Humans have taken advantage of geothermal heat since the Paleolithic era. In recent years, it has become a stronger trend. In 2007, 28 gigawatts (GW) of geothermal heating capacity was installed around the world, satisfying 0.07 percent of global primary energy consumption.
Geothermal energy originates from the heat retained within the Earth’s core from the original formation of the planet, radioactive decay of minerals and solar energy absorbed at the surface. Most high-temperature geothermal heat is harvested in regions near tectonic plate boundaries where volcanic activity rises close to the Earth’s surface. In these areas, the ground and groundwater have unusually high temperature. However, even cold ground contains heat; only 10 feet under the surface, the ground maintains a consistent temperature of 55°F.
On account of this heat potential and due to recent advances in pump performance, extracting heat from the earth is now a rapidly growing market in the United States. According to the National Association of Home Builders (NAHB) Research Center’s Annual Builder Practices Survey data, 1.3 percent of all new homes had a geothermal heat pump in 2004, increasing to about 2 percent in 2009.
Geothermal heat pumps use the natural heat storage capacity of the earth or groundwater to provide energy-efficient heating and cooling. They should not be confused with air-source heat pumps, which rely on air. Geothermal technology is appropriate for retrofit and new construction and can be used for virtually any size home or lot in any region of the country.
In winter, water circulating inside a sealed system absorbs heat from the earth and carries it to the pump unit, where it is compressed to a higher temperature and sent as warm air throughout the home. In the summer, the system reverses and expels heat from the house to the cooler earth through the loop system. The ground loop can be installed in either a vertical well or a horizontal loop.
Vertical wells are usually more expensive and tend to be used where space is limited. The length of loop pipe required varies with soil type, loop configuration and system capacity. An open-loop system draws well water for use as the heat source and returns the water to a drainage field or another well.
Special heat pump features can include variable speed blowers and multiple-speed compressors. Add-on features include the capability to produce hot water.
“Using geothermal technology can cut a homeowner’s electrical bills up to 80 percent,” said Evie Sibert, marketing communications manager for ClimateMaster Inc., Oklahoma City.
It does not require fossil fuels, reducing the carbon footprint; it eliminates usage spikes; it provides a more constant, even temperature control; the pipe carries up to a 50-year warranty; it’s quiet; and there are no open flames, flammable fuels, or potentially dangerous fuel storage tanks to consider.
According to Galen Beachy, sales and technical support for Yoder Drilling and Geothermal Inc., Sugarcreek, Ohio, cost is the biggest block to market acceptance.
“It’s the biggest complaint the company hears. It is not a cheap system to install, and the return on investment depends on the homeowner’s current HVAC [heating, ventilating, and air conditioning] system,” he said.
Return on investment estimates range from as little as two years to as many as 11, with averages of five to seven years. According to the NAHB Research Center, the ground loop is generally the most expensive component of a geothermal heat pump system and is highly dependent on local labor rates and drilling conditions. Overall, a homeowner could expect to pay between $4,000 and $11,000 more for a 3-ton geothermal heat pump system than for an air-source system.
However, geothermal heat pumps offer high efficiency, low operating cost, and improved energy management. According to the Environmental Protection Agency, geothermal heat pumps can save homeowners 30 to 70 percent on heating and 20 to 50 percent on cooling costs over conventional systems. Reports by builders who monitor their in-place systems indicate heating and cooling savings that range between $358 and $1,475 annually.
Geothermal and the EC
According to both Beachy and Sibert, there is nothing out of the ordinary about geothermal heat pumps in terms of the electrical wiring.
“However, contractors have an opportunity to position themselves, particularly in the retrofit residential market, as being the provider to upgrade the home’s electrical system to handle the 200 amps required by the geothermal heat pumps,” Beachy said.
In addition, most HVAC contractors would prefer to have the contractor’s electrical expertise on the team.
Geothermal organizations and providers offer information about the technology, how the systems work, and the environmental benefits. Contractors can use this data to partner with geothermal installers and add their owngeothermal offerings.
BREMER, a freelance writer based in Solomons, Md., contributes frequently to ELECTRICAL CONTRACTOR. She can be reached at 410.394.6966 and firstname.lastname@example.org.