Experimental work over borehole filling material to reinforce characterization and model validation of Ground Heat Exchangers

Ground Heat Exchangers (GHE) are part of Ground Source Heat Pumps (GSHP), employed as a renewable source in air conditioning systems. Models implemented are quite in tune to the real behaviour, enabling reliable designs and optimization, once several thermal properties of the surrounding soil and borehole are known. Since some values of those properties are evaluated from experiments, other ones are selected and approached from data base, leading sometimes to poor reproductions, due to the lack of their specific knowledge. This work demonstrates the effectiveness of the experimental evaluation of the filling material properties in a vertical GHE, to guarantee more reliable values to model its thermal behaviour: moisture content, density, and both thermal capacity and conductivity. Experiments must be easy and fast to perform, because their values must be known previous to the GSHP design. In addition, an identification process over a numerical model has been developed. In order to check its consistency, results have been compared with those determined experimentally. As well as a high model accuracy, it has been demonstrated the importance of the presented assays to be included in the previous experimental work to the design step of a GSHP system, providing a valuable borehole characterization.