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WHAT IS A GEOTHERMAL SYSTEM? *
Geothermal systems use a ground source heat pump that
utilizes the earth's relatively constant temperature to provide
heating, cooling, and hot water for homes and commercial buildings.
Unlike other types of heating systems, which convert fuel to
heat, a heat pump is designed to move heat from one
place to another.
In the past, most heat pumps were the air-to-air or air source
type. Air source heat pumps rely on outdoor air for their heat
source. Geothermal heat pumps extract heat from the ground or
from water, either below or on the surface. Because ground and
ground water temperatures are a constant 7° - 13° C (45°-55° F)
year-round, this type of system is much more efficient.
There are basically two ways to move energy
from the ground and into your home – a closed loop or
an open loop. These loops are buried either vertically or horizontally.
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Vertical loops are
the ideal choice when available land surface is limited.
Drilling equipment is used to bore small-diameter holes
from 75 to 300 feet deep. |
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Pond/lake loops are
very economical to install when a body of water is available,
because excavation costs are virtually eliminated. Coils
of pipe are simply placed on the bottom of the pond or
lake. |
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Horizontal
loops are often considered when adequate
land surface is available. Pipes are placed in trenches,
in lengths that range from 100 to 400 feet. |
Closed Loop Systems
In a closed-loop system, a loop is buried horizonatlly
or drilled vertically in the earth around the home, or laid in
a nearby lake or pond. A mixture of antifreeze and
water is circulated continuously through the loop and heat
pump, transferring heat from or to the soil respectively, as
heating or air conditioning is needed. This process creates
free hot water in the summer and delivers substantial hot water
savings in the winter.
Virtually all loops
built today use high-density polyethylene (HDPE) pipe. This
type of pipe was designed to be buried in the ground; and last
50 years or more. Joints are made by fusing or melting the
pipe and fittings together, which makes a nearly leak-proof
connection. In a closed-loop
system, the fluid never comes in contact with the soil. It
is sealed inside the loop and heat pump.
Open Loop Systems
In an open-loop system, ground water is drawn up from a well
and through the heat pump, then typically pumped back into a return well. New
water is always being pumped through the system when it is in operation. It is
called an open-loop system because the ground water is open to the environment.
What
are the advantages and disadvantages of horizontal
and vertical installations?
Horizontal installations are simpler,
requiring lower-cost equipment. However, they require longer
lengths of pipe due to seasonal variations in soil temperature
and moisture content. Since a horizontal heat exchanger
is laid out in trenches, a larger area is usually required
than for a vertical system. Ground-based horizontal loop
systems draw their heat from loops of piping buried 1.8
to 2.4 metres (six to eight feet) deep in trenches. The
piping for water loop systems is installed below the winter
ice level in pond or lake, or below low tide level in the
ocean.
Where land is limited, vertical installations can
be ideal. If regional soil conditions include extensive hard
rock, a vertical installation may be the only available choice.
Vertical installations tend to be more expensive due to the
increased cost of drilling versus trenching, but since the
heat exchanger is buried deeper than with a horizontal system,
vertical systems are usually more efficient and can get by
with less total pipe. Vertical loop systems use holes bored
45 to 60 metres (150-200 feet) deep with U-shaped loops of
piping.
The land area needed for the vertical loop, however, depends
on the depth to which the boreholes can be drilled cost-effectively. For
example, if a geothermal system required 1000ft of borehole
in total, four 250ft holes would use the least amount of
area, however, depending on soil conditions, it may be easier
and more cost effective to drill five 200ft holes, seven
143ft holes or even ten 100ft holes. There must be a minimum of
10 feet of space between each bore hole, so the more holes
needed, the larger the area required.
How can I make sure the
job is done right?
Use a reputable contractor.
Don't be afraid to ask for and use references. Reputable dealers
and loop installers will be happy to give names and phone numbers
for you to call and confirm their capabilities. |
