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Review of new methods for in situ assessment of the subsurface heat capacity

Raymond, Jasmin
Koubikana Pambou, Claude Hugo
Giordano, Nicolò
Langevin, Hubert
Lamarche, Louis
Gosselin, Louis
Heat storage properties can hardly be determined with conventional thermal response tests. New field methods were therefore developed for in situ assessment of thermal diffusivity and heat capacity. The objective of this paper is to review recently developed field methods that can be conducted in either vertical ground heat exchangers or horizontal trenches. The first method consists of reproducing a vertical temperature profile measured in a ground heat exchanger using an empirical formula. The second method is an oscillatory thermal response test made with water circulation in a ground heat exchanger and producing an oscillatory temperature response whose phase and amplitude are affected by the storage of heat in the material surrounding the heat source. The third method relies on a heating cable installed in a horizontal trench and used to inject heat, again with an oscillatory heat injection rate. These new methods can be used in the scope of ground-coupled heat pump projects where there is a need to evaluate the ground thermal diffusivity or heat capacity, for example, to design underground energy storage systems.