Performance Evaluation of Two-Stage Air-Source Heat Pump for Cold Climates considering the effects of Frosting

Air-source heat pumps (ASHPs) are energy-efficient alternatives to conventional natural gas heating systems. At very low ambient temperatures, the coefficient of performance (COP) of an ASHP drops drastically with rising refrigerant discharge temperatures at the compressor exit. Two-stage ASHPs have a staged compression process, which improves the COP and reduces discharge temperatures. The current study investigates the performance of a two-stage ASHP used to supply heat to an office building in Saskatoon, considering the effects of frosting on the evaporator. The average annual COP of two-stage ASHP is 2.04, while frosting and defrosting cycles increase energy consumption by 12.5%. The GHG emissions from two-stage ASHP operation are compared with natural gas heating systems indicating that two-stage ASHPs can reduce emission by 8% compared with natural gas heating systems in Saskatoon.