Geothermal heat pumps (GHP) or Geoexchange are able to heat, cool, and supply a building with hot water.

TECHNOLOGY
GHP technology relies on the fact that the Earth (beneath the surface) remains at a relatively constant temperature throughout the year, warmer than the air above it during the winter and cooler in the summer, very much like a cave. The geothermal heat pump takes advantage of this by transferring heat stored in the Earth or in ground water into a building during the winter, and transferring it out of the building and back into the ground during the summer. The ground acts as a heat source in winter and a heat sink in summer.1

TYPES
Using the Earth as a heat source/sink, a series of pipes, commonly called a "loop," is buried in the ground near the building to be conditioned. It circulates a fluid (water, or a mixture of water and antifreeze) that absorbs heat from, or relinquishes heat to, the surrounding soil, depending on whether the ambient air is colder or warmer than the soil. The loop can be buried in a number of different ways:

• Horizontal installation of the loops is most cost-effective for residential installations where sufficient land is available.

• Vertical loops are installed in the instances when land area required for horizontal installation is insufficient.

• If a residential home is next to a pond or lake, the option to lay horizontal loops sideways under the body of water, using the water as a source/sink, is available.

• There exists an open loop technology that takes in water directly into the heat pumps. 2

ENVIRONMENTAL IMPACT
Geothermal heat pumps can reduce energy consumption - and corresponding emissions - up to 44% compared to air-source heat pumps and up to 72% compared to electric resistance heating with standard air-conditioning equipment. GHPs also improve humidity control by maintaining about 50% relative indoor humidity, making GHPs very effective in humid areas.3

BENEFITS
The biggest benefit of GHPs is that they use 25% to 50% less electricity than conventional heating or cooling systems. GHP systems have relatively few moving parts, and because those parts are sheltered inside a building, they are durable and highly reliable. Since they usually have no outdoor compressors, GHPs are not susceptible to vandalism. On the other hand, the components in the living space are easily accessible, which increases the convenience factor and helps ensure that the upkeep is done on a timely basis. Systems typically have a 25 year life with the ground loop lasting 50+ years.4

DISADVANTAGES
The initial cost of a GHP system varies greatly according to labor costs, geology, system type, permits, and equipment selected. Overall a 3-ton GHP system initially costs $4,000 to $11,000 more than an air-source heat pump system, with a return on investment seen in 5-10 years. Finance and incentives are available for commercial buildings, but limited incentives for residential applications.

GEOTHERMAL HEAT PUMPS IN THE GREAT CENTRAL VALLEY
From 2003 to 2004, the San Joaquin School District chose to install GHP systems for nine of its new community schools in Stockton, Tracy, Lathrop, and Manteca.

VALLEY ACCESS POTENTIAL
There are numerous GHP consultants, engineers, designers, drillers, and loop installers throughout California. Many installations can be found throughout the Valley and the rest of the state. It is estimated that there are approximately 50,000 GHPs installed in the U.S. every year.

For more information on geothermal heat pumps visit the U.S. Dept. of Energy at
http://www1.eere.energy.gov/geothermal/heatpumps.html

1 US DOE EERE: www1.eere.energy.gov/geothermal/heatpumps.html (last accessed April 23, 2009)
2 US DOE EERE: www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12650 (last accessed April 23, 2009)
3 US DOE EERE: www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12660 (last accessed April 23, 2009)

4 Ibid.