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Energies 2018, 11(11), 3059;

Distributed Thermal Response Tests Using a Heating Cable and Fiber Optic Temperature Sensing

Institut National de la Recherche Scientifique, Centre Eau Terre Environnement, Québec, QC G1K 9A9, Canada
Universidad de Medellín, Programa de Ingeniería Ambiental, Medellín 050026, Colombia
BRGM, Georesources Division, 45060 Orléans CEDEX 2, France
Univ Rennes, CNRS, Géosciences Rennes—UMR 6118, F-35000 Rennes, France
École de Technologie Supérieure, Département de génie mécanique, Montréal, QC H3C 1K3, Canada
Authors to whom correspondence should be addressed.
Received: 25 July 2018 / Revised: 19 October 2018 / Accepted: 2 November 2018 / Published: 7 November 2018
(This article belongs to the Special Issue Geothermal Energy: Utilization and Technology)
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Thermal response tests are used to assess the subsurface thermal conductivity to design ground-coupled heat pump systems. Conventional tests are cumbersome and require a source of high power to heat water circulating in a pilot ground heat exchanger. An alternative test method using heating cable was verified in the field as an option to conduct this heat injection experiment with a low power source and a compact equipment. Two thermal response tests using heating cable sections and a continuous heating cable were performed in two experimental heat exchangers on different sites in Canada and France. The temperature evolution during the tests was monitored using submersible sensors and fiber optic distributed temperature sensing. Free convection that can occur in the pipe of the heat exchanger was evaluated using the Rayleigh number stability criterion. The finite and infinite line source equations were used to reproduce temperature variations along the heating cable sections and continuous heating cable, respectively. The thermal conductivity profile of each site was inferred and the uncertainly of the test was evaluated. A mean thermal conductivity 15% higher than that revealed with the conventional test was estimated with heating cable sections. The thermal conductivity evaluated using the continuous heating cable corresponds to the value estimated during the conventional test. The average uncertainly associated with the heating cable section test was 15.18%, while an uncertainty of 2.14% was estimated for the test with the continuous heating cable. According to the Rayleigh number stability criterion, significant free convection can occur during the heat injection period when heating cable sections are used. The continuous heating cable with a low power source is a promising method to perform thermal response tests and further tests could be carried out in deep boreholes to verify its applicability. View Full-Text
Keywords: geothermal; thermal response test; fiber optic; thermal conductivity; heating cable geothermal; thermal response test; fiber optic; thermal conductivity; heating cable

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Vélez Márquez, M.I.; Raymond, J.; Blessent, D.; Philippe, M.; Simon, N.; Bour, O.; Lamarche, L. Distributed Thermal Response Tests Using a Heating Cable and Fiber Optic Temperature Sensing. Energies 2018, 11, 3059.

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