CFD Study of Vertical U-Loop Thermo-Active Foundations for Cold Climates

Ground source heat pump (GSHP) systems have received considerable interest for their efficient and relatively stable performance for building heating and cooling. To reduce the high initial cost of this technology, coupling the ground heat exchanger of the GSHP system with the building foundation aka “thermo-active foundation” is a promising approach. However, the performance of such systems in cold climates has not been explored sufficiently. This work computationally investigates the performance of a U-loop helical pile heat exchanger. The conjugate heat transfer between the heat exchanger and the ground domain is solved using a transient computational fluid dynamics (CFD) model validated with an existing experimental study. The realizable k-ϵ turbulence model was used for turbulence closure. Moreover, to accurately predict heat transfer and fluid flow in the near-wall regions, the enhanced wall treatment model was used with y+ values of less than 1.The CFD model is used to explore the transient performance of the system in a cold climate where the high heating dominant loads lead to a significant thermal imbalance of the ground. Furthermore, the performance at various inlet temperatures and fluid velocities is investigated.