Simulations of the energy performance of variable refrigerant flow system in representative operation modes for residential buildings in the hot summer and cold winter region in China

Predicting the energy performance of household variable refrigerant flow (VRF) systems in the hot summer and cold winter (HSCW) region in China accurately is particularly challenging due to the frequent defrost operations of the VRF systems during winter. Hence, an improved energy model was developed to determine the energy performance of household VRF systems, taking into account the defrost operations. The energy model was validated by experiments and the energy performance of the VRF system for typical residential buildings in Chongqing, Changsha, Nanjing, and Shanghai was determined based on representative operation modes (full-time-full-space and part-time-part-space modes). The results indicate that the efficiency of the VRF system increases as the outdoor temperature decreases. However, the efficiency of the VRF system decreases as the part-load ratio decreases, which leads to variations in the cooling seasonal performance factor for the representative operation modes and cities. The heating seasonal performance factor is not only influenced by the outdoor temperature and part-load ratio distribution, but also defrost operations. Compared with the part-time-part-space mode of C1 and C2, the annual energy consumption for the C4 mode performs lower from 26.3% to 51.7% for typical residential buildings in the four representative cities.