Efficient Finite Element Modeling of Shallow Geothermal Systems

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 introduced by the author, to simulate three dimensional heat transfer processes in multiple borehole heat exchangers embedded in 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 few hundreds to few thousands elements. Accordingly, significant reduction of CPU time is gained, rendering thus the suitability of the model for utilization in engineering practice.