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This paper presents an experimental performance investigation and exergy analysis using R1234yf in an automotive air conditioning system. The R1234yf system with an internal heat exchanger (IHX) was compared with an R1234yf system without the IHX and an R134a system. The R1234yf system had 4.0–7.0% smaller cooling capacity and 3.6–4.5% lower COP compared to the R134a system. With the IHX, the R1234yf system showed almost equivalent cooling capacity to the R134a system. The COP of the R1234yf system with the IHX is lower than that of the R134a system by 0.3–2.9% for a compressor speed of 800–1800 rpm. The COP increased by 0.9% at a compressor speed of 2500 rpm. The second law efficiency of the R1234yf system was 3.4–4.6% lower than that of the R134a system at all compressor speeds. The second law efficiency of R1234yf with the IHX was improved by 1.5–4.6% compared to the R1234yf system without the IHX. The EDR of the R1234yf system was 0.5–3.3% higher than that of the R134a system in the range of 800–1800 rpm. However, the R1234yf system with the IHX had 1.2% lower EDR than the R134a system at a compressor speed of 2500 rpm.

In this study, performance was assessed by charging the same automotive refrigeration systems with the refrigerants R134a and R1234yf, respectively, to compare the characteristics of the refrigeration cycle of the two refrigerants. The internal heat exchanger was installed in order to improve cooling performance of R1234yf and to investigate the level of performance improvement in comparison with conventional R134a system. Performance test by using R1234yf and R134a in the same system showed low power consumption and cooling capacity for using R1234yf, that is, up to 4% and 7%. In particular, performance comparison between the R1234yf and R134a for automotive air conditioning revealed that cooling capacity and COP of the 1234yf system without the IHX decreased by up to 7% and 4.5%, respectively, but those with the IHX decreased by up to 1.8% and 2.9%, respectively.

A microchannel heat exchanger was numerically analyzed using the finite volume method. The air and refrigerant-side heat transfer coefficients and pressure drops were calculated using the existing correlations that were developed for microchannel heat exchangers. To verify the present model, performance tests of the microchannel heat exchanger were conducted at various test conditions with R134a. The present model yielded a good correlation with the measured heat transfer rate, demonstrating a mean deviation of 6.8%. The performance of the microchannel evaporator for CO2 systems can be improved by varying the refrigerant flow rate to each slab and changing fin space to increase the two-phase region in the microchannel. Based on the comparison of the performance of the microchannel heat exchanger with that of the fin-tube heat exchanger designed for CO2 systems, it was proposed that the arrangement of the slabs and inlet air velocity in the microchannel heat exchanger need to be optimized by considering heat exchanger size, air outlet conditions and required capacity.