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How does geothermal energy work? Use the Earth to cool your home



"I think there is an enormous untapped potential in the country," said Jeff Tester, an expert in geothermal energy at Cornell University in New York.


"People really don't know about it yet," said Fred Mayes, a senior technology analyst at the Energy Information Administration, the statistical arm of the Department of Energy. "People have seen solar panels before, but may not think of geothermal heat pumps."

Now, with generous new federal subsidies, could geothermal become Florida's next big thing?

• • •

To sell a geothermal system, you've got to start with education, said Todd Boudreau, who has installed dozens of geothermal heat pumps. Few homeowners know how they work.

"It hasn't been widely publicized the way it should have been, but with things changing in our economy, and rising utility costs the way they are, people are very interested in how to save money," Boudreau said.

In most ways, geothermal systems in Florida work the same as a regular air-conditioning system, Boudreau said. Both systems use a combination of refrigerant and compression to transfer heat in or out until the house reaches the desired temperature. For the customer, the thermostat is almost exactly the same.

To understand the big difference, think of the Earth as a giant battery heated by the sun. Geothermal taps that natural battery by snaking a pipe a thousand or so feet long under the surface. It is filled with water, or a mix of water and other fluid, like antifreeze. The loop can be laid in horizontal squiggles snaking under a property at a depth of six to 10 feet. If the lot is small, the ground loop can be drilled vertically to depths of several hundred feet.

In Florida's colder months, the ground loop absorbs the ground's 72 degree heat and transfers it to a heat exchanger, where it becomes hotter. A fan then draws the home's air through the system, heating the air and circulating it back through the house.

In cooling mode, a fan sucks hot air from the house into the system, where the heat in the air is removed. Just like your fridge, the heat is removed from the inside and transferred outside, in this case to the cool ground.

Why is geothermal more efficient than conventional systems?

In winter, it uses the ground's heat instead of burning fossil fuels or using electricity to make heat. In summer, the ground acts as a natural condenser, replacing the electric condenser.

The system is also more efficient because of the ground temperature. For instance, in the summer a conventional unit transfers hot air from the home to the hot air outside. Geothermal systems transfer the hot air to the cold ground. The cold ground is better at absorbing the heat than the hot outside air.

To think of it another way, when you jump into a cold lake on a hot day you lose body heat much faster than if you are standing on the shore.

As a bonus, the geothermal system transfers heat all year long to the home's water pipes, giving customers free hot water.

The Energy Department estimates that it cuts electric bills by 25 to 50 percent. Boudreau said energy savings in Florida can reach 80 percent.

"The benefits of this are unbelievable," Boudreau said.

• • •

If it works so well, why isn't everybody doing it?

"That old four-letter word: cost," Mayes answered.

Boudreau estimated that a geothermal system costs about two to three times a conventional heating and air-conditioning system. In these tough times, it's hard to talk a homeowner into parting with that kind of cash.

Andy Bednarz, a pilot, recently installed a geothermal heat pump at his new lakeside property in Lutz. He got a $9,000 estimate for a conventional four-ton system but decided to spend $23,000 on a geothermal system.

His old 2,000-square-foot house had power bills from $265 to $350 a month. His new 2,359-square-foot-house has power bills of about $150 a month.

"It seems like a big bite, and I don't like to give away money by any means, but I did some higher math, and this should pay for itself in six years," Bednarz said.

Boudreau agreed, saying the typical payback time is four to six years. The systems are quieter and last 25 to 30 years, two to three times longer than conventional systems. Replacement costs are comparable because the drilling only need be done once.

It's a logic that appeals to home­owners facing rising electric bills, Boudreau side. His company, Air Conditioning Solutions, has seen sales double in recent years as his handful of satisfied customers spread the word to neighbors, friends and family. Although it's still just a fraction of his business, he's seeing more interest than he has in the past.

"People are willing to spend money to save money," he said.

• • •

Bednarz is part of an upward trend in geothermal.

Florida has been on the leading edge of the growth. The state is home to one of the best-known heat pump manufacturers, and it is among the top five states for installing geothermal heat pumps, and is also in the top five for exporting them to other states.

Shipments of geothermal heat pump capacity increased 53 percent in 2006 and 19 percent in 2007, according to a recent report from Mayes' office. In 2007, the most recent year Mayes has numbers for, the United States shipped enough geothermal heat pumps to heat and cool 97,000 U.S. homes.

Despite the steep growth, geothermal heat pumps make up a tiny share of the market. In 2005, the pumps were installed in just one in every 1,000 U.S. homes, the Energy Information Administration estimates. Even with the annual growth predicted between now and 2030, it estimates that only slightly more than one in every 100 U.S. homes will have geothermal heat pumps.

The recently passed American Recovery and Reinvestment Act might kick-start interest in the heat pumps. The stimulus legislation gives homeowners a tax credit that covers 30 percent of the cost of the system.

"We don't know that answer yet, but it should bump it up a little bit," said John Symbalsky, a research analyst with the Energy Information Administration.

Boudreau thinks he knows what the response will be. Armed with information on the new tax credits, he's already fielding calls from potential customers.


Did you know? The average U.S. homeowner uses a 3-ton system for heating and cooling. Geothermal heat pumps can cut electricity use by 25 percent to 50 percent. Geothermal heat pumps have been used in some cold states to melt snow on driveways and walkways. • The underground coils for geothermal heat pumps are expected to last 50 years or more. Geothermal heat pumps are expected to last 25 years. Source: Energy Information Administration, Department of Energy

How does geothermal energy work? Use the Earth to cool your home 04/03/09 [Last modified: Friday, April 3, 2009 6:19pm]
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