Energy piles for ground source heat pump applications: Comparison of heat transfer performance for different design and operating parameters

Geothermal energy piles allow both heating and cooling of buildings by using the ground as a renewable energy source. In this paper, the authors propose an efficient numerical model, based on a mixed ID-3D approach, to analyze the heat transfer process in the coupled system probe-pile-ground. The numerical model developed allows to simulate the three-dimensional heat transfer in the pile and in the surrounding ground, and the one-dimensional heat and fluid flow inside the probe, with consequent reduction of computational time with respect to full 3D models. The numerical model has been employed to investigate the heat transfer performance of different configurations of energy piles, analyzing the effects of both design and operating parameters, such as diameter of probe and pile, properties of the employed materials, flow rate and probe configurations (U-tube, Double U-tubes, Triple U-tubes, spiral coil).