The correct design of a low enthalpy geothermal system is a priority to ensure the expansion of this renewable energy in the alarming world energy panorama. In this sense, the present research has analyzed how the estimation of the initial energy demand of a space plays a fundamental role in the corre-sponding geothermal design. Thus, the main tools used in Spain (location of the study case) in the calculation of the energy demand have been used for then de-signing the shallow geothermal system. Results show that the official tools (HULC and CE3X) provide lower energy demand values and adjusted to the construction conditions of the building that allow the optimization of the geo-thermal well field. On the contrary, simpler, and more intuitive applications (regular spreadsheets and GES-CAL software) assume a higher value of heating energy demand, which in turn implies an oversizing of the geothermal scheme. Even though all the procedures ensure to cover the energy requirements of the building, the most precise tools manage to reduce the initial investment of the system and its operating costs, in addition to reducing the global CO2 emissions because of the lower power of the associated geothermal heat pump.
