Three-Dimensional Analysis of the Thermal Interaction of Multiple Vertical Ground Heat Exchangers

Abstract

The use of ground heat pumps for heating and cooling buildings is receiving increasing attention due to their many benefits. But such systems have some challenges regarding the long-term use of groundwater for thermal purposes, including the sustainability of the systems. Interference between adjoining installations is being reported, raising issues of sustainability in terms of performance and equitable sharing of natural resources. To help address this issue, an investigation is reported here of the thermal interaction of vertical ground heat exchangers, in which two- and three-dimensional transient heat conduction is examined in the soil around vertical ground heat exchangers. A finite volume numerical solution is applied using FLUENT software. The research extends a previous study in which the analytical results of the line source theory are validated using two-dimensional numerical results, which inherently neglects axial heat transfer effects. The three-dimensional numerical study reported here accounts for axial heat transfer in the soil surrounding a borehole. It is demonstrated that a specified length exists for which the heat from the borehole wall is only conducted in the radial direction and the results of the two-dimensional heat conduction approach are valid.