A comprehensive review of research and applied studies on bifunctional heat pumps supplying heating and cooling

Heat pumps (HPs) have gained popularity as an energy-efficient substitute for traditional heating and cooling systems. This is due to their ability to transfer heat rather than generate it, resulting in higher efficiency, lower operating costs, and a reduced carbon footprint, thereby making them competitively applicable in different sectors for heating and/or cooling supply. In this study, the focus is on bi-functional HPs (bi-FHPs), machines that provide both heating and cooling, either simultaneously or in different seasons via cycle reversing. This way, the machine becomes suitable for a wide range of applications such as heating and cooling in buildings, industrial processes, electric vehicles, etc., although its performance will still depend on various factors such as climate conditions, working fluid, system design, compressor efficiency, and so on. This study reviews all literature on bi-FHPs and any effective technical or environmental parameters on their techno-economic and environmental effectiveness. It is observed that research activities on bi-FHPs come in several directions such as developing advanced control strategies, investigating the impact of environmental and operational factors, assessing economic feasibility, developing operation strategies, integrating with renewable energy sources, hybridization with other energy systems for better flexibility and resource sharing, and examining suitability for different applications and building types. It is found that bi-FHPs have great potential for cost reduction and sustainability owing to their multi-functionality but there are several challenges to overcome and factors to consider making them impactful. Pursuing research in these areas can help better understand their potential, enhance their performance and sustainability, and promote their widespread adoption as key technology for sustainable heating and cooling.