Thermodynamic Comparison of Two- and Three-Stage Cascade Refrigeration Systems: A Dynamic Energy Assessment in Hospital Environments

The design of ultra-low-temperature refrigeration systems has gained increasing importance in recent years, driven by the growing demand for very-low-temperature storage cabinets for many applications, such as the preservation of vaccines and biological materials. In the first part of this study, the thermal design of both two-stage and three-stage cascade refrigeration systems was developed using the Engineering Equation Solver (EES). The systems were evaluated under evaporator temperatures of −85 °C, −80 °C, and −75 °C and ambient temperatures ranging from −5 °C to 40 °C. For the two-stage configuration, the R170/R161 refrigerant pair was assessed as an alternative to the conventional R170/R290 combination. In the three-stage configuration, the performance of the R1150/R170/R290 and R1150/R170/R161 refrigerant combinations was analyzed. The results indicate that under identical operating conditions, the three-stage system demonstrated lower compressor power consumption and reduced exergy destruction compared to the two-stage configuration, while achieving higher coefficients of performance (COPs) and exergy efficiency. In the second part of the study, long-term dynamic simulations of energy consumption for both two-stage and three-stage systems were carried out using TRNSYS 18 under varying ambient temperature conditions. The simulations were performed for hospital installation rooms located in three different cities: Muğla (Turkey), Milan (Italy), and Warsaw (Poland). The results of the dynamic simulations indicate that the use of R161 leads to significant energy savings compared to R290. Specifically, when comparing the three-stage cascade system using R1150/R170/R161 with the conventional two-stage R170/R290 system, energy consumption reductions of 20.5% in Warsaw, 23.6% in Milan, and 26.6% in Muğla were achieved.