ESTIMATION OF SOIL AND GROUT THERMAL PROPERTIES THROUGHGEOTHERMAL RESPONSE TEST

The Thermal Response Test (TRT) is a method often adopted in geothermal application, especially in vertically oriented loops, to recover the values of the soil and the grout thermal properties necessary to the design of ground heat exchangers (GHE); the comparison between TRT data and the Line Source Model (or Cylinder Source Model) solution allows to set out the soil thermal conductivity and the borehole thermal resistance. More accurate approaches to improve the TRT predictive capabilities can be found within parameter estimation procedures supported by numerical tools; this methodology was adopted to estimate soil and grout thermal conductivity and heat capacity per unit volume as well through parameter estimation procedures coupled with numerical transient two-dimensional models of the GHE; more recently, they have been coupled with numerical transient tri-dimensional GHE models, which allow a better description of the heat transfer phenomenon. In the present paper, a flexible parameter estimation technique based on a tri-dimensional numerical model of the geothermal system is applied to simulated TRT data, in order to validate a procedure aimed to restore the proper value of both the soil and the grout thermal properties necessary to the GHE design. The 3D simulation of the Geothermal Energy Storage System behaviour during the TRT is performed by adopting the finite element method implemented within the Comsol Multiphysics® environment. The parameter estimation procedure applied to simulated TRT data enables to discuss the capability of this method, with regards to the characterization of GHE in real conditions.