Abstract: Ground Thermal Response (TRT) tests are employed to calculate ground thermal characteristics for Ground Heat Exchanger (GHE) design and optimization purposes. There are plenty of 3D models to increase the accuracy of the calculated characteristics, with which the fluid outlet temperature is obtained based on the experimental inlet temperature. To simulate other behaviours not tested in the GHE, it is necessary to correctly simulate the conduct of the fluid inside the test equipment. For this reason, a simple model has been obtained which considers the absorption of heat by the elements of the equipment during an initial time through a variable equivalent heat capacity term and a load factor.