Portland, Maine's new airport expansion is to be the first in the country to use a dead-simple but often overlooked technology to significantly reduce its heating and cooling bills. They're calling it a geothermal system, but it's not like the kind that produce power in Iceland; it's more properly called a "ground-source heat pump."

The system will use the ground beneath an employee parking lot as a giant heat sink. To transport energy to and from the sink, the system will run fluid through pipes snaking through 120 wells dug 500 feet into the ground. Below a meter or two, the earth has a constant year-round temperature of about 55 degrees F, so it's potentially a source of 55 degree fluid in the summer (which can be used to chill air for an air conditioning system).

It can also be used in the winter, however, which is a little more critical in Maine. During cold months, the same fluid can be used to pre-heat air before it's fed into the heating system. In both cases, the ground source heat pump saves significant energy that would otherwise be expended to heat or cool the air inside the new airport terminal.

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Builders estimate the system will save the airport 50,000 gallons a year in heating oil, which translates to $160,000-$200,000 per year.