This paper describes the design of a geothermal air conditioning system aiming at to contribute to reduction of the energy consumption in a residence or small business. The conditioning system here described takes advantage of the surface geothermal heat as a universal, silent, odourless, renewable and clean source of thermal energy. The whole set is based on a liquid refrigerant circulating inside the buried hose hose with the help of a small water pump, so that the soil can balance different temperatures both for summer and winter. The heat is then exchanged with the ground mass, that is, if the temperature inside the building is less or higher than the underground that heat or cool can be exchanged between them without any heat pump arrangements. The prototype system is working at the moment with a geothermal heat exchanger in conjunction with an electronic control to maximize the action of the water pump and the ventilation system.