Residential clothes washers
The residential clothes washer was introduced to the US market in the 1920s, but fully automated washing machines, which filled and drained water automatically and spun clothes to reduce the amount of water left after rinsing, were not available until the late 1930s (Shehan and Moras 2006). Since the 1940s, the sales of home laundry appliances have grown dramatically (Stawreberg 2011). According to the United States Energy Information Administration (2009), 82.0% of US households have clothes washers, and the households that own a clothes washer do two to nine laundry loads each week, resulting in an average of 400 washing loads per year.
Conventional vertical-axis clothes washers
Conventional vertical-axis clothes washers are top-loading washers with a vertically mounted tub that contains an agitator at the center of the drum. During the washing cycle, the tub will be filled with water, and the agitator will rotate or pulse, turning the clothes around in the water to clean them. Conventional washers use a large amount of water per load, allowing the clothes to easily float and move in the detergent solution. Because energy is required to heat the water, conventional washers use a vast amount of energy as well as water (Bansal et al. 2011). However, conventional washers are sold for a lower price and complete a washing cycle faster than HE washers (Consumer Reports 2012).
High-efficiency (HE) clothes washers
There are two types of HE clothes washers in the US market, the front-loading, horizontal-axis HE washer and the top-loading, vertical axis HE washer. Front-loading HE washers represent about 90% of the HE washing machine market in the US (Healthy House Institute 2010). Front-loading HE washers require less water for washing because the tub is typically filled only one-third or one-half full of water. These washers use the horizontal axis to create a tumbling action, rotating clockwise and counterclockwise to tumble the laundry items back and forth through a small pool of water. The rotating motion flexes the weave of the fabrics and forces water and detergent through each garment, removing soils with the use of less mechanical agitation than that used by conventional washers. Top-loading HE washers differ from the conventional top-loading type in that there is an agitating plate at the bottom of the tub instead of a vertical agitator midway between the top and bottom of the tub. The cleaning action occurs as the plate bounces the clothes in a small amount of water.
In addition to saving water, HE washers can also save energy. As much as 80–90% of the energy used by washers is for heating the water used in the washing cycle (Electric Power Research Institute 2010). Because less water is required in HE washers, if the garments are washed in either hot or warm water, less energy is needed to heat the water. Another energy saving benefit of HE washers is a shorter drying time. Since HE washers have a significantly higher spin speed than conventional washers, water can be extracted more effectively. Less water means a shorter drying time after washing, resulting in energy cost savings of as much as 50% (United States Environmental Protection Agency, Energy Start 2012). According to ENERGY STAR, a program developed by the United States Environmental Protection Agency, Energy Star (2017), which promotes energy efficiency in products, a HE clothes washer needs to use at least 33% less water and 28% less energy than the minimum efficiency standards required by conventional washers to be able to carry the ENERGY STAR logo.
Another advantage of HE washers is that it requires less detergent, since less water is used for the laundry process, thus reducing the environmental impacts of detergents such as surfactant toxicity (Hill 2015). However, detergents specifically designed for HE washers need to be used. Such detergents are formulated to create a small amount of suds and be able to be dispersed quickly in low water volume machines. In addition, the tumble action of HE washers usually creates more suds than a conventional agitator action due to the interaction of the tumbling water and detergent (American Association on Textile Chemists and Colorists (AATCC) 2012). Therefore, the amount of water used by HE washers cannot sufficiently clean out the suds created by a traditional detergent.
Studies on comparisons of conventional and HE washers
Limited academic studies on the comparisons of conventional and HE washers have been published in research journals. One study of interest was conducted by Klausing et al. (2012), who compared a conventional top-loading washer and a HE front-loading washer in dimensional change of knit fabrics after five laundering cycles. One laundering cycle includes one washing cycle and one drying cycle. The same tumble dryer was used to dry the specimens washed in the conventional and the HE washer. Their results showed no significant differences in dimensional change between the fabrics washed in the two types of washers.
Schlag and Ordonez (2010) presented their study at a conference, reporting the comparisons of several care performances (appearance smoothness, dimensional change, color change, skewness change, and stain removal) of woven and knitted fabrics between washed in a conventional top-loading washer and a front-loading HE washer after five laundering cycles. For the woven fabric, the HE washer had better performance in appearance smoothness than the conventional washer, but no significant difference in appearance smoothness was found for the knit fabric. In addition, no significant differences were found in dimensional change and color change between the two types of washers for both the woven and the knit fabric. Schlag and Ordonez also reported some mixed results. A significant difference in skewness change was found for the woven test fabric after five laundering cycles, but no significant difference was found for the woven ballast fabric. (Ballast fabric was used to bring the total weight of the laundry load to a specified value, which was 4.00 ± 0.13 lb). In stain removal, spectrophotometric measurements of Delta E showed that the HE washer had better performance in removing used motor oil and mustard stains for both woven and knit fabrics, but the conventional washer had better performance in removing lipstick stains. However, the Gray Scale Color Change results were opposite to the spectrophotometric results; the conventional washer had better performance in removing used motor oil and mustard stains for both woven and knit fabrics, but the HE washer had better performance in removing lipstick stains.
Cotton Incorporated and Whirlpool Corporation published a study comparing (a) a conventional top-loading, vertical axis washer, (b) a front-loading, horizontal axis HE washer, and (c) a top-loading, vertical axis HE washer for a cotton knit fabric after 20 laundering cycles (Ankeny et al. 2014). The authors indicated that the specimens washed in the two HE washers “seemed to have” less color change than the specimens washed in the conventional washer. Because statistical analysis was not used in the study, it is unclear if the findings were statistically different between the types of washers or within the sample/testing variance. The specimens washed in two HE washers had consistently lower degrees of shrinkage than those washed in the conventional washer after 5, 10, 15 and 20 laundering cycles. These findings were inconsistent with the results of Klausing et al. (2012) and Schlag and Ordonez (2010), who found no significant differences in shrinkage and color change after five laundering cycles. Among the few studies that compared conventional and HE washers (Ankeny et al. 2014; Klausing et al. 2012; Schlag and Ordonez 2010), many mixed findings were reported, indicating an essential need for further studies.
Residential clothes dryers
Residential clothes dryers were available in the early 1940s; however, they were expensive, and most families could not afford them. In 1955, only 10% of US households had one (Morris 2017). After 1955, companies were able to sell automatic clothes dryers at a much lower price; therefore, clothes dryer sales increased considerably. According to the United States Energy Information Administration (2009), 79.4% of US households have a clothes dryer (63.2% electric clothes dryer, 15.3% gas clothes dryer, and 0.9% propane clothes dryer). The averaged number of annual dryer loads varies in different households, but is estimated to be 439 (McCowan et al. 2015). However, using a clothes dryer is a habit peculiar to the US and Canada (81% in 2009; Statista 2017). Many Europeans and Asians who can afford to purchase clothes dryers still tend to hang clothes up to dry. It is possible that US consumers prefer convenience and time saving and worry that clothes hung outdoor will absorb environmental dust and/or car exhausts. Many people in other countries, however, consider having a clothes dryer a waste of energy and money. In addition, most households do not have enough room for both a washer and a dryer.
Tumble dryers have been most widely used in the US. They continuously draw in the cool, dry, ambient air around them, heat it, and then pass it through the tumbler, where moisture is absorbed from the clothes. The hot, humid air produced in the drying process is usually vented outside the house to make room for more cool, dry air to continue the drying process. This design does not recycle the heat put into the load and thus is considered environmentally wasteful.
To address this issue, new clothes dryer technologies, such as heat pumps, was introduced in Europe for more than 10 years (Meyers et al. 2010) and have recently become available in the US market (Evergreen Economics 2016). Heat pump clothes dryers cool the warm, moist air produced in the drying process and condense the moisture into water. The cool, dry air is then heated and re-circulated back into the drum. Depending on the model, the manufacturers claim that heat pump dryers use 25–70% less energy than the average electric dryer. Consumer Reports (2015) tested a heat pump clothes dryer and found that the heat pump clothes dryer used about 40% less electricity, but took 112 min to dry a 12-pound load, 38 min longer than the time used in a regular clothes dryer. Heat pump clothes dryers are not popular among US consumers, with a market share of almost zero (Evergreen Economics 2016). Meyers et al. (2010) found that heat pump clothes dryers had economic benefits only for households with high clothes dryer usage (over 700 cycles per year), which were 6% of the sample households, or for households in regions with high electricity price (i.e., the Northeast of the US and California) after about 500 cycles of usage per year. Another study, conducted by Martin et al. (2016), found that although the heat pump clothes dryer used less electricity than a conventional dryer, it released significantly more heat than a conventional dryer, leading to an increase of energy used to cool the house.
In the US market, almost all the clothes dryers paired with a HE clothes washer are still tumble dryers. However, some of these dryers do save energy by using more accurate moisture sensors than those used in conventional dryers to better detect the dampness of the laundry and shut off the machine when the clothes are dry (Consumer Reports 2015). In this way, energy can be saved and the clothes will not be over dried. Many of these dryers also use low heat and long drying times to save energy. However, the money saved from a HE dryer may not be significant according to consumer Reports (2015). A dryer with an ENERGY STAR label may save about $20 a year in electricity compared with the conventional dryers. However, the longer drying time means that more indoor air is drawn by the dryer and moved from the house through the vent to the outside after the drying process. This air movement may increase the energy of heating or cooling the house. Therefore, the net money saving from a HE dryer may be minimal.
Residential fabric softeners
The synthetic detergents used in a clothes washer can clean clothes effectively; however, they can also remove the fatty finish and lubricating waxes on the fabric when they remove dirt and oil, thereby changing the fabric hand of the washed garment (McCarthy and Drozdowski 1989). Fabric softeners were introduced to the US market in the early 1950s to provide a pleasant odor and improve the hand of laundered clothes (Simpson 1958). Fabric softeners can make the washed fabric soft and smooth by coating the washed fabric with lubricants and humectants. Since the introduction of fabric softeners to the market, their use has grown continuously. Currently, most households (about 80%) in the US regularly use fabric softeners during home laundering (American Association on Textile Chemists and Colorists (AATCC) 2012).
Between the two common types of fabric softeners for home laundering (rinse cycle softener and dryer sheet softener), the dryer sheet softener is more popular in US households (over 60% of households) (American Association on Textile Chemists and Colorists (AATCC) 2012). Dryer sheet softeners, which were introduced to the US market in the early 1970s (Williams 1982), are fabric softeners saturated onto sheets of a non-woven fabric or polyurethane foam. Compared with rinse cycle softeners, dryer sheet softeners provide better anti-static properties, air permeability retention, water absorbency retention, and whiteness retention (Chen-Yu et al. 2009; Williams 1982; Wilson 1987). Dryer sheet softeners also form smaller pills and have no effect on flammability (Chen-Yu et al. 2008; Chiweshe and Crews 2000). However, dryer sheet softeners tend to have uneven softener deposition and are less effective in softening fabrics (Williams 1982). Although many households use fabric softeners during home laundering, no study comparing conventional and HE washers has included a fabric softener.