Frosting-defrosting performance variations of air source heat pumps with the type of refrigerants: R410A and R32 as an example

Abstract

Refrigerant substitution is an important topic in developing air-source heat pumps (ASHPs). The new refrigerants were selected based on their environmental impact indices, thermodynamic performance, safety, and economy. However, their effects on frosting have always been neglected. To quantify the variations in the frosting–defrosting performance of ASHPs using different refrigerants, twenty-one ASHPs from nine manufacturers were selected and tested at 2 ℃/1 ℃. The most commonly used refrigerants, R410A and R32, were employed in this study. Variations in frosting operating time (Tf) and optimal defrosting initiation time (Topt) were investigated for different values of the characteristic indice for configuration and operation (CICO). The results show that the frosting–defrosting performance of ASHPs is significantly affected by the type of refrigerant. The frosting rate of ASHPs using R32 was 31%–48% faster than that of R410A for a similar heating capacity. The Topt of ASHPs using R32 should be advanced by 29%–35%. Based on the experimental results, two prediction models for the Tf and Topt of ASHP using R410A and R32 were established. They predicted the Tf and Topt values by calculating the CICO values, which can be used to inform the design of frost-suppressing mechanisms and the implementation of accurate defrosting procedures for ASHPs.