Hamilton County Schools officials are finding that a quick way to trim their energy costs lies just beneath the surface.
Underground geothermal systems installed in three of the county's newest schools are cutting in half the costs of heating and cooling the buildings, officials said.
At Signal Mountain Middle-High School, which opened in the fall of 2008, going underground with geothermal pipes for the school's heat pump saved $185,000 in energy costs in the first school year, Hamilton County Schools Assistant Superintendent Gary Waters said.
"It should pay off in less than two years," he said. "Our savings were really greater than we anticipated and have been phenomenal."
Encouraged by such savings and financially spurred with part of a $3 million federal grant to Tennessee schools, Hamilton County will consider installling another geothermal heating and cooling system at Brainerd High School, according to Greg Higgins, the district's energy manager.
"We're still working out the details, but we hope to get part of the (Department of Energy) grant to retrofit Brainerd," he said. "I've been pleased with the results at our other schools, and we hope to do other buildings over time."
In neighboring Bradley County, a geothermal system also is being installed in the new Parkview Elementary School, where school system energy manager Johnny Mull expects the $200,000 extra cost of the system should pay off in less than five years.
"If you look long term, it is definitely better for the taxpayer," said Mr. Mull, noting the success of other geothermal systems installed in four Cleveland city schools and at the Ringgold Primary School in Catoosa County, Ga.
Geothermal systems use the stable, year-round temperature underground to help preheat or cool down water circulated through heat pumps for heating and cooling school buildings. Beneath the surface, the ground temperature in Tennessee is a relatively constant 66 degrees to 68 degrees Fahrenheit.
At the Signal Mountain school, 402 wells were dug for 6-inch-wide pipes that go down 300 feet into the rock of the mountain. The school has a total of 45.6 miles of geothermal piping and the entire heating and cooling system cost more than $4.9 million to install for the 262,250-square-foot building, Mr. Waters said.
But the geothermal system cost only $270,000 more than conventional boiler and chiller systems, which the school system just installed for the new East Ridge Elementary School.
The school system projected it would need to save at least 30 cents per square foot in energy costs to justify the extra expense of installing the geothermal unit, Mr. Waters said, but the actual savings amounted to about 70 cents per square foot below the average for all schools in the county.
Geothermal systems require adequate land and the right material underground to support the network of pipes that captures the thermal heating or cooling of the earth. Such systems are more cost effective when installed with new schools, but proponents contend that retrofits such as what may be done at Brainerd High School also can be cost effective.