Investigation on CO2 hybrid ground-coupled heat pumping system under warm climate

• A concept of CO2 hybrid ground-coupled heat pumping system was developed.
• Energy performance of heat pumping system was investigated under both full and partial capacity.
• Annual ground thermal imbalance for CO2 hybrid GCHP system was studied.
• Application of CO2 hybrid GCHP system to different warm climates was discussed.

This article introduced a concept of CO2 hybrid ground-coupled heat pumping system for warm climate. The CO2 transcritical system takes advantage of the temperature glide during heat rejection process to increase the energy efficiency. This hybrid system utilises the heat sink by combining city water, ground and ambient air in cooling mode, while only the ground is utilised as the heat source in heating mode. During the space cooling mode, part of rejection heat can be recovered for heating the service hot water to 65 °C. Besides, the separated gas coolers enable simultaneous space heating and service hot water supply in the heating mode. Simulation result shows the combined COPshw&space varies from 3.0 to 5.5, and the annual ground thermal imbalance for the hybrid GCHP system could be decreased to 0% for the reference building. At last potential application of CO2 hybrid GCHP system to different warm climates was discussed.