Carbon dioxide and acetone mixtures as refrigerants for industry heat pumps to supply temperature in the range 150–220 oC

Industry decarbonization is a key a challenge towards the transition to climate neutrality. Indeed, there is a need to satisfy heat at temperatures higher than 150 degrees C in relevant industrial sectors by upgrading lower temperature heat flows, such as heat from renewable heat sources, ambient heat or industrial waste heat. High temperature heat pumps (HTHP) can upgrade such heat flows enabling great savings in carbon emissions. New refrigerants are needed to develop HTHPs achieving high performances at high temperatures. This paper proposes the use of a new zeotropic mixture composed of carbon dioxide and acetone as the refrigerant of HTHPs working in the temperature range of 150-220 degrees C. The new fluid is compared with existing pure refrigerants currently used. The thermodynamic characterization of the CO2/acetone mixtures shows temperature glides below 50 K for CO2 mass fractions up to 10%. The best HTHP performance is shown for the mixture 5% CO2/95% acetone in mass fraction. For instance, such a mixture obtains a COP of 5.63 when the target outlet sink temperature is 200 degrees C and the temperature difference between the outlet heat sink and the inlet heat source is 70 K, showing an improvement of 46% compared to pure acetone.