Thermal plume simulation of VRF air conditioners for cooling system in high-rise buildings: a case study in China
AbstractVariable refrigerant flow (VRF) air conditioning system is widely used in commercial and residential buildings for space cooling and heating, due to its great energy saving potential, low greenhouse gas emissions, high flexibility and reliability. However, the thermal performance of VRF system highly depends on its working conditions and environment. In real applications, some VRF systems used in high-rise buildings cannot work efficiently or even stop working because of the relatively high ambient air temperature, caused by the thermal plume effect of exhaust heat from outdoor units. In this paper, the thermal plume air flow of the layer-based VRF systems is investigated through computational fluids dynamics (CFD) simulation. Moreover, an illustrative example of practical VRF system in a 30-storey office building in China is conducted and analyzed to optimize the layout of the 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, even exceeding the warning upper threshold value. It also indicates that enlarging the distance between outdoor units on different floors is an effective way to impair the thermal plume effect for VRF outdoor units and improve the thermal performance of the whole system. For the studied case, a modified layout of VRF outdoor units is presented with floor interval and the average inlet temperatures can be decreased substantially by 22%. This work can offer guidance the optimization layout design of practical VRF air conditioning systems used in high-rise buildings.
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