Probabilistic approach to TRT analysis: evaluation of groundwater flow effects and machine - borehole interaction

Thermal Response Test (TRT) measures the temperature response of a Borehole Heat Exchanger (BHE) to heat injection or extraction. The temperature response is related to the ground and borehole thermal parameters such as thermal conductivity and heat capacity; TRT is therefore used to obtain estimates on the equivalent values of these parameters. After all, the test results can be affected by different elements such as: ground temperature variations, groundwater movement (GW), weather conditions, seasonal event, etc. This work aims to analyse the relationships among the TRT results and the variability of these factors, and in particular it tries to study the effect of groundwater flow on thermal parameters. This paper aims to provide a new framework to seek possible solutions, integrating classical methodologies with probabilistic and multivariate geostatistical modelling. The instruments are the variogram and cross covariance, which are sensitive and informative with regard to the effects of groundwater flow on the TRT results. Also, the behaviour of the TRT machine with different operating and boundary conditions is captured with the geostatistical approach, yielding a good understanding of the heat exchange.