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Geothermal systems: An old technology gets a second look

Consumer Reports News: June 20, 2011 12:20 PM

The biggest chunk of your utility bill comes from heating and cooling your home, and heating hot water. So what if you could do all those things without burning much fuel? That’s the promise of a home geothermal system, which uses the relatively constant temperature of the earth to heat your home in the winter and cool it in the summer.

Geothermal is an old technology that’s getting a second look as we search for renewable energy sources. While common in some European countries, geothermal systems haven’t been as readily embraced in the U.S. That may change once homeowners see how much money they can save.

Here’s how it works. Instead of using oil, gas or electricity for heating and cooling, a geothermal system uses the temperature difference between the ground and the air. Air temperatures fluctuate throughout the day and seasons, while the temperature six feet below the surface stays relatively constant. Depending on where you live, it can range from 45 degrees Fahrenheit to 75 degrees Fahrenheit.

The magic happens when a heat pump exchanges air through a series of pipes called a loop that’s installed in the ground adjacent to your home. In the winter, the pipes have a refrigerant in them that absorbs the heat from the ground and carries it into the home and in the summer the process is reversed. These systems can also heat water thus replacing not only the water heater, but the furnace and air conditioner too. The system relies on a heat exchanger that collects or removes as much heat as is needed to condition the indoor air or water.

Pros. Geothermal heat pumps use between 25 percent and 50 percent less electricity than traditional systems. Compared to traditional systems, maintenance costs can be lower too because much of the system is underground and protected from the elements. Geothermal systems are also mechanically simple, quiet and can last longer. Plus, you can get a 30 percent federal tax credit until at least 2016.


Cons. The installation price of a home geothermal system can be several times that of an air-source system of the same heating and cooling capacity, depending on how much drilling you have to do to install the pipes underground. While initial costs can run into the tens of thousands, federal, state and local tax credits could help bring the price down to a manageable level.

A report issued in 2008 by the Indiana Office of Energy and Defense Development put the average cost of a new geothermal system at around $14,000, depending on size and location. Payback time can be as little as 10 years, taking into account your home’s insulation and other variables. Annual energy savings will vary based on what type of fuel you were using before and the local price of electricity, but the DOE says typically annual energy savings run between 30 percent and 60 percent.

Because of the cost of installation, geothermal systems may be more practical in new home construction because you’re already excavating for the foundation, plumbing and other major systems. Whether you’re building a new home or retrofitting an old one you’ll need the help of a professional. Both the International Ground Source Heat Pump Association (IGSHPA), Geothermal Exchange Organization (GEO) maintain lists of qualified installers. The Department of Energy has information on how to evaluate your site for a geothermal system.

Sari Krieger

   

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