Investigation of Construction Specification Effects on Energy Pile Efficiency

The combination of the Ground Source Heat Pump (GSHP) with energy piles has become a viable alternative to traditional indoor climate control. As geothermal energy pile applications increase in size and demand, maintaining the highest possible efficiency is paramount. Therefore, a numerical analysis was performed to investigate the relationship between construction specifications and energy pile efficiency. In particular, inlet flow rate and concrete cover were parameterized within two heat exchanger tube configurations including “U-shape” and “W-shape” configurations. Additionally, cyclic and constant thermal loadings were compared using COMSOL multi-physics software. Simulation results indicate that heat rejected is limited by surface area of the heat exchangers and residence time of working fluid. For this model, an apparent maximum heat rejected was achieved at 240 cm 3 /s/pile (3.8 gpm) for both U-shape and W-shape configurations. Beyond 240 cm 3 /s, the increase of rejected heat was negligible. The study also demonstrated that concrete cover contributes significantly to energy pile efficiency. A reduction of concrete cover decreased potential cyclic heat rejected by up to 20%. The comparison of tube configurations bolstered conclusions in the literature that the W-shape configuration is most effective at rejecting heat, improving efficiency by approximately 20% compared to the U-shape configuration.