Performance evaluation of the variable refrigerant flow (VRF) air-conditioning system subjected to partial loadings at different outdoor air temperatures

This paper shows the performance evaluation of the variable refrigerant flow (VRF) air-conditioning system at different outdoor air temperatures during cooling and heating operations. The purpose of this study is to determine the real performance of the system when operating at different outdoor temperatures. The one outdoor unit's and two indoor units' VRF 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 partial to full thermal loadings for the different outdoor air temperatures. The results showed that the outdoor air temperature much affected the performance of the VRF air-conditioning system. It showed that during the cooling operation, as the outdoor air dry bulb temperature increases, the coefficient of the performance ratio decreases. In the heating operation, as the outdoor air dry bulb with corresponding wet bulb temperature decreases, the coefficient of the performance ratio decreases. The defrosting mode, which occurs during the heating operation, affects the indoor chamber's temperature as the air temperature becomes very low due to the indoor units having become an evaporator. The results of the study showed the importance of the VRF air-conditioning system performances at different outdoor air dry bulb and wet bulb temperatures. Hence, it is important to consider the outdoor air temperatures when calculating the energy consumption of the VRF air-conditioning system to be installed in new and/or retrofitted buildings as they affect the electric energy consumption.