MINNEAPOLIS — The new, $1.1 billion U.S. Bank stadium is the largest public works project in Minnesota history. Built on the site of the former Metrodome, it is at 1,750,000-sq.ft. nearly twice the size of the Viking’s old stadium and combines cutting-edge architecture with the latest in sustainable technology.
The design-assist mechanical contract for the stadium went to Harris Mechanical, one of the Harris Companies headquartered in St. Paul, Minnesota. The Harris team provided all the plumbing, HVAC and temperature controls, working in concert with various department heads and suppliers.
Harris Mechanical has been in business since 1948 when founder Charles Harris struck out on his own after 17 years working with his brother Aaron. Today, the company has divisions dedicated to mechanical contracting, design-build, service and controls. In 2016 they ranked No. 20 on CONTRACTOR Magazine’s annual Book of Giants with revenues of $220 million.
One of the primary concerns when designing the new stadium was snow abatement. Minnesota averages 54 inches of snow a year, and large accumulations had caused the roof of the old Metrodome to collapse five times over the course of the building’s life.
While the new stadium’s A-frame design is able to shed snow and ice more efficiently than the old Metrodome, the new building owners weren’t taking any chances. Harris installed 84-in. diameters supply air ducts off the stadium’s upper catwalk to aid in melting the snow, and created an enormous storm drain system to handle the run off.
To help speed the melting process, a Bell & Gossett Technoforce booster package provides 400 gallons of hot water per minute to hose down the roof, sending melted snow into concrete gutters along the sides of the stadium.
“The roof system is surrounded by wide troughs that collect the snow as it begins to melt off the roof,” James Nolan, market development manager, North-Central States for Xylem (a Bell & Gossett brand) said.
Those 6-ft. wide, 10-ft. deep troughs contain a radiant snowmelt system (using a heated water-glycol mixture) to finish the job. Melted snow travels down through the storm drain system and into the city sewer.
Yet another Technoforce booster package (the XLS) supplies all the water (2,000 GPM) to the facility. That includes the stadium’s 979 bathroom stalls, which see heavy use on game days.
The booster package uses four Bell & Gossett end suction pumps, three large and two small. 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 in concert with the 75 HP variable frequency drives installed to assure optimum efficiency.
The pumps use an innovative split case design. Typically, these pumps have modular pieces and require the lifting of a heavy, cast-iron cover in order to access the bearings or mechanical seals for service. The new design allows access to the internals without having to disturb the piping or remove large parts of the pump.
“It also has a smaller footprint,” Nolan said, “so we don’t require long radius elbows for the water to enter the pump. Also, the flanges on the pump can accept some of the building piping, so some of the pressure from the piping can be transferred on to the pump and the pump will hold up.”
All 979 bathrooms served use low-flow fixtures to help conserve water. “There is extremely low water usage compared to a standard building,” Nolan said. “That was part of [the designers’] attempt to achieve a LEED-status building… I believe they are still going through the evaluation process… they want to make sure all the systems are running as they are designed to.”
The system was tested with a Super Flush. “What they do,” Nolan explained, “is they get everybody who is on the site, all the construction workers, all the trades, and each one will stand at a toilet or a sink and when the signal is given everyone will open up all the fixtures, flush all the toilets. It’s a pretty common practice in large buildings like this, where they want to make sure that all the equipment will perform and the pressure will recover.”
While the Super Flush was designed to simulate the stadium at maximum capacity, 95 percent of the time the building simply isn’t full of cheering fans. For every-day use, a small jockey pump is sufficient to power the system.
From the beginning, the stadium project was on a tight schedule. The total time frame was two-and-a-half years (which included tearing down the old stadium). The Minnesota Vikings football franchise had a lease with the University of Minnesota stadium during construction, but the lease was up in the fall of 2016.
Key to delivering the project was manpower. More than 8,000 workers committed up to 4 million hours to design and build the stadium. Harris Mechanical recruited and contributed to the training and development of more than 150 new tradespeople in the St. Paul and Minneapolis area.
Another factor was Harris Mechanical’s just-in-time delivery strategy; all mechanical systems were modeled, prefabricated, assembled and then delivered to the job site just at the phase of construction when they were required. The system helps to maximize productivity, control quality and improve safety.
“They accepted all our equipment,” Nolan said, “they engineered it, laid it out according to CAD drawings, and built all our pumps onto packaged piping skids… They could just install the pump with the piping already in place and just make their connections. It saved a lot of time.”
Thanks to the hard work and efficiency of the entire project team, U.S. Bank Stadium was issued its certificate of occupancy six weeks ahead of schedule. The first event at the stadium was held in August of 2016, and it has seen all the wear and tear a full NFS season can provide.
“Far as I know,” Nolan said, “the system has been working with little to no problems.”