Validation of a Simplified Model to Determine the Long-Term Performance of Borehole Heat Exchanger Fields with Groundwater Advection

Finite element simulations performed through COMSOL Multiphysics (© COMSOL AB.) are used to study the long-term performance of BHE fields placed in a water-saturated porous soil subjected to groundwater movement. The heat transfer problem is written in a dimensionless form and the long-term time evolution of the mean surface temperature of the BHEs, sketched as cylindrical heat sources subjected to a regular time periodic heat load, is determined with reference to a single line of three BHEs and to a square field of twenty-five BHEs. A simplified model to determine the long-term performance of BHE fields, based on the superposition principle, is proposed and validated. The accuracy of the simplified model is found to be excellent for design purposes.