Research On Performance Of A Secondary Loop Heat Pump Air-conditioning System For Electric Vehicle With Environmentally Friendly Refrigerants

Electric vehicles are one of the effective ways to solve the environmental pollution and energy consumption,and have gained extensive attention in recent years.As one of the main components of electric vehicles,the performance of the air conditioning system has an important impact on driving safety and comfort.Because of the structural differences with the conventional fuel vehicles,electric vehicles are usually heated by the less efficient PTC(positive temperature coefficient)heaters,which seriously affect the driving range.The vapor compression heat pump not only has superior stability and safety,but also improves the energy efficiency,which has gained more and more attention in recent years for using in electric vehicles.With global warming becoming a more acute issue,the environmental impact has become one of the main criteria in selecting appropriate refrigerant for automotive air-conditioning systems.To meet the gradual and stringent environmental regulations,it has become inevitable that R134 a will be replaced by low Global Warming Potential(GWP)refrigerants for automotive air-conditioning systems.In this paper,R152 a,R513A and R1234 yf are selected as alternative refrigerants to R134 a based on a heat pump air-conditioning system for electric vehicle.The feasibility of alternative refrigerants for heat pump air-conditioning systems was investigated through theoretical analysis and experimental research.And the influence law of key factors such as compressor speed and ambient temperature on performance is analysed.1.The thermodynamic properties of the refrigerants are extracted from the REFPROP 9.1 software to compare the main property differences between R152 a,R513A and R1234 yf and R134 a,as well as to analyse the feasibility of directly substituted.Based on the theoretical analysis of the cycle process of the heat pump air conditioning system for electric vehicle,a thermodynamic model is established and thermodynamic simulations of alternative refrigerants for vehicle air conditioning are carried out for variable working conditions.Variations in condensation temperature,evaporation temperature,subcooling and superheating were found to have an impact on performance of the air-conditioning system.Compared to R134 a system,the cooling capacity and Coefficient of Performance(COP)of R513 A and R1234 yf systems are reduced.The cooling capacity of R152 a system is similar to R134 a,but the COP and discharge temperature are significantly higher.2.The cooling and heating loads are calculated for the whole electric vehicle,and a heat pump air-conditioning system for electric vehicles with three heat exchangers was designed and built.The operating mode is determined by the switching of electromagnetic shut-off valve.The system performance and cycle characteristics of R513 A,R134a and R152 a at different ambient temperatures and compressor speeds are investigated,and the performance differences between the different refrigerants are compared and analysed.Based on the influence of the refrigerant charge on system performance,the optimal charges under cooling modes of R134 a,R513A and R152 a system are 1100 g,1050g and 750 g respectively.The optimal charges of cooling modes are reduced for the secondary loop.And the optimal charges under heating modes of R134 a,R513A and R152 a system are 650 g,625g and 450 g respectively.The optimal charges of R513 A and R152 a system are lesser than that of R134 a,which are determined by the liquid density of different refrigerants.With the ambient temperature increasing,the heating performance of the system can be improved,but cooling capacity and COP decreases.With the increase of compressor speed,the cooling and heating capacity increase,but the COP decreases for increasing compressor power consumption.Results revealed that when directly substituted,the cooling and heating capacities of R152 a and R513 A systems are similar to that of R134 a.The mass flow rate of system is increased for the thermal properties of refrigerants when R134 a is replaced by R513 A.The COP and COPh of R513 A system is 2.1% and 5.1% lower than that of R134 a for the increasing of capacity and compressor power consumption.The mass flow rate of R152 a system is lower than that of R134 a,which results in the compressor power consumption reduced.The COP and COPh of R513 A system is about 13.6% and 10.3%higher than that of R134 a system.3.According to the principle of complementary advantages,the R152 a,R1234yf and R134 a are selected to form a new refrigerant to overcome the shortcomings.The refrigeration cycle calculation programs for mixing working fluids are compiled based on the cycle calculation programs for pure working fluids.The new refrigerant R152a/R134a(the mass fraction of R152 a is 0.5 to 1)was studied experimentally based on theoretical calculations.The results show that the optimal charge and mass flow rate is reduced with the mass fraction of R152 a increases.The cooling and heating capacities display a trend of decline,but the coefficient of performance is significantly increasing.Studies showed that the mixing refrigerants can improve the deficiencies of pure refrigerants.