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1. Geothermal Energy Systems
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.
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.
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.
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.
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.
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.
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.
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.)
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.
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.
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 size for new home construction). 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.
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.
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.
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.