Performance investigation of double tube ground heat exchanger by adjusting the inner tube position and consideration of bending effect

The thermal energy that is stored in the ground can be extracted and used in our daily lives by a ground-source heat pump (GSHP) system. A ground heat exchanger (GHE) is a very important part of the GSHP system. This study investigates the performance of double tube GHE under two practical installation scenarios: moving the inner tube away from the center and bending of the inner tube. Polyvinyl chloride (PVC) and High-density polyethylene (HDPE) were utilized as inner tube materials. The performance of GHE was numerically tested by moving the PVC inner pipe at various distances, including 12.5 mm, 22.5 mm, and 32.5 mm from the center, since the inner tube moves away from the center when the support plate is not used during installation. The inner tube, which is long and thin, bends, however. Because HDPE is more flexible than PVC, the performance was tested in one case for PVC, involving 4 bends, and three cases for HDPE, involving 4, 8, and 12 bends. The outlet temperature, pressure drop, heat exchange rate, and temperature distribution are numerically analyzed and compared with conventional for each of those scenarios. When an inner tube moves away from the center, the heat exchange rate deviates from traditional by 3.68 %, 3.06 %, and 0.45 %, respectively. In comparison to straight traditional, the bending scenario showed a 1.09 % change for PVC pipe and a 0.93 %, 2.28 %, and 3.54 % change for HDPE pipe. The rate of heat exchange and the pressure drop both slightly increased in the bending condition. When the inner pipe was closer to the outer wall, the degradation of the performance was not significant. The findings suggest that keeping the inner pipe in center position by using support plates is not crucial to maintain maximum heat transfer.