Parametric study of a room air conditioner during defrosting cycle based on a modified defrosting model

Abstract

Reverse cycle defrosting is widely used in room air conditioner (RAC) system. The objective of this study is to investigate system transients during defrosting from a numerical simulation perspective and provide control guidance for maximizing defrosting performance without wet compression. For this purpose, a system-level defrosting model for RAC system is developed in line with its practical application. A modified first-principle hot gas defrosting model is developed to eliminate the mass non-conservation error. Model validation against experimental data demonstrates the model could predict the system transients within reasonable accuracy. Wet compression during defrosting under basic control strategy is captured in the simulation and experiments. The model is applied to evaluate the effect of compressor frequency and electronic expansion valve (EEV) opening on defrosting. The results show that wet compression could be eliminated by decreasing EEV opening. The compressor frequency has little impact on the time point when wet compression occurs, however, it could weaken wet compression by reducing defrosting duration. Based on the operation maps, the EEV opening and compressor frequency are recommended in the range of 40–60 % and 70–90 Hz, respectively, which could guarantee safe compression with short defrosting duration and low energy consumption.