Distributed Thermal Response Test on a U-pipe Borehole Heat Exchanger

In a Distributed Thermal Response Test (DTRT) the ground thermal conductivity and borehole thermal resistance are determined at many instances along the borehole. Here, such a test is carried out at a 260 m deep water filled energy well, equipped with a U-pipe borehole heat exchanger, containing an aqueous solution of ethanol as working fluid. Distributed temperature measurements are carried out using fiber optic cables placed inside the U-pipe, during four test phases: undisturbed ground conditions, fluid pre-circulation, constant heat injection, and borehole recovery. A line source model is used for simulating the borehole thermal response. Fluid temperature profiles during the test are presented. The results show local variations of the ground thermal conductivity and borehole thermal resistance along the borehole depth, as well as a deviation of the latter as compared to the one resulting from a standard thermal response test.