Efficient numerical modeling of borehole heat exchangers

This paper presents a finite element modeling technique for double U-tube borehole heat exchangers (BHE) and the surrounding soil mass. Focus is placed on presenting numerical analyses describing the capability of a BHE model, previously reported, to simulate three-dimensional heat transfer processes in multiple borehole heat exchangers embedded in a multi-layer soil mass, in a computationally efficient manner. Geothermal problems which require very fine meshes, of the order of millions of finite elements, can be simulated using coarse meshes, of the order of a few hundred to a few thousand elements. Accordingly, significant reduction of CPU time is gained, rendering the model suitable for utilization in engineering practice. A validation example comparing computed results with measured results is presented. Parametric analyses are also presented describing the possible utilization of the model for research works and design optimization.