Innovative thermal response tests technique with a low power source

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Thermal response tests (TRTs) provide an estimate of the subsurface thermal conductivity to design ground-coupled heat pump systems. The conventional testing method commonly used by the geothermal industry aim to reproduce heat transfer phenomena taking place at a ground heat exchanger (GHE) to infer the subsurface properties. Heavy mobile apparatus were developed to conduct the tests, in which water flowing in the GHE is circulated with a pump and heated with an electric element at surface to inject heat undergroun. The transient temperature response is analyzed to infer the subsurface thermal conductivity. The total heating power needed to conduct such a TRT in a GHE that is 150 m long is therefore between 7.5 to 12 kW, which requires a current intensity of 31 to 50 A when the electric potential difference is 240 V. This conventional testing method is generally considered expensive. In this research project we propose a new TRT method that is potentially cheaper than the conventional TRT because it operates with a low power source, that provides a vertical profile of the subsurface thermal conductivity and that can be deployed everywhere. This new method uses heating cables inserted into a single pipe of the GHE to inject heat in the subsurface. The former TRT method with heating cables has however been modified such that a chain of heating cable sections is lowered in the GHE, which allows a reduction of the required electric power source when compared to conventional TRT or TRT with continuous heating cables. The temperature is measured at depth along heating sections during the thermal recovery following the heat injection, requiring a monitoring time longer than that of the conventional TRTs. A fisrt prototype has been used to evaluate the new method. The main objective of the project is to develop and verify a new better prototype that can be used by industrials to validate the technology in order to create interest before it is fully commercialized.