Thermodynamic Performance Evaluation of R744 Supermarket Refrigeration Systems by employing Advanced Exergy Analysis

It is a well-known fact that, at high outdoor temperatures, it is necessary to adopt some expedients in order to make the basic R744 refrigeration cycle energetically competitive with the solutions using synthetic refrigerants. The most effective design procedures to apply to any refrigerating plant can be suitably revealed by employing some advanced thermodynamic tools. This paper deals with the application of the advanced exergy analysis to a transcritical CO2 refrigeration system using an auxiliary compressor and a subcooler and to the one employing a dedicated mechanical subcooling. The evaluation was carried out by selecting the typical running modes of a supermarket and a design external temperature of 30 °C. The results obtained showed that, in both the investigated cases, the avoidable irreversibilities associated with the evaporator and with the main compressor were completely and mainly endogenous, respectively. On the other hand, a large amount of the inefficiencies related to the subcooling loop, the auxiliary compressor and the gas coolers could be dropped by improving the other components