Comparison of the Thermodynamic Performance and Total Equivalent Warming Impacts of Various Refrigerants Alternative to R134a in Automobile Air Conditioning Systems for Cooling Mode Operations

The variations of significant energetic and exergetic performance parameters of automobile air conditioning systems operated in cooling mode for refrigerants R1234yf, R1234ze(e), R152a, R430A and R440A, which can be used as alternatives to R134a, were evaluated and presented comparatively for typical evaporating and condensing temperatures and a cooling capacity of 4 kW. Furthermore, the direct and indirect total equivalent warming impacts (TEWI) caused by operating automotive air conditioning systems in cooling mode with the specified refrigerants were calculated and compared for the automobile using gasoline, diesel fuel and LPG. It was found that R1234yf and R1234ze(e) provided 4.11% and 0.16% lower coefficient of performance (COP) than R134a, respectively, while R152a, R430A, and R440A yielded 3.20%, 1.52%, and 4.46% higher COP, respectively. In agreement with the COP results, R440A has the highest exergetic efficiency, followed by R152a, R430A, R134a, R1234ze(e) and R1234yf, respectively. For all refrigerants, the compressor is the component destroying the highest rate of exergy, while the evaporator is the component destroying the lowest rate. These results reveal that the most energy and exergy efficient refrigerant is R440A. For the case of an automobile using gasoline, R134a has the highest TEWI value, namely 5834 equivalent kg CO2, while R1234ze(e) offers the lowest TEWI, namely 2857 equivalent kg CO2. In the TEWI ranking, R134a is followed by R440A, R152a, R430A, R1234yf, and R1234ze(e). The TEWI results for the automobile using diesel fuel are quite close to those for the automobile using gasoline. In the automobile fueled with LPG, the TEWI caused by the air conditioning system operated in cooling mode is 9−18% lower than those obtained for the gasoline and diesel cases for all refrigerants. Moreover, the AAC system using the refrigerant with the greatest GWP, R134a, accounts for only 9.5−10.5% of the vehicle’s TEWI, depending on the fuel type.