Comparison between new enhanced thermal response test methods for underground heat exchanger sizing

For the efficient design and implementation of a Ground Source Heat Pump (GSHP) system, the local subsoil stands as the core element. Alongside the conventional Thermal Response Test (TRT), recent research has developed improved approaches that garner more detailed information about ground thermal properties. One such technique is the fiber optic-based distributed thermal sensing. It relies on copper wires to thermally stimulate the ground, while optical fibers collect temperature variations over time along the cable. Another pioneering technology, the enhanced GEOsniff (produced by enOware GmbH), enables high-resolution, spatially-distributed representation of subsoil thermal properties along the Borehole Heat Exchanger (BHE) via wireless data transmission. This study compares and discusses data acquired through these two innovative techniques at the new campus for the humanities of the University of Padova, situated in Northern Italy's Eastern Po river plain. The findings are further juxtaposed with conventional TRT results, in terms of thermal conductivity and borehole thermal resistance. The thermal conductivity vertical profiles are also compared with direct measurements conducted on samples. These advanced techniques show promise in aiding the optimization of borehole length design, particularly in geological settings of heightened complexity. • Wireless (W) and Fiber Optic (FO) ETRTs investigate a complex geological site. • Resulting thermal conductivity and BHE resistance profiles are compared. • Both techniques are reliable to yield detailed, spatially-resolved estimation. • FO provides thousands of data while W-ETRT 1 vertical profile for each sensor. • The spatial non-averaging makes W-ETRT more effective for very thin layers.