Performance enhancement of hybrid absorption-compression heat pump via internal heat recovery

Heat pumps, especially the air-source systems, have been regarded as promising technology for deep decarbonization of thermal energy, but its industrial application is strongly constrained by its small temperature lift. Three-stage hybrid absorption-compression heat pump cycles have been proven as an effective way to achieve large temperature lift, but suffer from performance degradation under high temperature lift. In this study, different internal heat recovery configurations for the three-stage hybrid cycle are investigated for performance enhancement under high temperature lift. Results show that the three-stage hybrid cycles with internal heat recovery can reach output temperature of 100–190 °C with COP of 1.26–2.23, under the ambient temperature of 30 °C. By effectively recovering the condensation heat of absorption sub-cycle, the maximum output temperature and maximum temperature lift of three-stage hybrid cycles are increased by 10 °C and 20 °C, respectively, and the COP under 100 °C temperature lift is improved by 13 %. More importantly, sub-zero operation of the three-stage hybrid cycle is enabled by the internal heat recovery. The comprehensive enhancement of three-stage hybrid cycle with internal heat recovery shows the great potential in promoting the industrial application of air-source heat pump.