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Heat Exchangers

The heat exchanger refers to the underground pipe network used to reclaim heat from the ground. This piping system is the key to the system's efficiency. The choice of whether to use horizontal or vertical ground heat exchangers usually boils down to land area and economics.

If land area, without hard rock, is available, a horizontal system is usually the most economic. If the soil conditions are rocky or sandy, then a vertical system may well be the choice. Trenching and drilling costs are obviously major factors.

A horizontal system will use a number of horizontal trenches. Piping system designs range from a single pipe, to multiple pipes arranged vertically in a narrow trench, to multiple pipes in a wider trench.

Another approach is the increasingly popular "Slinky " in either a compressed coil or the extended version. A slinky is a coil of plastic tubing laid in a trench and buried. The advantage of a slinky is that a large heat exchanger can be installed in a relatively small area.

Slinky coils are popular in residential applications since they use less trench length, and can be quickly installed in a slit trench where they are self supporting or they can be laid flat in an excavated area, as in a commercial application.

Vertical borehole systems are used where land area is limited, where the soil is too rocky for an economic horizontal system, and for large commercial or educational facilities.

A number of boreholes are drilled. Long "hairpin" shaped loops, U-bend pipes, are inserted. They're backfilled, plugged or grouted, and the pipes connected to headers in a trench leading back into the building. The drilling depth is determined by the lowest total cost based on conditions at the job site. Typical borehole depth is 150 to 250 feet. The objective is to install a specific amount of pipe.

Spacing vertical boreholes for commercial systems can be done in a variety of ways lines, squares, rectangles, grids depending on available land areas.

Designers must consider the effects of long term temperature build-up, typically using computer resources available from heat pump manufactures and IGSHPA, which offer computer modeling tools for this purpose.

These vertical earth coils should also be spaced away from foundations, property lines, utility lines, drain fields, wells and sewage sources.

And furthermore . . .

Ground Coupling Systems Design
Ground Heat Exchanger Design