Performance analysis of an R744 ground source heat pump system with air-cooled and water-cooled gas coolers

• An R744 GSHP system with air-cooled and water-cooled gas coolers was designed.
• Earth's energy imbalance degree for the proposed R744 system was analyzed.
• Investment and operation costs of the R744 system were decreased.
• Effect of ground heat exchanger depth on system performance was analyzed.

In order to decrease the earth's energy imbalance degree, an R744 ground source heat pump system (GSHPS) with air-cooled and water-cooled gas coolers was designed, and the performances of this system were analyzed numerically. The results show that, for the proposed R744 system in different regions, the earth's energy imbalance degree can always be decreased to zero by optimizing the cooling load proportion of air-cooled gas cooler. Comparing with the system without air-cooled gas cooler, the investment cost of the proposed R744 system is decreased by 14.5–25.5% due to the decreasing cost of ground heat exchanger, and the coefficient of performance is increased. With the increase of ground heat exchanger depth, the performance deteriorates, and the ground heat exchanger with shorter depth is preferred in the GSHPS. The investment and operation costs of the proposed R744 system are lower than that of the existing R134a system.