Investigation of Frosting Performance on Air-Sourced Heat Pump Evaporator for Cold Climate

Frost formation on the evaporator surface of air-source heat pumps (ASHPs) operating in cold climates significantly degrades heat transfer performance and increases compressor power consumption. Accurate prediction of frost accumulation and the associated defrosting thermal load is therefore essential for evaluating ASHP operation under low-ambient-temperature conditions. This study presents a detailed simulation investigating the spatial temperature distribution across finned-tube evaporator surfaces and quantifying frost-formation dynamics under non-uniform air-velocity profiles and dynamic psychrometric air properties. The evaporator surface is meticulously discretized into multiple computational segments, enabling a three-dimensional temperature field analysis. This field is obtained by simulating discrete fin-tube segments with boundary conditions that represent the interactions among ambient air, refrigerant flow, and non-uniform air velocity. The local surface temperature, precisely derived from this analysis, is then used as an independent variable within a condensation-based frost growth formulation to estimate local frost thickness, total accumulated frost mass, and the corresponding defrosting thermal load. These decision variables are primarily determined by two factors: the ambient dry-bulb temperature and the local air velocity. The defrosting thermal load notably increases with rising air velocity and decreases as the dry-bulb air temperature rises. The proposed modeling approach provides a computationally efficient tool for predicting frost formation and evaluating evaporator thermal behavior of air-source heat pumps in cold climates. By explicitly resolving the temperature distribution across the fin surface and linking it to frost growth dynamics.