Reverse engineering of fluid selection for thermodynamic cycles with cubic equations of state, using a compression heat pump as example

The considered model-process works between the temperature levels of 273.15 and 333.15 K and can be used as heat pump for supplying buildings with heat, typically. The objective functions are the COP (coefficient of performance) and the VHC (volumetric heating capacity) as a function of critical pressure, critical temperature, acentric factor and two coefficients for the temperature-dependent isobaric ideal gas heat capacity. Also, the steam quality at the compressor entrance has to be regarded as a problem variable. The results give clear hints regarding optimal fluid parameters of the analyzed process and deepen the thermodynamic understanding of the process. Finally, for the COP optimization a strategy for screening large databases is explained. Several fluids from different substance groups like hydrogen iodide (COP = 3.68), formaldehyde (3.61) or cyclopropane (3.42) were found to have higher COPs than the often used R134a (3.12). These fluids will also have to fulfill further criteria, prior to their usage, but the method appears to be a good base for fluid selection.