Engineering Tomorrow reduces multi-use building's energy consumption and aids in demand response programs

Monday, July 27, 2015

After several retrofit projects, the U.S. Steel Tower has installed more than 150 Danfoss VLT® Drives, which are producing more than $1.1 million in documented energy savings and helping to give the building a greener reputation.

In 1970, the U.S. Steel Corporation built a unique headquarters that still stands 64 stories above the Pittsburgh, Pa., skyline. Built to last 100 years, the skyscraper now known as the U.S. Steel Tower is architecturally unique. It features a distinctive triangular footprint using U.S. Steel-developed COR-TEN® steel to form an external girding system that allows each story to contain an acre of floor space. While ahead of its time in the 1970s, the building fell behind with mechanical equipment that was installed when kilowatts cost pennies and oil was $3 per barrel. That’s why Winthrop Management, the building's property manager, began a series of retrofits using Danfoss variable frequency drives (VFDs) to cut energy costs – resulting in over $1 million in energy savings and a greener reputation that’s attracting tenants.

"We have been applying Danfoss VLT® Drives in various retrofit projects for nearly 15 years," says Gary Sechler, engineering manager for Winthrop Management. "After every retrofit project phase, we’ve found the energy savings on pump motors and fans have been outstanding. So we would embark on another phase. As it stands now, we’ve installed more than 150 VLT®Drives – with more to come.”

Danfoss drives meet retrofit challenges

The 64-story, 841-foot (256.34 m) U.S. Steel Tower, once known as the USX Tower, provides more than 2.3 million square feet of leasable space in downtown Pittsburgh. It is the city's tallest skyscraper and one of the highest commercial buildings between Chicago and Philadelphia – with major tenants including U.S. Steel and the University of Pittsburgh Medical Center (UPMC), which occupies 40 percent of the space.

"We're moving a lot of water and air up, down, and around this building," says Sechler. "Water is supplied by two redundant water mains. In addition, there are four redundant, 100-HP water pumps in the building. Each one can serve the entire building, if needed. There are also two boilers on the sixty-fourth floor and three centrifugal chillers on the sixty-third floor to provide redundant heating and cooling. So there is a lot of pumping needed for domestic water circulation and for the chilled water loops, all of which consume a lot of energy."