Types of Geothermal Heat Pumps Available and How They Work

The basic elements of a geothermal heat pump (GHP) system include a:

• 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.

How GHPs Work
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 Systems
Geothermal heat pumps are generally classified as "closed-loop" or "open-loop" systems based on the type of ground loop that they use:

• 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).

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 purchased.
• 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.

The sites below provide more detailed information on how geothermal heat pumps work:

• How GeoExchange Systems Work
  Provides a basic overview of how GeoExchange (or, geothermal heat pump) systems work, and some of the benefits these systems provide. Includes an informative "how it works" animation.
  
  From the Geothermal Heat Pump Consortium, a non-profit organization working to promote the growth of energy-efficient, environmentally friendly heating and cooling technologies.
  
  
• Different Types of Ground Loops
  This page provides some diagrams of different open-loop and closed-loop system configurations.
  
  Excerpt from An Information Survival Kit for the Prospective Geothermal Heat Pump Owner, a publication of Oregon Institute of Technology's Geo-Heat Center.