14 oct 09 | The Architect's Newspaper

They might be giants: Willis Tower

by Jennifer Krichels

In 1973, it was enough to be the tallest building in the world. More than three decades later. Sears Tower, this year rechristened as Willis Tower, seems a bit of a slouch next to some of the current decade's shorter but greener buildings. So in June. owner 233 S. Wacker Drive, LLC announced a $350 million retrofit of the Willis Tower to reduce its energy use by 80 percent, which, including energy savings and cogeneration, will save the equivalent of 68 million kilowatt hours per year.

"The nice thing about existing buildings is that they're quantifiable. You can assess what measures are practical to take," said Gordon Gill, co-founder of Chicago-based Adrian Smith + Gordon Gill Architecture, the firm hired to design the Willis greening project as well as a 50-story net-zero hotel to be built on the south side of the tower. The architects are working with structural engineer Thornton Tomasetti and MEP engineer Environmental Systems Design.

For a 4.5 million square-foot building that can hold 20,000 people, small changes add up. One of the most basic yet beneficial improvements is re-glazing the building's 16,000 single-pane windows. For years, building owners were told that the curtain wall couldn't withstand the increased load of insulated glass, but new thin film technology will have the insulating properties of a triple-glazed system withoutthe weight. Gill describes an aging building as a strand of pearls, one improvement leading to the next; the re-glazing creates effective day-lighting and ultimately 40 percent less lighting energy consumption a far cry from Sears Tower's original heat-by-light system, whereby lighting fixture heat was trapped and piped through ducts to warm the building's rooms. As soon as outdated HVAC, elevator, and plumbing systems are replaced, they will operate as much as 90 percent more efficiently. The new plan also integrates wind turbines, which along with solar hot water panels and green roofs are being tested to withstand high-altitude wind conditions on the tower's setback rooftops.

Drawing zero energy from the city's power grid and using less than half the energy saved by the Willis retrofit. the teardrop-shaped hotel will be wider to the west than it is to the east, increasing airflow between the buildings and around the new structure. The building will have solar decks and its own turbines, in addition to one of Chicago's first double-wall envelopes, a 750-millimeter fixed glazed insulating cavity that will push air through a plenum in the ceiling or exhaust it through slats on the exterior wall.

Now even more than technical accomplishment, the Willis Tower-in concert with its new appendage-represents AS+GG's goal of designing more fluid energy networks. Eventually, Gill hopes the firm will apply the concept across an entire city, smoothing out peak consumption times for offices and residential buildings and changing building economics as a w hole. "We see a lot of opportunity in the U.S. for a much more disciplined and prolific approach to energy sharing, so that one single project would offer a tremendous benefit for everyone else,'' he said. "For us, this project has spawned the whole notion of energy sharing."