Investigation on Current Control Defrosting Method of Multi-split Variable Refrigerant Flow System

There are many indoor units in the multi-split variable refrigerant flow (VRF) system. The continuous operation of heating in winter is longer than that of ordinary household air conditioning, so that the precise defrosting control is energy-saving and improves the comfort for users. In this paper, during the experiment, the indoor temperature was 20℃, the outdoor dry bulb temperature was 7℃, 0℃, -5℃ and -7℃, and the wet bulb temperature was 6℃, 0℃, -6℃ and -8℃ respectively. The defrosting temperature, liquid pipe temperature, defrosting time and the current value change rate of the condenser fan were compared when the heating capacity was reduced by 15%. The experiments showed that the current change rate was little affected by the outdoor temperature. It was only related to the frost mass, which could reflect the real frosting situation. Then through the maximum cycle heating capacity, air supply temperature and capacity decay rate, the most reasonable defrosting time could be seen when the fan current change rate was 15% - 20%. Compared with the traditional defrosting, the current control defrosting had a higher heating capacity. Under the four working conditions, the heating cycle capacity was increased by 2.3%, 4%, 2.8% and 5.8% in turn. At the same time, the control was precise. The phenomenon of thermosensor falling off and the uneven frost formation had little impact on the current control defrosting.