Residential energy use and potential conservation through reduced laundering temperatures in the United States and Canada

Authors


Abstract

A residential energy-use model was developed to estimate energy budgets for household laundering practices in the United States and Canada. The thermal energy for heating water and mechanical energy for agitating clothes in conventional washing machines were calculated for representative households in the United States and Canada. Comparisons in energy consumption among hot-, warm-, and cold-water wash and rinse cycles, horizontal- and vertical-axis washing machines, and gas and electric water heaters, were calculated on a per-wash-load basis. Demographic data for current laundering practices in the United States and Canada were then incorporated to estimate household and national energy consumption on an annual basis for each country. On average, the thermal energy required to heat water using either gas or electric energy constitutes 80% to 85% of the total energy consumed per wash in conventional, vertical-axis (top-loading) washing machines. The balance of energy used is mechanical energy. Consequently, the potential energy savings per load in converting from hot-and-warm- to cold-wash temperatures can be significant. Annual potential energy and cost savings and reductions in carbon dioxide emissions are also estimated for each country, assuming full conversion to cold-wash water temperatures. This study provides useful information to consumers for conserving energy in the home, as well as to manufacturers in the design of more energy-efficient laundry formulations and appliances.

INTRODUCTION

The energy required to supply a typical North American household with hot water for laundering, bathing, dishwashing, and other purposes represents a large proportion of the total residential energy budget (Energy Information Administration 2001c). Recent innovations in household appliances and consumer products enable significant energy conservation and cost savings to be realized in the home. Significant energy and water conservation and cost-savings opportunities, with corresponding reductions in emissions from regional fossil-fuel power plants, are possible through reductions in the temperature and/or the volume of hot water used in the home (Energy Star 2004). Detergent products specifically formulated to perform effectively in cold water have been introduced recently to the consumer market in the United States and Canada to enable temperature reductions in washing clothes. Horizontal-axis (i.e., high-efficiency or front-loading) washing machines are available that use less water per load, and hence conserve the thermal energy required to heat water (Oak Ridge National Laboratory 1998). The type of hot-water heater used in the home may also facilitate energy savings. Consumers, therefore, have a range of options in the home to maximize energy and water conservation.

While the potential for energy conservation and cost savings from reduced-temperature and/or water usage in home laundering is intuitive, the factors that determine the magnitude of the savings vary widely across North American households. These can be distinguished in 2 categories: appliance-related factors, related to the types of washing machines and water heaters installed in the home; and consumer-selected factors, related to the operation of the appliance. Consumers now have a broad range of choices among washing machines and hot-water heaters with varying efficiency, but these purchases occur infrequently (e.g., 10–20 y). In contrast, consumers often vary the water temperature settings for different types of laundry (e.g., white or colored fabrics, permanent-press garments). It is estimated that 80–85% of the energy required per load of wash using hot water in a top-loading machine, such as that conventionally used in washing white, non-permanent-press garments, is consumed to heat the wash water (Office of Energy Efficiency and Renewable Energy 2004a). Other consumer choices that impact water and energy use during laundering include the hot-water heater temperature setting, the size of each load of laundry, and the number of loads run per week.

A number of studies of the energy, raw materials, and waste products of detergent formulations have been previously published. Aspects of detergent production from alternative raw materials have been reported by Pittinger et al. (1993), Berna et al. (1995), Stalmans et al. (1995), and Thomas (1995). Saouter and van Hoof (2001) constructed a database of detergent ingredients for life-cycle inventory analyses. Saouter et al. (2001, 2002) presented the environmental profile of compact detergents in the United Kingdom. These studies have supported the observation of Office of Energy Efficiency and Renewable Energy (2004a) that the majority of energy consumed per load of wash stems from the heating of water. In particular, Saouter and van Hoof (2001) concluded that the majority (ca. 80%) of energy consumption across a detergent's life cycle occurs during consumer use. This suggests that individual consumers have a range of viable options available to significantly minimize energy consumption during home laundering. While a number of the studies above have addressed detergents manufacture and laundering from a broad, life-cycle context, few if any have focused on the energy- and water-usage options available to consumers in the residential setting.

The aims of this study were to characterize the range of parameters that define typical, representative energy budgets for home laundering in North American households and to estimate the potential energy and cost savings that could be realized by consumers in varying several residential home-laundering conditions and practices. This study specifically focuses on those factors over which consumers can exercise control, including the selection of washing-machine temperature settings for wash and rinse cycles, the type of washing machine used (horizontal- or vertical-axis models), the type of water heater (gas or electric), and the temperature setting of the water heater thermostat (140 or 120 °F). The study scope is narrowly defined as those household conditions and practices that determine energy and water usage and conservation opportunities in home laundering.

The study focuses on energy and water usage and conservation. It does not evaluate consumer satisfaction with the cleaning performance or efficacy of alternative laundering practices, nor the relative costs of purchasing or replacing 1 appliance model or detergent formulation with another. We recognize that these dynamic marketing and economic factors are critical to realizing energy conservation, but fall beyond the scope of this analysis. As this study focuses on consumer options in residential settings, the life-cycle energy costs of manufacturing alternative appliances (i.e., horizontal- versus vertical-axis machines, conventional and low-temperature detergent formulations) are not estimated in this study. Given the similar dosage of detergent recommended for conventional and cold-water formulations, the production-energy difference among detergents is likely to be small, based on the studies cited above, and are not included.

Initially, a basic residential energy-use model was developed in Microsoft Excel® to calculate energy budgets for appliances and consumer-washing practices that are representative of US and Canadian households. Using this model, comparisons in energy consumption among alternative wash temperatures (hot-, warm-, and cold-water wash and rinse cycles), gas versus electric water heaters, and water-heater temperature settings were calculated on a per-wash-load basis. Demographic data for current laundering practices in the United States and Canada were then incorporated to estimate household and national energy consumption on an annual basis for each country. Finally, the model was applied in calculating potential energy and cost savings, and carbon dioxide (CO2) emissions reductions from power plants, from a wide array of domestic scenarios for reducing wash temperatures, wash-water volume, and water-heater settings. The data and information from this study will be valuable in informing consumers of potential energy and cost savings based on their individual household laundering conditions and practices. It will also be useful to appliance manufacturers and consumer-product formulators in designing new laundering products to improve energy consumption and environmental profiles.

METHODS

Scope and boundary conditions

Typical and representative conditions of household appliance use and consumer laundering practices were estimated from public information sources, including government organizations (e.g., the US Department of Energy, the US Environmental Protection Agency, and Natural Resources Canada), independent organizations (e.g., the American Council for an Energy-Efficient Economy, the Consortium for Energy Efficiency, the Clean Air Partnership), industry associations (e.g., the Gas Appliance Manufacturers Association), and the technical published literature. The study focused specifically on residential settings for home laundering. Alternative settings, such as self-service laundries (laundromats) and commercial laundering services (e.g., dry cleaning services) were not evaluated. These often employ larger, heavy-duty appliances with energy budgets and power sources that are different from household laundering conditions.

From a life-cycle laundering perspective, this study specifically evaluates the energy associated with the routine domestic use of residential appliances involved in home laundering (i.e., washing clothes). It does not include energy required to dry clothes, the production of laundry products, the manufacture of appliances, or any related transportation costs. Variables that are highly dependent on localized household conditions, such as heat losses from household water feed lines, insulation of the hot-water heater, or seasonal/regional temperature variations in inlet water temperatures, were beyond the scope of this analysis.

Given the study focus on the residential setting, a single power-source matrix was assumed, to represent average conditions across the North American power grid (Energy Information Administration 2004c). Regional differences in energy procurement costs and CO2 emissions due to varying sources of power across North America (e.g., fossil fuels, nuclear, hydroelectric) were not distinguished.

Energy-consumption data for North American household appliances

Energy-consumption data per laundry load for gas and electric water heaters and for vertical- and horizontal-axis washing machines are presented in Table 1. These are representative of appliances currently used in North America; the appliance data and assumptions are shown in Table 2. Comparisons or extrapolation of results in this study to other geographies, e.g., Europe, are tenuous due to differences among appliances and energy sourcing. The energy data in Table 1 were derived from annual energy consumption estimates of the American Council for an Energy-Efficient Economy (Wilson et al. 2003).

All energy-use calculations reported here are based on full capacity, large loads of wash. This basis was selected as a reasonable upper-bound estimate of water use for a majority of North American washing machines, as there are considerable differences among appliances in partial load selections and varying volumes of water associated with each load size. However, the data presented can be reapplied to estimate energy savings for many laundering conditions. It was assumed that 40 US gallons (151.4 L) of water are used per full-size load in a vertical-axis machine versus 23 US gallons (87.1 L) per load in a horizontal-axis machine (Home Energy 2000). This is supported by the estimate of the Clean Air Partnership (2005) that energy-efficient washers use 35% to 50% less water than the average conventional washer. (The midpoint of this range, 42.5%, translates to 23 gallons.) Unpublished data from Procter&Gamble indicate that North American households prefer large size loads (43%) over very large or medium loads (21% each). Small and very small loads constitute less than 10% of total washes. To tailor energy savings estimates reported here for a particular appliance and load size, consumers may refer to their appliance operating manual to determine water volumes used for smaller loads and proportionately estimate the actual energy savings per load.

Table Table 1.. Energy use (kWh) per load for gas and electric hot water heaters with thermostat settings of 140 and 120 °F. Data for vertical axis washing machines are from Wilson et al. (2003); data for horizontal axis machines were calculated assuming they require 42.4% of the energy of vertical axis machines (Oak Ridge National Laboratory 1998). Natural gas energy values in therms were converted to kWh for purposes of comparison, assuming 1 therm equals 29.3 kWh (OnlineConversion 2004)
 Energy use per laundry load (kWh)
Washing machine type and temperatureGas hot water heater (Wilson et al. 2003)Electric heater (Wilson et al. 2003)Electric heater (thermodynamic calculations)
Wash temperatureHotWarmColdHotWarmColdHotWarmCold
Rinse temperatureHotWarmColdWarmColdColdHotWarmColdWarmColdColdHotWarmColdWarmColdCold
  1. a Original value reported by Wilson et al. (2003), 4.3 kWh per load, was assumed to be a typographical error based on thermodynamic calculations, and was corrected to 3.4 kWh.

Vertical-axis machine, water heater temperature setting 140 °F (60 °C)9.67.24.84.82.40.48.36.34.34.32.30.48.276.324.264.371.820.26
Vertical-axis machine, water heater temperature setting 120 °F (48.9 °C)7.35.43.63.61.80.46.54.93.4a3.41.90.46.324.853.293.392.310.26
Horizontal-axis machine, water heater temperature setting 140 °F (60 °C)a4.13.12.02.01.00.23.52.71.81.81.00.23.512.651.811.850.770.11
Horizontal-axis machine, water heater temperature setting 120 °F (48.9 °C)a3.12.31.51.50.80.22.82.11.41.40.80.22.682.061.391.440.980.11

Gas and electric water heaters were distinguished in Table 1 and throughout this study, due to the substantial effect of heater type on household energy budgets for all hot-water applications, including laundering. Gas water heaters have an average recovery efficiency (conversion of gas or electrical energy to thermal energy) of 77%, compared with 98% for electric heaters (Gas Appliance Manufacturers Association 2004) (Table 2). However, these recovery efficiency values are based on the end-use of gas or electricity in the home. They do not reflect the energy loss in converting fossil fuels to electrical power, or the transmission loss in relaying power to the home. Energy-efficiency estimates based on power production at the source (e.g., power plants) would favor natural gas as a more efficient fuel source. Thus, the apparent energy savings of electric versus gas water heaters is not realistic; it is an artifact of the household context evaluated in this study.

Similarly, horizontal- and vertical-axis washing machines were distinguished in Table 1 due to their impact on household laundering energy budgets. The data reflect machines with 3 temperature selections, common in most conventional models; more elaborate machines (e.g., with internal booster heaters and more options for temperature selection) were not included in this analysis. According to Energy Star (2004), a federal government-supported program to promote energy efficiency in appliances, the minimum standard for Energy Star certification for horizontal-axis washing machines is an annual consumption of 300 kWh, versus 450 kWh for vertical-axis machines (Table 2). This difference is due in part to the differences in water volume consumed by the 2 types of machines (23 versus 40 U.S. gallons per load, respectively; Home Energy Online 2004). Due to the higher cost of horizontal-axis machines and their more recent emergence on the consumer market, vertical-axis machines dominate the North American market, representing >95% of the washing machines used in the United States and Canada (BC Hydro 2004; Energy Information Administration 2001a).

The data from Wilson et al. (2003) presented in Table 1 were verified independently in this study by thermodynamic calculations, assuming that total energy consumption per load is the sum of

  • 1.thermal energy required to heat water in conventional gas or electric hot water heaters, and
  • 2.mechanical energy in vertical- or horizontal-axis washing machines required to agitate clothes (i.e., rotate the drum), and to power the control system.
Table Table 2.. Appliance energy and water use, annual operating costs, and emissions data
 UnitsUnited States and Canada
  1. a Home Energy (2000).

  2. b Pacific Northwest National Laboratory (2004).

  3. c Washington State Univ (2003).

  4. d Gas Appliance Manufacturers Association (2004).

  5. e Energy Information Administration (2001c).

  6. f Office of Energy Efficiency (1997).

  7. g Energy Information Administration (2004c).

  8. h Ontario Canada (2004).

  9. i Energy Information Administration (2004d).

  10. j EnergyShop TM (2004).

  11. k Converted using 1 therm = 29.3 kWh (OnLine Conversion 2004).

  12. l Canadian Geographic (2001).

  13. m Wilson et al. (2003). 12.1 lb CO2/therm natural gas converted using 1 therm = 29.3 kWh (Online Conversion 2004). 23.8 lb CO2/gallon converted using 1 gallon automotive gas = 36.6 kWh (Online Conversion 2004).

Average water use per load, vertical-axis washing machinesaGallons23
Average water use per load, horizontal-axis washing machinesaGallons40
Average mechanical energy use of vertical-axis washing machinesbkWh/load0.26
Average mechanical energy of horizontal-axis washing machinesbkWh/load0.20
Washer efficiency ratingsc
Front-load clothes washers annual energy use, minimum standardkWh/year350
Front-load clothes washers annual energy use, Energy StarkWh/year300
Front-load clothes washers annual energy use, bestkWh/year180
Top-load clothes washers annual energy use, minimum standardkWh/year1000
Top-load clothes washers annual energy use, Energy StarkWh/year450
Top-load clothes washers annual energy use, bestkWh/year450
Recovery efficiencies of water heatersd
Average recovery efficiency for electric water heaters%98
Average recovery efficiency for gas water heaters%77
Energy Costs USCanada
Average annual household energy consumptione USA, f CanadakWh27,02123,367
Average unit costs of residential energy source: electricityg USA, h Canada$/kWh (US)$0.0896$0.063
Average unit costs of residential energy source: natural gasi USA, j Canada$/therm (US)$1.13$0.596
Average unit costs of residential energy source: natural gas, converted to kilowatt hoursk$/kWh (US)$0.039$0.020
Average annual household energy expenditurese USA, l Canada$ (US)$1,493$1,102
Emissions datam US and Canada
Electricity carbon dioxide (CO2) emissionsPounds CO2/kWh1.55
Natural gas CO2 emissionsPounds CO2/kWh0.413
Gasoline CO2 emissionsPounds CO2/kWh0.65

Thermal energy requirements per load (ΔQ) can be calculated from the equation:

equation image

where ΔQ is the change in thermal energy (heat content) in Joules, m is the mass of water in kilograms (1 gallon of water = 3.785 kg), c is the specific heat capacity of water in J/(kg·°C), and ΔT is the change in temperature in °C. The specific heat capacity of water is 1 calorie/g·°C, or 4.186 joule/g·°C (Weast and Astle 1982), or 1.16 E10−6 kWh/g·°C (Online Conversion 2004). In Table 1, the Wilson (2003) data were reasonably consistent with our thermodynamic calculations (i.e., usually within 1–5% of each other). The minor differences observed in Table 1 can be attributed to different assumptions of mechanical energy, because the greatest differences were observed under cold/cold, wash-/rinse-cycle comparisons. Mathematical rounding errors may also have introduced minor errors in both approaches. The thermodynamic calculation approach was useful in identifying a likely typographical error for one value published by Wilson et al (2003) (3.4 vs 4.3 kWh per load). The thermodynamic value of 3.4 kWh per load was assumed to be correct, based on the consistency among other comparisons, and was applied in subsequent calculations in this study.

Table Table 3.. Demographic and laundering practices data for the United States and Canada
 United StatesCanada
  1. a Energy Information Administration (2001c).

  2. b Canadian Housing Observer (2004).

  3. c Energy Information Administration (2001a).

  4. d The Fraser Institute (2002).

  5. e BC Hydro (2004).

  6. f Office of Energy Efficiency (1997).

  7. g Office of Energy Efficiency (2004b).

Millions of households per countrya United States, b Canada10712
Percent households with clothes washersa United States, c Canada7981
Percent top-loading washersd United States, e Canada9798
Percent front-loading washersd United States, e Canada32
Average annual number of washes per householdd United States, f Canada392328
Percent electric water heaters in householdsd United States, f Canada38.150.6
Percent natural gas water heatersd United States, g Canada54.244.1
Percent other fueled water heatersd United States, g Canada7.75.3

In Table 1, a uniform inlet water temperature of 58 °F (14.4 °C) was assumed for both the United States and Canada, representing average annual groundwater temperatures across North America (Office of Energy Efficiency and Renewable Energy 2004b). Two water-heater thermostat settings typical of North American households were compared by Wilson et al. (2003) and in this study: 140 °F (60 °C) and 120 °F (48.9 °C). It was assumed that warm-water temperatures achieved in the washing machine were an equal blend of hot and cold water, with the averages calculated as 99 °F (37.2 °C) for the 140 °F thermostat setting and 89 °F (31.7 °C) for the 120 °F setting. Heat losses through hot water feed lines from the water heater to the washing machine could not be distinguished at the scale of the present study because they vary widely among households due to water feed-line length, pipe diameter, insulation, room temperature, etc.

Mechanical energy requirements per load of laundry (i.e., to agitate the drum and power the control system) are represented in Table 1 by the energy requirements for laundering under cold/cold wash-/rinse-cycle conditions. Under these conditions, no thermal energy input from the hot-water heater is required. Under hot/hot wash/rinse conditions, mechanical energy accounts for only approximately 5% (0.4/8.3 kWh) of the total energy used (in houses equipped with an electric water heater set at 140 °F, and a vertical-axis washing machine), and 4% (0.4/9.6 kWh) for a gas water heater under similar conditions.

Energy cost and CO2 emissions data

Table 2 presents costs ($US) of electrical and gas energy based on average energy costs to the consumer. The costs determined at the time of writing were obtained from on-line services of US and Canadian government agencies, recognizing that energy costs to consumers typically fluctuate on a daily and regional basis. Electricity costs were assumed to be $0.0896/kWh in the United States (Energy Information Administration 2004c), and $0.063/kWh ($US) in Canada (Ontario Canada 2004). Natural gas costs, typically reported in therms (1 therm = 29.3 kWh), were converted to $0.039/kWh in the United States (Energy Information Administration 2004a) and $0.020/kWh in Canada (EnergyShop 2004). These data are incorporated in subsequent calculations in the residential energy-use model, to enable estimation of potential cost savings for households in converting appliances and/or laundering practices.

Table 2 lists CO2 emissions data for the production and use of gas and electric energy per kilowatt-hour of energy produced at the source. The data were reported by Wilson et al. (2003) in a study sponsored by the American Council for an Energy-Efficient Economy. To estimate reductions in CO2 emissions associated with energy-conservation estimates, conversion factors of 1.55 pounds CO2/kWh for electricity and 0.413 pounds CO2/kWh for natural gas (Wilson et al. 2003; Energy Star 2004, respectively) were used. (Natural gas energy is typically reported in therms; the reported value of 12.1 pounds CO2 per therm was converted to kWh, assuming 1 therm = 29.3 kWh [OnLine Conversion 2004].) These data were incorporated in subsequent calculations to estimate reductions in global-warming potential that would be associated with potential national energy savings due to conversions in household appliances and/or laundering practices. The national values were then compared with target levels of CO2 reductions for the United States and Canada, as recommended under the Kyoto Convention (Emission Strategies 2004).

Figure Figure 1..

Current frequencies of hot, warm, and cold wash and rinse laundering cycles in the United States (Energy Information Administration 2001d) and Canada (Office of Energy Efficiency 2004b).

Demographic and laundering-practices data

Table 3 provides demographic and laundering practices data used in this analysis to estimate energy consumption on a per-household and national basis; it also presents the energy and cost savings that could be realized by lowering wash temperatures. All the calculations are based on the assumption of 392 loads per year in the United States (Energy Information Administration 2001a) and 328 loads per year in Canada (Office of Energy Efficiency 1997). Gas and electric water heaters, each with 2 thermostat temperature settings (120 and 140 °F), were considered in the calculations. In general, demographics were similar for the United States and Canada; the greatest difference observed was the higher proportion of gas water heaters in the United States (54%) than in Canada (44%).

Figure 1 compares the frequencies of hot-, warm-, and cold-water wash and rinse cycles representative of US and Canadian households, based on data from the US Energy Information Administration (2001d) and Natural Resources Canada's Office of Energy Efficiency (2004b). Unpublished data from Procter&Gamble are consistent with these frequencies. Warm water is most commonly used for the wash cycles (59–66% for the United States and Canada), followed by cold water (29–34%), and finally hot water (6–7%). Cold-water rinse cycles are most common (79%), significantly exceeding rinses in warm water (20–21%) and hot water (1–2%).

Annual energy savings per household were calculated by multiplying savings per load by the number of loads at each wash- and rinse-cycle temperature combination. Energy savings nationally were calculated by multiplying energy savings per household by the number of households with electric and gas heaters in the United States and Canada.

Scenarios for energy conservation, cost savings, and CO2 emissions reductions

The residential energy-use model developed in this study enables a broad range of comparative estimates of potential energy conservation (along with associated cost savings to the consumer and CO2 reductions nationally) that would be possible by making wholesale changes in household laundering conditions. Four energy conservation options were evaluated, individually and in combination. First, energy savings were estimated for reductions in wash- and rinse-cycle temperature settings (i.e., from hot to warm, and from hot to cold wash and/or rinse cycles). Second, energy savings from lowering the water-heater thermostat setting from 140 to 120 °F were estimated. Third, potential energy savings by converting from electric to gas water heaters are presented for both US and Canadian households. Fourth, energy savings were estimated in converting from a vertical-axis washing machine to a horizontal-axis machine.

RESULTS

Energy savings per load of laundry

Table 4 presents calculated energy savings per load of laundry for each of the 4 scenarios described above. Because the calculations on a per-load basis required no demographic data, the estimated energy savings are relevant for the United States and Canada. Energy savings range from 0 to 9.6 kWh per load. The greatest energy savings among all scenarios, 9.6 kWh per load, was estimated for a scenario wherein wash/rinse temperatures are reduced from hot/hot to cold/cold and the water-heater thermostat setting is lowered from 140 to 120 °F. Additional savings can be realized if the household converts from an electric to a gas water heater, and from a vertical-axis to a horizontal-axis washing machine.

For all water heaters, washing machines, and thermostat settings, maximum energy savings were evident in converting from hot/hot to cold/cold wash/rinse temperatures. Lowering water temperatures from warm to cold is estimated to save approximately one-half the energy saved in converting from hot to cold, because warm water was assumed in this study to be a 1:1 blend of hot and cold water. (Minor differences in this trend in Table 4 are due to rounding errors.) For the same reason, converting from hot/cold wash/rinse cycles to warm/warm cycles produces no net energy savings.

Vertical-axis washing machines use more energy than horizontal-axis machines; consequently, the cost savings potential of lowering wash temperatures in vertical-axis machines is greater. Similarly, gas water heaters convert energy to heat less efficiently (77%) than do electric water heaters (98%) (Table 2). However, if the losses of energy in converting fuels to electrical power and in relaying that power to the home are considered, electric water heaters would be considered less efficient than gas. The higher cost of heating water with electricity versus gas is also a major consideration; for example, in the state of California, USA, it typically costs 3 times the amount to heat the same water volume with electricity than with gas (Consumer Energy Center 2005).

Table Table 4.. Calculated energy savings per load of laundry in the United States and Canada from reducing temperatures of wash and rinse cycles, for households equipped with electric or gas hot water heaters (at 140 and 120 °F), and vertical- and horizontal-axis washing machines
 Vertical-axis clothes washer (kWh per load)Horizontal-axis clothes washer (kWh per load)
Wash/rinse cycle temperature conversionElectric water heaterGas water heateraElectric water heaterGas water heatera
 140 °F120 °F140 °F120 °F140 °F120 °F140 °F120 °F
  1. a Gas water heater values were converted from therms to kilowatt hours (kWh) for ease of comparison to electric water heaters, assuming 1 therm = 29.3 kWh (Online Conversion 2004).

Hot/hot to hot/warm2.01.62.41.80.850.681.00.77
Hot/hot to hot/cold4.02.24.83.61.70.932.01.5
Hot/hot to warm/warm4.02.24.83.61.70.932.01.5
Hot/hot to warm/cold6.04.67.25.42.52.03.12.3
Hot/hot to cold/cold7.96.19.67.33.32.63.92.9
Hot/warm to hot/cold2.00.62.41.80.850.251.00.77
Hot/warm to warm/warm2.00.62.41.80.850.251.00.77
Hot/warm to warm/cold4.03.04.83.61.71.32.01.5
Hot/warm to cold/cold5.94.57.25.42.51.92.92.1
Hot/cold to warm/warm00000000
Hot/cold to warm/cold2.01.52.41.80.850.61.00.77
Hot/cold to cold/cold3.93.04.83.61.71.21.91.4
Warm/warm to warm/cold2.01.52.41.80.850.61.00.77
Warm/warm to cold/cold3.93.04.83.61.71.21.91.4
Warm/cold to cold/cold1.91.52.41.80.810.640.850.60
Cold/cold to cold/cold00000000

Annual energy conservation and cost-savings potential per household

Table 5 presents potential annual energy conservation and cost savings in US and Canadian households that could be achieved by converting from the current distribution of wash temperatures to all cold-water settings. For illustrative purposes, only data for vertical-axis machines are shown. Corresponding estimates for horizontal-axis machines can be calculated by multiplying the data in Table 5 by the respective ratio of energy savings between horizontal- and vertical-axis machines (Table 4). Current frequencies of hot-, warm-, and cold-water wash loads in the United States and Canada (Table 3 and Figure 1) are incorporated into the annual household energy-savings estimates. Hence, potential energy savings for each temperature setting differ between US and Canadian households, as do the total household energy savings for all loads.

Despite the differences in the frequency with which various wash-load temperatures are used, trends in the total annual household energy-savings potential are consistent between the United States and Canada (Table 5). The greatest potential energy savings for households in both countries (914 and 795 kWh/y, respectively) are possible for those households using gas water heaters set to a temperature of 140 °F. Households using electric water heaters at the same temperature have the potential to save 812 and 709 kWh/y. Households with water heaters set to 120 °F have lower savings potential, because they consume less energy than 140 °F households. Even though households with gas water heaters can potentially conserve the most energy by converting to electric, the potential cost savings is greater for homes with electric water heaters, due to the higher cost of electrical power relative to gas. Cost savings are greater in the United States than in Canada, because both electricity and gas cost more in the United States. Potential annual savings as great as $72.77 and $44.65 are possible in US and Canadian households equipped with electric water heaters set to 140 °F.

Table Table 5.. Estimated annual energy (kWh/year) and cost ($US) savings per household for vertical axis washing machinesa
  US energy savingsb Canadian energy savingsc
   140° F Water heater temperature120° F Water heater temperature 140° F Water heater temperature120° F Water heater temperature
Temperature settingsUnitsLoads per yearGas water heatersElectric water heatersGas water heatersElectric water heatersLoads per yearGas water heatersElectric water heatersGas water heatersElectric water heaters
  1. a Assumes energy costs of electricity are $0.0896/kWh in the USA (Energy Information Administration 2004c), and $0.063/kWh ($US) in Canada (Ontario Canada 2004). Costs of natural gas are $0.039/kWh in the USA (Energy Information Administration 2004b), and $0.020/kWh ($US) in Canada (EnergyShop 2004).

  2. b Based on 392 loads/y (Energy Information Administration 2001b).

  3. c Based on 328 loads/y (Office of Energy Efficiency 1997).

Wash cycles
 Hot to coldkWh/year29139.8120.4105.494.319.794.581.771.864.0
 Warm to coldkWh/year231.7556.6498.1420.9393.9216.5519.6465.4389.7368.0
 Cold to coldkWh/year131.3000095.10000
Rinse cycles
 Hot to coldkWh/year6.732.127.724.221.73.315.713.612.010.7
 Warm to coldkWh/year77.2185.5166.0140.3131.268.9165.3148.1124.0117.1
 Cold to coldkWh/year308.10000259.10000
Total household energy savingskWh/year914812691641795709597560
Total household cost savingsa$US/year$35.65$72.77$26.94$57.44$15.90$44.65$11.95$11.19
Table Table 6.. Energy, cost and emissions reduction potential for US and Canadian households equipped with vertical axis washing machines, expressed on annual household and national bases, relative to key benchmarks. Ranges of values reflect assumed temperature reductions from water heater thermostat settings of 120 and 140 °F
  United StatesCanada
 UnitsElectric water heaterGas water heaterElectric water heaterGas water heater
  1. a 1 gallon of automotive gas = 36.6 kWh (Online Conversion 2004).

  2. b Based on assumed average price per gallon of automotive gas (10 October 2005) is $2.85 (Energy Information Administration 2005).

  3. c 1 kWh releases 1.55 lb CO2 for electricity (Office of Energy Efficiency 1997). 1 kWh releases 0.413 lb CO2 for natural gas (Wilson et al. 2003). Assuming 1 therm = 29.3 kWh (Online Conversion 2004), 12.1 lb CO2 is released per therm of natural gas.

  4. d Assumes energy costs of electricity were $0.0896/kWh in the USA (Energy Information Administration 2004c), and $0.063/kWh ($US) in Canada (Ontario Canada 2004). Assumed costs of natural gas were $0.039/kWh in the USA (Energy Information Administration 2004a), and $0.020/kWh ($US) in Canada (EnergyShop 2004).

  5. e Based on US Kyoto Protocol target emissions reductions of 419 Tg CO2 equivalents, and Canadian target emissions reduction of 36 Tg CO2 equivalents (Emission Strategies 2004).

Household savings per year
Savings in gallons automotive gasagallon/y18–2219–2515–1916–22
Cost savings in gallons of automotive gasb$US/y$54–71$51–63$43–54$46–63
Reduction in annual CO2 emissionscPounds CO2/y994–1259285–378868–1099247–328
Fraction of electricity consumption%/y2.4–3.2%2.7–3.6%2.4–3.0%2.6–3.4%
Fraction of energy consumption by appliances%/y9.3–12%10–13%
Fraction of energy used for water heating%/y26–32%28–36%
National savings per year
Total national energy savingskWh/y29–36 billion43–57 billion3.5–4.4 billion3.2–4.3 billion
Total national cost savingsd$US/y$2.6–$3.2 billion$1.7–$2.2 billion$218–$276 million$65–$86 million
Fraction of Kyoto targetePounds CO2/y5.01–6.35%2.15–2.85%7.01–8.88%1.89–2.52%
Fraction of national CO2 emissionsePounds CO2/y0.35–0.44%0.15–0.20%0.42–0.53%0.11–0.15%

Annual energy conservation and cost savings-potential nationally for the United States and Canada

Table 6 provides key benchmarks for the annual energy and cost savings and CO2 emissions reductions for US and Canadian households equipped with vertical-axis washing machines. The benchmarks demonstrate the significance of the potential savings for households. Annual household energy savings are converted to gallons of gasoline, assuming that 1 gallon of gasoline has an energy content of 36.6 kWh (OnlineConversion 2004). From this conversion, the potential energy conserved from more efficient laundering is equivalent to 15–25 gallons of gasoline, or $43–71 of gasoline at a per-gallon cost of $2.85 (Energy Information Administration 2005).

The annual household energy savings possible through improved laundering practices and more efficient appliances are expressed in Table 6 as percentages of total household electricity consumption. By converting to cold water, households can reduce total electricity use by 2.4–3.2%, and the total energy use by home appliances can be reduced by 9.5–13%. The total amount of hot water used in the home can be reduced by 26–36%, demonstrating the significant proportion of household total hot water use that is consumed in laundering. On a national basis, these energy savings would constitute approximately 3% of the total energy consumed in households in both countries.

Converting to cold-water laundering could reduce an average household's annual CO2 emissions by as much as 868 (0.39 t) to 1,259 lb (0.57 t) CO2 for households equipped with electric hot-water heaters and by 247–378 pounds (0.11–0.17 t) CO2 for those with gas heaters. Table 6 also presents the total annual energy savings possible on a national basis for the United States and Canada. On a national basis, these reductions represent up to 0.44% of total CO2 emitted in the United States and 0.53% of total CO2 in Canada. These potential reductions are particularly significant in comparison with the targeted CO2 reductions recommended for the United States and Canada under the Kyoto Agreement (Emission Strategies 2004). Theoretically, the reductions in CO2 possible on a national basis through more efficient laundering and household appliances could account for as much as 7% of the US target and 9% of the Canadian target in CO2 reduction.

DISCUSSION

Results of this study demonstrate that households in the United States and Canada can potentially conserve energy, reduce monthly costs of utilities, and contribute to reductions in national greenhouse gas (CO2) emissions by exercising a number of selective options in the home. While the energy and cost savings for consumers can be significant, the actual amount of the savings depends on multiple factors that differ among households. First, households can maximize energy conservation in home laundering by switching to lower wash-and rinse-cycle temperatures on the washing-machine control panel. The temperature setting selected by consumers for each load of laundry dictates the amount of energy that will be consumed by the water heater. Reducing the temperature of the wash and/or rinse cycles in home laundering will reduce energy consumption in all types of households, regardless of the appliances installed. The Office of Energy Efficiency and Renewable Energy (2004a) estimates that, on average, 85% of the energy consumed in washing a load of laundry is used to heat the water. For this reason, any changes in laundering practice by consumers to reduce the volume of hot water used will conserve energy and save money proportionately.

The 2nd option available to consumers to conserve energy is to lower the water-heater thermostat setting. Turning the thermostat down from 140 to 120 °F can reduce energy consumption in home laundering by approximately 25% (Table 1). Home laundering accounts for 26% to 36% of total household hot-water use, but lowering the temperature setting of the water heater will reduce energy consumption associated with 100% of household hot-water uses.

The availability of household appliances with energy-efficient profiles provides additional options to US and Canadian consumers for energy conservation in home laundering. For example, the use of a gas water heater, where natural gas delivery is available, can provide greater energy efficiency to the consumer. The lower recovery efficiency of residential gas water heaters compared with electric is more than offset by the lower cost of natural gas and the efficiency of natural gas conversion and transmission to the home.

Another appliance option available to consumers is the relatively recent introduction of horizontal-axis (i.e., high-efficiency, front-loading) washing machines. Typical horizontal machines require 23 gallons (87 L) per wash, compared with 40 gallons (151.4 L) for vertical-axis machines (Oak Ridge National Laboratory 1998). This study clearly demonstrates the benefits of horizontal-axis machines, which typically require 42% of the energy needed for vertical-axis machines (Table 4), due largely to the smaller volume of water used.

The data and results in this study are idealized to represent the maximum savings that could occur across typical and representative household conditions in North America, on a national basis. These national estimates were derived from the savings calculated per wash, multiplied by the estimated number of households with washing machines in each country that currently rely on high-temperature washing. It could be argued that the typical and representative household does not physically exist or endure for any length of time. Given the wide disparity among households and consumer practices, it was only possible to present a limited number of household scenarios in this study. However, more accurate, household-specific savings could be estimated from the data presented here for particular washing machines. Energy Star (2005) maintains a website that provides specific water- and energy-use specifications for a broad range of washing-machine models.

To this end, a user-friendly calculator tool was created that enables prediction of energy use and savings possibilities under many alternative scenarios, both for US and Canadian consumers. Users can dial in changes in washing habits or appliance settings, and observe energy-savings results. Variables incorporated into the tool include nationality, type of water heater, its temperature setting, and proportions (average number of loads) of wash and rinse cycles under 6 distinct wash-/rinse-temperature combinations. All energy values are uniformly converted to the common unit of kilowatt-hours (kWh), although conversions to other metrics (BTUs, therms, or gigajoules) are also possible (OnlineConversion 2004). The calculator tool shows promise for user-friendly adaptation for consumer use via an Internet site, allowing consumers to more precisely estimate their potential energy savings based on their location, home appliances, and laundering practices. A version of this calculator tool is now available online on www.tide-coldwater.com.

We recognize that the potential national energy and cost savings described in this article would require broad and sustained consumer-habit changes to lower wash temperatures. Clearly, any conversion to lower wash temperatures or alternative appliance use by US or Canadian populations will be gradual. This is due to multiple factors, including the disinclination of some consumers to alter their proven, traditional habits and practices, even if parity performance can be demonstrated; the time required for market penetration of a new product; and the turnover time for consumers to replace their appliances (typically on a 10–20-y basis).

It was not within the scope of this article to predict consumer satisfaction with cold-water washing or high-efficiency appliances. It is relevant, however, to discuss the plausibility that such a conversion is supported by commercial technology. Based on internal Procter&Gamble data, whiteness and stain-removal benefits are the 2 major incentives for consumers to favor higher temperatures for certain loads of laundry. Traditionally, both whiteness and stain removal have been known to suffer at lower wash temperatures.

Figure Figure 2..

Model of residential laundering options available to North American consumers to conserve thermal, mechanical, and chemical energy through choice selection and operation of washers, water heaters, and detergents.

Recent innovations in chemical technology have been accompanied by claims that they may provide performance on a par with hot-water washing. These are largely based on chemical engineering modifications of the hydrophobe moiety of commodity, linear anionic surfactants to achieve an optimum balance between surface activity and solubility. By introducing a highly controlled methyl substitution in the middle of the hydrophobe chain, the anionic surfactant may exhibit similar surface activity and solubility at lower temperatures (Baillely et al. 2003). This substitution does not compromise the favorable environmental profile (i.e., biodegradability) of linear anionic surfactants.

Similarly, major appliance manufacturers are currently marketing more energy-efficient appliances, such as horizontal-axis washing machines with lower water requirements and machines with wider ranges of temperature control. High-efficiency models are available in both front- and top-loading configurations, and manufacturers continue to introduce more efficient models of both styles that provide superior washing and clothes-handling performance (Flex Your Power 2005) Gas heaters clearly provide energy savings, as shown in this article. In addition, residential-demand water heaters without storage tanks and maintenance heating requirements are now available. These heaters eliminate standby losses (constantly maintaining heated water) and are claimed to reduce water-heating bills by 10–20% (Consumer Energy Center 2005).

CONCLUSIONS

Conventional household laundering practices can be viewed on a total system basis as an interdependent investment of 3 forms of energy: thermal (heated water), mechanical (agitation), and chemical (detergents and additives) (Figure 2). To maintain parity performance and satisfaction to the consumer, conservation of any 1 form of energy requires compensation by 1 or both of the others. Consumers currently have the ability to control all 3: reducing thermal energy by lowering wash-/rinse-cycle temperatures (and/or water-heater settings), reducing mechanical energy consumption by selection of the wash cycle (regular, permanent press), and by selecting detergent products designed for cold-water washing. As this article demonstrates, the selection of detergent can also impact thermal-energy consumption. Because mechanical energy is a relatively minor component of overall energy used in laundering, thermal energy conservation offers the highest potential for cost savings. The key to realizing substantial thermal-energy savings is to use cold-water laundering practices. Some consumer resistance to such changes can be expected until it is widely demonstrated that new appliances and detergent products can remove stains and produce whiteness as well as hot-water washing.

This study provides quantitative data to estimate the potential energy conservation and cost savings for US and Canadian households that could be realized by making changes in home laundering practices and in the use of appliances involved in hot-water consumption in residential settings. The residential energy-use model developed in this analysis can help to inform US and Canadian consumers of potential energy savings across a range of laundering conditions in the home. It can also help to guide manufacturers of laundering products and household appliances in the design of more energy-efficient innovations to home laundering, as well as other household needs for hot water.

Acknowledgements

Development and publication of the residential energy-use model was funded by the Procter&Gamble Company. The authors wish to acknowledge Jennifer Moe of Procter&Gamble and Dreas Nielson of Exponent, for their helpful input.