Thermodynamic assessment of high-temperature heat pumps using Low-GWP HFO refrigerants for heat recovery

• Heat pumps supplying heat media of 160 °C with waste heat of 80 °C were studied.
• Energy efficiencies of 4 cycle configurations with HFO refrigerants were assessed.
• The primary energy efficiencies were observed to be greater than 1.3.
• A three-stage extraction cycle with R1234ze(Z) achieves the highest efficiency.
• A high-temperature heat pump can reduce the primary energy consumption in industry.

Reducing energy consumption by utilizing heat recovery systems has become increasingly important in industry. This paper presents an exploratory assessment of heat pump type heat recovery systems using environmentally friendly refrigerants. The coefficient of performance (COP) of 4 cycle configurations used to raise the temperature of heat media to 160 °C with a waste heat at 80 °C is calculated and compared for refrigerants R717, R365mfc, R1234ze(E), and R1234ze(Z). A multiple-stage “extraction” cycle drastically reduces the throttling loss and exergy loss in the condensers, resulting in the highest COP for R1234ze(Z). A cascade cycle using R1234ze(Z) and R365mfc has a relatively high COP and provides practical benefits. Even under adverse conditions, the primary energy efficiency is greater than 1.3 when the transmission end efficiency of the electric power generation is 0.37. The assessment demonstrated that high-temperature heat pumps are a promising approach for reducing primary energy consumption for industrial applications.