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Closed Loop Systems

The most common type of geothermal installation, a closed loop system can be buried underground in a number configurations.

Horizontal Loops

If adequate land area without hard rock is available, a horizontal loop installation is usually the most economic.

A horizontal system uses a number of trenches. The piping can be configured in the trenches in several ways:

The trenches are normally four feet deep or more, and vary in length depending on the number of pipes to be buried. One of the advantages of a horizontal loop system is being able to lay the trenches according to the size of the lot.

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Vertical Loops

If the land area available is limited or too rocky for trenching, a vertical loop may be installed for the geothermal piping.

To install a vertical loop, Sobieski Services will bore holes into the ground. Long, hairpin-shaped loops of pipe are then inserted. The hole is backfilled, plugged or grouted, and the pipes are connected to headers in a trench leading back to the building.

The drilling depth is determined by the lowest total cost based on the conditions at the job site. A typical borehole depth is 150 - 250 feet.

The objective of a vertical borehole is to install a specific amount of pipe, not to reach a certain depth. If 1,200 feet of pipe are required, three 200-foot boreholes are acceptable and may be  more cost-effective.

Drilling boreholes for geothermal loops is much simpler than drilling to find well water. The borehole is generally smaller, which reduces drilling time, and no casing is required because the hairpin-shaped loop is the casing.

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Pond (Lake) Loops

Pond or lake loops are very economical to install when a large body of water is available for use by the geothermal heating and cooling system. Coils of pipe, often referred to as "slinky" coils, are simply placed on the bottom of the pond or lake to capture the geothermal energy.

A slinky can also be used in the horizontal closed loop applications. This method concentrates the heat transfer surface into small volume, requiring less land area and shorter trenching - a big plus for homeowners.

A compact slinky will reduce trench length by about two-thirds; an extended slinky will reduce trench length by about one-third. Specific design lengths will vary with the climate, soil and the heat pump's run fraction.

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Source: WaterFurnace & Alliant Energy