The Tower at PNC Plaza to tap into Pittsburgh's geothermal 'river'
By Thomas Olson
Published: Wednesday, October 19, 2011
When PNC Financial Services Group breaks ground in April on its 40-story headquarters tower Downtown, it will tap into "the fourth river" to cool and heat it.
An aquifer that runs deep underneath Downtown will supply The Tower at PNC Plaza with water year-round for a state-of-the-art geothermal system. Aside from being environmentally friendly, the system will make the building more energy-efficient, said the bank's director of development.
"We're working on our (building) systems right now, so we can't identify the dollar savings," John Robinson said. "But we think we could heat and cool 35 percent to 75 percent of the building."
The geothermal system is one of the key features that should help PNC achieve LEED Platinum certification as an ecofriendly building. LEED stands for Leadership in Energy and Environmental Design, a rating of a building's energy efficiency developed by the U.S. Green Building Council in Washington. Platinum is the highest level.
"We put (geothermal) on the table early because we wanted to find ways to reduce our energy profile on the building as much possible," said Robinson.
"This is a proven technology that been going on for at least 50 years," he said. "Fifty years ago, there were a lot of buildings Downtown that used geothermal."
Robinson said it's too early in the design process to estimate the cost or savings involved in the geothermal project.
At least four other Downtown buildings employ a geothermal system for cooling and/or heating.
"It works beautifully in the Century Building," said William Gatti, president of Trek Development Group, Downtown. The firm remodeled the building on Seventh Street, constructed in 1907, to include geothermal in 2009.
"We use this 58-degree water 365 day a year to cool the building in the summer and warm it in the winter," Gatti said. "We estimate about 30 percent of our heating and cooling load is from geothermal."
The aquifer runs at a depth of between roughly 30 and 60 feet under Downtown, then flows into both the Allegheny and Monongahela rivers. The water in the aquifer remains at a constant 55 to 60 degree Fahrenheit year-round, which makes it suitable for cooling in summer and heating in winter.
Geothermal systems use a heat exchanger to draw the aquifer water's cooler-than-outside temperatures from the water in summer, and its warmer-than-outside temperatures in winter.
PNC is most likely to drill four holes 16 inches in diameter to tap into the aquifer, said Javaid Alvi, president of Geo-Mechanics Inc., the geotechnical engineering services company PNC employed to conduct test drilling, both for the skyscraper's foundation and for geothermal system.
Geo-Mechanics' test drilling two weeks ago found one hole could draw water at about 600 gallons a minute, Alvi said. So, four holes would be more than enough to deliver the 2,000 gallons a minute that PNC's system would require, he said.
"The business district is blessed that the underlying soils are glacial deposits," Alvi said. "Those deposits are very porous, so there's lots of capacity from the aquifer."
When completed in 2015, the PNC tower will rank among Downtown's six tallest buildings. It will provide about 800,000 square feet of office space for 3,000 employees.
At least two other plans for constructing buildings near Downtown will incorporate geothermal energy.
Phipps Conservatory and Botanical Gardens' Center for Sustainable Landscapes will include a geothermal system when it's built next spring, said Christopher Minnerly, the principal in charge of the project. Phipps plans to drill 14 holes at the Oakland site to a depth of 500 feet.
The former Connelley Technical Institute, located in the Lower Hill District, will include a geothermal system when it's renovated into a "green technology" training center.
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