Energy and exergy analysis of bus refrigeration system using two-phase ejector with natural refrigerant R744

Abstract

In conventional bus refrigeration systems, R134a is used extensively as working fluid. According to the international agreements and European parliament directive, studies of mobile refrigeration systems have focused on the alternative refrigerants which have lower global warming potential (GWP). Natural refrigerant R744 (CO2) is one of the best alternative refrigerants with low GWP value, but R744 transcritical refrigeration systems have very low coefficient of performance (COP) value with respect to artificial refrigerant systems. In this study, a two-phase ejector was added as an expansion valve in the transcritical refrigeration system in order to overcome low COP. Transcritical ejector refrigeration system is compared with a standard transcritical refrigeration system for different parameters based on energy and exergy analysis. Results show that COP improvement can be achieved by about 26% and exergy destruction decreased by about 22% for proper design in a Mediterranean climate zone.