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The frosting type and frosting degree of the outdoor heat exchanger of air source heat pump (ASHP) in the heating season are greatly affected by the local environmental temperature and humidity. China has a vast territory, and the climate varies greatly in different regions. Therefore, when the ASHP is running in different climate zones for heating in winter, there are significant differences in the frosting type and frosting degree. In order to achieve deeper understanding of frost formation and provide more accurate guidance for the suitability application of antifrosting and defrosting technologies, a study on the division of frosting type and frosting degree was performed in this work. Based on the three-phase diagram of water and combined with the theory of phase change dynamics, the outdoor heat exchanger of the ASHP in the heating season was divided into four states: neither frosting nor condensation, condensation, condensation frosting, and sublimation frosting, and the proportion of each state in a typical city in different climate zones was calculated. The results showed that more than 80% of the heating seasons in Nanjing, Shanghai, Wuhan, Changsha, Xi’an, and Harbin had the frosting phenomenon. Sublimation frosting was the main frosting type in Xi’an, Beijing, and Harbin, while Chongqing was all condensation frosting. Moreover, a frosting model was developed and the frosting degree was divided into mild frosting, moderate frosting, and heavy frosting, according to the performance attenuation of the ASHP under frosting conditions. The proportion of each frosting degree in a typical city was achieved. About 50% of the heating seasons in Nanjing and Changsha were distributed in the heavy frost area and 100% in Chongqing.

Division of Frosting Type and Frosting Degree of the Air Source Heat Pump for Heating in China