Open Loops
While the majority of geothermal installations use a closed lop system, another option is an open loop system. Instead of using an antifreeze solution sealed inside the buried piping, an open loop system uses water from a surface or underground source - such as a pond, lake, or well. The water is pumped into the heat pump unit where the heat is extracted; the water is then discharged back into the original source. Well water designs are the most common and most cost-effective. The well supplies both household water and water for the heat pump. Approximately three gallons per minute of well water are needed per ton of cooling capacity. A 3,000-square-foo, well-insulated home would typically require 10 to 15 gallons per minute. Water quality is an important issue with open-loop systems. Mineral deposits can build up inside the heat exchanger, iron and other impurities can clog a return well, and organic matter from ponds and lakes can quickly damage a geothermal system. Water should be tested for acidity, mineral content and corrosiveness. Since plastic pipe is buoyant even when filled, headers and service lines must be anchored in place. The loops, anchors and service lines should be assembled, leak checked and pressure tested on land. The assembly should be filled with air, not water, and floated into place with the weights attached. When in the proper location, the system is filled wit water and sunk into position. Service lines must be buried from the structure, across the shore and out into the body of water. They may be secured to docks or piers at or near the bottom. There have been a number of successful installations where polyethylene or polybutylene pipe coils are set in lakes or ponds.
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