This paper implements a sensitivity analysis of a vertical Geothermal Heat Exchanger model from a Ground Coupled Heat Pump system, simulated with the software TRNSYS. Afterward, the optimization software GenOpt is applied in an iterative calibration process, calibrating those factors that were proven to be the most important in the sensitivity analyses. A comparison is made between the calibrated simulation and the experimental data collected from the system, obtaining a significant reduction in the error. The results demonstrate that the methodology used is effective, which indicates that a sensitivity analysis is an appropriate method to determine which parameters should be calibrated, while avoiding biases of the modeler and decreasing the number of iterations required in the calibration by approximately 89%.