Superefficient Clothes Dryers to the Rescue!
Clothes dryers account for 6% of residential electricity consumption in the United States. Approximately 85% of U.S. households have a clothes dryer, and 6–7 million new dryers are sold every year. Clothes dryers consume as much energy annually as the entire state of Massachusetts consumes for all purposes. Energy used for clothes dryers nationwide costs U.S. consumers about $9 billion per year. Yet clothes dryers are the only major household appliances without an Energy Star label, and utility incentive programs for clothes dryers are rare.
In a recent editorial (HE May/June '13, p. 2) Alan Meier noted a historic milestone (at least for residential energy geeks): Plug loads, water heating, and lighting now account for more residential energy consumption than space heating and cooling. In other news, the American Council for an Energy-Efficient Economy recently reported that both funding and savings goals for energy efficiency programs are up again. Energy Star surveys show increasing popularity for the brand, and increasing market share for labeled residential appliances. Finally, the inefficient incandescent lightbulb's days are numbered in North America, as successive tiers of national lighting efficiency standards come into force.
What does this gumbo of residential energy news mean? Good news for energy efficiency, but the average residential energy efficiency program is now caught between greater expectations for savings and a decreasing number of tools to work with. There are more programs with bigger budgets and higher savings goals, while at the same time there are fewer measures that provide lower savings per measure than the measures that are already in force. As each residential energy end use becomes more efficient, there are fewer and fewer potential savings remaining to be squeezed out of each one.
Wanted: innovative technology that can dramatically cut the energy use of a popular electric household appliance. The appliance should be a real energy hog that has been ignored by federal minimum efficiency standards and by Energy Star.
The Clothes Dryer
The electric clothes dryer was commercialized sometime during the first quarter of the 20th century, but few U.S. homes had clothes dryers until after World War II. Unlike clothes washers, which have become much more technically complicated over time, the average North American clothes dryer today does more or less the same thing as its counterpart in 1953: heat air and blow it through wet, tumbling clothes to dry them. The main change over the last 60 years has been in price, as clothes dryers have become steadily cheaper to buy. As a result, whereas in 1953 fewer than 10% of U.S. homes had a tumble clothes dryer, today the market is saturated; and every home that has the space for a dryer already has one. The United States and Canada have the highest penetration of tumble clothes dryers worldwide, but Europe and Australia are catching up.
Most U.S. tumble dryers are electric; the rest burn natural gas (and in a few cases propane). While you may think that homes with gas furnaces have gas dryers, that is not necessarily the case. Only 50% of U.S. homes are heated by natural gas and 80% of dryers are electric; this means that more gas-heated homes have electric dryers than gas dryers. The historic trend has been toward the increasing electrification of clothes drying. An electric clothes dryer typically comes equipped with a 5kW heating coil, which cycles on and off as needed to create heat. As a result, the dryer uses a lot of electrical energy (kWh), and also contributes significantly to peak electricity demand (kW) from the grid.
Although we know that dryers are significant energy users, we don't know very much about their actual energy use. While it is fairly easy to measure dryer energy use in a lab, real people and real laundry make things complicated. We do not have good information on what people tend to put into dryers, or about the cycle options they choose, but we know that both of these factors can have a big impact on energy consumption. That said, it is reasonable to assume that the amount of energy used per clothes dryer has dropped over time for three main reasons:
- The average number of people per home has decreased. More dryers in more homes with fewer people per home probably means fewer dryer cycles per machine per year.
- Clothes washers have become more efficient. Under current DOE test procedures, a clothes washer can improve efficiency by removing more water from clothing before it is ready for the dryer. In other words, the washing machine becomes more efficient by leaving less work for the dryer to do. The average remaining moisture content in wet laundry at the end of the wash cycle has dropped as Energy Star-qualified washers have gained market share.
- Many clothes dryers have moisture sensors to prevent overdrying. Once the laundry in a clothes dryer is dry, blowing more hot air through it only wastes energy. Starting in the late 1950s, moisture sensors were introduced to disconnect the dryer's heating element once the laundry was dry. Today all but the least expensive clothes dryers have moisture sensors. Moisture sensors save energy when they actually do a good job of measuring remaining moisture content (sensor effectiveness is not part of the DOE test spec), and when users don't override the sensor. Again, we have little information on what people actually do.
There has been limited past field research of consumer clothes dryer use behavior, and actual energy consumption. Recent field research sponsored by the Northeast Energy Efficiency Alliance on dryer energy consumption in homes in the Pacific Northwest yielded an estimate of 773 kWh per year, and research by Cadmus Associates in California in 2009 suggests 736 kWh per year. The majority of homes in both studies had Energy Star clothes washers.
Because vented dryers use ambient air, ambient conditions may also play a role. Drying a load of laundry in a high, dry location (like Denver, for example) probably requires less electricity than drying a load of laundry in a low-lying, humid location (like Chapel Hill, North Carolina). Because clothes dryers are usually installed indoors, that ambient air has usually also been heated or cooled before being sucked into the dryer and eventually blown out through the dryer vent. We are only beginning to study these secondary effects on energy consumption.
However, none of these trends indicate a significant increase in the technical efficiency of the clothes-drying process. This is why there is no Energy Star rating for dryers, and why, unlike other household appliances, clothes dryers don't have to participate in the U.S. Federal Trade Commission's EnergyGuide labeling program. (Natural Resource Canada runs a similar labeling program, EnerGuide.) Fortunately, this is all about to change in several big ways.
Energy Star Emerging Technology Award for Advanced Dryers
On June 12, 2013, Samsung Electronics became the first manufacturer to receive EPA's Energy Star Emerging Technology Award for Advanced Dryers for its DV457 model. By meeting the requirements of the Emerging Technology Award, Samsun's winning dryer will save up to 25% of the energy used by conventional models. The Samsung DV457 uses a combination of better controls and heat modulation to reach the efficiency target.
The Samsung DV457 should be broadly available this year, and other manufacturers may qualify for the Emerging Technology Award before the Advanced Dryers award category closes. Energy efficiency programs in Canada and the United States are preparing to offer customer rebates.
Energy Star for Clothes Dryers
Since washers and dryers are normally sold together in the United States and Canada, manufacturers and retailers have long been calling for an Energy Star for dryers program to match the successful Energy Star for clothes washers program. Manufacturers and retailers want to be able to put Energy Star-qualified washers and dryers side by side on the showroom floor.
During the summer of 2012, EPA started the process of launching an Energy Star for dryers program and issued a first draft of the Energy Star technical specifications for review. The first draft set a minimum energy efficiency performance level for product qualification that was about 13% more efficient than the current market average baseline.
It's important to understand that all of this action in North America is taking place in the shadow of a huge market transformation on the other side of the Atlantic. Europe has a lower penetration of tumble clothes dryers than North America does. In 2012, the percentage of homes with dryers ranged from 60% (Netherlands) to around 18% (Italy). The dryers are also different. Due to different residential construction practices, most European residential models are unvented condensing dryers. Rather than getting rid of the water removed from laundry by blowing it out a vent as vapor, condensing dryers collect the removed water as liquid, which then goes down the drain. We have a very small number of condensing dryers in North America, most of which are installed in apartment buildings where venting isn't an option. Electric-resistance condensing clothes dryers are even less energy efficient than electric-resistance vented clothes dryers, and they also take a long time to dry a load of laundry.
In 1995, the European Commission looked across the ocean, saw a future when there would be a dryer in most European homes, and required that the European Union (EU) energy label be placed on all dryers.
When the label was introduced, most dryers on the European market were rated C or D, and none was capable of achieving the A class energy efficiency level. In 1998, AEG (a subsidiary of Electrolux) brought the first A-rated dryer to market—a condensing dryer, which used a heat pump. This new technology was efficient and successful. By 2012, over 80 residential heat pump dryer models from 18 different manufacturers were available across the European market.
The city of Zurich hosted some of the earliest efforts to promote heat pump clothes dryers, and Switzerland leads Europe in moving to this new technology. In 2011, 47% of all dryers sold in Switzerland were heat pump models. In 2012 the Swiss made it official by setting a new minimum national efficiency for clothes dryers, which allows only A-rated dryers. All clothes dryers sold in Switzerland last year were heat pump models, and the market transformation seems to have gone smoothly.
How efficient are heat pump clothes dryers? The Collaborative Labeling and Appliance Standards Program (CLASP) recently sponsored apples-to-apples laboratory research by Ecova comparing three conventional vented electric-resistance dryers purchased in the United States with four heat pump models imported from Europe. The dryers were subjected to the same test procedures, and the same loads of laundry. The verdict was that the European heat pump clothes dryers used half the electricity of the conventional U.S. clothes dryers. Several of the manufacturers currently producing heat pump clothes dryers for the European market are looking at bringing heat pump models to North America. The first of these über-efficient dryers probably won't be available until 2014 at the earliest.
Three Tiers of Transformation
Sometime in 2015, instead of today's relatively superficial differences between clothes dryers on the market, shoppers could see three well-defined levels of energy efficiency. Energy Star for clothes dryers specifications will produce dryers that are approximately 13% more efficient; Energy Star Emerging Technology Award winners will be 30% more efficient; and heat pump dryers (when they get here) will be nearly 50% more efficient than conventional clothes dryers. There are several options for identifying the highest tier of products, including Energy Star Most Efficient and TopTen, among others. These three efficiency tiers could be a convenient way for energy efficiency programs to offer increasing incentives for increasing energy efficiency.
Can Old Habits Be Preserved?
Most readers of the same vintage as the author probably have memories of widely used, ultraefficient, solar laundry-drying technology. The pendulum has swung pretty far in the other direction, and today hanging laundry out to dry is downright rare, and not infrequently illegal, in the United States and Canada on aesthetic grounds. Are electric tumble dryers simply an inevitable technology that will completely replace clotheslines, or is there an opportunity to encourage more efficient clothes drying behavior in addition to clothes drying technology?
Maybe getting a clothes dryer doesn't mean giving up line drying completely. As anyone who is on laundry duty for his or her household has learned, not everything that can go in the washer should go in the dryer. Line drying persists for practical reasons, and some people would like to preserve the option of at least occasionally using a clothesline to save energy and money. There is now a backlash to bans on outdoor clothes drying, and six states—Colorado, Florida, Hawaii, Maine, Maryland, and Vermont—have passed laws that explicitly prohibit the banning of clotheslines. In 2008, Ontario became the first Canadian province to pass so-called Right to Dry legislation (though it exempted condos and apartments). An interesting option might be for energy efficiency programs to package a clothesline and clothespins with each super efficient dryer rebate check.
Download information on heat pump dryers in the European and Swiss markets.
Download Denkenberger, Dave, et al. Analysis of Potential Energy Savings from Heat Pump Clothes Dryers in North America.
The Super Efficient Dryer Initiative (SEDI)
For the past four years, the Super Efficient Dryer Initiative (SEDI) has been involved in many of the North American developments discussed in this article. In 2012, SEDI found an institutional home at the Vermont Energy Investment Corporation, and evolved from a group of interested parties to a more formal organization with a dozen institutional sponsors. SEDI is run by a core team of experienced consultants who provide sponsor services and define SEDI's scope of work. Recently, SEDI created technical and program design working groups intended to help energy efficiency programs lay the groundwork for the market introduction of energy-efficient clothes dryers.
One of SEDI's main functions in the near term will be to coordinate existing dryer research and to commission new research as requested by sponsors (including the CLASP testing report referenced above). SEDI also maintains regular communication with laundry industry contacts, particularly those manufacturers and retailers most likely to be involved in bringing energy-efficient dryers to the North American market.
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