Comparative Performance of an Automotive Air Conditioning System Using R1234yf and R134a

Due to their large global warming potential, R134a will not be used in new vehicles fitted with air conditioning beginning on January 1, 2017. CO2 and a new fluorinated olefin, R1234yf, are possible candidate refrigerants among various alternatives to R134a in autumotive air conditioning (AAC) systems. Because it works at considerably lower pressures than CO2 and has thermodynamic properties similar to R134a, R1234yf has recently taken more attention than CO2. This study aims at determining thermodynamic performance parameters of an AAC system using R1234yf and comparing them with those of the system using R134a. For this purpose, the performance parameters of an AAC system with an evaporator load of 5 kW were evaluated for two refrigerant cases by varying evaporating and condensing temperatures and assuming that evaporator superheat, condenser subcooling and compressor isentropic efficiency will remain constant. Then, the same performance parameters were determined for a constant evaporating temperature of 0 °C by changing the evaporator load and condensing temperature. It was determined that R1234yf yields lower pressure ratio, compresor discharge temperature and coefficient of performance but results in higher refrigerant mass flow rate, compressor power and condenser heat rejection rate compared with R134a.