PNC PLAZA

Dubbed the greenest high-rise in the country, Pittsburgh’s new 33-story Tower at PNC Plaza is a great example of embracing highly energy-efficient technologies, while maintaining the visual glass aesthetic. Thanks, in part, to its double-skin facade, insulated glazing, solar chimney, and automated blinds, the tower is anticipated to use 50 percent less energy than ASHRAE 90.1-2007 requirements.

Photo courtesy of Connie Zhou Photography/Gensler

The double-skin facade, insulated glazing, solar chimney, and automated blinds at Pittsburgh’s 33-story PNC Plaza contribute to what is anticipated to be 50 percent less energy consumption than ASHRAE 90.1-2007 requirements for the building.

Offering part of the backstory as to how the designers identified the strategies to be incorporated in the project, Tranel remembers that the team was not in search of a particular technology to solve the energy-efficiency issue. Instead, they were more focused on architectural solutions. The process began with studying ventilation schemes, which revealed that the stack effect, as opposed to cross ventilation, was found to be more predictable and reliable.

“We then had to figure out how we would heat in the winter, cool in the summer, and ventilate in the spring and fall,” he explains. “Because ventilation was possible 42 percent of the time, and that 91 percent of the floor plate could have access to daylighting, when we put all that together, we saw that the facade was going to be the element that drives all this.”

“We added depth to the double facade to make it a nice user experience,” he continues, “and installed blinds in the cavity where motorized, automation systems are tied into weather-integrated data, which operate them up and down and control the tilt.”

By incorporating a triangular shaft on the building’s “attic,” the naturally heated air from the double-facade cavity rises up to the top of the solar chimney, while additional heat beats down from the roof, thereby creating free heating for the building. In the summer, the chimney pulls hot air from the facade cavity, via convention, where it is then released through the rooftop. “To us, that was the fundamental chassis of the project,” says Tranel.

Image courtesy of Gensler

PNC Plaza’s solar chimney harvests free heating for the building in the winter and exhausts hot air from the facade cavity in the summer.

While the building uses a sophisticated building automation system (BAS) to operate the two facades based upon air quality, temperature, and humidity, the design team tried to keep things simple by installing the same motor for all of the blinds, in addition to building a mock-up to test all of the systems prior to construction.

The outer facade is made of aluminum and clear glass with no low-e glazing, as the blinds are able to take care of glare and solar gain issues, while preserving the clearest views to the city. The inner facade is made with insulating glass and glulam lumber inside a fully unitized curtain wall to create a warmer, hospitable aesthetic.

The outer facade windows opens to less than 4 inches, to meet the building safety code of 4 inches, and occupants can access the inner facade doors to enjoy the patio areas incorporated into the cavity.

Image courtesy of Gensler

In passive mode, the double-facade windows are opened, drawing fresh air into the building and expelling hot air created by solar heat gain into the solar chimney. In active mode, the facade is closed and a chilled beam system is used for cooling.

The striking, high-profile project is certainly turning heads, but as compared to a typical building, such a highly sustainable effort required a very high degree of interdisciplinary collaboration to get there. Fortunately, having a clear client vision helped quite a bit, according to Tranel.