ENERGY STAR Market and Industry Scoping Report Residential Clothes Dryers

ENERGY STAR Market & Industry Scoping Report
Residential Clothes Dryers
November 2011
U.S. Environmental Protection Agency (EPA) consistently looks for new opportunities to expand
ENERGY STAR to new product categories that will deliver significant benefits to consumers and
the environment in the form of energy and dollar savings plus greenhouse gas reductions. A key
step in this evaluation is the development of a scoping report that provides a snapshot of the
product market, energy use, and savings potential associated with an ENERGY STAR program
for the scoped product type. EPA uses scoping findings to prioritize product specification
development work. While scoping reports are drafted primarily for internal evaluation purposes,
and are not intended to be exhaustive but rather a guidepost for the ENERGY STAR program,
EPA makes the reports available with the interest of benefiting other efficiency programs
evaluating similar opportunities. For more information about the ENERGY STAR specification
development process, go to: www.energystar.gov/productdevelopment.
1. Product & Technology Overview
For the purposes of this report, a clothes dryer is defined as a cabinet-like appliance designed
to dry fabrics in a tumble-type drum with forced air circulation, with blower(s) driven by an
electric motor(s) and either gas or electricity as the heat source. The U.S. Department of Energy
(DOE) latest appliance standards classify clothes dryers into a number of different product
classes (Table 1), based on whether or not the product is vented, the energy source (gas or
electric), input voltage, and the dryer's capacity in cubic feet (ft3).
Table 1: Clothes Dryer Product Classes
U.S. DOE Product Classes (as shown in 10 CFR 430.32(h))
Vented
Electric, Standard (4.4 ft3 or greater capacity)
Electric, Compact (120V) (less than 4.4 ft3 capacity)
Electric, Compact (240V) (less than 4.4 ft3 capacity)
Gas
Ventless
Electric, Compact (240V) (less than 4.4 ft3 capacity)
Electric, Combination Washer-Dryer
Note, these product classes correspond to the energy conservation standards for which manufacturers must comply
beginning January 1, 2015.
Vented and Ventless Dryers
In vented dryers, ambient air comes in from the surrounding environment via opening in the
metal structure. Ambient air is heated with a heating element and blown into the drum, where
the drying process occurs. Once the warm air is saturated with the laundry moisture, it is
evacuated outside through a flexible pipe. The drum is set into rotation by the motor in order to
spread the load in the whole available volume.

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Figure 1: Electric Vented Clothes Dryer1
Di 11111
Driving belt
Air filter
Heating device
M oto i
Instead of exhausting the air, ventless dryers typically use a heat exchanger to cool the air and
condense the water vapor into either a drainpipe or collection tank. Although not as common in
the U.S., two types of condenser dryers can be found of the market: air and water condenser
dryers. The difference lies in the heat exchange process; the internal warm air is cooled either
using ambient air or cold water. Water condensation is most common for combination all-in-one
washer-dryers whereas the majority of condensing dryers use air condensation.
Ventless dryers offer the versatility of not needing to be vented to the outside (useful in spaces
such as apartments and condominiums). Waste heat goes to the surrounding environment
rather than being vented outside. If the dryer is installed in a home's conditioned space, this can
be a benefit on cold days but a drawback on hot days.
Energy Source: Gas and Electricity
Clothes dryers are powered by either utility supplied electricity or gas (natural gas or propane).
Electric dryers require a dedicated 240 or 120 volt (V) outlet while gas dryers, which tend to
have lower operating costs, require a dedicated gas hook-up. Due to safety risks associated
with the combustion of gas, gas dryers are always vented, while electric dryers can be vented or
ventless.
Product Components
The basic components of a conventional clothes dryer are described in Table 2.
1 PricewaterhouseCoopers. Ecodesign of Laundry Dryers. Preparatory Studies for Ecodesign Requirements of Energy-using
Products (EuP) - Lot 16. Final Report March 2009.
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Table 2: Clothes Dryer Main Product Components
Component
Description
Drum
Heated air evaporates water from the clothes in the drum, which typically rotates around 40
revolutions per minute (RPM). Evaporating water cools the air to 90 - 170°F and increases its
humidity as it leaves the drum.
Motor
Motor rotates the drum and drives the fan to move the air. Typically draws 200 - 300 watts (W)
of electricity. Most dryers use a single-phase capacitor-run induction motor. Inverter-fed three-
phase permanent magnet synchronous motors can be used, but their use is cost-dependant.
Motor options include brushless direct current (DC) motor, brushless direct drive, and three
phase motors and their associated controls. Some clothes dryers use separate motors to rotate
the drum and to drive the fan.
Fan
The fan draws the air through the other components at 100 - 150 cubic feet per minute (CFM).
Electric Heater
Electric resistance heaters typically draw about 5,000 - 5,500 watts (230 volts and 22 amps).
The air from the cabinet is drawn into the heater duct and heated to 200°F to 300°F. The main
technologies are sheathed element heaters and open coil heating elements.
Gas Burner
Gas burners are typically rated at 20,000 - 25,000 British thermal units/hour (Btu/hour), which
equals 6-7 kilowatts/hour (kWh). Most standard gas dryers today use inshot style burners to
deliver heat to the drum.
2. Market Assessment and Usage Assumptions
U.S. Market and Usage Patterns
Existing Stock of Clothes Dryers
Household penetration of clothes dryers has increased by nearly 6% over the last decade.2 As
of 2009, almost 80% of U.S. households have a clothes dryer. Approximately 80% of the
installed base of clothes dryers in U.S. households are electric, while the remaining are gas
dryers. The mix of electric dryers and gas dryers has remained relatively stable, with electric
dryers experiencing just over 2% increase in household penetration over the last decade.3 The
vast majority of dryers in the U.S. require an exhaust vent, as ventless dryers represent less
than 1% of the market.4
Table 3: Household Penetration of Clothes Dryers by Energy Source5
Clothes Dryer
U.S. Households (millions)
Percentage of Total
Households
Use a Clothes Dryer At Home
90.2
79%
Electric
71.8
80%
Natural Gas
17.5
19%
Propane/LPG
1.0
1%
Do Not Use a Clothes Dryer At Home
23.4
21%
2 DOE- EIA. Residential Energy Consumption Survey 2001, 2005, 2009 Public Use Data Files.
3 Ibid.
4 Meyers, S., Franco, V., Lekov, A., Thompson, L., and A. Sturgen. Do Heat Pump Clothes Dryers Make Sense for the U.S.
Market? Presented at the 2010 ACEEE Summer Study of Energy Efficiency in Buildings. August 2010.
5 DOE- EIA. Residential Energy Consumption Survey 2009 Public Use Data Files.
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U.S. Retail Sales of Clothes Dryers
In 2010, 6.5 million clothes dryers were sold in the U.S.,6 80% of which were electric dryers.
Similar to other durable goods, sales of clothes dryers have decreased over the past few years,
largely due to the economic downturn.
Clothes Dryer Lifetime
The average lifetime of clothes dryers is generally estimated in the range of 127-168 years.
Table 4 provides the most recent data for the age distribution of clothes dryers. This report
assumes an average lifetime of 16 years.
Table 4: Age Distribution of Clothes Dryers9
Age of Clothes Dryer
U.S. Households
(millions)
Percentage of Total
Households
Less than 2 Years
11.9
13%
2 to 4 Years
21.4
24%
5 to 9 Years
30.1
33%
10 to 14 Years
16.2
18%
15 to 19 Years
6.2
7%
20 Years or More
4.5
5%
Consumer Usage Behavior
The current DOE test procedure for measuring the energy consumption of clothes dryers
assumes 416 cycles per year. In the amended test procedure for clothes dryers that DOE
published in January 2011, the number of cycles was revised to 283 cycles per year, based on
data from the 2005 Energy Information Agency (ElA) Residential Energy Consumption Survey
(RECS).10 Within homes that have a clothes dryer, about 82% use the clothes dryer every time
clothes are washed.
Table 5: Clothes Dryer Frequency of Use (2009)11
Clothes Dryer Use
U.S. Housing Units
(millions)
Used Every Time Clothes are Washed
74.4
Used For Some, But Not All Loads
13.8
Used Infrequently
2.1
Do Not Use a Clothes Dryer At Home
23.4
6 Appliance Magazine. 2010 U.S. Appliance Shipment Statistics. April 2010.
7 Appliance Magazine and Association of Home Appliance Manufacturers
8 U.S. Government, Federal Register / Vol. 76, No. 4 / Thursday, January 6, 2011 / Rules and Regulations page 972-1036
9 DOE- EIA. Residential Energy Consumption Survey 2009. Public Use Data Files.
10 Appendix D to Subpart B of Part 430 - Uniform Test Method for Measuring the Energy Consumption of Dryers
11 DOE- EIA. Residential Energy Consumption Survey 2009. Public Use Data Files.
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Pricing
Generally, gas dryers cost around $50 more than comparable electric dryers, although savings
in fuel costs typically make up the difference in the long run.12 Additionally, some gas utilities
offer consumers rebates (usually, in the range of $50-100) for installing gas dryers. Condensing
dryers are available in the U.S. from at least five manufacturers (GE, LG, Bosch, ASKO, and
Miele). These units typically cost $950-$2,050 and are available in small to medium
capacities.13
U.S. Consumer Preferences
TIAX, a technology processing and commercialization company, conducted a consumer survey
prior to the development of its heat pump clothes dryer prototype for Whirlpool Corporation, in
an effort to identify the attributes most important to consumers. The top three purchase criteria
for clothes dryers were listed as reliability, features and functions, and price.14 The survey found
that consumers were willing to pay significantly more for energy savings, though cost sensitivity
varied by location, and consumers were skeptical of claims of significant energy savings.
Consumer interest in clothes dryer energy efficiency was also found to be more closely coupled
to a desire to be environmentally sound, than to the payback.
International Markets and Usage Patterns
It is worth noting the differences of among various domestic markets for clothes dryers. For
instance, condenser dryers and compact sizes have a far higher prevalence in Europe than in
the U.S., and the market penetration of electric dryers is even greater in Europe. As a result,
European consumers are more accustomed to longer drying times and ventless models.15
Canada and Australia are more similar to the U.S. in household characteristics and in the
penetration of natural gas dryers. Additionally, almost all dryers in Canada are vented models.16
3. Clothes Dryer Test Procedures and Standards
U.S. Department of Energy Test Procedure
(as shown in Appendix D and Appendix D1 of 10 CFR Part 430, Subpart B)
Clothes dryer energy consumption in the U.S. is measured in accordance with the DOE test
procedure. DOE published an amended clothes dryer test procedure on January 6, 2011.17
Manufacturers will be required to use this amended test procedure to determine compliance
with the new clothes dryer energy efficiency standards starting in 2015. Main changes to the
amended DOE test procedure include:
1. Incorporates measures of standby and off mode consumption
12 Consumer Energy Center. Clothes Dryers - Buying Smart. 2011. Available online at:
www.consumerenergycenter.org/home/appliances/dryers.html
13 Bendt, P., Calwell, C., and L. Moorefield. 2009. Residential Clothes Dryers: An Investigation of Energy Efficient Test Procedures
and Savings Opportunities. Ecova (formerly Ecos Consulting) prepared for Natural Resources Defense Council.
14 Pescatore, P., and P. Carbone. High Efficiency High Performance Clothes Dryer: Final Report to Department of Energy. TIAX.
March 2005.
15 PricewaterhouseCoopers. Ecodesign of Laundry Dryers. Preparatory Studies for Ecodesign Requirements of Energy-using
Products (EuP) - Lot 16. Final Report March 2009.
16 Nipkow, J., Josephy, B., Bush, E., Werle, R., and C. Granda. Energy-efficient heat pump dryers - European experiences and
efforts in the U.S. and Canada. May 2011.
17 U.S. Government, Federal Register / Vol. 76, No. 4 / Thursday, January 6, 2011 / Rules and Regulations page 972-1036
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2. Includes ventless clothes dryers18
3. Clarifies test conditions for gas dryers and dryer drum capacity measurements
4. Updates detergent specifications for dryer test cloth preconditioning
5. Adopts technical changes to better reflect current usage patterns and capabilities of
clothes washers and dryers
Both existing and amended DOE test procedures normalize the per-cycle energy consumption
equation to represent the energy consumption required to dry the test load to between 2.5 and 5
percent remaining moisture content (RMC) at a single setting (highest heat). Both test
procedures multiply the per-cycle energy consumption by fixed field-use factors to account for
energy consumption due to over-drying by time termination dryers (field use factor = 1.18), and
automatic termination dryers (field use factor = 1.04). This does not test the effectiveness of the
clothes dryer's auto termination. However, testing by both Ecos Consulting for the National
Resources Defense Council (NRDC)19 and Consumer Reports has found wide variation in how
effectively moisture sensors operate. In August 2011, DOE released a Request for Information
(RFI) to further investigate the effects of automatic termination.
U.S. Federal Energy Conservation Standards
The current energy efficiency performance metric for clothes dryers is Energy Factor (EF),
which measures the pounds of clothing (saturated to a certain standardized extent) that can be
dried per electric kilowatt-hour (kWh) of electricity (for gas dryers, per "equivalent" kWh of
natural gas consumed). The DOE's new energy efficiency performance metric, Combined
Energy Factor (CEF), integrates energy use in the standby mode and off mode with the energy
use of drying. DOE recently amended the federal energy conservation standards for clothes
dryers. Manufacturers will be required to demonstrate compliance with these new standards
beginning January 1, 2015. Tables 6 and 7 summarize existing and amended standards,
assumption on number of cycles per year for dryer categories, and annual energy use.
Table 6: Existing Federal Standards (as shown in 10 CFR Part 430.32(h))

Existing Federal Standard
Calculated with Existing Test
Procedure
Product Class
EF
(Ib/kWh)
Average Annual Energy
Use in kWh
(416 cycles/yr)
Electric, Standard (4.4 ft3 or
greater capacity)
3.01
967
Electric, Compact (120V) (less
than 4.4 ft3 capacity)
3.13
399
Electric, Compact (240V) (less
than 4.4 ft3 capacity)
2.90
430
Gas
2.67
1091
18 The existing test procedure for clothes dryers requires the use of an exhaust restrictor to simulate the backpressure effects of a
vent tube. The amended test procedure altered this requirement so that it only applied to vented clothes dryers and included
separate procedures and product class definitions for "ventless" clothes dryers.
19 Bendt, P., Calwell, C., and L. Moorefield. 2009. Residential Clothes Dryers: An Investigation of Energy Efficient Test Procedures
and Savings Opportunities. Ecova (formerly Ecos Consulting) prepared for Natural Resources Defense Council.
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Table 7: Amended Federal Standards (as shown in 10 CFR Part 430.32(h))

Amended Federal Standard
Calculated with Amended Test
Procedure
Product Class
CEF
(Ibs/kWh)
Average Annual
Energy Use in kWh
(283 cycles/year)20
Vented Electric, Standard (4.4
ft3 or greater capacity)
3.73
684
Vented Electric, Compact
(120V) (less than 4.4 ft3
capacity)
3.61
305
Vented Electric, Compact
(240V) (less than 4.4 ft3
capacity)
3.27
340
Vented Gas
3.30
748
Ventless Electric, Compact
(240V) (less than 4.4 ft3
capacity)
2.55
372
Ventless Electric, Combination
Washer-Dryer
2.08
463
4. Energy Efficiency Assessment
Conventional dryers are about 50-70% efficient at removing water.21,22 Using heat recovery,
heat pumps, or the desiccating potential of dry air can theoretically present efficiencies of over
100%.23 Residential clothes dryers account for approximately 6% of residential electricity use.24
Traditionally, it's been assumed that the energy efficiency of clothes dryers does not vary
appreciably. Publically available data on clothes dryer supports this, suggesting all models have
similar energy use. This view has begun to change in the last few years as a result of new
research that is suggesting different methods of testing may reveal greater differences in
efficiency and through the development of new and improved technologies for improving dryer
efficiency.
Clothes dryer testing conducted by Ecova (formerly Ecos Consulting) for NRDC has suggested
that when tested under conditions different than current DOE test (which does not assess the
effectiveness of automatic termination or multiple cycle settings), conventional dryers can vary
by about 20 to 30% in the amount of energy required to dry the same load of clothes.25
20 U.S. Department of Energy - Technical Support Document for Residential Dryers, EERE-2007-BT-STD-0010.
21 Converting water from a liquid state to a vapor state requires about 500 kcal of heat per kg of water (0.308 kWh per pound).
Multiplying by 0.308 kWh per pound of water removed from the load, and dividing by the energy consumption associated with each
cycle provides an estimate of overall dryer efficiency.
2 Bendt, P., Calwell, C., and L. Moorefield. 2009. Residential Clothes Dryers: An Investigation of Energy Efficient Test Procedures
and Savings Opportunities. Ecova (formerly Ecos Consulting) prepared for Natural Resources Defense Council.
23 Ibid.
24 Bendt, P. Are We Missing Energy Savings in Clothes Dryers? Presented at the 2010 ACEEE Summer Study of Energy Efficiency
in Buildings. August 2010.
25 Bendt, P., Calwell, C., and L. Moorefield. 2009. Residential Clothes Dryers: An Investigation of Energy Efficient Test Procedures
and Savings Opportunities. Ecova (formerly Ecos Consulting) prepared for Natural Resources Defense Council..
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Savings Opportunities
The most energy efficient way to reduce clothes dryer energy use is to spin more moisture from
the load after it washed and before it enters the clothes dryer. Today, clothes washers with a
horizontal axis configuration and high spin speeds of more than 1,000 revolutions-per-minute
(RPM) are common.
The following section discusses a variety of technology design options to increase the energy
efficiency of clothes dryers, broken into different categories. For each category, a table is
provided summarizing available technology options largely drawn from recent DOE research
and analysis,26 a short description of these options, and estimated savings for these options.
Estimated savings are based on initial review of research reports and discussions with
manufacturers, and DOE's review of various trade publications, research reports, discussions
with manufacturers, and product literature. Some of these options are then further discussed,
along with some of the additional considerations for improving the energy efficiency and
reducing the environmental impact of clothes dryers.
Dryer Control or Drum Upgrades
Table 8: Energy Efficient Technology Options - Dryer Control or Drum Upgrades
Technology Option
Description
Estimated Savings
Improved Termination
Automatic termination by temperature, moisture sensing,
end-of-cycle detection
10% for temp., 15% for
moisture
Increased Insulation
Insulating the dryer drum reduces heat loss
Up to 6%
Modified Operating
Conditions
Reducing air flow and/or heat input rate
5-8%
Improved Air
Circulation
Better drum design or dryer booster fans to improve airflow
1-2% for better drum
design, N/A for dryer
booster fans
Reverse Tumble
Reverse rotational direction early to increase the
separation of clothing and dry more evenly and quickly
N/A
Improved Drum Design
Improving the drum design, including internal vane design,
which can promote clothes separation during tumbling
N/A
Instead of only having a timer that terminates the dry cycle after a certain time interval selected
by the consumer, many new clothes dryers offer an automatic termination setting. However, this
feature may be over-ridden by consumers who continue to operate dryers on a timed basis as
they have in the past.
Auto termination controls the length of the drying cycle, using temperature sensors and/or
moisture sensors to terminate the cycle when the clothes are dry. Automatic termination can be
accomplished using a temperature sensor that detects the temperature of exhaust air.
Manufacturers have indicated to DOE that moisture sensing (that assess conductivity) can
increase accuracy of auto termination relative to only using a temperature sensor.27 Several
26	U.S. Department of Energy - Technical Support Document for Residential Dryers, EERE-2007-BT-STD-0010.
27	Ibid.
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sources have claimed that temperature sensors provide 10% real-world energy savings,
whereas moisture sensors yield a 15% savings.28
Research has also suggested the accuracy of moisture sensors and controls varies among
clothes dryers currently available on the U.S. market.29 According to one source, the location of
the moisture sensor has the potential to increase accuracy and save energy. Placing moisture
sensors in the "fins" located around the drum perimeter instead of the in a fixed location on the
front inside of the dryer cabinet can lead to more clothes coming in contact with sensors and
better detection of proper cycle termination.30
Research by Ecos Consulting for NRDC has estimated that the difference between a standard
clothes dryer and one that is effective at turning itself off when clothes are actually dry is about
0.76 kWh per load (5,000 kWh over typical lifetime).31 Auto termination can be improved by
increasing the accuracy of resistance sensors near the end of the dry cycle when RMC is low,
and by improving the accuracy of end-of-cycle detection through new dryer process modeling.
Dryer process modeling and algorithms can improve drying performance and energy efficiency.
Intelligent load control systems are capable of adapting the drying process to the load inside the
dryer, thus optimizing the performance, which has advantages for partial loads. The Ecodesign
study indicates that an intelligent load sensor could increase efficiency about 4-5%.32
Some clothes dryers also incorporate air flow sensors to alert user of lint filter clogging, duct
clogging, and improper installation of the duct. A manufacturer indicated that reduced air-flow
may reduce overall energy efficiency by over 30% and could be a fire hazard. However,
Consumer Reports' product testing suggested the performance of these sensors is
inconsistent.33
Ecodesign estimates that improved insulation could have energy savings of about 4% for air
condensed dryers and 3% for vented dryers. DOE cites that consumer simulations by
researchers have shown a 6% energy savings, although most manufacturers have suggested
there is little efficiency gain from insulation.34
Heat Recovery
Table 9: Energy Efficient Technology Options - Methods of Heat Recovery
Technology Option
Description
Estimated Savings
Recycle Exhaust Heat
Portion of the exhaust air stream is reintroduced at the
dryer air inlet, thus reducing the energy needed to raise
inlet air temperatures
3-6% in NIST testing
Inlet Air Preheat
Heat exchanger used to recover exhaust heat energy and
to preheat inlet air
2-6%
28 Ibid.
29 Bendt, P., Calwell, C., and L. Moorefield. 2009. Residential Clothes Dryers: An Investigation of Energy Efficient Test Procedures
and Savings Opportunities. Ecova (formerly Ecos Consulting) prepared for Natural Resources Defense Council.30 Ecos Consulting.
4 Aug. 2011. E-mail correspondence.31 Bendt, P., Calwell, C., and L. Moorefield. 2009. Residential Clothes Dryers: An Investigation
of Energy Efficient Test Procedures and Savings Opportunities. Ecova (formerly Ecos Consulting) prepared for Natural Resources
Defense Council.
30 Ecos Consulting. 4 Aug. 2011. E-mail correspondence.31 Bendt, P., Calwell, C., and L. Moorefield. 2009. Residential Clothes
Dryers: An Investigation of Energy Efficient Test Procedures and Savings Opportunities. Ecova (formerly Ecos Consulting) prepared
for Natural Resources Defense Council.
31 Bendt, P., Calwell, C., and L. Moorefield. 2009. Residential Clothes Dryers: An Investigation of Energy Efficient Test Procedures
and Savings Opportunities. Ecova (formerly Ecos Consulting) prepared for Natural Resources Defense Council.
32 PricewaterhouseCoopers. Ecodesign of Laundry Dryers. Preparatory Studies for Ecodesign Requirements of Energy-using
Products (EuP) - Lot 16. Final Report March 2009.
33 Consumers Union. "Dryer Danger" http://www.consumerreports.org/cro/video-hub/appliances/laundry~cleaning/dryer-
danger/16601904001/102824143001/ Accessed August 2011.
34 U.S. Department of Energy - Technical Support Document for Residential Dryers, EERE-2007-BT-STD-0010.
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Technology Option
Description
Estimated Savings
Inlet Air Preheat,
Condensing Mode
Use condenser to capture some of the heat in the exhaust
air stream
Up to 7% in closed cycle;
and up to 14% in open cycle
About 20-25% of the total heat input energy for a dryer is lost through the dryer vent.35 It is
possible to recycle exhaust heat, by reintroducing into the dryer air inlet, some of the hot, dry
exhaust air available late in the drying cycle when most of the moisture has already been
evaporated. A mesh filter can be used to minimize re-circulated lint. It is also possible to use a
heat exchanger to recover heat from the exhausted air and pre-heat inlet air. Heat exchangers
have the advantage of being able to be used with gas dryers because none of the exhaust air
re-enters the drum. According to the Ecodesign study, the recovery could lead to 8% energy
savings.36 DOE estimates savings of up to 6%.37
Inlet air can also be pre-heated with a condenser that captures some of the sensible and latent
heat available in the exhaust air stream. The water vapor in the exhaust air condenses out and
therefore more heat energy can be transferred than in a sensible heat exchanger system.
Research has shown that compared to a conventional air vented dryer, an open-cycle
condensing dryer is about 14% more efficient and a closed-cycle condensing dryer is 7% more
efficient.38 However, manufacturers have indicated that only minimal (1-3%) efficiency can be
attained with inlet air preheat.39 One manufacturer has also indicated a condensation dryer is
most efficient when loaded at or near full capacity, a condition not reflected in the DOE test
procedure. Although there are a number of condenser dryer models available in the U.S. (where
they are used to avoid the need for venting), these condenser dryers are not using heat
recovery, but instead use a heat exchanger to dissipate waste heat from the dryer.
An alternative approach is to compress the exhaust air in order to extract water vapor and
transfer the latent heat to the remaining gaseous stream. After water is drained from this
compressor, the pressurized air is allowed to expand and be superheated before re-entering the
drum. Some research has suggested this can be as efficient as heat pump dryer, while having a
shorter drying time.40
Heat Generation Options
Table 10: Energy Efficient Technology Options - Heat Generation Options
Technology Option
Description
Estimated Savings
Heat Pump, Electric
Only
Recirculating exhaust air back to the dryer while moisture is
removed by a refrigeration-dehumidification system
20-60%
Microwave, Electric
Only
Water absorbs microwave energy, and heating the water enough to
cause evaporation
Up to 26%
Modulating Heat
Matching the heat input rate to the load's moisture level
Up to 25%
Water-Cooling,
Ventless Electric Only
Internal water-cooled condenser heat exchanger system
condenses the water vapor in the air exiting the drum
N/A
35 Ibid.
36 PricewaterhouseCoopers. Ecodesign of Laundry Dryers. Preparatory Studies for Ecodesign Requirements of Energy-using
Products (EuP) - Lot 16. Final Report March 2009.
37 U.S. Department of Energy - Technical Support Document for Residential Dryers, EERE-2007-BT-STD-0010.
38 Ibid.
39 ik;^i
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Technology Option
Description
Estimated Savings
Indirect Heating
Heat energy derived from home's heating system
Up to 50%
(estimated by one
technology
manufacturer)
A heat pump dryer works by having a heat pump that extracts heat from the ambient air and
releases that heat at a higher temperature inside the drum. A typical heat pump uses 1 kWh of
electricity to move 2 kWh of heat.41 The air in a ventless heat pump dryer moves in a closed
loop, where air is recycled and heated again. It is possible to create an open system where a
portion of the exhaust air is vented outside. Energy savings estimates from heat pump
technology range from 20-60%. Based on several manufacturer estimates, the potential
payback period could be within the average estimated lifetime of the model. However, a paper
presented at the 2010 ACEEE Summer Study on Energy Efficiency in Buildings indicated that
based upon the current price differential for a heat pump model (estimated to be about $400),
there is only positive economic benefit for households with high clothes dryer usage (> 700
cycles/yr). For regions of the country with high electricity rates, they found there was a positive
economic benefit for households with moderately high clothes dryer usage (>500 cycles/yr).42
As of November 2011, there are no heat pump dryers available in the U.S., although they are
readily available in Europe and Australia from a number of different manufacturers. Those
models typically have a drying time of about twice as long as a typical U.S. dryer; prototypes
have been developed for the U.S. market that keep drying times closer to typical U.S. models by
using higher temperatures and airflows.43
Conventional gas dryers use a single burner at a fixed input rate and turn off and on as needed,
depending on the cycle chosen, and the temperature of the exhaust air. Modulating the heat
source can avoid overheating clothes and thereby save energy, particularly as the load
approaches dry. The aim is to match the heat input rate to the load's moisture level, as this
technology can respond subtly to changes in dryer temperature and humidity levels.44 This can
be accomplished with a modulating gas valve and additional controls.
TIAX developed a modulating gas dryer prototype that achieved up to 25% energy savings and
20-40% time-savings relative to a conventional natural gas dryer for small- and medium-size
loads.45 A second prototype developed by Cameo, a General Electric subsidiary, confirmed
shorter drying times but did not achieve equivalent energy savings.46 Modulating technologies
may provide consumers interested in lower dry times a viable option for energy savings as
opposed to heat pump technologies that tend to increase dry times and cost more.47 Heat can
also be modulated in an electric dryer using multi-element resistance heater or single element
with modulating current.
"Eco-Mode" options or other similar settings can save energy by reducing power output while
lengthening the drying process and/or stopping the dryer before clothes are completely dry.
Such settings may also incorporate a variable heat source. One manufacturer has noted a 40%
41 Bendt, P., Calwell, C., and L. Moorefield. 2009. Residential Clothes Dryers: An Investigation of Energy Efficient Test Procedures
and Savings Opportunities. Ecova (formerly Ecos Consulting) prepared for Natural Resources Defense Council.
42 Meyers, S., Franco, V., Lekov, A., Thompson, L., and A. Sturgen. Do Heat Pump Clothes Dryers Make Sense for the U.S.
Market? Presented at the 2010 ACEEE Summer Study of Energy Efficiency in Buildings. August 2010.
43 Bendt, P., Calwell, C., and L. Moorefield. 2009. Residential Clothes Dryers: An Investigation of Energy Efficient Test Procedures
and Savings Opportunities. Ecova (formerly Ecos Consulting) prepared for Natural Resources Defense Council.
44 Pescatore, P., and P. Carbone. High Efficiency High Performance Clothes Dryer: Final Report to Department of Energy. TIAX.
March 2005.
45 Ibid.
46 Bendt, P., Calwell, C., and L. Moorefield. 2009. Residential Clothes Dryers: An Investigation of Energy Efficient Test Procedures
and Savings Opportunities. Ecova (formerly Ecos Consulting) prepared for Natural Resources Defense Council.
47 U.S. Department of Energy - Technical Support Document for Residential Dryers, EERE-2007-BT-STD-0010.
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dryer energy savings from using this energy efficient mode or cycle. However, recent testing by
Ecova (formally Ecos Consulting) on behalf of NRDC, found that "eco modes" on two dryer
models provided no energy savings if clothes are dried to a similar level of dryness reached in
other modes.48 Ecova suggested a truly energy-saving "eco-mode" could be accomplished by
modulating the heater power and fan speed.
A lower heat setting can also improve energy efficiency and reduce energy consumption, since
less energy use used to heat air, cloth and metal. For example, Ecova testing for NRDC found
a 13% difference in energy consumption between the highest and lowest heat settings for one
clothes dryer model tested when drying the same load, at the expense of a 14-minute increase
in drying time.49
It is possible for the necessary heat for clothes dryers to be derived indirectly, from a home
hydronic heater system. The dryer would use some form of heat exchanger or radiator to utilize
heat from the heater system's hot water that is brought to the dryer through plumbing. One
source claims that energy savings up to 50% and time-savings up to 41% are possible.50
Component Improvements
Table 11: Energy Efficient Technology Options - Component Improvements
Technology Option
Description
Estimated Savings
Improved Motor
Efficiency
Improving the overall efficiency of the motor or using a split motor
design to adjust airflow rates
1-5%
Improved Fan
Efficiency
Increasing blower efficiency
N/A
Many dryers use a single motor to rotate the drum and move the air using a fan. According to
manufacturers, potential efficiency gains can result from improving the motor design, which
could increase savings by 1-5%, and through using a split motor design and decoupling the two
functions of rotation and airflow, which could theoretically improve efficiency.51 Changing the
blade curves of the blower fan could also possibly lead to efficiency gains, but these gains have
not been quantified.52
Standby Power Improvements
Table 12: Energy Efficient Technology Options - Standby Power Improvements
Technology Option
Description
Estimated Savings
Switching Power Supply
Better power supplies on the control board
N/A
Transformerless Power
Supply with Auto-Powerdown
Implementing a transformerless power supply for the
microprocessor logic, as well as a conventional power
supply activated when the dryer is in active mode
N/A
48 Denkenberger, D., Mau, S., Calwell, C. and Wanless, E. 2011. Residential Clothes Dryers: A Closer Look at Energy Efficiency
Test Procedures and Savings Opportunities. Ecova prepared for Natural Resources Defense Council.
49 Bendt, P., Calwell, C., and L. Moorefield. 2009. Residential Clothes Dryers: An Investigation of Energy Efficient Test Procedures
and Savings Opportunities. Ecova (formerly Ecos Consulting) prepared for Natural Resources Defense Council.
50 U.S. Department of Energy - Technical Support Document for Residential Dryers, EERE-2007-BT-STD-0010.
51 Ibid.
52 Iki^l
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Energy used to operate dryer controls in standby mode varies between 1.4 to 3.1 watts, adding
about 180-400 kWh over the life of the dryer.53 A switching power supply could provide a
modest reduction in standby power use and there are a large number of dryers on the market in
the U.S. that already incorporate a switching power supply.54
HVAC Effects
A clothes dryer releases heat to the surrounding environment. Conventional vented dryers also
vent air outside the building. The associated heating, ventilation, and air conditioning (HVAC)
impact of dryers depends upon a number of variables including climate and placement of a
dryer (i.e., in a conditioned or unconditioned space). It is an area of ongoing research. In a
recent rulemaking analysis, DOE estimated the impact of home heating/cooling loads on total
clothes dryer energy use is about 6% for vented dryers and 11% for ventless dryers, while
concluding that the HVAC impact is similar across different levels of dryer efficiency.55 There
could also be energy savings from using outside air intake in the summer. When coupled with
heat recovery (which would allow the outside air intake to be advantageous in both summer and
winter), initial estimates have suggested the savings may be as much as 2.35 kWh per load.56
Site v. Source Considerations
Gas dryers not only tend to have lower operating costs for consumers, but allow for significant
savings of C02 emissions compared to electric dryers since they use primary energy, and
therefore avoid the efficiency losses of electric dryers as a result of the electricity generation
and distribution. In the clothes dryer test procedure, natural gas consumption is converted into
an equivalent electrical consumption on a site-basis, which does not take into account these
generation and distribution losses.
To more fully compare savings between electric and gas dryers, some stakeholders have
suggested methods that focus on source BTUs, total C02 emissions, or energy cost. The
standard natural gas dryer uses less source energy, costs less, and emits less carbon dioxide
per pound of water removed than most other options, potentially including heat pump dryers.
However, the efficiency (as measured by EF or CEF) of gas dryers is generally lower than that
of standard electric dryers.57
5. Energy and Cost Savings Potential
The only two known databases of clothes dryer energy data relevant to the U.S. market are
maintained by the California Energy Commission (CEC) and Natural Resources Canada
(NRCan). However, the data given from these databases are of EF levels measured under the
DOE test procedure currently used by manufacturers to comply with federal appliance
standards. The savings analysis below considers the efficiency of dryers as measured by CEF
and rated under the 2011 amended DOE test procedure.58
53 Ibid.
54 Ibid.
55 U.S. Government, Federal Register / Vol. 76, No. 4 / Thursday, January 6, 2011 / Rules and Regulations page 972-1036
56 Bendt, P., Calwell, C., and L. Moorefield. 2009. Residential Clothes Dryers: An Investigation of Energy Efficient Test Procedures
and Savings Opportunities. Ecova (formerly Ecos Consulting) prepared for Natural Resources Defense Council.
57 Ibid.
58 As noted in Section 4, this amended DOE test does not address the effectiveness of auto termination, though manufacturers and
efficiency advocates have filed a petition requesting the further test procedure revisions to address auto termination be considered
by DOE.
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Initial estimates of energy and C02 savings were developed for two efficiency scenarios. The
first scenario assumes energy savings of 10%, achieved using a collection of designs and
technologies highlighted in the previous section. The second scenario assumes more
aggressive energy savings of 30% for standard electric dryers and 20% for gas dryers that
could be realized by achieved using more advanced technology such as heat pumps or
modulation technology.
Baseline CEF levels of 3.25 (for a gas dryer) and 3.66 (for an electric dryer) were used based
on an estimated shipment-weighted average of the least efficient models on the market. These
levels are slightly lower than the 2015 federal minimum efficiency standards levels and assume
a standby power consumption of 1.5 W. For these initial savings estimates, efficient CEF levels
of 3.61 (gas) and 4.06 (electric) represent a 10% energy savings over baseline. CEF levels of
4.06 (gas) and 5.22 (electric) represent a 30% energy savings for electric dryers and 20%
energy savings for gas dryers.59
Under the first scenario, the estimated annual household savings ranges from $3 (for gas
dryers) to $7 (for electric dryers), which translates into lifetime savings of $47 to $114.60 The
second, more aggressive scenario offers annual savings that range from $6 (gas) to $21
(electric), which provides lifetime savings of $95 to $342.61
Assuming 25% of dryers sold in the U.S. were more efficient,62 the first-year savings on a
national scale ranges from 86,000 MWh and 76 billion Btu (first scenario) to 256,000 MWh and
152 billion Btu (second scenario). These savings translate into annual C02 emission reductions
on the order of 141 to 412 million lbs per year (assuming a conversion of 1.54 lbs C02 per kWh
and 117 lbs C02 per MBtu).
6. Key Market Players
Trade Associations
The Association of Home Appliance Manufacturers (AHAM) aims to enhance the value of the
home appliances industry through leadership, public education, and advocacy. AHAM provides
services to its members including government relations, certification programs for room air
conditioners, dehumidifiers, and room air cleaners; an active communications program; and
technical services and research.
Manufacturers
Common clothes dryer brands on the U.S. market include Frigidaire (Electrolux), GE, Kenmore,
LG, Maytag, Samsung, and Whirlpool. Whirlpool is the largest U.S. manufacturer of clothes
dryers with well over half the market share (Maytag, Whirlpool, and Kenmore brands).
Energy Efficiency Program Sponsors
A number of utilities across the nation have expressed interest in promoting efficient clothes
dryers to customers through incentives.
59 Note: CEF levels set here are used for illustrative purposes, to demonstrate 10% and 30% improvements in energy savings. CEF
level in Scenario 2 for gas is higher than the maximum technology level set by DOE in their TSD documents (3.61 CEF). CEF level
in Scenario 2 for electric is lower than the maximum technology level set by DOE in their TSD documents (5.42 CEF).
60 Assumes $0.1089/kWh (Source: 2011 U.S. Electric Rate: Energy Information Administration, Annual Energy Outlook 2011 (Early
Release) edition, (converted from 2009 to 2010 dollars)), $10.50/MBTU (Source: 2011 U.S. Electric Rate: Energy Information
Administration, Annual Energy Outlook 2011 (Early Release) edition (converted from 2009 to 2010 dollars)) and,
and 16 year lifetime (Source: 2011 DOE Clothes Dryer Final Rule).
61 Ibid.
62 Unit shipments are estimated based on 2010 U.S. Appliance Shipment Statistics from Appliance Magazine.
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7. Stakeholders and Existing Programs
International Level
European Union
Virtually all conventional electric dryers in the EU have migrated steadily upward from the F and
G-rating to the C-rating since the EU adopted categorical labeling. Some units with advanced
sensing capabilities have been able to achieve a B-rating; A-rated units are almost all heat-
pump models. Gas dryers are excluded from the EU label.
European Eco-Design Requirements for Energy-Using Products (EuP)
Under a Directive for defining eco-design requirements of energy-using products, the European
Council and European Parliament completed a preparatory study of clothes dryers in March
2009 analyzing technical, environmental, and economic aspects. A proposed draft regulation
released in June 2010 set forth that the energy label shall be revised, but no Eco-design
requirements shall be set for clothes dryers.
Other International Programs
Canada has a mandatory EnerGuide label for clothes dryers and minimum energy efficiency
regulations. Australia also has an established Star-rating scheme for clothes dryers.
Collaborative Labeling and Appliance Standards Program (CLASP)
Established in 1999, CLASP's mission is to serve as the primary resource and voice for
appliance energy efficiency worldwide. CLASP recently chose to focus on energy efficient
clothes dryers, a technology with a strong potential to generate energy savings and carbon
reductions.
U.S. Initiatives
Super Efficient Dryer Initiative (SEDI)
The Super Efficient Dryer Initiative (SEDI) was launched in North America to bring together
energy efficiency program providers, manufacturers and governments and to learn from
European experiences. SEDI aims to accelerate the market introduction of energy efficient
clothes dryer technologies.
EPA ENERGY STAR Emerging Technology Award 2012
EPA created the ENERGY STAR Emerging Technology Award to recognize innovative
products that face initial barriers to U.S. market entry, such as high cost or low consumer
awareness. As such, these products may not be immediately eligible for consideration within an
ENERGY STAR labeling program but still have the potential to significantly reduce greenhouse
gas emissions. The ultimate goal of the award is to raise the profile and demand for the
technology, so that costs are reduced and the technology becomes more widely available.
EPA elected advanced clothes dryers to be the 2012 Emerging Technology Award category.
The Award seeks to encourage manufacturers to bring super efficient clothes dryer technologies
to the market within the next year.
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On-Going Research and Technology Development
Peaked interest in energy efficient clothes dryers in the last few years has resulted in multiple
extensive research and development studies. Table 13 provides a brief overview some on-
going clothes dryer research initiatives in the U.S.
Table 13: Summary of Clothes Dryer Research Initiatives
Organization
On-going and Future Research
GE
GE was granted a $24.8 million Advanced Energy Manufacturing Tax Credit the U.S.
Department of the Treasury through the Economic Recovery Act, including $4.8 million
under the heading, "GE will manufacture a commercially viable Heat Pump Clothes
Dryer for residential application in Louisville, Kentucky. GE's expects production of
energy-efficiency dryers in the U.S. to commence in 2013.
Porticos
On June 17th, 2010, the DOE awarded $1.7 million to Porticos, a product development
engineering firm in Morrisville, NC to develop a "Next-Generation Clothes Dryer
(NGCD)" designed to provide equivalent performance with a lower energy expenditure
than conventional vented electric clothes dryers. The prototype is based on a novel
heat-reclamation scheme (not a heat pump) that aims to use only 50% of the energy of
a conventional dryer, place little to not burden on the HVAC system, and dry clothes in
the same amount of time as a comparably-sized conventional dryer.
Ecos
Consulting
(now Ecova)
Ecos Consulting, on behalf of NRDC, conducted research in 2009 on the real-world
energy use of clothes dryers, and provided recommendations based off of available
savings opportunities.
In 2011, Ecos Consulting (now Ecova) conducted additional research assessing the
efficiencies of clothes dryers using the amended DOE test procedure, as well as an
Ecos-developed test procedure more reflective of real-life conditions.
For CLASP, Ecova is expanding both laboratory and field studies of conventional and
European heat pump dryers later this year.
NEEA
Northwest Energy Efficiency Alliance (NEEA) is conducting a study of dryer use in 80
households in four states a part of a larger residential sub- metering study to better
understand consumer usage behaviors and actual electricity consumption.
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References
Association of Home Appliance Manufacturers (AHAM). 2008. De-identified Clothes Dryer Data
-Collected December 2007 for DOE Rulemaking. Updated 4/11/2008. April 11, 2008.
Docket No. EERE-2007-BT-STD-0010, Comment Number 14.
Appliance Magazine. 2010 U.S. Appliance Shipment Statistics. April 2010.
California Energy Commission (CEC). Appliance Efficiency Database. Sacramento, CA. 2008.
www.appliances.energy.ca.gov
Badger C., and C. Granda. Super Efficient Dryer Initiative Update. Summer 2011.
Bendt, P. Are We Missing Energy Savings in Clothes Dryers? Presented at the 2010 ACEEE
Summer Study of Energy Efficiency in Buildings. August 2010.
Bendt, P, Calwell, C., and L. Moorefield. 2009. Residential Clothes Dryers: An Investigation of
Energy Efficient Test Procedures and Savings Opportunities. Ecova (formerly Ecos Consulting)
prepared for Natural Resources Defense Council.
Denkenberger, D., Mau, S., Calwell, C. and E. Wanless. 2011. Residential Clothes Dryers: A
Closer Look at Energy Efficiency Test Procedures and Savings Opportunities. Ecova prepared
for Natural Resources Defense Council.
Joslin, D.F.. Reversing Clothes Dryer and Method. U.S. Patent No. 5,555,645, issued
September 17, 1996.
European Commission. Commission Directive 95/13/EC of 23 May 1995 implementing Council
Directive 92/75/EEC with regard to energy labelling of household electric tumble dryers.
http://ec.europa.eu/energy/efficiency/labelling/energy_labelling_en.htm
European Parliament and Council. Directive 2005/32/EC of the European Parliament and of the
Council of 6 July 2005 establishing a framework for the setting of ecodesign requirements for
energy-using products and amending Council Directive 92/42/EEC and Directives 96/57/EC
and 2000/55/EC of the European Parliament and of the Council. Can be downloaded at:
http://eur-lex.europa.eu/LexUriServ/LexUriServ. do?uri=CELEX:32005L0032: EN: NOT
European Parliament and Council. Directive 2009/125/EC of the European Parliament and of
the Council of 21 October 2009 establishing a framework for the setting of ecodesign
requirements for energy-related products (recast).
Meyers, S., Franco, V., Lekov, A., Thompson, L., and A. Sturgen. Do Heat Pump Clothes
Dryers Make Sense for the U.S. Market? Presented at the 2010 ACEEE Summer Study of
Energy Efficiency in Buildings. August 2010.
Nipkow, J., Josephy, B., Eric Bush E., and A. Michel. Tumble Driers: Recommendations for
policy design. September 2010. Available at: www.topten.eu
Nipkow, J., Josephy, B., Bush, E., Werle, R., and C. Granda. Energy-efficient heat pump dryers
- European experiences and efforts in the U.S. and Canada. May 2011.
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Pescatore, P., and P. Carbone. High Efficiency High Performance Clothes Dryer: Final
Report to Department of Energy. TIAX. March 2005.
PricewaterhouseCoopers. Ecodesign of Laundry Dryers. Preparatory Studies for Ecodesign
Requirements of Energy-using Products (EuP) - Lot 16. Final Report March 2009.
Super Efficient Dryer Intiative (SEDI). Market Potential for Energy Efficient Residential
Clothes Dryers in North America. Version 3.0. December 2010
Topten International Group. Top Ten Website of Energy Efficient European Appliances.
www.topten.info
U.S. Department of Energy - Energy Information Administration (EIA). Residential Energy
Consumption Survey 2001, 2005, 2009 Public Use Data Files.
U.S. Department of Energy - Technical Support Document for Residential Dryers, EERE-
2007-BT-STD-0010.
U.S. Government, Federal Register / Vol. 76, No. 77 / Thursday, April 21, 2011 / Rules and
Regulations page 22454
U.S. Government, Federal Register / Vol. 76, No. 4 / Thursday, January 6, 2011 / Rules and
Regulations page 972-1036
U.S. Department of Energy /10 CFR Part 430/ Docket Number EERE-2011-BT-TP-0054/ RIN:
1904-AC63/August 2011.
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