Willis Tower’s $500 million renovation includes an innovative hydronic heating and cooling system

Updating Chicago’s tallest building, the Willis Tower, was a tall order. The $500 million renovation of the 110-story edifice took five years, and included a 300,000-square-foot, five-level addition on its southern side, filled with stores, eateries, and a landscaped terrace on the rooftop.

The existing 4.5-million-square-foot high skyscraper underwent a transformation as well, adding cafes, lounges, a large fitness center, and a revamped Skydeck observatory. The updates restored the Willis Tower’s stature as a premier commercial building that fulfills the requirements of today’s employees, tenants and visitors.

“The way you get people to come back in (to the city) is to deliver a commute-worthy experience,” Bob Chodos, an office tenant broker and vice-chairman in the Chicago office of Newmark, told UrbanLand about the renovation.

The creature comforts and activities the tower renewal brought to downtown Chicago are hard to miss. Behind the scenes, some equally impressive modernization occurred, making Willis Tower the largest building in the U.S. to earn LEED Platinum certification under LEED’s latest v4.1 rating system, the U.S. Green Building Council’s strongest and boldest rating system to date.

“Our tenants and their employees are passionate about working in offices where sustainability is a priority, and we’re proud that our commitment to sustainability, which extends throughout our portfolio, has earned Willis Tower the prestigious LEED Platinum certification,” says David Moore, senior vice president and portfolio director for EQ Office, in a press release about the certification.

Sustainability efforts may not make as big a splash as an expansive rooftop terrace, world-class art, quaint cafés or swanky lounges, but they do reduce the building’s environmental impacts. The tower’s sustainable building enhancements included:

• Installing cutting-edge HVAC technology to reduce energy use up to 20 percent.
• Replacing electric hot-water generators with natural gas hot-water boilers.
• Upgrading the lighting control system and installing energy-efficient LED lights.
• Installing low-flow high-efficiency sink faucets, toilets and urinals to reduce water use up to 30 percent.

Moving to natural gas

“The work focused on renovating and repurposing different areas (in the building), using some for residential and others for business,” says Dave Everhart, president of Bornquist Inc., a Bell & Gossett representative in the Chicago area. “When they renovated, they also decided to switch from electric power back to natural gas.”

To some, this may seem backward as natural gas prices rise, supplies diminish, and the federal government pushes electric and alternative energies instead.

But Everhart explains the decision to switch to natural gas was made eight years ago.

“It was better for them to switch to natural gas,” he stresses. “This meant the boilers had to change from electric to gas fired, and just a few pumps had to be added or changed to circulate hot water to new tenant spaces.”

Whatever energy source is used, Everhart stresses hydronic systems offer many strengths, one of which is the ease in which a building can switch from electric to natural gas and vice versa.

“The water efficiently delivers energy for heating and cooling systems throughout the building.  But if you switch from one energy source to the other, you don’t have to redo all the piping in the building to make it possible,” he says. “Should Willis Tower building operators want to switch back to electric at some point, all they need to do is switch out the boilers.”

Everhart explains the systems are considered technology agnostic, meaning the equipment can accommodate any energy source.

“Hydronics provide an ideal distribution system that enables these alternative technologies to perform,” according to “Building a Sustainable Future: Solving Modern Building Challenges With Hydronic Systems,” a whitepaper by Xylem.

Engineers selected hydronic heat for the Willis Tower because of its efficiency and the lower capital equipment costs.

“We also didn’t have to do a total redesign to change where the energy came from,” Everhart says. “Hydronic systems are energy agnostic. This is a significant advantage to transition a building from natural gas to electricity and vice versa. If you compare that to using a different technology, like VRF or refrigerant technology, that would be impossible. It was just a matter of replacing and updating the pumps, for example. The coil pumps have lower installation and operating costs.”

Buildings can even opt for a “mixture of electric and natural gas boilers. The ability to change over without a complete redesign illustrates the flexibility of hydronic systems,” Everhart says.

The move to hydronic helped the phased Willis Tower construction, he added. Construction crews demolished the space, then began renovation work. All the while, the entire building still required heat and cooling.

“We had to be pretty careful about delivering the (HVAC) equipment on time and exactly when it was needed,” Everhart says.

Most of the work went off without a hitch, except for when the building flooded after a large rainfall. Everhart says that the area equipped with the system’s large pumps and variable speed drives that move water around the building were submerged in water.

“It caused substantial damage from an installation standpoint. All equipment needed to be dried out, repaired and replaced,” he says.

Ronnie Wendt is a freelance writer based in Minocqua, Wisconsin.

This article will be published in the May issue of Building Operating Management. The original article incorrectly called the product a hydraulic system instead of hydronic, and included other technical errors. The primary source for the information in this article was Dave Everhart, president of Bornquist, Inc., a Bell & Gossett representative for the Chicago area. The correct information has been updated in both this online article and the May digital edition of Building Operating Management.

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