Commercial Architecture February 2018 - 40

PROJECT

hvac

U.S. Steel Tower
Grows Greener
With Retrofit
Danfoss VLT drives
provide more than $1
million in energy savings.

n 1970, the U.S. Steel Corp. built a unique head-

which occupies 40% of the building's space.

quarters that still stands 64 stories above the

"We're moving a lot of water and air up, down,

Pittsburgh skyline. Built to last 100 years, the sky-

and around this building," said Sechler. "Water is sup-

scraper, now known as the U.S. Steel Tower, is archi-

plied by two redundant water mains. In addition,

tecturally unique. It features a distinctive triangular

there are four redundant, 100-hp water pumps in the

footprint using U.S. Steel-developed Cor-Ten steel

building. Each one can serve the entire building, if

to form an external girding system that allows each

needed. There are also two boilers on the sixty-fourth

story to contain an acre of floor space. While ahead

floor and two centrifugal chillers on the sixty-third

of its time in the 1970s, the building fell behind

floor to provide redundant heating and cooling. So

with mechanical equipment that was installed when

there is a lot of pumping needed for domestic-water

kilowatts cost pennies and oil was $3 a barrel. That's

circulation and for the chilled-water loops, all of

why Winthrop Management, Boston (winthroppgh.

which consume a lot of energy."

com), the building's property manager, began a series

The first drive retrofit project was in the year 2000

of retrofits using Danfoss, Baltimore (danfossdrives.

when VLT drives were applied to four 100-hp pump

com), VLT variable-frequency drives to cut energy

motors responsible for the building's domestic water.

costs, resulting in more than $1 million in energy sav-

"The old drives were two-step drives like they

ings and a greener reputation that's attracting tenants.

used in steel mills back in the day," said Jim Rice,

"We have been applying Danfoss VLT drives in

owner of M&R Affiliates, Upper St. Clair, PA, the

various retrofit projects for nearly 15 years," said Gary

Danfoss sales representative who has been working

Sechler, engineering manager for Winthrop Manage-

with Sechler since he has been in charge. "They

ment. "After every retrofit project phase, we've found

weren't true variable-frequency drives. We replaced

the energy savings on pump motors and fans have

them with four Danfoss VLT model FC102 drives

been outstanding. So we would embark on another

that delivered 100 hp at 460 V and provided a true

phase. As it stands now, we've installed more than

soft start."

150 VLT drives, with more to come."

Above. Energy savings from the Danfoss drives is helping give the building
a greener reputation. Seventeen of the floors have qualified for Silver LEED
certification and six for Gold.

According to Sechler, the soft start eliminated a

The 841-ft. U.S. Steel Tower, once known as

lot of wear and tear on the motors-and also saved

the USX Tower, provides more than 2.3-million

energy. "We're talking big motors to pump water to a

sq. ft. of leasable space in downtown Pittsburgh. It

300-gal. cushioning tank on the sixty-fourth floor.

is the city's tallest skyscraper and the highest com-

From there, gravity feeds the water down fountains,

mercial building between Chicago and Philadel-

sinks, and toilets on the floors below. Only two of the

phia-with major tenants including U.S. Steel and

four pumps run at any given time in a lead-lag se-

the Univ. of Pittsburgh's Medical Center (UPMC),

quence that alternates weekly. But the old motor
speed controls were obsolete and parts were no longer
available. I don't have a record of energy savings from
that time. But I do know with the soft start on VLT
drives, pump motor rebuilds have been zero."
The next retrofit opportunity presented itself after
the state of Pennsylvania passed legislation in 2008
requiring Electric Distribution Companies (EDCs)
to reduce electricity consumption and peak demand.
In

response,

Duquesne

Electric,

Pittsburgh

(duquesnelight.com), provided a rebate program for
businesses that install variable-frequency drives to replace old-style motor speed-throttling technology.
"We jumped on this program," said Sechler. "We
knew what VLT drives did for our house water pumps.
So in 2010, we looked at what they could do for our
large 200- to 250-hp fan motors. These fans circulate
conditioned air in large office areas at a given static
pressure to satisfy the temperature setpoint. We ended up applying about 40 more FC102 drives for motors ranging from 30 hp to 250 hp.
"We were absolutely delighted with the energy
Built in 1970, the U.S. Steel Corp. headquarters stands 64 stories above the Pittsburgh skyline. While ahead of its time, the mechanical equipment was installed when
kilowatts cost pennies and oil was $3 a barrel. A series of retrofits using Danfoss VLT variable-frequency drives cut energy costs by more than $1 million.

COMMERCI A L A RCHI T EC T URE

FEBRUARY 2018

commercialarchitecturemagazine.com

savings, because the drives cut electricity costs by
$535,000 annually. And, along with those savings, we
got rebates that produced a one-year payback. So nat-

http://www.duquesnelight.com http://www.commercialarchitecturemagazine.com

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