A thermodynamic investigation of a cold storage facility based on a modified cascade refrigeration system

The present work investigates the performance of a modified cascade refrigeration system that can be used as a cold storage facility. The literature on cascade refrigeration systems largely focuses on performance-enhancing modifications. In contrast, this study introduces a unique modification designed for cold storage to accommodate a wide range of food storage temperatures. The first half of the present work deals with the feasibility of the proposed modification, wherein the performance of various refrigeration system configurations is compared with that of the modified cascade refrigeration system. Later, the modified cascade refrigeration was analysed using 8 different refrigerant pairs. Various parameters such as Coefficient of Performance (COP), compressor power, refrigerant discharge temperatures, and exergetic efficiency have been analysed and discussed. The refrigerating capacity of the system was considered to be 55 kW throughout the analysis. The condenser temperature in the present work was considered between 25 and 50 ℃. It was observed that the COP of the modified system decreases as condenser temperature increases, while the exergy destruction rate rises with increase in condenser temperatures. Among the refrigerants evaluated, the R290-R717 pair required the least compressor power, while the R744-R1234yf pair exhibited the highest. The analysis also revealed that R717 offers the highest volumetric refrigeration effect for high-temperature cycles (HTC), while R600a has the lowest. At condenser temperatures below 35 ℃, R1234ze(E) is a feasible alternative to R717 due to its comparable compressor power input per ton of refrigeration. Notably, R717 displayed a significantly higher compressor discharge temperature than other HTC refrigerants. The R290-R717 pair achieved the highest coefficient of performance (COP) and exergetic efficiency, as well as the lowest TEWI, whereas the R744-R1234yf pair had the highest TEWI. Overall, R290 was found to perform more efficiently than R744 in the low-temperature cycle (LTC), while R717 outperformed other HTC refrigerants. Thus, the R290-R717 pair emerges as an ideal refrigerant choice for the modified cascade refrigeration system in terms of energy efficiency and environmental impact.