Performance evaluation of the variable refrigerant flow (VRF) air-conditioning system during the heating-defrosting cyclic operation

摘要

This paper shows the performance evaluation of the variable refrigerant flow (VRF) air-conditioning system subjected to very low outdoor air temperature at which the heating-defrosting cyclic operation occurred. The objectives of the study are to know the effect of the heating-defrosting cyclic operation in the VRF air-conditioning performances and of the indoor environment thermal conditions. The one outdoor unit's and two indoor units' VRF air-conditioning system was used as a test specimen in the controlled testing chambers in which temperature and humidity were controlled. Several test cases were done covering from constant dry bulb temperature with different wet bulb temperature and for both dry bulb temperature and wet bulb temperature different. The results of the study show that the heating-defrosting cyclic operation affected the performance of the VRF air-conditioning system. It shows that the heating time changes depend on both dry bulb and wet bulb temperatures. It shows that the defrosting time is almost the same for different dry bulb and wet bulb temperatures for different heating times. The cyclic heating-defrosting operation affected the indoor air temperature by lowering the indoor air temperature during defrosting. Based on the results, necessary measures are needed to address the effect of the defrosting in the VRF air-conditioning system performance and of the indoor thermal environment conditions. The heating-defrosting cyclic operation is expected to occur when the VRF air-conditioning system is installed in an actual building in a temperate climate, and in the performance evaluation of the different VRF air-conditioning systems under these conditions, it is important to know how it affects the system's operation behavior, energy consumption and support of the indoor environment thermal conditions.