Numerical characterization of heat transfer in closed-loop vertical ground heat exchanger

Abstract

A series of numerical analyses has been performed on the characteristics of heat transfer in a closed-loop vertical ground heat exchanger (U-loop). A 2-D finite element analysis was conducted to evaluate the temperature distribution over the cross section of the U-loop system involving high-density polyethylene (HDPE) pipe/grout/soil to compare the sectional efficiency between the conventional U-loop and a new latticed HDPE pipe system, which is equipped with a thermally insulating lattice in order to reduce thermal interference between the inlet and outlet pipes. In addition, a 3-D finite volume analysis (FLUENT) was adopted to simulate the operation of the closed-loop vertical ground heat exchanger with the consideration of the effect of a distance between the inlet and outlet pipes, grout's thermal properties, the effectiveness of the latticed HDPE pipe system, and the rate of circulation pump. It was observed that the thermal interference between the two strands of U-loop is of importance in enhancing efficiency of the ground heat exchanger. Consequently, it is recommended to modify the configuration of the conventional U-loop system by equipping the thermally insulating lattice between the two pipe strands.