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"Mining" the Earth for Heat:
 | Americans usually rely on two familiar systems to heat homes or
buildings: fuel-powered furnaces or boilers (which burn gas, oil, or
propane) and electric-powered air-source heat pumps or baseboard radiant
heat. However, these traditional systems present two drawbacks. First,
even highly efficient models pollute the environment because fuel must be
burned to produce heat. Second, energy prices are rising. Accordingly,
people want cost-effective long-term heating and cooling options.
Geothermal systems are one such option: they are being installed in homes,
businesses, and schools across the country.
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Geothermal 101:
| What is a "geothermal" system? It takes advantage of the Earth’s
ability to store vast amounts of heat in the soil ("geo" means earth and
"thermal" refers to heat). This heat energy is maintained at a constant
temperature (50°F to 70°F depending on latitude) in the soil and
near-surface rocks. In Wisconsin, the soil maintains a 50°F temperature
beginning approximately four feet down, well past the winter frost line.
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| Geothermal heating systems, also called ground-source heat pumps,
"capture" this steady supply of heat energy and "move" it from the Earth
and through a home or building. Basically, once installed, a home or
building owner will use much less energy, save money each month, and
reduce the amount of pollution produced by fossil fuel systems. In
Wisconsin, for example, two school districts recently began installing
geothermal systems at area high schools. In both Fond du Lac and
Evansville, district administrators were "sold" on this technology’s
energy efficiency and its ability to yield long-term cost savings. Schools
across Wisconsin and the country have faced skyrocketing energy bills and
they are searching for cost-effective alternatives. Geothermal systems
represent a proven option. In addition, they utilize a renewable energy
source—the Earth’s naturally-occuring heat energy.
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What’s Wrong With Good, Old-Fashioned Combustion?
| Traditional heating systems rely on combustion (the burning of fuel)
either on site or at the power plant. Fuel-powered heating units, such as
gas and boiler systems, burn fuel at the site to produce heat energy.
Electric-powered heating and cooling systems do not require combustion at
the site of the furnace; instead, it occurs at power plants. In 1998,
approximately 80% of U.S. electricity was produced by burning fossil
fuels. Only nuclear, wind, and hydroelectric plants do not burn fossil
fuels.
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| The problem with combustion systems is that the by-products they
produce contain harmful emissions. These emissions degrade air quality and
contribute to other environmental problems including acid rain and the
greenhouse effect. For the health of individuals and communities
throughout the world, it makes sense to develop heating and cooling
technologies that reduce or eliminate fossil fuel combustion.
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How Ground Source Heat Pumps Work:
| A heat pump is a mechanical device that transfers heat from one source
to another. Ground-source units pull heat from the earth and transfer it
to homes or buildings. Heat pumps (despite their name) can provide both
heating and cooling. The cooling process is simply the reverse of the
heating process: heat is taken out of a building and returned to the
Earth.
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| Typical ground-source heat pumps transfer heat using a network of
tubes, called "closed loops." Basically, the loops are filled with either
water, refrigerant or an anti-freeze solution. They run through the ground
in the vicinity of a building and the liquid absorbs the Earth’s heat
energy. Then, this warmed liquid is pumped back through the system into
the building. This process provides heat to the building space. Once the
fluid passes through the building and transfers its energy, it flows
through the loop system back to the Earth and the process repeats itself.
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| In the summertime, these systems "reverse" into cooling mode.
Technically, the system does not "run backwards." Instead, a series of
valves enables the system to switch the "hot" side and the "cold" side.
The heat from the building is transferred to the liquid in the loop and
this liquid is pumped back into the ground. When the ground source heat
pump is in cooling mode, it usually has an excess of warmed liquid in the
system. This liquid can heat water for the building and basically
eliminate the use of the hot water heater during the summer months.
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Saving Energy:
| Ground-source heat pumps can use 25%-70% less electricity than
conventional electric heating and cooling systems. First, in winter
heating mode, a ground-source heat pump uses energy from the Earth to
provide heat, whereas air-source heat pump try to extract the last bits of
heat energy out of cold winter air. Because of the long, cold Wisconsin
winters, air-source heat pumps are not effective or efficient.
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| Second, ground-source heat pumps are more energy efficient than
conventional electric heaters because they maximize the thermodynamic
advantage of a heat transfer fluid. This benefit enables the ground source
heat pump to produce more heat energy output than electric energy input.
Conventional electric heaters on the other hand don’t quite produce as
much heat output as electric input. (Under some conditions, a ground
source heat pump cannot meet the required heating needs. In these cases,
supplemental heat must be provided from another source–usually
conventional electric units.)
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| Third, during the summer, the ground source heat pump "reverses" into
cooling mode. This fact makes the ground-source heat pump more energy
efficient for cooling than a traditional air conditioner.
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| Finally, when a desuperheater is installed, energy from the ground
source heat pump can be transferred to the hot water tank. As a result,
building occupants receive "free" hot water in the summer and very
low-cost hot water in the winter.
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| Most of a ground-source heat pump’s electrical energy requirement (70%
to 80%) is consumed by the compressor and pump that combine to move heat
energy to or from the ground, through the loop system, and into or out of
a building. The remaining 20% to 30% of the electricity is used for fan(s)
and controls to distribute the conditioned air throughout the building.
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Saving Money:
| A ground source heat pump system, including the underground loops,
costs about $2,500 per ton of capacity, or roughly $7,500 for a 3-ton unit
(typical residential size). Approximately half of this cost is related to
the geothermal loop configuration. It can be expected to last from 20 to
30 years with minimal maintenance. A conventional heating and cooling
system costs up to $4,000.
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| At first glance, this price difference of $3,500 may seem impractical
and too costly. However, buyers must carefully consider monthly energy
costs over the life of the equipment when making a decision. As the school
administrators in Fond du Lac and Evansville learned this past year,
rising energy prices can destroy annual budgets and geothermal systems are
a good way to minimize future price shocks.
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| Since these systems use from 25% to 50% less energy than conventional
systems, users will spend less on their monthly energy bills. In fact,
many homeowners could spend from $35 to $70 less per month, meaning that
most ground source systems will "pay for themselves" in 2 to 10 years. The
additional cost of $3,500 will be recovered from the monthly energy
savings. After the "payback" period, the owner will simply pay
much-reduced utility bills.
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| Ground-source heat pumps can be retrofitted in existing homes that
have traditional forced-air systems. In most cases, the heat pump can be
connected to the existing ductwork while the loop system is installed
outside in the ground adjacent to the home.
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