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The exterior of U.S. Bank Stadium in Minneapolis resembles an A-framed ship, a fitting visual for a stadium built in the land of ice and snow, and home to the NFL’s Minnesota Vikings. The asymmetrical Nordic design also serves a functional purpose — it helps prevent build-up of snow and ice on the roof, aided by its south-facing slope and translucent lightweight ETFE plastic panels.
The extreme climate of Minnesota played a large role in the design of U.S. Bank Stadium where average snow totals are more than 50 inches per year. Large volumes of snow accumulation caused ongoing problems at the Metrodome, the Vikings’ former stadium, resulting in the roof collapsing five times between the 1980s and 2010.
In addition to natural snow-melt measures, the design team integrated a snow gutter system into the structure, which lines the top of the stadium. Snow-melt systems typically are installed at the ground level, but U.S. Bank Stadium’s roof-melting system is the first of its kind and one of the largest snow gutter systems in the world.
The 80,000-square-foot snow catchment contains and melts the snow that slides off the roof. A Bell & Gossett Technoforce booster package provides the 400 gallons of hot water per minute that are used 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 are lined with 15 miles of snowmelt tubing containing glycol. The melted snow is carried through the stadium’s storm-water control system and down to the ground where it is drained into the city sewer.
The Technoforce booster package is installed seven stories up on the top floor of the stadium, separate from the stadium’s domestic hot water system, another unique feature of the snow gutter system. Ensuring the required pressure and flow are maintained for the snow-melt system to meet the flow and head requirements is the primary function of the booster package. Just like irrigating a field of tomatoes, the rooftop hoses spray an even pattern across the roof to get full coverage and the Technoforce booster pumps ensure the pressure is consistent, increasing or decreasing pump speed to maintain that pressure.
The duplex system consists of two pumps, two variable frequency drives (VFDs) and a TECHNOLOGIC pump controller. The booster station is designed so that one pump can provide the full demand with the second pump as a standby. The TECHNOLOGIC pump controller is designed to alternate between both pumps so each pump receives equal run time. When the system is activated, the first pump will turn on to boost pressure to the 60 psi needed to get the water to the roof with enough pressure and flow to evenly cover the rooftop.
The controller monitors the system for amperage being drawn by the motors so they don’t overload and to ensure both incoming and discharge pressure are adequate. Overall discharge pressure for the snow-melt system is 110 psi.
Technoforce booster systems can be enabled to run automatically from the interface’s keypad, or via Modbus or BACnet, staging on and off and varying speed to meet the design requirements of flow and head. The booster system continuously monitors parameters such as speed, amperage, voltage and pressure to provide total system protection.
U.S. Bank Stadium will host Super Bowl 52 on Feb. 4, and the temperature outside will not affect inside comfort, due, in part, to the Bell & Gossett pumps selected for the heating and cooling system.
The ultra-compact 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 percent smaller than traditional split-case and vertical inline pumps.
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,” says Jim Burns, vice president at Mulcahy Co. in Eagan, Minnesota, 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.”
The 70,000 Super Bowl patrons will test the stadium’s plumbing system — including the 979 bathroom stalls in the facility.
A Bell & Gossett Technoforce XLS Booster Package supplies all of the water — 2,000 gallons per minute — to U.S. Bank Stadium. This includes providing water to the bathroom stalls.
The booster package, which is installed in the stadium’s basement, contains four 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 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.
Because the stadium is so large and water use 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 end-suction pumps, but to keep operational costs down, the mechanical contractor specified a small jockey pump to power the water system when the stadium isn’t full of cheering fans — 95 percent of the time. On event days, three large 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.
U.S. Bank Stadium opened in July 2016 as the largest public works project in Minnesota history. It’s praised not only for its unique architecture but also for its commitment to sustainability. In November 2017, it received a design award from the World Architecture Festival in Berlin, Germany, and also in November 2017, it was awarded LEED Gold certification from the U.S. Green Building Council, only the second NFL stadium to achieve LEED Gold.
“At work behind the scenes at U.S. Bank Stadium are Bell & Gossett pumps,” says 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.”