Although fans might not see them, pumps move water throughout the largest public works project in Minnesota history, U.S. Bank Stadium. It is not just a multipurpose stadium in Minneapolis — it is a work of art. Built on the site of the former Metrodome, it is nearly twice the size of the National Football League’s (NFL) Minnesota Vikings’ old home, and it is praised for its unique architecture and commitment to sustainability.
The stadium opened ahead of schedule in July 2016, after a construction period of more than two years. More than 8,000 workers committed nearly 4 million hours to design and build the 1,750,000-square-foot stadium. The pumps moving water around the stadium and are an essential part of this stadium.
Among other factors, the extreme climate of Minnesota influenced the stadium’s design. Its roof resembles an A-framed ship so it can shed snow and ice efficiently, preventing buildup on the roof. In the past, snow accumulation caused problems at the Metrodome, and the roof collapsed five times.
A booster package of pumps move water that provides 400 gallons of hot water per minute to hose down the snow-filled roof, sending melted snow down concrete gutters along the side of the stadium. The 6-foot-wide and 10-foot-deep gutters, which contain plastic tubes with glycol, carry the melted snow through the storm-water control system and down to the ground where it drains into the city sewer. Installed seven stories high on the top floor, this booster package is not part of the stadium’s domestic hot water system, which is rare. Typically, snow-melt systems are installed at the ground level, but this one is the first of its kind.
Water system efficiency
In addition to the booster package used for snow removal, another booster package supplies 2,000 gallons of water per minute for 979 bathroom stalls and all other water needs. Installed in the basement, the booster package contains four end-suction pumps: three large pumps and one small pump.
While only one pump sends water throughout the building at 1,200 gallons per minute, all four were designed to work with the 75-horsepower variable frequency drives (VFDs) installed in the water system to ensure optimal efficiency. A VFD-based booster pump system maintains more precise control across a wider range of flow rates while reducing energy consumption and pump wear.
Water usage is drastically different during the week versus on game days making pump specification challenging. The stadium was originally designed with three large end-suction pumps, but to keep operational costs down, a small jockey pump was specified to power the water system when the stadium is not full of cheering fans, which is 95 percent of the time. On event days, three large pumps alternate pumping water throughout the building. The redesign including the small jockey pump improved efficiency and 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, all the participants simultaneously flushed all the toilets and urinals and turned on all the sinks in the stadium for about 30 minutes. The pumps successfully handled the test.
With a capacity of up to 70,000, the stadium offers more than 18 different styles of seating, including luxury seating that is closer to the field than any other stadium in the NFL. The first row of seats is just 41 feet away from the sideline, and the field seats get fans even closer to the action at 25 feet.
The ultra-compact pumps are the primary feature of the stadium’s heating, cooling and air conditioning (HVAC) system, which supplies 7,000 tons of heating and cooling. These pumps were selected because of their compact footprint, 40 percent smaller than traditional split-case and vertical inline pumps.
The part of the HVAC system in which pumps move water was prefabricated on a skid before it was installed. This prefabrication enabled the skid to be built in a controlled environment while contractors worked on other parts of the building to meet the project’s scheduling demands. The size of the pumps enabled the skid to be smaller, reducing installation time. The pumps were chosen because of their ease of installation and maintenance. They fit seamlessly into the piping and will withstand heating and cooling demands of the stadium.
U.S. Bank Stadium will host the 2018 Super Bowl; the National Collegiate Athletic Association Basketball Final Four in 2019; and an array of events year-round. The pumps will work efficiently behind the scenes to enhance environmental sustainability and the fan experience.
Mark Handzel is vice president, product regulatory affairs, and director, HVAC commercial buildings, at Bell & Gossett, a Xylem brand. He is a member of the Appliance Standards and Rulemaking Federal Advisory Committee’s Commercial and Industrial Pumps Working Group. He may be reached at [email protected].