Sustainability with prospective refrigerants: a thermodynamic perspective for systems design

The pressing need for decarbonization of the Refrigeration, Air Conditioning, Heat Pumps (RACHP) sector has promoted the sake for new low Global Warming Potential (GWP) fluids. However, there is a general agreement that the share between direct and indirect emissions is about two-thirds for indirect ones. Hence, it is mandatory to minimize the energy consumption of vapour compression systems. This goal can be pursued through the optimization of the heat exchangers design and the minimization of the compression work for a specific refrigerant. In this work, several low GWP synthetic or natural fluids are considered for different RACHP applications. The use of suitable performance evaluation criteria implemented for in-tube flow condensation and boiling can guide the optimal design of condensers and evaporators for a given fluid and application. Through the definition of suitable compression losses indexes, it is possible to rank different refrigerants to exploit the impact of the fluid thermophysical properties on the compression efficiency. The results of the proposed general thermodynamic perspective can drive the overall system design towards energy consumption minimization, including part-load operations and off-design working conditions.