Geothermal Cooling:
Use the Earth for Home Comfort

We looked to sunny Florida to see how efficient geothermal cooling could be. Dig down a couple of yards below the surface, and you'll find Florida's earth stays at a steady 72 degrees, a perfect heater in winter and a cool respite in summer.

Florida lacks the scorching heat and steam that makes geothermal electricity, but its balmy earth can help Florida save power. By some estimates, home owners can cut their heating and cooling bills by 50 percent or more. The technology for geothermal cooling has been around for decades but has only recently begun to gain traction.

In most ways, geothermal cooling systems in Florida work the same as a regular air-conditioning system. 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 five or six 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 heating and cooling 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 cooling reverses the system to 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 cooling system transfers 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. Energy savings in Florida can reach 80 percent.

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

The short answer: the initial cost. A geothermal heating and cooling system costs up to three times as much as 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. 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.

Demand for geothermal cooling is growing and 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.

Geothermal Cooling: Use the Earth for Home Comfort copyright 2011