Performance study on hybrid solar-assisted CO2 heat pump system based on the energy balance of net zero energy apartment

Because of low cooling efficiency, it is usually difficult for a conventional carbon dioxide heat pump (CO2 HP) to meet the annual demands of cooling, heating, and domestic hot water (DHW) for a building. Thus, a hybrid solar-assisted CO2 HP, which integrates a solar thermal-driven absorption chiller with a conventional air-source CO2 HP, was developed. The technological solution for the integration is first presented. The experiment was then carried out to validate the calculated results of system design. The experimental result showed that the coefficient of performance (COP) of the hybrid HP operating in a conventional CO2 HP mode could reach 2.64. Further, system simulation showed that compared to the conventional CO2 HP, the hybrid CO2 HP can reduce electricity consumption by 13.7%. In addition, the exergy efficiency of the hybrid CO2 HP, and the influence of the environmental conditions on the COP were also discussed for performance evaluation. Finally, the feasibility of using the hybrid CO2 HP for realizing the net zero energy aim was confirmed through an energy balance analysis, based on the experimental and simulated results.

► We carry out an analysis of thermal balance between supply of hybrid CO2 HP and building load.
► Cooling COP of hybrid CO2 HP in hybrid mode is appropriate 4.0 based on theoretical analysis.
► System simulation results show that the energy saving rate of hybrid mode is 22.6%.