Volume 50, Issue 10 - October 2015

Double Take
With High-Performance Glazing and Features, PNCís New Home was Designed with a Purpose
by Ellen Rogers

Some buildings are designed for aesthetics, others for functionality and energy performance. There’s even been a drive toward designing with occupants in mind. But what happens when an architectural firm combines all of these components and more into one structure? You get what might just be the greenest skyscraper in the world.

Located in Pittsburgh and sheathed in glass—two façades of it, in fact—the recently completed Tower at PNC Plaza is PNC’s new 800,000-square-foot headquarters. Through the use of high-performance materials and technologies, the tower was designed to naturally ventilate at least 42 percent of the year and consume 50 percent less energy than a typical office building. Plus, the building’s floor-to-ceiling windows and narrow floor plates allow daylight to illuminate 90 percent of all open workspaces. The tower is expected to exceed Leadership in Energy and Environmental Design (LEED) Platinum certification.

In 2011, PNC announced its intent: to build “the world’s greenest skyscraper.” The architectural firm Gensler, with which PNC had worked on 3 PNC Plaza, also in Pittsburgh, and PNC Place in Washington, D.C., among other projects, took the job of designing the tower. Benedict Tranel, principal and technical director with Gensler, says the overarching goal to be the greenest high-rise in the world powered the firm’s design approach.

And only one material would work: glass. Not only does the tower incorporate a double skin façade for energy efficiency, these features also contribute to the overall comfort and experience of the occupant.

For the Tower at PNC Plaza, PPG and J.E. Berkowitz supplied 400,000 square feet of fabricated vision glass panels.

Design Intent

Glass might get a bad rap sometimes, being called out as an energy waster, but there was never a question that it would be the material of choice in the design of this tower.

“If you’re building an office, people want to see out, so it needs windows of some kind,” says Tranel. “As we thought about this design, we knew daylighting the space would be a measure to achieve energy efficiency, but we also asked, ‘how can we get the most of what Mother Nature has to offer?’ It turns out she has a lot to offer in Pittsburgh.” According to Tranel, the team found that the area’s climate is conducive to natural ventilation much of the year, in both fall and spring.

“Pittsburgh has a lot of overcast days, but natural light is available a good amount of time,” he says.

And there was no doubt from PNC that the use of glass would help meet its design aspirations.

“We proposed a double façade, which allowed us to have a very efficient envelope,” says Tranel, explaining that the envelope is one of the key drivers in a building, and one in which they have some level of control. Other drivers, such as the building occupants, can’t be controlled, nor can the equipment in the building that needs to be plugged in. “You need them so you can’t get rid of them.”

He continues, “We made a big bet on the façade being as energy-efficient as possible, so the double façade makes the envelope insulating in the winter and allowed us to put external sunshades in the cavity, which makes it very efficient and a way to control daylight, provide views and connect to nature … it’s an important part of sustainability that’s often overlooked.”

Another unique detail of this double-skin façade is that it is completely accessible to building occupants.

Tranel questions, “If you’re creating a user experience, why do you have to step outside for fresh air? This design allows the occupants to step inside the cavity where there is natural ventilation, which is warm in the winter and cool in the summer,” says Tranel of the three-foot-deep cavity, which he likens to an accessory space of the office.

A parallel sliding glass door from Permasteelisa and its sister company Gartner provides access to the cavity. “This is the door that allows people to go into the cavity,” says Roberto Bicchiarelli, senior vice president/general manager – south, with Permasteelisa North America Corp., the project’s contract glazier. “They can spend time there, enjoy the view … everyone has the freedom to open the sliding doors. But no one can operate the mechanical/pop-up vents, because they are controlled by the building.

“This is a unique building in terms of the integration between the façade, the structure and the mechanical systems. It is completely controlled by the building maintenance system, so there is a high level of integration and function of the skin,” he adds.

Bicchiarelli explains that blinds are also integrated into the façade. The compact cavity has a unitized system that’s operable and accessible to everyone. That access was important for control and maintenance of the blinds.

Bicchiarelli adds that his company had a solid understanding of what the project would entail thanks to the details provided upfront.

“We received the package of specifications as well as the drawings that were very detailed,” he said. “It was definitely a big task in terms of the design, and we approached it completely in 3-D. We didn’t do any 2-D production drawings. All of the systems and models were done in 3-D.”

Speaking of the complexity of the design, he adds, “The shape of the building is extremely complex, and it [goes from having] straight lines to notches and niches, and there are segment/curved areas with different radiuses on the outside/inside. There was not much that was repetitive.”

Glazing Selection

When it came to selecting the glass, the decision was driven by the way architects needed the façade to perform: insulating in winter and blocking solar heat in summer.

“We used a transparent outer façade, which is low-iron laminated. The interior is an insulating unit that’s argon-filled and with warm-edge technology,” says Tranel. “Also, on the interior we used wood [framing] while the outside is a light aluminum. We were able to do that because we had the sunshades in the cavity to block solar heat,” which he adds retract when they are not needed.

As for glass supplies, “PPG was a natural choice because they are local,” says Tranel. “We were focused on performance, and one of our goals was to use local labor and supply as much as possible as part of the sustainability goal,” says Tranel. “That was achieved by using PPG, and they were great because they offered the product we needed and provided materials they had in research and development and were able to bring those forward to commercial production in time for use.”

The solar chimney draws warm air out of the tower and pulls refreshing air in through the automated air gates and open dampers in the inner skin.

Mehran Arbab, Ph.D., PPG director, glass science and technology, says his company is gratified that its glass products were used for this project, among other PNC buildings also in Pittsburgh.

“… Gensler and PNC asked us to help them establish a new standard for green building with the Tower at PNC Plaza by incorporating [our] glasses into the curtainwall and solar chimney [see sidebar below],” he says. “We very much appreciate the trust Gensler and PNC have put in our glass technologies to help them achieve their ambitious sustainability goals. [We are] proud to partner with Gensler to help with the construction of the world’s greenest skyscraper in its corporate home city of Pittsburgh.”

Permasteelisa selected Pedreicktown, N.J.-based fabricator J.E. Berkowitz (JEB) to supply the 13-foot laminated glass panels and coated IG units. JEB and PPG together supplied 400,000 square feet of fabricated vision glass panels for the project. The glazing consisted of Starphire ultra-clear and Sungate 400 passive low-E glasses. Kuraray (formerly DuPont) supplied SentryGlas Plus ionoplast as the interlayer used by JEB to process the laminated panels.

“Over 1.3 million square feet of glass was cut, heat-treated, laminated and insulated by JEB, totaling more than 125 truckloads/containers of finished product, delivered sequentially, ahead of project schedule,” says Arthur Berkowitz, president of JEB. He adds that the glass was then shipped to Permasteelisa’s unitizing facilities in Pennsylvania, Connecticut, Florida, Canada and Italy. “All needed capacity to keep pace with the project’s needs.”

Permasteelisa, in fact, opened a mobile factory in Pittsburgh just for this project, which also served as a way to involve the local community.

“We assembled the entire interior cavity (wood) in Pittsburgh,” says Bicchiarelli. “We used that facility as much as possible … it could also be used as a warehouse to transport materials to the jobsite, etc., which helped serve as a point of coordination for just-in-time delivery.”

Heat Trap: Unique Feature
Adds to Performance

When it came to constructing the Tower at PNC Plaza, architects at Gensler incorporated many passive features designed to help make the structure as energy efficient as possible. One unique design detail is the solar chimney, which helps draw air into the building.

Benedict Tranel, principal and technical director with Gensler, explains, “At the top of the tower is the solar chimney, a vertical shaft all the way down the center of the building … that traps heat, like a greenhouse, and it creates a thermal stack affect.” Tranel adds that there is a seven-foot cavity below the glass and then a black, corrugated concrete slab that acts as a heat sink.

According to project information from Gensler, “Just inside the tower’s angled glass roof is a massive concrete pad. As sunlight warms the concrete, air inside the space heats up and vents out through a louver high in the mechanical penthouse. Warm air vacating the building creates an updraft in shafts that go down to each floor, pulling cool air through the office space … In the winter, warm air in the chimney will be recirculated to help heat the building.”

“The glass traps the heat and heats the air to create a thermal draw, creating a shaft down through the building,” he says. “We found that the roof could act as a fifth façade, and we covered it with glass so we could capture a lot of that heat. That’s free heat from the sun.”

But Will it Work?

Mock-up testing was also a critical component. In 2013, a 1,200-square-foot mock-up was built, replicating the southwest corner of the 33-story building and implementing its technology and design elements on a small scale. Located just outside of downtown Pittsburgh, the mock-up was positioned to receive the same solar exposure as the actual southwest corner of the tower.

For more than a year, various features of the building’s design were tested, including its double-skin façade. The mock-up allowed those involved with the project to work out any kinks with that system, among other features of the façade.

Tranel explains it was important to be mindful of the level of complexity and risk involved in projects like this, particularly with the use of so many different products and technologies.

“The mock-up and testing brought all the elements together that we knew on their own would be successful,” he says, explaining that they were then able to see how they would perform when working together.

Final Thoughts

Bicchiarelli says many times with double skins the buildings can look complicated from the outside. Not so in the case of this project.

“This doesn’t seem that way in my opinion. From the interior particularly, it’s very friendly. There’s lots of open space and there’s a good feeling … [that] people will experience…”

Tranel adds, “We’ve created a great user experience and something that was designed with that user experience in mind. It’s something experienced from inside and out.”

the author

Ellen Rogers is the editor of USGlass magazine. Follow her on Twitter @USGlass and like USGlass on Facebook to receive updates.

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