Performance evaluation of air source heat pump under unnecessary defrosting phenomena for nine typical cities in China

Defrosting under unnecessary conditions is a typical and undesirable operating phenomenon for air source heat pump (ASHP). This paper aims to evaluate the ASHP performance under unnecessary defrosting phenomena in different regions of China. Firstly, energy loss for two kinds of unnecessary defrosting phenomena was quantified by 60 days field test. Secondly, a method was developed to predict unnecessary defrosting times. The prediction accuracy can be controlled within 10%. Furthermore, the ASHP performance of unnecessary defrosting was evaluated for nine typical cities in China. It was found that the average unnecessary defrosting rate was 53% for northern cities, 38% for mid-land cities, and 15% for southern cities during a heating season. Correspondingly, the total energy loss was 233 MJkW−1, 161 MJkW−1, and 44 MJkW−1. These results indicate that unnecessary defrosting processes should not have been ignored. It is a valuable work to improve the defrosting control method.