State of the art and working fluids for high temperature heat pumps

In the current framework of the European policy that pushes toward the ecological transition by promoting the use of low GWP refrigerants and the system electrification, high temperature heat pumps (HTHPs) can be considered as an important technology with huge applicative potential. Their capacity to boost the heat quality from lower to higher temperatures, in fact, makes these machines very interesting across numerous domains. On this regard, this paper presents a comprehensive critical review of the state of the art for applications and working fluids related to high temperature heat pumps. The focus is on the analysis of the heat pump thermodynamic cycles and performance, possible suitable refrigerants, operating source and sink temperatures, potential applications and related technical challenges. More than 25 scientific papers are reviewed, showing large application potential in the food, paper, metal and chemical industries, together with the residential sector.