Abstract
The performance of the variable refrigerant flow (VRF) system becomes poor at a very low ambient temperature because of the decrease in the suction mass flow rate. The vapor injection is applied to the heat pump system to enhance the performance of the systems in a cold season. In this study, the influence of the vapor injection under different intermediate pressures and outdoor ambient temperatures was investigated mathematically, and the results were validated with experimental data. In addition, the performance variation was observed with different indoor ambient temperatures in nine indoor units. The intermediate pressure affected the heating capacity, input power, coefficient of performance (COP), and isentropic efficiency of the compressor. The improvement of the COP with vapor injection was dominant at a low ambient temperature. The heating capacity at different indoor ambient temperatures was observed with different refrigerant mass flow rates in each indoor unit.
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