Design and rating of dedicated mechanical-subcooling vapour compression refrigeration systems

Subcooling of the refrigerant at the exit of the condenser in a vapour compression refrigeration system allows the refrigerant to enter the main cycle evaporator with a lower quality and thus allows the refrigerant to absorb more heat in the evaporator, thereby improving the coefficient of performance (COP) of the system. In a dedicated mechanical-subcooling vapour compression refrigeration system, the subcooling is performed by utilizing a small dedicated vapour compression refrigeration cycle. This cycle is coupled to the main cycle at the exit of the condenser. In this paper, thermodynamic models of the dedicated mechanical-subcooling systems are developed to simulate the actual performance of the system, particularly with respect to the subcooler saturation temperature in addition to the heat exchanger areas. It is demonstrated that the performance of the overall cycle is improved over the corresponding simple cycle and this improvement is found to be related to the refrigerant saturation temperature of the subcooler. The models are also used to predict an optimum distribution of the total heat exchanger area between the evaporator and condenser.