With tax breaks, geothermal system promises deep cuts in heating, cooling costs

By Christopher J. Gearon
Special to The Washington Post
Tuesday, March 2, 2010

Just before Thanksgiving, my family swore off fossil fuels to heat and cool our 4,400-square-foot suburban home. Instead, we're relying on the Earth itself: We've converted to geothermal energy, which taps the constant temperature of the ground below our house. ¶ The project took us into completely unknown territory -- before this started, my knowledge of our forced-air heating system was pretty much limited to cleaning the electronic filter -- and it required a harrowing period of construction that included drilling two 375-foot holes in our yard in Derwood, not far from Rockville.

But we felt the results would be worth it. We looked forward to reducing our carbon footprint by replacing our 24-year-old oil-burning furnace and an aging and inefficient air conditioning system.

And the statistics we'd gathered were awesome. "Geothermal systems expel zero emissions," I was told by Errol Nicholson of Griffith Energy Services of Cheverly. "For every kilowatt of energy consumed by [running] a geothermal heat pump, it yields approximately five kilowatts of heating or cooling. Geothermal heat pumps are over 400 percent efficient. It's hard to beat that."

Just as important, we counted on saving a lot of money. First, the net cost of installation was about the same as that of replacing the oil furnace and AC unit with a new system: about $10,000. Notice the word "net": That price tag is due to an extraordinary assortment of federal, state and local tax credits and incentives that have recently become available as part of economic-stimulus and energy-saving initiatives. Further, we have been assured that our utility bills will be reduced so dramatically that we'll recoup every dime we spent within a few years; from then on, the savings will be pure gravy.

Four months after breaking ground on this project -- months that included record-breaking snowfall and weeks of freezing temperatures -- we are comfortably warm and glad we did it. Here's our story.

The science

Although about a million geothermal systems have been installed in the United States -- about half residential, half commercial -- the technology still is not well known.

The basic principle isn't complicated. The temperature of the Earth a few feet below the surface (and for hundreds of feet below that) is moderate and fairly constant. In the Washington area, it stays in the mid-to-upper 50s year-round. The idea of geothermal is to transfer that heat into the house, then make the relatively small leap from there to a comfortable level.

In practice, it means a homeowner needs three basic components: an underground loop system, a geothermal heat pump and an air-delivery system.

The loop system is hundreds of feet of polyethylene piping that is buried in the ground and filled with a water-antifreeze mixture. This fluid circulates repeatedly through the pipes, where it absorbs the underground temperature and brings it indoors.

Inside the house is the heat pump. Heat pumps work like refrigerators: They use electricity to transfer heat from one space to another. During the winter, typical heat pumps extract heat from the outdoor air and bring it indoors. There is heat in the outdoor air, even on freezing days, though it takes a lot more electricity to extract that heat when the temperature plummets.

That's where geothermal heat pumps come in. They work on the same principle, but instead of extracting heat from the air, they extract it from the 55-degree fluid circulating in the loop system.

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