Experimental study on the effects of melted frost icing on the operating performances of air source heat pump

Abstract

Defrosting operation is always used to solve its frosting problem at a high humidity environment for air source heat pump units (ASHPs), and at the end of defrosting operation, the residual melted frost may exist on the surface of outdoor coil and freeze into ice in sequent frosting. However, till now, as the residual melted frost icing environment is difficult to create, its quantitative influences on the heating performance of ASHPs is still unknown, especially at different icing levels. To resolve this issue, a control strategy was firstly proposed to make it possible for the residual melted frost to ice. Then, based on the control strategy, the effect of five different icing levels on operating performances of an ASHP unit were investigated. Results indicated that ice can promote the frost formation, and the operating performances of ASHP unit were significantly affected by different icing levels. When the percentage of iced outdoor coil surface was increased from 0% to 15% and 35%, the output heating capacity of ASHP unit was decreased by 11.2% and 23.8%, and meanwhile the COP of ASHP unit was decreased by 7.7% and 16.1%, respectively. The results can assist with the defrosting control optimization of practical products.