Minneapolis stadium scores with sustainable pipe system
U.S. Bank Stadium is considered one of the largest public works projects in Minnesota history. Built on the site of the former Metrodome in Minneapolis, the $1.1 billion stadium is nearly twice the size as the National Football League’s Minnesota Vikings’ old home and is praised not only for its unique architecture but also for its commitment to sustainability.
U.S. Bank Stadium opened ahead of schedule in July 2016, after a 2.5-year construction period. More than 8,000 workers committed upwards of 4 million hours to design and build the 1,750,000-sq-ft stadium.
“At work behind the scenes at U.S. Bank Stadium are Bell & Gossett pumps,” said James Nolan, market development manager for Xylem AWS. “We are proud to not only enhance the fan experience by satisfying the unique heating and cooling needs at this spectacular venue, but also help the stadium meet its energy conservation goals.”
The extreme climate of Minnesota — averaging 54 in of snow per year — influenced the design of the stadium. The roof of the facility resembles an A-framed ship so it is able to shed snow and ice efficiently, preventing buildup on the roof.
A Bell & Gossett Technoforce booster package provides the 400 gpm of hot water used to hose down the snow-filled roof, sending melted snow down concrete gutters along the side of the stadium. The 6-ft wide and 10-ft deep 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 Bell & Gossett Technoforce booster package is installed seven stories up on the top floor of the stadium and is not part of the stadium’s domestic hot water system, which is very rare. Typically, snow-melt systems are installed at the ground level, but U.S. Bank Stadium’s roof-melting system is the first of its kind.
A Bell & Gossett Technoforce XLS Booster Package supplies all of the water — 2,000 gpm — to U.S. Bank Stadium. This includes providing water to the 979 bathroom stalls in the facility. The booster package, which is installed in the stadium’s basement, 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 VFDs installed in the water system to ensure optimal efficiency. A VFD-based booster pump system is advantageous in a highrise structure because it can maintain more precise control over a wider range of the pumps’ flow rates while reducing energy consumption and pump wear.
Because the stadium is so large and water usage is drastically different during the week versus on game days, specifying pumps to efficiently circulate water throughout the facility was a challenge. The stadium was originally designed with three large Bell & Gossett end-suction pumps, but to keep operational costs down, the mechanical contractor specified a small Bell & Gossett jockey pump to power the water system when the stadium isn’t full of fans, which is 95% of the time. On event days, three large Bell & Gossett pumps alternate pumping water throughout the building. The redesign of the water system to include a small jockey pump improves efficiency and reduces energy costs.
The jockey pump saves an average of $8,000 to $10,000 annually on energy. To make sure the water system was fully operational before the stadium opened, hundreds of workers and volunteers participated in a Super Flush test. During the test, everyone simultaneously flushed all toilets and urinals and turned on all sinks in the stadium for about 30 minutes. Bell & Gossett pumps successfully handled the Super Flush.
The Bell & Gossett VSX Series pumps are the primary feature of the stadium’s HVAC system, which supplies all the heating and cooling — 7,000 tons — to the stadium, from the front-row seats to the Cabin Suites on the upper level. The VSX Series pumps were selected due to their compact footprint — 40% smaller than traditional split-case and vertical inline pumps, according to the manufacturer.
The portion of the HVAC system that runs on the Bell & Gossett VSX Series pumps was prefabricated on a skid before it was installed. Prefabricating this section was advantageous because it enabled the skid to be built in a controlled environment while contractors worked on constructing other portions of the building to meet the scheduling demands of the project. The size of the VSX pumps enabled the skid to be smaller, reducing 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 at Mulcahy Co. in Eagan, MN, a B&G 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.”
U.S. Bank Stadium will host the 2018 Super Bowl, the NCAA basketball Final Four in 2019, and a wide array of sporting, cultural, and entertainment events year-round.