Thursday, April 24, 2014
PORTLAND — Drivers who use a new parking lot at the Portland International Jetport won't notice, but their vehicles will be atop more than 11 miles of plastic tubing.
Workers push 1,000 feet of high-density polyethylene pipe into one of 120 500-foot drilled holes that will be one “loop” of the geothermal system being installed to help heat and cool the Portland International Jetport’s expansion when it opens in 2012.
Photos by Gordon Chibroski/Staff Photographer
If they could slice open the earth, they would see 120 loops extending 500 feet into bedrock. And if they could peer through the tubing, they would see fluid circulating at 500 gallons a minute.
Drill rigs will run every day for the next month to turn the land under the new parking lot into a giant heat exchanger. The fluid will absorb some of the earth's stored heat in winter and help warm a new addition at the jetport. The process will be reversed in summer, with heat being dumped into the cooler earth.
When the jetport's $75 million expansion opens in 2012, it will be heated and cooled by Maine's largest geothermal system. The system is expected to cut the amount of oil that would otherwise be used for the new terminal by 90 percent -- nearly 102,000 gallons a year.
Geothermal heating and cooling isn't new, but it has been slow to catch on in Maine. That may be because it's less familiar to contractors here, and because the systems are expensive to install.
But supporters say geothermal, when properly financed, can compete with oil heat because of its low operating costs. They hope high-profile systems such as the one being installed at the jetport will draw more attention to geothermal as an alternative, especially in commercial buildings that are climate-controlled year-round.
One advocate is Paul Bradbury, the jetport's director. Trained as a mechanical engineer, Bradbury sees geothermal as a way to help control long-term energy costs at the city-owned airport.
"There's no question in my mind that it's an underutilized technology in this state," he said.
The system will warm and cool the jetport's 137,000-square-foot addition, which is being built to high energy-efficiency standards.
The system will cost $3 million. Roughly $2.5 million is coming from a federal program aimed at reducing air pollution and climate change emissions at airports. Portland is the first commercial airport to use the money. The balance will come from fees paid by airport passengers.
The system is being designed and installed by National Geothermal of Plymouth, Mass., with help from local contractors and drilling companies.
Visitors can see the work as they drive by the airport entrance across from the Hilton Garden Inn. On a recent day, the roar of four drilling rigs filled the air as their bits gnawed away at the bedrock.
"This isn't a huge technological leap for Maine," Bradbury said, noting that the work is similar to installing a well.
The bore holes are 20 feet apart in the well field. Steel casings stick up from the earth at the finished holes, with sprouts of black polyethylene tubing. The tubing will be tied together to a manifold and routed underground to the jetport's mechanical room via 10-inch supply and return lines. The system is a closed-loop design; it's sealed and won't exchange fluid with groundwater.
Indoors, warmth will come from radiant floors heated electrically to around 100 degrees. Because the earth below the frost line in Maine averages about 50 degrees year round, it will take relatively little energy for heat pumps to raise the temperature to a comfortable level in the building.
A small oil boiler and baseboards will still be needed, to temper winter heat loss against a stretch of big windows.
Geothermal systems have been installed in Maine since the late 1970s. The state has at least 500 homes that use geothermal heat, according to industry estimates, and at least two dozen commercial buildings.
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click image to enlarge
Roy Williams, jetport deputy director, explains how the geothermal system works. Fluid circulating in tubes will absorb the earth’s heat in the winter and dump heat in the summer.