How Does A Geothermal
Home Heating System Work?
The basic elements of a geothermal heat pump (GHP) system include
- Ground loop — system of fluid-filled plastic pipes buried in the shallow ground, or placed
in a body of water, near the building
- Heat pump — removes heat from the fluid in the pipes, concentrates it, and transfers it to
the building (for cooling, this process is reversed)
- Air delivery system — conventional ductwork used to distribute heated or cooled air
throughout the building.
Simply put, a GHP works much like the refrigerator in your kitchen, with the addition of a few
extra valves that allow heat-exchange fluid to follow two different paths: one for heating and one for
cooling. The GHP takes heat from a warm area and exchanges the heat to a cooler area, and vice versa. The
beauty of such a system is that it can be used for both heating and cooling—doing away with the need for
separate furnace and air-conditioning systems—and for free hot water heating during the summer
Geothermal heat pumps use electricity to heat and cool, just like a conventional heat pump.
However, unlike a conventional heat pump, GHPs use the relatively constant temperature of the shallow Earth
as a source of heat in the winter and as a repository for heat in the summer.
In the winter, the fluid passing through the underground (or underwater) loops of piping is
warmed by the Earth's heat. The collected heat is extracted and concentrated by the heat pump, and
distributed through the building's ductwork.
To cool the building in the summer, this process is reversed — the heat pump moves heat from the
indoor air into the underground loops, where it is transferred to the relatively cooler ground. The heat
removed from the indoor air during the summer can also be used to produce some of your hot water, or to heat
swimming pools, instead of transferring it to the ground.
Types of GHP
Geothermal heat pumps are generally classified as
"closed-loop" or "open-loop" systems based on the type of ground loop that they
- Closed-loop systems. Closed-loop systems circulate a solution of
water and antifreeze through a series of sealed loops of piping. The loops can be
installed in the ground horizontally or vertically, or they can be placed in a body
of water, such as a pond.
- Open-loop systems. Open-loop systems circulate water drawn from a
ground or surface water source. Once the heat has been transferred into or out of the
water, the water is returned to a well or surface discharge (instead of being
recirculated through the system). Open-loop systems are not recommended for residential
Heating Water for Buildings and Pools with GHPs
- Buildings. Most geothermal heat pumps sold today are equipped with a "desuperheater"
to meet up to half of your home or business's hot water needs. Desuperheaters provide the greatest
benefit during the summer, when hot water is produced using the excess heat removed from the building
during the cooling process. In the winter, desuperheaters can also reduce your hot water bills by
preheating water. Desuperheaters are standard on some units, optional on others. Stand-alone systems that
will heat water on demand (instead of only when space heating/cooling takes place) can also be
- Pools. Pool heating using a GHP is effective in warm climates, where a great deal of
excess heat is produced during the space cooling season. You will need to purchase a separate
"water-to-water" heat exchanger to heat your pool.
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