Developing a new frosting map to guide defrosting control for air-source heat pump units

The development of a new frosting map for air-source heat pumps (ASHPs) based on a temperature-humidity chart is reported in this paper. Through a parametric analysis, two boundary lines (a condensing line and a frosting line) were obtained, dividing the map into three regions: a non-frosting region, a condensing region and a frosting region. Using the simulation results from a generalized numerical model of frost growth, the frosting region was further divided into three indicative zones representing different frosting levels: a severe frosting zone, a moderate frosting zone (I, II) and a mild frosting zone (I, II). Lab and field tests were conducted in order to verify the correctness of the zoning and to obtain indicative defrosting intervals for ASHPs operated at different zones. Based on the test results and using the developed map, reference defrosting intervals were suggested for different frosting zones, and they can be used in conjunction with a conventional defrosting control method to avoid potential mal-defrosting.