Preliminary Assessment of Residential Exhaust-Air Heat Pump Applications in the Pacific Northwest

摘要

We provide a technical and economic assessment of residential exhaust-air heat pumps for water heating with option for space heating. Compact one-cabinet heat-pump units containing a hot water tank with refrigerant condenser, exhaust fan, refrigerant evaporator, compressor and controls have recently become available on the US market. The study concerns applications in the Pacific Northwest with three representative locations: Portland, Oregon, Spokane, Washington and Missoula, Montana. Our approach is to simulate system performance for a full year in both a typically-insulated and a well-insulated house. TRNSYS, a transient building system simulation package, is used allowing detailed simulation of heat pump (and other HVAC equipment) operation including control action (on, off and hysteresis effects). Ventilation and energy performance of the heat-pump houses is compared to that of 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 range from about 5000kWh in Portland to about 7500 kWh in Missoula if the house with the heat pump has a lower average ventilation rate than the naturally ventilated house used as a basis for comparison. An economic analysis indicates that heat pump installations are cost competitive from the homeowner's point of view in the colder interior parts of the Pacific NW. The impact of exhaust ventilation on indoor radon concentrations and radon entry rates into houses is examined using recently-developed models. (ERA citation 12:026933)