- A ground source or geothermal heat pump works in much the same way as the heat pumps that power air conditioners and refrigerators. All of these devices work by transporting heat from one area to another using a fluid called a refrigerant. Unlike refrigerators and air conditioners, however, ground source heat pumps are capable of both heating and cooling.
- The refrigerant is driven by a powerful centrifugal pump called the compressor into a chamber called the condenser. A centrifugal pump has a series of curved blades spinning at a high rate of speed. Centrifugal force channels the fluid to the outside of the blades, where it is compressed and shot out into the condenser.
- The condenser is a length of copper tubing. The refrigerant in it is pressurized by the compressor. When the pressure on a liquid is increased, it rises in temperature. As the fluid flows through the condenser, the extra heat leaks out of the tubing either into the ground or into the house.
- At the end of the condenser is a small valve which sprays the refrigerant into the evaporator. The evaporator is a low-pressure section of piping. As the refrigerant expands in the evaporator, it cools rapidly. Heat flows into the evaporator through the tubing, either from the house or the ground. At the end of the evaporator is the compressor, which starts the whole process again.
- Ground source heat pumps are reversible. They can pump heat into the earth or out of it by changing the direction the refrigerant flows in. A heat exchanger inside the house typically blows air past one of the pipes. If the exchanger is being used to heat the house, this pipe functions as the compressor, and the air picks up its heat as it flows past. If the pump is being used to cool the house, the air blows past the evaporator, which sucks heat out of the air and cools the house. The other pipe moves heat into and out of the ground in a variety of ways.
- A direct exchange heat pump is the most direct and efficient way heat is moved. The pipe runs directly under ground or into a body of water. Because large bodies of water and the ground stay at a relatively constant temperature, the heat exchanger can efficiently pump heat into the ground to cool a building on warm days, then pump it out of the ground to warm the building back up when the weather turns cold.
- Many buildings use closed or open loop systems. The copper tubing in the primary loop flows to a heat exchanger, where it comes into contact with a secondary ground loop. If the heat pump is being used to cool the house, heat flows from the primary loop into the ground loop, which then pumps it into the ground and, for cooling, it flows in the opposite direction. These systems come in two types: closed and open loop. In closed loop, the ground loop is a closed loop which continuously circulates fluid. In an open loop system, the ground loop sucks water from a lake or other body of water to the heat exchanger, then transports it back out into the water.
