Direct expansion solar assisted heat pumps: A review of applications and recent research

Direct expansion solar assisted heat pump systems have widely been used in solar drying, water heating, space heating, space air conditioning and cold storage applications. With the high potentials of its efficient heat retrieving unit to effectively use low temperature solar energy, the investigation of the heating and cooling applications of the system has advanced within the past decade. Also, large numbers of refrigerants with high potentials for use in direct expansion solar assisted heat pump have been explored. Investigation results have shown ways of evaluation and various factors determining the performance of the system. These investigations are necessary in order to extend design and performance knowledge and to improve the technology in general. This paper summarizes various investigations and analysis of direct expansion solar assisted heat pump systems. The review rightly point out the obvious shortage of investigation in the cooling application area of the technology and suggest possible investigation area for improving its cooling applications.