Environmental Engineering Reference
In-Depth Information
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There are four basic types of ground-loop geothermal heat pump systems. Three of
these—horizontal, vertical, and pond/lake—are closed-loop systems. The fourth
type of system is an open-loop option. Which one of these is best depends on the
climate, soil conditions, available land, and local installation costs at the site. All of
these approaches can be used for residential and commercial building applications
(EER E , 2014b).
Closed-Loop Systems
•
Horizontal
—This type of installation is generally most cost effective for
residential installations, particularly for new construction where sufficient
land is available. It requires trenches at least 4 feet deep. The most com-
mon layouts use either two pipes, one buried at 6 feet and the other at 4
feet, or two pipes placed side-by-side 5 feet in the ground in a 2-foot-wide
trench. The Slinky™ method of looping pipe allows more pipe in a short
trench, which cuts down on installation costs and makes horizontal instal-
lation possible in areas where conventional horizontal applications would
not be possible.
•
Vertical
—Large commercial buildings and schools use vertical systems
when the land area required for horizontal loops would be prohibitive.
Vertical loops are also used where the soil is too shallow for trenching,
and they minimize the disturbance to existing landscaping. For a vertical
system, holes (approximately 4 inches in diameter) are drilled about 20 feet
apart and 100 to 400 feet deep. Into these holes go two pipes that are con-
nected at the bottom with a U-bend to form a loop. The vertical loops are
connected with horizontal pipe (i.e., manifold), placed in trenches, and con-
nected to the heat pump in the building.
•
Pond/lake
—If the site has an adequate water body, this may be the lowest
cost option. A supply line pipe is run underground from the building to
the water and coiled into circles at least 8 feet under the surface to prevent
freezing. The coils should only be placed in a water source that meets mini-
mum volume, depth, and quality criteria.
DID YOU KNOW?
Geothermal system life is estimated at 25 years for the inside components
and 50+ years for the ground loop. Approximately 50,000 geothermal heat
pumps are installed in the United States each year. Even with the large num-
ber of annual installations, it is important to keep in mind that heat pumps
are relatively expensive to install new. This is especially true of the deep-
ground source type. It may take a long time for a new system to pay for itself.
