During the summer, the geothermal heat pump operates as a standard central air conditioner: It removes heat from the house and vents it to the outside. A liquid refrigerant is pumped through an evaporator coil of tubing. The liquid expands as it moves through the coil, changing to its gaseous state as it absorbs heat from the air surrounding the coil. A blower then pushes air around the cooled coil through ducts and into the house. The gas, now carrying considerable heat, moves through a compressor and begins the liquefying process. It then moves to a condenser coil outside the house, where the compressed gas releases its heat and returns to a liquid state.