Geothermal Systems for Your Home
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Courtesy Eddy Smalley
Vertical drilling faces obstacles in the city, such as trees and owerlines above and sewer and telephone lines below.
Given space limitations in urban settings, most geothermal systems will involve vertical closed-loop fields. Here, a hole is bored 50 to 200 feet into the ground (200 feet is about the height of a 20-story building), and two U-shaped loops of pipe are inserted in the hole, followed by a special grout sealing material. In suburban areas with more space, a horizontal field may be used where the piping is buried 4 to 6 feet deep using a “slinky style” technique or looping the pipe back over itself, and covering each length with soil.
When comparing different geothermal heating systems, make sure the systems are certified based on the efficiency of their performance from two independent programs: Energy Star and the Air Conditioning, Heating and Refrigeration Institute. According to the U.S. Department of Energy, if in doubt, make sure the geothermal heat pump has a coefficient of performance (COP) of 2.8 or greater and an energy efficiency ratio (EER) of 13 or greater.
Due to the technical aspects and equipment needed for geothermal heat-pump systems, they’re not do-it-yourself projects. Have them installed by professional dealers who specialize in various heat-pump systems and the technical details of local geology and hydrology. Check with your local utility, the International Ground Source Heat Pump Association or the Geothermal Exchange Organization for installers in your area.
Investing in Energy Savings
According to the U.S. DOE, geothermal heat pumps are priced based on their capacity, running about $2,500 per ton of capacity. A geothermal heat-pump system designed for an average American residence (three or four people in a 1,500- to 2,000-square-foot home) will cost about $7,500 for a 3-ton unit (before federal or state incentives), including installation, though that cost will likely be higher for vertical systems.
Depending on soil conditions, climate, system features and incentives, your initial investment can be recovered within two to 10 years as a result of energy savings. Most geothermal systems can be covered under your homeowner’s insurance policy and do not require any other liability coverage.
Among the first steps in evaluating your site and home for a geothermal heat pump system is determining just how much heat loss you might expect from your building, then sizing the system to meet these needs. That’s why having a well-insulated home can help reduce your space-heating and -cooling needs. An installer will help you evaluate the level of insulation, exposure of the building to the sun, type and number of windows, and a host of other construction and design issues. The results of these calculations will determine the amount of heat (or cooling) needed to keep your home comfortable. More isn’t better when it comes to planning a geothermal system. You want the system to be just enough to meet your needs.
About the Author: John Ivanko co-authored Rural Renaissance (New Society Publishers, 2008) and the award-winning ECOpreneuring (New Society Publishers, 2009). He and his family operate Inn Serendipity, a bed-and-breakfast completely powered by the sun and wind.
This article originally appeared in the January/February 2011 Urban Farm.
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