Performance simulation and exergy analysis of a hybrid source heat pump system with low GWP refrigerants

Low global warming potential R1234ze series refrigerants have been widely accepted as the working fluids for high temperature heat pump system in industrial applications. To improve the system performance of a single source R1234ze(Z) heat pump system with waste heat recovery, a hybrid source heat pump system combined with a CO2 transcritical heat pump cycle and a R1234ze(Z) subcritical heat pump cycle is proposed in this paper. To compare the system performance of proposed hybrid source heat pump and single source heat pump systems, thermal characteristic is investigated for each system. Exergy analysis and economic analysis are also conducted to compare the system efficiencies of hybrid and single source heat pump system. The study indicates that total power consumption and heating capacities of the proposed system increase with CO2 discharge pressure increasing. There also exists an optimal CO2 discharge pressure for hybrid source heat pump system to achieve the best system COP. The system exergy efficiency increases with CO2 discharge pressure increasing before it reaches to a relative stable level. Compared with the single source heat pump, both the system COP and exergy efficiency are improved by 24.8% and 27.2% at 100 °C condensing temperature.