Comparison of zeotropic working fluid mixtures in different heat pump cycles

Heat pumps are often integrated into boundary conditions with a temperature glide, resulting in inevitable inefficiencies due to heat transfer. Zeotropic mixtures have the potential to match the temperature profiles but require a screening procedure to select the best performing working fluid during the heat pump design. Hybrid compression-absorption heat pumps are an alternative technology, in which a recirculation pump can adjust the temperature profile of a pre-selected working fluid e.g., ammonia/water. This cycle is more complex but enables to avoid the working fluid screening. This paper compared the two approaches with each other and to pure working fluids to evaluate the potential under different boundary conditions. Both systems outperformed conventional systems using pure fluids. The optimal zeotropic mixtures were found to show the highest thermodynamic performances while the hybrid cycle with ammonia/water enabled more compact compression equipment.