THE BIG DIG
(Page 3 of 5)
If you're considering an open-loop system, make sure your
water supply or well can meet the following guidelines.
(Note: More specific questions regarding the chemical
content of nonpotable water and its suitability for use are
best directed to an equipment manufacturer.)
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• Untreated water must be potable (no brackish or
rotten egg odors).
• The water table should be within 100 feet of the
surface.
• The volume of available water should be equal to
twice the peak household use.
• Wells drilled into shallow bedrock and specifically
into karst (cavernous limestone) formations function best
if the casing can extend below the pumping water level.
(Shallow water is easily contaminated.)
• Wells drilled into sand and gravel formations
function best if a well screen is installed. (Well screens
dramatically increase the capacity of a well and assure a
longer lasting and more reliable water supply.
• Lastly, always avoid the use of galvanized pipe
fittings and steel pipe with any water system. Galvanized
steel is easily corroded by electrolysis and will fail
within a few years.
Closed-loop systems are clean, very low-maintenance
and usually carry a loop materials warranty of 25 to 55
years.
CLOSED-LOOP SYSTEMS
The good thing about closed loop geoexchange systems is
that they can be installed almost anywhere. The loop is
filled once with clean water and nontoxic antifreeze, and a
small pump recirculates the antifreeze solution between the
loop and the exchange system. Closed loop systems remain
clean, are very low on maintenance and usually carry a loop
materials' warranty of 25 to 55 years. The three types of
closed-loop systems are pond, horizontal and vertical.
Pond Loops For a six-ton geothermal system
a pond loop typically requires a pond size of at least half
an acre and a minimum depth of eight feet. Smaller ponds
may experience thermal fluctuations from the geoexchange
system, which can be stressful to aquatic life. In central
Ohio, we find our larger ponds typically run temperatures
of 70°F at eight feet in the summer, and 38°F in
the winter.
Pond loops are typically the lowest costing design of
closed loop heat exchanger. The average cost per ton of
capacity runs $500 to $600 for materials, antifreeze and
labor. A complete installation of equipment, a 10-year
warranty and a loop attached to existing ductwork costs
from $10,400 for a 2.5-ton unit to $15,300 for a two-speed,
six-ton size unit. To make trenching to a pond practical,
the pond should be at a lower elevation than the home and
no more than 300 feet away. Soil conditions should allow
for trenching without encountering bedrock or difficult
terrain.
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