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Types of
Geothermal Heat Pump Systems
There are four basic types
of ground loop systems. Three of these—horizontal, vertical, and
pond/lake—are closed-loop systems. The fourth type of system is
the 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.
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 four feet deep. The
most common layouts either use two pipes, one buried at six
feet, and the other at four feet, or two pipes placed
side-by-side at five feet in the ground in a two-foot wide
trench. The Slinky™ method of looping pipe allows more pipe in a
shorter trench, which cuts down on installation costs and makes
horizontal installation possible in areas it would not be with
conventional horizontal applications.
Vertical
Large commercial buildings
and schools often use vertical systems because 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 four inches in diameter)
are drilled about 20 feet apart and 100–400 feet deep. Into
these holes go two pipes that are connected 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
connected 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 eight feet under the surface to
prevent freezing. The coils should only be placed in a water
source that meets minimum volume, depth, and quality criteria.
Open-Loop
System
This type of system uses
well or surface body water as the heat exchange fluid that
circulates directly through the GHP system. Once it has
circulated through the system, the water returns to the ground
through the well, a recharge well, or surface discharge. This
option is obviously practical only where there is an adequate
supply of relatively clean water, and all local codes and
regulations regarding groundwater discharge are met.
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