연구홍보포털

논문 초록 (Abstract)

Most commercial and industrial facilities require very low temperatures for refrigeration and high temperatures for space heatingand hot water purposes. Single stage heat pumps have not been able to meet these temperature demands and have been characterized by low capacities and coefficient of performance (COP). Cascade heat pump has been deve loped to overcome the weaknesses of single stage heat pumps. This study reviews recent works done by researchers on cascade heat pumps fo r refrigeration, heating and hot water generation. Selection of sui table refrigerants to meet the pressure and temperature demands of each stage of the cascade heat pump has been discussed. Optimization of desi gn parameters such as intermediate temperature (low stage condensing and high stage evaporating temperatures), and temperature difference in the cascade heat exchanger for optimum performance of the cascade he at pump has been reviewed. It was found that optimising each design para meter of the cascade heatpump is necessary for maximum system perform ance and this may improve the exergetic efficiency, especially of cas cade refrigeration systems, by about 30.88%. Cascade heat pumps have wider range of application especially for artificial snow production, in the supermarkets, for natural gas liquefaction, in drying clothes a nd food and as heat recovery system. The performance of cascade heat pu mps can be improved by 19% when coupled with other renewable energy sou rces for various real time applications. Also, there is the need for muc h research on refrigerant charge amount of cascade heat pumps, refrigerant-refrigerant heat exchangers to be used as cascad e heat exchanger, cascade heat pumps for simultaneous cooling, heat ing and hot water generation and on the use of variable speed compressor s and their control strategies in matching system capacity especially at part load conditions.