Modelling and optimization of helical steel piles as in-ground heat exchangers for Ground-Source Heat Pumps

Abstract

Ground source heat pumps are a sustainable way to provide building heating and cooling due to their efficient use of near-constant ground temperatures as mediums for heat exchange. Conventional in-ground heat exchangers are limited by the large size of required borehole field installations and the high economic costs, therefore the pairing of in-ground structural helical piles with these heat exchangers offers a system of geothermal heating and cooling which can be more accessible and lower cost than traditional equipment. In this research, a novel helical steel pile was modelled using a 3-D numerical model and finite element analysis. This model was first validated with experimental data from a double-tube pile, with 24-hr transient operation outlet temperatures accurate within 3%. Finally, the steady state heat exchange rate per unit area was calculated, with the new helical steel pile geometry yielding an increase of 8.6 W/m, 13.2 W/m, and 16.2 W/m (for 2 L/min, 4 L/min, and 8 L/min flowrates respectively) over the validation model.