Determination of interface temperatures at scaled borehole heat exchanger physical models using distributed temperature sensing

The ongoing energy transition in Germany has led to an increased use of the shallow subsurface for heating, cooling, and energy storage. This approach represents a viable alternative to conventional, e.g. fossil fuel derived, thermal energy provision. To ensure a sustainable geothermal usage and operation, especially for large scale systems, various models can be used to predict induced temperature anomalies in the vicinity of the Borehole Heat Exchanger (BHE) analytical and numerical. However, only a few physical models exist that allow comparison of predicted with actually measured temperature data. To close this knowledge gap, laboratory to medium scale experiments were undertaken to improve the understanding of the thermal behaviour within and at the BHE’s interface to the subsurface. To measure temperature distribution that was generated by thermal exaggeration, fibre optic Distributed Temperature Sensing (DTS) was used. The possibilities offered by DTS, were used to measure spatial high-resolution BHE integral temperatures at the BHE/subsurface-interface as well as temperature evolutions along the interface of inlet and outlet pipes to grouting. Therefore, a 1:3 scaled physical BHE model wrapped with optical fibre was used to measure the BHE’s integral temperature. A second installation consisting of a five meter long BHE (to scale) using DTS wrapped around inlet and outlet pipes was used to measure the temperature evolution at the interface of the pipelines to grouting. This study provides continuously measured, high spatial resolution (between 0.03 to 0.1m at laboratory and medium scale respectively) temperature data along the BHE’s physical models, under different experimental set-ups. Results allow us to get a thorough insight of the temperature evolution of BHEs.