System information

34
Geothermal Applications
Carrier: Turn to the Experts.
Pond/Lake Applications
Pond loops are one of the most cost effective applications of
geothermal systems. Typically 1 coil of 300 ft of PE pipe per ton [26
meters per kW -- one 92 meter coil per 3.5 kW of capacity] is sunk
in a pond and headered back to the structure. Minimum pond sizing
is 1/2 acre [0.2 hectares] and minimum 8 to 10 feet [2.4 to 3 meters]
deep for an average residential home. In the north, an ice cover is
required during the heating season to allow the pond to reach an
average 39°F [3.9°C] just below the ice cap. Winter aeration or
excessive wave action can lower the pond temperature preventing
ice caps from forming and freezing, adversely affecting operation
of the geothermal loop. Direct use of pond, lake, or river water is
discouraged because of the potential problems of heat exchanger
fouling and pump suction lift. Heat exchanger may be constructed of
either multiple 300 ft. [92 meter] coils of pipe or slinky style loops as
shown in Figure 9. In northern applications the slinky or matt style is
recommended due to its superior performance in heating. Due to
pipe and antifreeze buoyancy, pond heat exchangers will need weight
added to the piping to prevent fl oating. 300 foot [92 meter] coils
require two 4” x 8” x 16” [102 x 203 x 406 mm] blocks (19 lbs. [8.6
kg] each) or 8-10 bricks (4.5 lbs [2.1 kg] each) and every 20 ft [6
meters] of 1-1/4” supply/return piping requires 1 three-hole block.
Pond Coils should be supported off of the bottom by the concrete
blocks. The supply/return trenching should begin at the structure and
work toward the pond. Near the pond the trench should be halted
and back fi lled most of the way. A new trench should be started from
the pond back toward the partially backfi lled fi rst trench to prevent
pond from fl ooding back to the structure.
Building Entry
Seal and protect the entry point of all earth coupling entry points
into the building using conduit sleeves hydraulic cement.
Slab on Grade Construction
New Construction: When possible, position the pipe in the proper
location prior to pouring the slab. To prevent wear as the pipe
expands and contracts protect the pipe as shown in Figure 10. When
the slab is poured prior to installation, create a chase through the
slab for the service lines with 4 inch [102 mm] PVC street elbows
and sleeves.
Retrofi t Construction: Trench as close as possible to the footing.
Bring the loop pipe up along the outside wall of the footing until it
is higher than the slab. Enter the building as close to the slab as the
construction allows. Shield and insulate the pipe to protect it from
damage and the elements as shown in Figure 11.
Pier and Beam (Crawl Space)
New and Retrofi t Construction: Bury the pipe beneath the footing and
between piers to the point that it is directly below the point of entry
into the building. Bring the pipe up into the building. Shield and insulate
piping as shown in Figure 12 to protect it from damage.
Below Grade Entry
New and Retrofi t Construction: Bring the pipe through the wall as
shown in Figure 13. For applications in which loop temperature may
fall below freezing, insulate pipes at least 4 feet [1.2 meters] into the
trench to prevent ice forming near the wall.
Figure 9: Typical Pond/Lake Loop Confi gurations
Pressure Testing
Upon completion of the ground loop piping, hydrostatic pressure test
the loop to assure a leak free system.
Horizontal Systems: Test individual loops as installed. Test entire system
when all loops are assembled before backfi lling and pipe burial.
Vertical U-Bends and Pond Loop Systems: Test Vertical U-bends and
pond loop assemblies prior to installation with a test pressure of at
least 100 psi [689 kPa]. Perform a hydrostatic pressure test on the
entire system when all loops are assembled before backfi lling and
pipe burial.
Closed Loop Design/Installation Guidelines