Heat Pumps for Cold Climates

Abstract

The majority of air-source heat pumps (ASHPs) are installed in moderate to warm areas of the United States, mostly south of the Mason-Dixon Line. Two major issues make conventional ASHPs unattractive as a heat source in cold climates. First, buildings in colder climates often have appreciably smaller design cooling loads than design heating loads. Second, ASHP heating capacity and coefficient of performance (COP) decrease as the outdoor temperature, T o , decreases because the temperature lift across the compressor increases. For these reasons, conventional ASHPs sized to meet cooling loads cannot meet the full heating loads at lower T o , necessitating extensive use of costly, and energy-inefficient, electric resistance heating. Conceptually, a heat pump designed for a cold climate would have sufficient capacity to meet heating loads around T o ~0°F at a reasonable COP, and would require limited (ideally, no) electric-resistance heat on an annual basis. Such a design would enable effective use of heat pumps in much colder climates than current designs. For example, it could extend the region where heat pumps could reduce heating primary energy consumption or cost over much of the northern U.S. Several design modifications and technologies have been proposed or introduced (alone and in combination) for coldclimate heat pumps. Sizing the ASHP for heating instead of cooling