Thermal Response Test in Borehole Heat Exchangers Equipped with Fiber Optics

Four double-U borehole heat exchangers (BHEs) 100m long are installed in the Sart-Tilman region (Liege, Belgium). The installation procedure and technical difficulties are presented. Fiber optic cables are attached along the length of one pipe loop in each BHE. Temperature is measured along the fibers based on the fiber optic distributed temperature sensing (DTS) technique. Thermal response test (TRT) is conducted in order to determine the rock thermal properties. The DTS instrument records the temperature evolution along the pipe loop during the TRT. Rock thermal conductivity through depth can be estimated based on the recorded data. A 3D model is developed using the finite element code LAGAMINE in order to simulate the TRT. The accuracy of the numerical model is improved by simulating the potential variation of the rock thermal conductivity.