Experimental study about frost formation and growth in the evaporator of an air-to-water heat pump

• Characterization of frost formation process in finned-tube heat exchangers. • Analysis of the frost growth under real conditions for air-to-water heat pump. • Evaluation of air flow reduction on the degradation of the heat pump performance. • Criterion to estimate the defrost initiation based on the evaporation temperature. Frost formation in the evaporator of air-to-water heat pumps (AWHPs) is one of the most crucial aspects that affect the efficiency of these systems. This paper analyzes the frost formation and growth in a finned-tube evaporator to monitor the degradation of a commercial heat pump's performance. The analysis includes the characterization of the various frost formation processes that may occur in real operating conditions, as well as a detailed examination of the water vapor sublimation process as a function of evaporation temperature and relative humidity. The results are presented in terms of the air-side pressure drop, evaporation temperature evolution, and the amount of condensed water recovered. From these results, key factors in the evolution of this process, like the frost structure, are critical in the system performance degradation, and parameters like air-side pressure drop are not enough to determine the optimum time for initiating the defrost process.