The way it works is simple. The geothermal heat pump system moves heat from the ground, which has a fairly consistent temperature year-round, to a building (or from a building to the ground) through a series of flexible pipe "loops" containing water. In the winter, heat from the relatively warmer ground goes through the heat exchanger into the building.
In the summer, hot air from the building is pulled through the heat exchanger into the relatively cooler ground. Heat pump systems are so efficient that they have proven that they can lower energy bills by up to 70% over traditional types of heating systems.