Assessment of residential exhaust-air heat pump applications in the United States

Abstract

We provide a technical and economic assessment of residential exhaust-air heat pumps for water heating with an option for space heating. Compact one-cabinet heat pump units containing a hot water tank with refrigeration condenser, exhaust fan, refrigerant evaporator, compressor, and controls have recently become available on the U.S. market. The emphasis is on U.S. applications with three representative climates: moderate (Northwest), cold (Midwest), and hot and humid (Southeast). Our approach is to simulate detailed system performance for a full year for two typical houses equipped with the heat pump. Ventilation and energy performance of the heat pump houses is compared to the same houses equipped with air-to-air heat exchangers and to naturally ventilated houses. Exhaust-air heat pumps are found to provide a nearly constant ventilation rate throughout the year, as opposed to the natural ventilation rate that is found to be highly variable. Energy savings realized with the heat pumps are greater than those obtained with heat exchangers. Both heat pumps and heat exchangers are cost-competitive with natural ventilation in cold climates and are clearly uneconomical in hot and burned climates with present electric rate predictions.