Ground properties evaluation for the design of geothermal heat pump systems and uncertainty measurement during the Thermal Response Test

The exploitation of low enthalpy geothermal resources for building heating and cooling purposes represents an important opportunity for saving energy in the domestic and service sectors, that cover about 30% of the demand of primary energy in the European Union. Vertical Borehole heat exchangers (BHE) are the most frequently adopted solution for ground coupled heat pump (GCHP) applications. The heat transfer between the borefield and the surrounding ground is driven by the ground thermophysical properties, the borefield geometry and the temporal distribution of heating and cooling loads. For these reasons the estimation of the ground properties, thermal conductivity above all, is crucial in the borefield design analysis. The thermal response test (TRT) is well assessed technique for evaluating the ground conductivity together with the equivalent borehole resistance. In this paper the ground modeling and measurement analysis are discussed with respect to TRT experiments. Starting from a set of real TRT investigations carried out in different parts of Italy, an uncertainty analysis is presented with special attention devoted to the measurement errors and disturbances, including the important effects of the typical non steady condition of the applied heat transfer rate.