP) U. S. Department of Housing and Urban Development Office

of Policy Development and Research

451 7th Street, S.W.

Washington, D.C. 20410

13. Type of Report & Period Covered

Final

15. SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FIPS' Software Summary, is attached.

16. ABSTRACT (A 200-word or lose factual summary of most significant information. If document includes a significant bibliography or

literature survey, mention it here.) A study has been undertaken to quantify appliance water consumption and the

effectiveness of various consumer usage techniques and manufacturer design

modifications for saving water. Appliances considered are clothes washers and

dishwashers. Through a comparison of estimated water savings, the study indicates

that the most significant means of saving water are those which are already

commercially available — front-loading machines and suds-saver options for

clothes washers, and short-cycle settings for dishwashers. Water savings of

about 20 to 30 percent estimated with these features or about 10 gallons for

clothes washers and 3 gallons for dishwashers.

Several appliance design modifications are also evaluated but do not offer the same level of savings. Water usage characteristics such as supply and discharge

flow rates and the effect of supply pressure and cycle selection are presented.

17. KEY WORDS ( six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name

separated by semicolons)

Appliances; clothes washer; discharge; dishwasher; residential;-'

supply; water conservation; water consumption.

18. AVAILABILITY Unli mi ted

For Official Distribution. Do Not Release to NTIS

I

• Order From Sup. of Doc., U.S. Government Printing Office, Washington, DC

20402, SD Stock No. SN003-003- PC Order From National Technical Information Service (NTIS), Springfield,

VA, 22161

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF

PRINTED PAGES

32

22. Price

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