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Geo Thermal

What is GEO Thermal?

Geothermal power (from the Greek roots: geo, meaning earth, and thermos, meaning heat) is power extracted from heat stored in the earth. This geothermal energy originates from the original formation of the planet, from radioactive decay of minerals, and from solar energy absorbed at the surface. It has been used for space heating and bathing since ancient roman times, but is now better known for generating electricity. About 10 GW of geothermal electric capacity is installed around the world as of 2007, generating 0.3% of global electricity demand. An additional 28 GW of direct geothermal heating capacity is installed for district heating, space heating, spas, industrial processes, desalination and agricultural applications.

Benefits

Geothermal power is cost effective, reliable, and environmentally friendly, but has previously been geographically limited to areas near tectonic plate boundaries. Recent technological advances have dramatically expanded the range and size of viable resources, especially for direct applications such as home heating. Geothermal wells tend to release greenhouse gases trapped deep within the earth, but these emissions are much lower than tho conventional fossil fuels. As a result, geothermal power has the potential to help mitigate global warming if widely deployed instead of fossil fuels.

How it works

 
 

Vertical closed loop field

A vertical closed loop field is composed of pipes that run vertically in the ground. A hole is bored in the ground, typically, 150 to 250 feet deep (45275 m). Pipe pairs in the hole are joined with a U-shaped cross connector at the bottom of the hole. The borehole is commonly filled with a bentonite grout surrounding the pipe to provide a good thermal connection to the surrounding soil or rock to maximize the heat transfer. Vertical loop fields are typically used when there is a limited square footage of land available. Bore holes are spaced 526 m apart and are generally 15 m (50 ft) deep per kW of cooling. During the cooling season, the local temperature rise in the bore field is influenced most by the moisture travel in the soil. Reliable heat transfer models have been developed through sample bore holes as well as other tests.

 

Horizontal closed loop field

A horizontal closed loop field is composed of pipes that run horizontally in the ground. A long horizontal trench, deeper than the frost line, is dug and U-shaped coils are placed horizontally inside the same trench. A trench for a horizontal loop field will be similar to one seen under the slinky loop field; however, the width strictly depends on how many loops are installed. Horizontal loop fields are very common and economical if there is adequate land available.

 

Closed pond loop

A closed pond loop is not as common, but is becoming increasingly popular. A pond loop is achieved by placing coils of pipe at the bottom of an appropriately sized pond or water source. This system has been promoted by the DNR (Department of Natural Resources), who support geothermal systems and the use of ponds for geothermal systems. The two images below show a pond loop close up and the pond loop as it is about to be sunk to the bottom of a pond. This loop field is for a 12-ton system, which is unusually large for most residential applications. As you can tell by the pictures; a pond loop is extremely similar to a slinky loop, except that it is attached to a frame and located in a body of water versus soil.