Thermal analysis of a double U-loop vertical ground heat exchanger for a solar-assisted ground source heat pump

Among the challenges to the wider adoption of ground-source heat pumps is the ground thermal imbalance caused by significantly different heating and cooling loads in cold climate regions. To address this, this study investigates the performance of a solar-assisted ground source heat pump (SAGSHP) system for space heating and cooling in a cold climate. The system includes a 150 m deep and 0.15 m diameter ground heat exchanger (GHE) with two U-loop pipes separately connected to the solar collector and the heat pump. The effect of solar collector size and GHE parameters on the operational performance of a double U-loop SAGSHP is examined using a validated finite-volume computational fluid dynamics model. Moreover, a new double U-loop GHE configuration is proposed, and its performance is evaluated in comparison with the conventional double U-loop GHE configuration. The findings of this study indicate an up to 29% increment in the coefficient of performance of the system while maintaining a relatively constant ground temperature. For the conventional double U-loop, results further show that changes in the shank spacing for the same borehole diameter have no significant influence on the heat pump performance. However, increasing the borehole diameter results in lower peak and higher minimum temperatures of the heat pump entering fluid. The proposed inline double U-loop configuration shows superior performance over the conventional double U-loop with an additional heating COP of 0.14 and heat pump annual energy saving of 4%. This study demonstrates the potential for optimal performance improvement of SAGSHPs with the proposed inline configuration in cold climates.