Transcritical high-temperature heat pump with hydrocarbon mixtures – experimental setup and model predictions
Industrial heat pumps must often overcome large temperature changes in the heat sink and heat source. Transcritical heat pump cycles with pure refrigerants can adapt to the temperature change in the heat sink but always have a constant temperature during evaporation. Transcritical refrigerant mixtures give an additional degree of freedom: The saturation temperature changes during evaporation and can match the heat source temperature change in counterflow configuration. This allows for independent temperature glide matching between the heat source and the heat sink. To verify this additional degree of freedom experimentally, a customized transcritical high-temperature heat pump prototype with 20 kW heating capacity was built and is introduced in this paper. A thermodynamic model of the heat pump is described and applied to an example application with source inlet and outlet temperatures of 90 °C and 60 °C and sink inlet and outlet temperatures of 100 °C and 150 °C, respectively. The model predicts a coefficient of performance (COP) improvement of over 10% and a volumetric heating capacity (VHC) improvement of over 50% for the best-performing R-290/R-601a refrigerant mixture compared to pure R-600a. The results encourage experimental verification as a basis for a pilot plant installation in an industrial environment.