Simulation and experimental validation of the variable refrigerant flows system under the cooling conditions.

Abstract

Variable refrigerant flow (VRF) air conditioning system gains widely attentions due to its better energy performance in the part load conditions. However, the outdoor air ventilation capacity of the VRF system is usually not satisfied. A VRF and variable air volume combined air conditioning system is investigated through simulation as a solution for the ventilation problem while taking advantage of its high part load energy efficiency. In the previous study, VRF models of component-number independence were developed. As another part of the study, this paper introduces the work in the experimental validation of simulation models. Firstly, the experimental rig is introduced, which consists of an outdoor unit (including a variable speed compressor and a heat exchanger), two indoor heat exchangers, two electronic expansion valves, pipes and accessories. A constant temperature and humidity room is used to ensure the required inlet conditions for all the heat exchangers. Secondly, the simulation models are validated using the experimental data. The maximum errors for cooling capacity and input power are less than 7%. The maximum relative error of COP is 10.54%. In addition, the control responses of the VRF system under the various conditions are validated. The results show that simulation matches the experiments very well indicating the accurate prediction of the models responding to the varying compressor speed, EEV opening position and evaporator inlet air temperature.