Performance Comparison of Single-Stage and Cascade Refrigeration Systems Using R134a as the Working Fluid

This study presents an experimental comparison of single-stage and cascade vapour-compression refrigeration systems using R134a as the refrigerant. The experimental plants employ a vapour-compression refrigeration cycle serving as a base unit, a cooling tower and another vapour-compression refrigeration cycle serving as a higher-temperature unit in the cascade operation. In the single-stage operation the condenser of the base unit was connected to the cooling tower, whereas in the cascade operation it was thermally coupled to the evaporator of the higher-temperature unit via a water stream. Using data obtained from steady-state test runs, the performance characteristics of both systems, namely evaporating and condensing temperatures, refrigerant mass flow rate, compressor power, coefficient of performance (COP), compressor discharge temperature, compressor volumetric efficiency and the ratio of compressor discharge to suction pressures, were evaluated. The results show that, for a given refrigeration capacity, the cascade system provides a lower evaporating temperature, lower compressor discharge temperature, lower ratio of discharge to suction pressures and higher compressor volumetric efficiency at the expense of a lower COP.