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Published: 1978

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An electric heat pump water heater with an operating efficiency, E/sub R/, of 2.5 in average conditions of 70 to 75°F ambient air and 55 to 60°F supply water has been designed. With losses taken into account, the coefficient of performance (COP) is 2.8 or within 10% of the design objective. Separate heat pump designs are available for new water heaters and for retrofitting of existing ones. For both models, the compressor, evaporator, fan and controls are mounted in a round cabinet set on top of the water heater. The condenser is a dual tube direct immersion type which enters the tank through a special 4-in. hole in the top of new tanks. For retrofit units, the condenser is in the form of a helix and is screwed into the tank through the hole normally used by the lower resistance element. Early estimates for the cost of the device are between $200 to $250 more than for an electric resistance water heater. Using this estimate, the payback for many applications will be between one and two years with some being less than one year. The payback period is dependent on the amount of hot water consumption and the price of electricity. In warm climates, the benefit/cost ratio will be improved by higher efficiency from warmer ambient air and by the value of free air conditioning and dehumidification provided while the unit is operating. In colder climates, the improved efficiency from colder supply water and the higher operating savings from higher kilowatt-hour use because of the colder water tend to offset the effect of the less favorable climate. A field demonstration of one hundred water heater heat pumps is planned in which each of 20 utilities will purchase, install and service five units, and install, service and monitor instrumentation packages supplied by DOE. This project will deterine the annual COP of each unit and its impact on the heating and cooling load of the house.