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

Abstract

In a Distributed Thermal Response Test (DTRT) the ground thermal conductivity and bore-hole 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 tempera-ture 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 re-sponse. Fluid temperature profiles during the test are presented. The results show local varia-tions 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. 1.