Design optimization of external variable displacement compressor with R1234yf for vehicle air conditioning system

Abstract

Due to the high global warming potential of the HFC-based R134a, it should be replaced by the HFO-based R1234yf as a working fluid for automotive air conditioning systems. In this study, for the external variable compressor whose stroke volume is controlled by the external signal used in the R134a air conditioning system, the optimization design of the compressor as the operating refrigerant changes from R134a to R1234yf is proposed. In order to analyze the working performance of the compressor a compressor simulation program was developed, and the drop-in test with R1234yf has been evaluated to replace R134a in the air conditioner system. From the drop-in test, both the cooling capacity and the coefficient of performance for the R1234yf decrease about 4 ~ 5% under the maximum stroke volume condition depending on the compressor operating speeds. And in the TEO5 control mode, where the lowest air temperature behind the evaporator is controlled at 5°C, it was found that there is only less than 4% reduction of the cooling capacity, while the coefficient of performance drops by up to 17% due to the increased compressor power. From the simulation result, we found that the reduced coefficient of performance of R1234yf might stem mainly from the increased losses by the suction and the discharge valves. By redesigning the suction and discharge valves within the designable range, as the results, the coefficient of performance is improved 1% at the MSV condition and 8% under the TEO5 control mode, respectively.