Abstract—The ground heat exchanger plays a major role in the thermal performance and economic optimization of the ground-coupled heat pump. The present study focuses on the effect of the borehole size and the grout and soil thermal properties on the thermal assessment of these heat exchangers. A double U-tube heat exchanger was studied numerically by the COMSOL Multiphysics 5.4 software in a 3-dimensional discretization model. The double U-tube was circuited as a parallel flow arrangement and situated in a parallel configuration (PFPD) deep in the borehole. The grout and ground thermal conductivities were selected in the range of (0.73-2.0) W/m.K and (1.24-2.8) W/m.K respectively. The results revealed that the ground thermal conductivity showed a more pronounced influence on the thermal performance of the ground heat exchanger and with less extent for the grouting one. Increasing the grout filling thermal conductivity from (0.73) W/m.K to (2.0) W/m.K at a fixed ground thermal conductivity of (2.4) W/m.K has augmented the heat transfer rate by (10) %. The heat transfer rate of the ground heat exchanger exhibited marked enhancement as much as double when the ground thermal conductivity was increased from (1.24) W/m.K to (2.8) W/m.K at fixed grout thermal conductivity range of (0.78-2.0) W/m.K. It has been verified that increasing the borehole size has a negligible effect on the ground heat exchanger thermal performance when a grout with a high thermal conductivity was utilized in the ranged of examined configurations. The steady-state numerical analysis model outcomes of the present work could be implemented for the preliminary borehole design for a ground heat exchanger.
Index Terms—3-Dimensional analysis, thermal assessment, vertical double U-tube, borehole size, a steady-state condition.
A. H. Tarrad is with the Université de Lorraine, CNRS, LEMTA, Nancy, France (e-mail: ali.tarrad@univ-lorraine.fr).
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Cite: Ali H. Tarrad, "A 3-Dimensional Numerical Thermal Analysis for A Vertical Double U-Tube Ground-Coupled Heat Pump," International Journal of Chemical Engineering
and Applications vol. 12, no. 2, pp. 12-16, 2021.
