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Earth power

Thanks to incentive programs, residential geothermal heat pumps are now viable options for metro homeowners.

Brendan Hoover July 27th, 2011

When Victoria Caldwell’s home was struck by lightning on Memorial Day weekend 2010, she faced the challenge of replacing her entire HVAC system.

“The house did not catch on fire, but that was a minor miracle,” she said.

While making the home repairs, Caldwell (pictured right), who was elected to Edmond’s City Council this spring, became intrigued with the idea of replacing her conventional HVAC system with a residential geothermal heat pump, which utilizes the Earth’s constant subterranean temperature to heat and cool a home.

The technology is sustainable and four to five times more energy efficient than a conventional HVAC system. Plus, available incentives can make a geothermal system economically feasible.

Caldwell installed a geothermal system in her home, allowing her to “save money for myself and be a better steward of our natural resources,” she said in a letter mailed to Edmond residents.

How it works
Residential geothermal technology is about 60 years old. It uses the Earth like a battery to store and draw heat, said Bob Corff, energy services manager for Edmond Electric, that city’s municipally owned utility company.

“When you’re cooling the house, you’re moving the heat out of the house and you’re putting it down in the ground and storing it. When you want to heat the house, you pull the heat from the ground and put it into the house,” Corff said.

Geothermal HVAC systems take advantage of the steady 50–60-degree temperature found in the upper 10 feet of the Earth’s surface.

Typically, when installing a geothermal system, a series of vertical holes are drilled into the ground, and polyethylene pipes are inserted into the holes, with U-bands fitted on the bottom. Drinking water is pumped through the pipes to conduct the heat.

The closed-water loop replaces the noisy condenser on a conventional air conditioning unit, Corff said.

“Water is a very good conductor of heat,” he said. “When you’re outside on a 98-degree day, it’s hot, but if you got in a hot tub that was 98 degrees, it would feel tepid at best. That’s because water pulls heat off the body so well.”

In the summer, water runs through the pipes and is cooled to about 60 degrees. The water is then pumped into a heat exchanger inside the home. There, heat is taken out of the air by refrigerated coils and transferred to the water. Cool air is forced into the home through existing ductwork, and the warmed water is pumped back down into the ground, where it is again cooled to about 60 degrees.

In the winter, the process is reversed. Heat is taken to warm the cold air. There is enough heat in 61-degree water to heat the home, Corff said.

“The refrigerant circuit multiplies the heat so that the heated air coming into the house is about 108 degrees,” he said.

Drilling the holes in the ground can  be messy, as with any construction project, said Corff, who also has a geothermal system in his home.

Corff had the holes drilled in his front yard because the drill rig could not fit in his backyard, he said.

Because the geothermal system is stored in a controlled environment, the heat exchanger can last 30 years and the closed-water loop can last 100 years, Corff said.

Caldwell said she saves about $60 per month on her utility bills. She keeps her home much more comfortable than she used to, and she feels good helping sustain the planet.

“The environmental factor was very important to me,” she said.

Cool incentives
After rebates, a geothermal HVAC system can rival a conventional system in price.

Caldwell said she took advantage of incentive programs through Edmond Electric and the Oklahoma Municipal Power Authority when installing her system.

The Wise Rebate Program, offered by Edmond Electric through the OMPA, can help customers save $800 per cooling ton when installing a geothermal system. Edmond Electric also offers free energy audits.

Only customers of the municipal electric systems of OMPA member cities and towns can qualify for rebates, and not all OMPA municipalities participate in the rebate program, said Roger Farrer, OMPA energy services manager.

The Oklahoma Comfort Program uses funds from the Stimulus State Energy Program, as administered by the state Department of Commerce, to provide energy audits and rebates for geothermal systems, saving customers up to $1,000 per cooling ton on systems 5.5 tons or less. Larger systems require special approval.

About 100 Edmond Electric customers have taken advantage of the OCP rebate, which expires in March 2012, Corff said. Call 340-5047 for more information.

OGE offers a $375 per cooling ton incentive for installing a geothermal system, and federal tax credits of 30 percent for residential customers and 10 percent for business customers are available. Financing is also available. OGE residential customers can call 553-3961 and business customers can call 553-3672.

Oklahoma City residents whose household income is $100,000 or less can apply for a green home loan up to $10,000 for energy-efficient improvements through the Community Action Agency. Call 232-0199 for more information.

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