Geothermal Heat Pumps
The geothermal heat pump takes advantage of energy
stored within the earth. This stored energy is collected from the sun's
energy striking the earth. This solar energy is absorbed by the ground
around your house all year long. The geothermal system uses this huge mass
of stored energy to heat and cool our homes and businesses.
How is heat exchanged?
There are two main components to the geothermal
system: the buried closed loop ( a loop of pipe buried in the ground ) and
the indoor unit which is tied into a proper ductwork system. There is no
outdoor unit used with this system as you would find with a conventional
heat pump system.
Heat is exchanged with the earth by using a buried
earth loop and a small circulating pump. Only two types of pipe are
acceptable for the earth loop - polybutylene and high density polyethylene
pipe. This earth loop must be installed by a certified contractor. The loop
is carefully assembled on location using heat fusion to join the pipes where
necessary. Once this is done, the loop becomes one piece of pipe with
parallel circuits. The integrity of this loop is such that a virtual
lifetime of trouble free use can be expected. Installation by any other
means may cause a failure of the pipe because of the unique conditions below
the ground.
Water, with an antifreeze solution, is circulated
through the earth loop. In the heating mode, the indoor unit extracts heat
from the solution in the loop, and with a refrigeration process, intensifies
that heat and delivers it through the duct system at temperatures ranging
from 95 to 105 degrees F. Since heat is being transferred - not produced -
the geothermal system is delivering over three units of energy for every
unit of energy it consumes. This is possible due to the fact that it takes
advantage of below ground temperatures that are warmer in the winter and
cooler in the summer than the outdoor air. Since the earth loop is buried in
the ground, where temperatures are constant, the outdoor temperature does
not adversely affect the high efficiency of the geothermal system.
In the cooling mode, the indoor unit extracts heat from
inside the home, and transfers that heat into the solution circulating
through the loop. The heat is then rejected to the earth. It is much easier
to transfer heat into the cooler earth than trying to transfer it into the
90 - 100 degree F. outdoor air.
Types Of Earth Loops
The earth loop can be installed in a horizontal or
vertical configuration and a pond or lake can be utilized under the right
conditions. All three types have similar performance characteristics and,
when designed properly, each will operate as efficiently as the next. The
choice will depend on the installation cost, geographic location, land area
availability, and local codes.
Horizontal loops are generally installed in a two-pipe
design. The trench length is approximately 250 feet long with the bottom
pipe at 5-6 feet deep and the top pipe at 3-4 feet deep. A total of 500 feet
of pipe per trench will furnish enough heat for one ton ( one ton = 12,000
btu/hr.) of capacity.
The average size home requires three tons of capacity.
For this home, there needs to be three trenches 250 feet long, at least
eight feet apart, with two small pipes buried in each trench. A header
system of pipe will tie the three pair of trench pipes together, bringing
just two larger pipes into the home. When space is limited, a four or six
pipe configuration in a wider trench can dramatically shorten the trench
length. Such wider trenches generally require a backhoe rather than a chain
trencher for excavation.
Vertical loops can be installed almost anywhere and are
ideal when land surface area is minimal. Drilling equipment is used to bore
small diameter holes 100 to 200 feet deep. Approximately 150 feet of bore is
usually required per ton. A typical three ton system will have three holes
bored at 150 feet each. Two pipes are joined with a U-bend and are inserted
into each hole. A header system connects these pipes to two larger pipes
that are brought into the structure.
Pond or lake loops are simply coils of pipe placed in a
lake or pond. The pond/lake loop eliminates much of the excavating in
horizontal or vertical installations. Heat is exchanged between the body of
water and the submerged loop in the same manner as the earth loop. In most
cases, one-fourth to one-half acre surface area with an eight foot depth is
required.
In all three installations, loop lengths must be
determined after sizing the geothermal system. Unit selection is based on
the heating and cooling requirements of the building. Sized properly, the
geothermal system will provide almost all of the heating requirements of the
home, thus little or no supplementary heat is required. In most
applications, a low wattage electric heater is installed with the geothermal
system to provide supplemental heat if needed.
Domestic Hot Water
Most manufacturers offer an option, which is
becoming a standard, that produces a large percentage of the annual hot
water requirements. A "desuperheater" is installed with a small circulating
pump between the existing water heater and the geothermal system. During the
winter, when the geothermal system is operating in the heating mode, hot
water is being produced at the same high efficiency. In the summer, the heat
that is being rejected by the geothermal system is transferred to the water
heater at little or no cost.
Savings
Because of its unique efficiencies, a geothermal
system, when used with CMEC's rate of 4.7 cents per kilowatthour, can lower
your heating costs by 40 to 70 percent and reduce cooling costs by 30 to 40
percent compared to conventional heating and cooling systems. In addition,
20 to 50 percent of the water heating costs can be realized. Exact savings
will depend upon building construction, consumer life style, and electric
rates.
Along with the energy savings, there will also be
reduced maintenance costs. Since the compressor is located indoors,
protected from the weather, its useful life will be greatly extended, most
having a life expectancy of twenty years or more.If you are interested in finding out more about a
geothermal system, contact the Marketing and Member Services Dept. We will
be happy to assist you in finding all the information you need to make a
decision.
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