A high-efficiency, air-to-air, split-system residential heat pump of nominal 3-ton capacity was instrumented and tested in the heating mode under laboratory conditions. The coefficient of performance (COP) and heating capacity of the system were measured during steady-state, dehumidifying, and frosting/defrosting conditions, with major emphasis placed on the dynamic frosting operation of the system. The study encompassed an evaluation of system and component performance for ambient temperature levels between 47 and 17°F (8.3 and –8.3°C) and for discrete relative humidity levels ranging from 50 percent to 90 percent.

Seasonal analyses were conducted for determination of the magnitude of frosting losses and defrosting losses for heat pumps having a one-row spine-fin outdoor heat exchanger.