Methods of Extraction, Methods to get Heat

Self Taken
Self Taken Photo. Chena Hot Springs Resort Geothermal Plant

To get the work or electrical energy from the water, you have to have access to the hot water in the ground. To get the water, you have to drill a well into the source. Sometimes, in the case of Chena Hot Springs, the well only has to be about 3000 feet deep to get water with the proper temperature. Other wells have to be drilled to 10,000 feet or more to get the temperature.
In the case of geothermal heating of your house, the ground 6 to 10 feet under the surface is a constant temperature: 45 to 80 degrees Fahrenheit depending on where you live. This is sufficient to heat a house. The commercial use of geothermal power needs the elevated temperatures of at least 160 degrees Fahrenheit.

Once you have the desired water temperatures, you can do a few things. You can pump the water up, send it through a condenser which will elevate the temperature if the water isn't high enough, then pipe a refrigerant chemical through the water.  When the refrigerant vaporizes, that steam will drive the turbine. This is known as a binary cycle. The other method of driving a turbine is to condense the water in such a way that it will vaporize, then the water vapor will drive the turbine. This is known as the flash steam method.
In both methods, the water is then cooled, and pumped back into the rock in a separate shaft.

Since it is unlikely that drilling a 5000 foot well in a backyard is possible, housing units utilize the constant temperature 6 to 10 feet under the ground. Pipes full of either water or an antifreeze liquid are run in horizontal trenches or vertically in about 50 foot holes and then hooked up to a system to extract the heat and heat the home. The housing units have a compressor which helps heat a refrigerant liquid to heat the air in the duct work in your house.

The refrigerant in both the residential and commercial cases is used only because it has a lower vaporization temperature. The refrigerant at Chena Hot Springs is Freon-134a.

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