Experimental investigations on the thermal performance of a novel ground heat exchanger under the synergistic effects of shape-stabilized phase change material and nanofluid

Ground source heat pump (GSHP) is known as the most promising green energy utilization technology in the 21st century. However, the heat transfer efficiency of GSHP systems cannot be significantly improved owing to the limitations of heat transfer fluid and surrounding backfill material, which has become a major obstacle to the widespread application of the system. In this paper, efforts had been made to enhance the heat transfer performance of the ground heat exchanger (GHE) under the joint actions of structure and material. For this purpose, an experimental platform for horizontal spiral-coil GHE was built to study the synergistic effects of using shape-stabilized phase change material (SSPCM) as backfilling and CuO/water nanofluid as the heat transfer fluid on thermal performance of the GHE. The results showed that the heat transfer amount increased by 69.9% and the thermal resistance decreased by 81.77% under the synergistic effects of SSPCM and nanofluid. The ground thermal influence radius with SSPCM backfill was about 80% of that with sand backfill. Nanofluid and SSPCM promote and reinforce each other. The performance improvement effect was more significant under the synergistic effects of SSPCM and nanofluid. The findings of this study can help designer to develop high-efficiency GHE.