Thermal plume simulation of VRF air conditioners for cooling system in high-rise buildings: a case study in China

Variable refrigerant flow (VRF) air conditioning system is widely used in commercial and residential buildings for space cooling and heating. However, some practical VRF systems used in high-rise buildings cannot work efficiently or even stop working because of the relatively high ambient temperature, caused by thermal plume effect of exhaust heat from outdoor units. In this paper, the thermal plume air flow of layer-based VRF systems is investigated through computational fluids dynamics (CFD) simulation. Moreover, an illustrative example in a 30-storey office building in China is conducted to optimize the layout of VRF outdoor units. Preliminary results show that the exhaust heat of outdoor units can cause ascending thermal plume flow, leading to higher inlet temperatures for VRF air conditioners on upper floors. It also indicates that enlarging the distance between outdoor units on different floors is an effective way to impair such thermal plume effect and improve the system thermal performance. For the studied case, a modified layout of VRF outdoor units is presented with floor interval, and the average inlet temperatures can be decreased by 22%. This work can provide guidance to the optimization layout design of practical VRF air conditioning systems used in high-rise buildings.