The earth acts like a massive heat sink that maintains a constant temperature year-round. Geothermal technologies utilize this fact to provide one of the most efficient heating and cooling technologies available. Geothermal systems transfer heat to and from the earth through a series of pipes, or loops, which are installed below the surface of the ground or submersed in a pond or lake. In the winter the fluid that circulates in the loop transfers heat from the earth to the building. In the summer the process is reversed and the fluid that circulates in the loop transfers heat from the building to the earth.