Numerical Modelling of Solar Heat Storage Using Large Arrays of Borehole Heat Exchangers

The storage of surplus heat in the underground and retrieval when required is a promising method for optimizing the energy efficiency of new housing estates. A new approach for the coupled numerical modelling of such problems will be presented. Here, the energy simulation software TRNSYS is directly coupled with the finite element subsurface flow and transport simulation software FEFLOW. This way it is possible to simulate the energy transfer between solar panels, building installations and thermal storage in the subsurface in an efficient and accurate manner. At the presented pilot installation the heat is transferred to the ground by using large arrays of borehole heat exchangers. For the simulation the borehole heat exchanger systems are modeled by a set of onedimensional representations, either using a finite-element or an analytical approach. This way the calculation time is significantly reduced compared to fully discretized calculations while still achieving precise results.