Study On The Performance Of Automotive Air Conditioning Systems With R1234yf

At present, the refrigerant used in the automotive air conditioning system is R134a,which has a high GWP value. Refrigerant R134a is harmful to the environment and is restrictto use in the automotive air conditioning system. Finding the substitute of R134a in future’sautomotive air conditioning system is very urgent and it has become a focus in the industryand academic. However, the next generation of refrigerant for automotive air conditioningsystem has not been decided until now. It is widely accepted that the next generation ofrefrigerant for automotive air conditioning system should has low GWP value. According tothis requirement, the probable candidate refrigerants for automotive air conditioning systemare CO2, R1234yf and R32. According to the recent years’ studies, R1234yf is considered asthe most probable replacement of R134a among these cndidants. In the present study, thethermodynamic analysis of the theoretical cycle of R1234yf under typical automotive airconditioning system working condition is investigated. The performances of R1234yf“drop-in” system are experimentally studied. The results are compared to other candidants,such as CO2and R32, and the conclusion is obtained that the system with R1234yf is themost probable candidate from the standpoints of system performance and operation condition.Hence the simulation models of components and system with R1234yf are developed andverified. It is found that the performance of R1234yf system could be optimized and becomecomparable to that of R134a system. The LCCP value of the R1234yf system is alsocalculated and compared to that of R134a system. In general, using R1234yf in theautomotive air conditioning system can decrease the impact to the environment.The maincontents and results of this study are as below:1) The thermodynamic and safety-related properties of R1234yf were compared withother low GWP refrigerants, such as CO2and R32. The theoretical cycles of these refrigerantsunder typical working condition of automotive air conditioning system were studied and theirperformances were compared. The effects of operation parameters to the performance oftheoretical cycles were investigated. 2) The performances of R1234yf “drop-in” system were experimentally investigated. Thesystem performance and operation condition were compared with those of systems withCO2and R32. R1234yf “drop-in” system obtained a little lower performance compared withR134a system. A compressor with small displacement should be employed when R32used inthe automotive air conditioning system. The pressure resistant requirement of eachcomponent in R32system should be higher. The system with R32had an acceptableperformance compared to R134a. The working pressure of CO2is extremely high and theredesign of the whole system is needed. The CO2system has a comparable performanceunder low heat load conditions. These results demonstrated that R1234yf system had the bestcharacteristics of replacement and it had the potential of optimization3) The system with R1234yf was considered as the most probable candidate for theR134a system. Hence the simulation models of evaporator and condenser using R1234yfwere developed and verified by experimental data. The suitability of different two-phase heattransfer correlations to R1234yf was investigated. It was found that Kandlikar’s boiling heattransfer correlation and Cavallini’s condensing heat transfer correlation had the bestsuitability to R1234yf. Moreover, the simulation model of R1234yf system was developedbased on the component models. The optimization of the R1234yf system was studied usingthe system model.4) The optimization of the R1234yf system was experimentally investigated. Theexpansion valve for R1234yf system was optimized by changing the charged fluid andadjusting the spring force. The optimized expansion valve could control the super heat ofR1234yf at a proper value and improve the system performance. Internal heat exchanger wasintroduced in the R1234yf system. It could improve the cooling capacity of R1234yf system.The performance of the optimized R1234yf system could be comparable to that of R134asystem. Besides, the performance of R1234yf system with variable displacement compressorwas investigated by bench test and practical vehicle wind tunnel test.5) The different criterions on the effects of automotive air conditioning system to theenvironment were investigated. The LCCP (life cycle climate performance) value ofautomotive air conditioning system was considered as the most comprehensive criterion. TheLCCP value of R1234yf system was calculated based on the GREEN-MAC-LCCP model. Itshowed that using R1234yf could obviously decrease the LCCP value of automotive airconditioning system.