Geothermal heating and cooling is based on one simple fact: that 6 feet down in the ground the temperature is the same—between 50˚F and 60˚F- the whole year round. This means that it is relatively cool in the summer, and relatively warm in the winter. Geothermal heating is thus quite different from solar heating: solar heating works worst when you most need it–in the cold, cloudy, snowy conditions of winter; the source for geothermal heating and cooling is not affected by the weather.
For geothermal cooling, all one needs to do is to circulate water in a pipe through the ground to cool it, and use this cool water to cool the air pumped through the house in the heating ducts.