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

• Published in: Applied thermal engineering 2017-09, Vol.124, p.1492-1504
• Main Authors: Carotenuto, Alberto, Marotta, Pasquale, Massarotti, Nicola, Mauro, Alessandro, Normino, Gennaro
• Format: Article
• Language: English
• Subjects: Energy foundation pile; Geothermy; Heat and mass transfer; Heat exchanger; Numerical modeling; Parametric analysis
• ISSN: 1359-4311
• DOI: 10.1016/j.applthermaleng.2017.06.038

•Up to 42% heat transfer increase can be obtained increasing concrete thermal conductivity.•Thermal benefits due to increasing pile’s diameter above 0.70m are less pronounced.•11% heat transfer increase can be obtained using a 40mm diameter probe instead of 20mm.•Thermal benefits due to increasing flow rate above 1.0m3/h are less pronounced.•Spiral coil ensures heat transfer performance comparable to 2U employing half flow rate. 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 1D-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). The obtained results show that a proper analysis of the system based on the chosen parameters is necessary.