The "Drop-In" Residential Heat Pump Water Heater

A market-driven solution to efficient electric heating

The Problem: How to Convince Consumers to Save Energy in Water Heating

About half of all domestic water heating is done with electric resistance storage water heaters. The most efficient resistance water heater has an energy factor (EF) of 0.95, only 5% below the maximum efficiency possible for that type of water heater. Yet by using electricity to "pump heat" from the surrounding space, the residential heat pump water heater (HPWH) can attain much higher efficiencies, reducing the electricity needed for water heating by at least half.

Despite such high efficiencies, today's U.S. market for residential HPWHs is small and stagnant (less than 2,000 units/year) and is served by only two or three manufacturers.

Why has the HPWH market remained small? Assessments conducted by DOE and others point to a number of issues:

The Solution: The "Drop-in" HPWH

The heat pump water heater

Building from a strong understanding of these technical and market issues, Enviromaster International (EMI) and Arthur D. Little, with support from the DOE ENERGY STAR Program through Oak Ridge National Laboratory, are developing a unique "market-optimized" ambient-air HPWH aimed at the large electric water heater replacement market.

Design Features

Market-Driven Features
Cost $375–400 above installed cost of conventional 50-gallon electric water heater
Economics Potential for 1-year simple payback
Warranty/lifetime target EMI is designing for a 10-year lifetime, since the HWPH is based largely on refrigerator components
Sizes 50-gallon tank to be used in field test; final product to be offered in 50- and 80-gallon tank sizes
Performance Efficiency based on DOE test procedure should be above EF = 2.0
Flexibility Can be installed in locations where there is no floor drain (e.g., a closet); where a drain is available, the HPWH will provide dehumidification, space cooling, and improved performance
Installation requirements Design minimizes or eliminates need for water heater piping changes. Uses conventional electrical water heater circuit, allowing easier installation
Maintenance requirements Minimal; evaporator air filter needs periodic cleaning
Noise HPWH uses a small, ducted evaporator fan; noise not expected to be an issue
Hot water runouts minimized At least one resistance element will be retained in the final design to meet unusually heavy draws; both elements will be retained in field test trials

National Field Testing and Demonstration

National field testing is scheduled to begin in FY 1999 with participation by selected utilities. The utilities will identify two or three test homes, install HPWH and monitoring instrumentation, administer participant surveys, remove or replace water heat at conclusion of the experiment, and assist DOE in follow-on demonstration and promotion activities.

EMI will provide HPWHs for the field test, maintain and repair the units, implement design improvements on the basis of field tests results, obtain product certification and approval, and develop product support materials (installation instructions, maintenance, etc.).

DOE will develop field test criteria, protocol, and coordinate overall testing; provide the instrumentation for utility installation; collect and analyze the data and share it with the utility participants; provide performance data and analysis to EMI; initiate follow-on field demonstration and promotion under DOE ENERGY STAR Program; and draft installation guidelines and performance predictions to support marketing efforts.

Following this initial field test, a larger field demonstration and promotion effort will be conducted. This will include open utility participation with 200–300 HPWH units and selected monitoring in partnership with the utilities. It is anticipated that the HPWH will be launched commercially in 2000.

For more information, contact

John Tomlinson
Oak Ridge National Laboratory
P.O. Box 2008, MS 6070
Oak Ridge, TN 37831-6070

Phone Number: (423) 574-0291
Fax Number: (423) 574-9338

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