Energy savings on cooling systems can be achieved using novel refrigeration cycles. To this end, vapor-compression/vaporabsorption cascade refrigeration systems may be a substitute for single-stage vapor-compression refrigeration systems. These cycles can use renewable energy sources such as geothermal and solar heat energy as well as waste heat from processes to provide cooling, and they also require less electrical energy than vapor-compression cycles with alternative refrigerants. In this

more »

... dy, vapor-compression and vapor-absorption cascade systems undergo second-law analysis for various cooling capacities. While lithium bromide-water and NH3/H2O are the working fluids in the vapor-absorption part, various refrigerants are used in the vapor-compression section. The refrigerants R134a and R600a as well as R410A and R407C are tested in the study. The effects on the coefficient of system performance (COP) of alterations in cooling capacity, superheating, and subcooling in the vapor-compression part; temperature in the generator and absorber; and degree of overlap in cascade condenser in the vaporabsorption part. The results were validated by values given in the literature. Improvements in the COPs of the vapor compression, vapor absorption, and cascade systems were obtained separately. According to the analyses, cascade systems' COP increases with generator and evaporator temperatures and also increase as condenser and absorber temperatures decrease. Moreover, the generator had the highest exergy-destruction rates, followed by the condenser and absorber, respectively. Electricity consumption and payback period were also determined by considering the various parameters of the study.