Recent advances in direct expansion solar assisted heat pump systems: A review

Direct-expansion solar assisted heat pumps (DX-SAHPs) have a great potential for various applications and are conductive to the environment by using low-temperature ambient energy and solar radiation. This review paper aims at presenting the advancements and the current status of DX-SAHPs. A systematic literature review highlights and discusses various aspects of this technology, including system configurations, performance optimisation, simulation models, and various applications in practice. This review indicates that integrating solar collector-evaporators with some advanced technologies, such as photovoltaic, PCM thermal storage and heat pipe, makes DX-SAHPs perform better under different climates and applications. This study concludes that there are clear trends for promoting commercialisation prospects of the technology with introducing DX-SAHPs into various industries and exploring multi-functional applications of DX-SAHPs. To realise greater commercial success, some suggestions for further research are also made. This review work is expected to serve as a good guide for researchers working or interested in the DX-SAHP field.