Experimental Research On Performances Of Heat Pump Air Conditioning System For Electric Vehicle

The mileage of electric vehicle(EV) decreases seriously due to the PTC (PositiveTemperature Coefficient) thermistor with higher energy consumption, when the EV runs inlow ambient temperature. In this paper, a heat pump air conditioning system (HPACs) withhigh coefficient of performance(COP) was used to control the temperature of the EV cabinroom. A test platform that included the HPACs, the data acquisition system and the simula-tion cabin was developed for EVs. Experimental performance investigations of the HPACswere performed in an environmental chamber which can simulate and control the environ-ment temperature. The main objects and findings in this study are as following:As the temperature of refrigerant rises, the specific enthalpy of refrigerant increaseswith linear law, the equilibrium pressure of the refrigerant increases fast when the HPACsis not running. The trend of average temperature in the cabin room is similar with the trendof temperature and pressure of refrigerant in the high pressure piping when HPACs is underthe heating mode, while it has the same trend of temperature and pressure of refrigerant inthe low pressure piping when HPACs is under cooling mode.Experimental evaluations of the effects of the ambient temperature on the perfor-mances of a HPACs working with R134a were carried out for two different compressors,the swash plate type variable displacement compressor and the scroll type fixed displace-ment compressor. As the ambient temperature decreases, the enthalpy difference betweenthe inlet and outlet of the condenser reduces for the system working with the swash platetype compressor, and that of the system working with the scroll compressor has no evidentchange. The system COP and the highest temperature of the cabin room decrease with de-creasing ambient temperature for both compressors.Experimental evaluations of the effects of the compressor rotational speed on the per-formances of a HPACs working with R134a were carried out for two different compressors,the swash plate type variable displacement compressor and the scroll type fixed displace-ment compressor. The power of compressor increases with the compressor rotationalspeeds, while the enthalpy difference between the inlet and outlet of the condenser almostkeeps constant, and the system COP decreases. The heat capacity of the HPACs increaseswith compressor rotational speeds, and the temperature of the EV cabin room is higher. The effects of the refrigerant type and the refrigerant charge on the performances ofthe systems working with R407c and R134a were investigated for the swash plate typecompressor and the scroll type compressor, respectively. The results indicates that the sys-tem working with R407c has a large temperature difference between the inlet and outlet ofthe condenser and has a low mean temperature in the cabin room，while the COP is lower.For the system working with R134a, as the refrigerant charge of R134a increases, reachingto a comfortable cabin temperature consumes less time, however, the system COP decreas-es.Experimental studies of the effects of the ambient temperature and the refrigerantcharge on the R134a system refrigeration performance were implemented for the systemintegrated with swash plate type compressor. For a constant system refrigerant charge, thetemperature and pressure of the working fluid in the pipelines increase with increasing am-bient temperature. Reducing to a comfortable cabin temperature also needs more time. Theenthalpy between the inlet and outlet of the compressor decreases with increasing ambienttemperature, which is the same as the evaporator. However, the EER has no evident change.For a constant ambient temperature, the temperature and pressure of the working fluid inthe pipelines increase with increasing refrigerant charge. Reducing to a comfortable cabintemperature also needs less time. The enthalpy between the inlet and outlet of the com-pressor increases with increasing refrigerant charge, which is the same as the evaporator.However, the EER decreases.This study designed a refrigerant work pressure regulation HPAC system for both therefrigeration and heating processes.