Field Comparison of Thermal Performance Between a Pre-Bored Grouted Planted Geothermal Energy Pile and a Borehole Heat Exchanger

This study introduces a pre-bored grouted planted geothermal energy pile (PGP-GEP), providing a new approach to constructing precast geothermal energy piles and installing heat exchange pipes. Its heat exchange performance was quantitatively compared with that of a conventional borehole heat exchanger (BHE). Field thermal response and thermal performance tests were conducted at the same site on a 60 m long PGP-GEP and an equal-length BHE, each equipped with an identical single U-tube. Their thermal responses were examined under constant heating power, and their performance was evaluated at preset inlet water temperatures under summer and winter conditions. This study shows that the two ground heat exchangers yielded similar estimates of effective ground thermal conductivity. After heat exchange stabilized, the unit heat exchange rate per unit length qu was generally similar between summer and winter conditions for each ground heat exchanger. Under the test conditions of this study, the qu of the PGP-GEP was approximately 1.4 times that of the BHE. These results indicate that the PGP-GEP offers better heat exchange performance and support its performance evaluation, thermal design, and engineering application.