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Stadium implements pumping systems to reach sustainability goals
U.S. Bank Stadium in Minneapolis, the new home of the Minnesota Vikings football team, is known for its unique architecture. But the multipurpose stadium also has been praised for another of its characteristics: its commitment to sustainability.
Built on the site of the Metrodome, the Vikings’ former home, the $1.1 billion stadium is the largest public works project in Minnesota history. It took 8,000 workers more than 4 million hours to design and build the 1.75-million-sq-ft stadium. It ultimately was completed ahead of schedule, in July 2016. The stadium is scheduled to host the Super Bowl in 2018 and the NCAA basketball tournament Final Four games in 2019.
Behind the scenes, pumping systems are at work to meet U.S. Bank Stadium’s heating, cooling and water supply needs while also helping it meet its sustainability goals. Bell & Gossett pump systems were implemented in three key areas: snow removal, water systems and HVAC.
The extreme winter climate in Minnesota, which receives an average of 54 in. of snow per year, proved problematic for the Metrodome. Large volumes of snow accumulation on the roof caused it to collapse five times. U.S. Bank Stadium was designed with the state’s heavy snowfall in mind. Its roof is shaped like an A-framed ship, allowing it to efficiently shed snow and ice.
A Bell & Gossett Technoforce booster package helps in the snow removal process. Unlike most snowmelt systems, which typically are installed at ground level, U.S. Bank Stadium’s first-of-its-kind system is installed seven stories up, on the stadium’s top floor. Separate from the stadium’s domestic hot water systems, the booster package provides 400 gal of hot water per minute to hose down the roof and melt the snow. The melted snow flows into 6-ft-wide, 10-ft-deep concrete gutters on the side of the stadium. The gutters, which contain plastic tubes with glycol, carry the melted snow through the stadium’s storm water control system and down to the ground, where it is drained into the city sewer.
“The powerful TechnoForce XLS pump controller gives customers superior capability for hardware expandability, unequal [horsepower] control, and a color touch screen with intuitive interface screens,” said John Collins, global product manager – booster packages for Xylem Inc.
Prefabricated VSX pumps used for the HVAC system at U.S. Bank Stadium helped meet the contractor's timeline.
U.S. Bank Stadium contains 979 bathroom stalls, and pumps are a key factor in ensuring consistent water supply to every one. A Bell & Gossett Technoforce XLS booster package supplies water to the entire facility—including the bathroom stalls—at 2,000 gal per minute (gpm).
The booster package is installed in the stadium’s basement and contains four Bell & Gossett end suction pumps: three large pumps and one small pump. While only one pump works to send water throughout the building at 1,200 gpm at a time, all four pumps were designed to work with the 75-hp variable frequency drives (VFDs) installed in the water system to ensure optimal efficiency. A VFD-based booster pump system is advantageous in a high-rise structure, because it can maintain more precise control over a wider range of the pumps’ flow rates while reducing energy consumption and pump wear.
The stadium’s varied water usage caused challenges when it came to specifying pumps to efficiently circulate water throughout the facility. Ninety-five percent of the time, the stadium is not full of cheering fans—but during that 5% of time that it is full, water demand is high. The original design specified three large end suction pumps, but in an effort to keep operational costs low, the mechanical contractor opted to include a small jockey pump to power the water system during low-demand times. On game days, the three large pumps alternate pumping water throughout the building. Adding the small jockey pump helped improve the system’s efficiency, resulting in savings of $8,000 to $10,000 in energy costs annually.
To ensure the water system could keep up with high-demand game days, hundreds of workers and volunteers participated in a “super flush” test before the stadium opened. The participants flushed every toilet and urinal at the same time and turned on all of the sinks for 30 minutes. The test was a success, with the pumps effectively handling the high demand.
U.S. Bank Stadium seats up to 70,000 people in more than 18 seating styles, ranging from standard seating to luxurious Touchdown Suites and field seats just 25 ft from the sidelines. With the comfort of 70,000 potential guests to consider, heating and cooling are important concerns.
The stadium’s HVAC system provides 7,000 tons of heating and cooling to the venue. The system utilizes ultra-compact Bell & Gossett VSX Series pumps, which have a footprint that is 40% smaller than traditional split-case and vertical inline pumps.
“The VSX split case pumps were selected because they are easy to service,” Nolan said. “Their compact, innovative design provides easy access to the rotating assembly.”
To keep the project on schedule, the portion of the HVAC systems that runs on the VSX Series pumps was prefabricated on a skid. This allowed contractors to work on other parts of the building while the system was constructed. The pump’s small size allowed for a smaller skid, leading to reduced installation time.
“Because of their ease of installation and maintenance, the VSX pumps were the best choice for U.S. Bank Stadium’s HVAC system,” said Jim Burns, vice president for Mulcahy Co. of Eagan, Minn., a Bell & Gossett representative. “The pumps fit seamlessly into the piping, and, because they’re Bell & Gossett, we know they’ll withstand the heating and cooling demands of the building for decades to come.”
No matter what the use—or the weather—pumps will be working efficiently and seamlessly behind the scenes to enhance environmental sustainability and the fan experience.
The Technoforce XLS supplies water at 2,000 gpm throughout U.S. Bank Stadium.