BY ROBERT P. MADER of CONTRACTOR’s staff
The Chicago Bears will open renovated Soldier Field on Monday Night Football Sept. 29 against their archrival, the Green Bay Packers. The new stadium has generated plenty of wisecracks by Chicagoans. Preservationists insisted that the historic colonnades of Soldier Field be maintained, and the new stadium, some say, looks as if a giant UFO has landed on top of it.
The mechanical contractors working on the project, however, say the inside is spectacular.
The new Soldier Field is a complete rebuilding of a stadium that held more than 100,000 people when it opened in 1924. It was, despite that impressive capacity, a lousy place to view a football game. The interior of the stadium inside the colonnades was gutted and an entirely new structure put in place.
An infrastructure contractor brought in the water supply, explains Jim Barnas, project manager for Great Lakes Plumbing & Heating. Great Lakes held the plumbing contract for the stadium.
Great Lakes brought the water in through two 12-in. lines into a Metropolitan Industries booster package of three 100-hp pumps that are controlled by a variable frequency drive. Total capacity is specified at 2,700 gpm, but the VFD can turn that down to as little as 20 gpm, Barnas says. Water comes out the booster pumps into a 14-in. feed main and then into an 8-in. cold-water loop that circulates through the entire lower level of the building.
Seventy-five risers come up from the loop, some up to 70 ft. and others as much as 120 ft. to the suite levels, Barnas says. Great Lakes used Victaulic fittings on galvanized pipe 5 in. and larger and Anvil’s Gruvlock fittings on Type L copper from 2 in. to 4 in. in diameter. Any pipe smaller was sweat.
Hot water pipe was not extensive because so much of it is point-of-use.
In the lower level, three Armstrong heat exchangers take water from Cleaver-Brooks boilers (installed by Hill Mechanical) and heat it to two temperatures for either cooking or bathing.
Two of the heat exchangers produce 50 gpm at 100°F rise for concourse level cooking and cleaning. The third heat exchanger produces 105 gpm at a 70°F rise and delivers water to the locker room showers at a maximum of 110°F.
“The rest of the hot water distribution is mostly horizontal,” Barnas says, such as a single water heater supplying suites on either side of it. The 120 Lochinvar water heaters range from 6 gal. to 120 gal. All but one are electric, the exception being an 80-gal. high-recovery unit on the top level of the stadium that supplies hot water to a food preparation area.
Great Lakes prefabricated loops and carriers on site. Much of that work was done with T-Drill fittings, Barnas notes. The company procured an expressway overpass, enclosed it with corrugated sheeting and heated it with propane heaters.
The stadium has 10 large toilet rooms that contain 45 to 50 fixtures, Barnas says. The bulk of the restrooms house 18 fixtures total, including the lavs. The building also contains numerous ADA-compliant or unisex washrooms. American Standard supplied 584 wall-hung water closets, including ADA compliant toilets; 134 two-piece water closets in suites; 307 wall-hung urinals and 55 ADA urinals; 340 wall-hung lavatories; 97 drop-in countertop lavs; and 133 stainless sinks in the luxury suites, which also have 136 bar sinks (a couple of the suites have two).
Symmons, American Standard and Chicago Faucet supplied the faucets. Flush valves are by Sloan Valve.
The building contains 115 showers for players and staff. Some of the showerheads are mounted at 8 ft.
All this water flowing downhill went through a DWV system that includes 16-in. ductile iron pipe with mechanical joints. Any DWV that was 15 in. and smaller was Charlotte Pipe bell-and-spigot soil pipe that consumed 22 tons of lead for the joints.
Great Lakes also installed an extensive storm drainage system that includes seven sump-pump systems for groundwater and storm drainage and five sewage ejector pump systems for sanitary drainage.
The heating system contains two systems — the 500-hp Cleaver-Brooks boilers in the basement and eight Lochinvar boilers on the fourth level for preheating the suites. The boiler water is used mostly for air tempering, notes Hill Mechanical Group Project Manager Pat Cooper. Most of the final comfort heating comes through electric duct coils.
All that air tempering is because the Chicago code calls for 60% outside air, Cooper explains. For example, 22 Trane water-cooled ventilation heat pumps do nothing but deliver 100% outside air to the suites.
Bell & Gossett base-mounted split-case pumps, controlled by variable frequency drives, pump water from the Cleaver-Brooks boilers through heating “legs” that are as large as 12 in. in diameter. All the piping originally was supposed to be welded, Cooper says, but ended up being Victaulic because of time constraints.
Victaulic has a Construction Piping Services division that offers both free and fee-based services including pre-bid cost studies, software drawing tools, project coordination, pre-planning and materials scheduling. CPS worked with Hill Mechanical on the project. The division provides services such as supplying materials tagged and bagged for easy installation. The Victaulic fittings were used on all pipe from 4 in. up to the largest, a 16-in. condenser water line.
Hill Mechanical also used Ridge Tool’s ProPress joining system on pipe 3 in. and smaller with the approval of the owner. Great Lakes Plumbing and Heating would have liked to use the ProPress system for domestic water, Barnas says, but it had not been approved yet for higher-pressure applications. Hill Mechanical, however, could use it for low-pressure heating pipe.
“It was a lot faster than brazing joints,” Cooper says.
The water is pumped to coils in 31 Trane packaged air handlers, which then supply tempered air through ductwork to water-source heat pumps. The air handlers also supply 110 VAV boxes in restaurants and bars at the club level.
There is no central chiller plant. Air conditioning is provided solely by 309 cooling-only water-source heat pumps. Seventy of the heat pumps are in the locker rooms and lower concourse area and the rest are up in the suite level. Eight Baltimore Air Coil evaporative fluid coolers temper the heat pumps’ water loop.
It took 12,000 man-days to install the ductwork, Cooper says. Hill fabricated the sheet metal in its Chicago-area shop in 56-in. sections and shipped it to the site for final assembly. Duct coming out of the air handlers is as large as 86-by-48 in.
Access for the ductwork was a problem, Cooper says, because the colonnades on the exterior prohibit lifting from the outside, and the shape of the interior makes it difficult to use a crane inside.
Most of the ductwork was delivered at night. One crew worked 12 hours a day and all they did between 4 p.m. and 6 p.m. was move ductwork and stage materials. Duct was moved on the elevator one piece at a time.
While that’s an impressive amount of mechanical work, there’s yet another 40 miles of pipe under the turf.
As any fan will tell you, football is meant to be played on natural grass. It should also come as no surprise that this notion is seconded by an overwhelming percentage of the men who make their living pounding each other against that turf. A recent survey by the National Football League Players Association found that 97% of its members prefer playing on the real thing. But problems arise in bitter cold weather, when real grass morphs into frozen tundra.
With the active involvement of the Chicago Bears management, the new gridiron has been equipped with natural grass and enhanced with an underground turf-conditioning system to keep the ground warm, pliable and player-friendly when the mercury begins to drop.
The system was designed and manufactured by Uponor Wirsbo and installed by local mechanical contractor Althoff Industries. The system should help to melt flurries and light snowfalls if the ambient temperatures aren’t too low. In fact, thanks to steady soil temperatures of between 50°F and 55°F, the grass may even grow a bit during December and January.
But the primary goal is not to ruin a White Christmas, but to secure the safety of the players.
“The players are the game,” says Bears head groundskeeper Ken Mrock. “By keeping the root zone beneath the grass at a temperature well above 32°F, we will make sure the players have a safe and soft playing surface even in subzero conditions.”
The turf conditioning system consists of nearly 40 miles (202,000 linear ft.) of 3/4-in. Wirsbo hePEX Plus tubing, installed on 6-in. centers and extending the length of the field, north to south, from end zone to end zone. Boilers located in a mechanical room under the north end zone stands move hot water to the system via a pair of heat exchangers. Mixing valves cool the 180°F water off the heat exchangers to 130°F before a primary pump sends it to the underground piping loops via 1,800 ft. of 4-in. copper supply-and-return piping, including roughly 800 ft. of manifold, all of it also located under the north end of the field.
Typically, Wirsbo designers prefer to use a high-density polyethylene manifold, but because the tubing was run end zone to end zone, rather than the more conventional sideline to sideline, the loop lengths became quite long: 820 ft. vs. 525 ft.
“Longer runs generate greater head pressure, which would bring us uncomfortably close to the working ratings of this material,” says Jeff Wiedemann the designer of the system and Wirsbo manager of strategic product development. “Going with a copper manifold gave us more leeway to accommodate the higher head pressures while permitting us to push the temperatures even higher than 130°F, if that were ever necessary.”
Why run the tubing end zone to end zone in the first place? The answer lies with the orientation of Soldier Field to the sun as it works its way across the winter sky, as well as the desire of the Bears to maintain an even ground temperature across the entire playing surface.
Because of the height of the new grandstand along the western wall of the stadium, an increasing percentage of the field will be in ever-lengthening shadows during the afternoon. To keep ground temperatures consistent, regardless of the play of sunlight and shadow, the 40 miles of tubing was divided into four longitudinal zones. That way, different water temperatures could be run in each zone to compensate for varying ground temperatures.
Each zone is served by two pumps in the mechanical room and by four sensors on the field. The sensors monitor ground temperatures and provide the mechanical room computer with an average reading for each zone, Wiedemann says. The computer then adjusts the temperature of the circulating water up or down, as required.
A computer in the stadium mechanical room controls the entire turf-conditioning system. That computer, in turn, can be monitored by Althoff and the Bears offsite.
“Sitting in their offices in Lake Forest [a Chicago suburb], the Bears can see the temperature of the field as well as the temperature of the water running through the system any time of the day,” says Althoff Senior Vice President Christopher J. Bennett, who supervised the installation with Althoff project manager Ken Capasso.
The end zone-to-end zone layout of the tubing created a major hurdle for Althoff’s crew of installers, further complicated by the order to avoid walking directly onto the field. That’s because the tubing was installed atop 6 in. of pea gravel, an ultra-fine granular material that covers the field drainage system. (Subsequently, the tubing was buried in 8 in. of sand, porous ceramic and peat moss, on top of which sits 15/8-in. of sod.) Stepping right onto the pea gravel would leave dimples, ultimately resulting in an uneven surface above.
So Althoff devised an ingenious solution. It developed a motorized carrier built from a child’s snow sled that could run unmanned the length of the field. During the installation process last spring, the crew fit the sled with a sheet-metal spool and tethered the sled to motorized pulleys behind each end zone. The tubing was looped around the spool. One end was held at the copper manifold; the other, to a reel holding the rest of the 825-ft. coil.
The sled ran atop numerous 4-by-6-ft. plywood sheets that were laid end to end across the field. (The sled was not permitted to dent the pea gravel either.) As it moved from end zone to end zone, the sled pulled the tubing over a series of plastic tracking rails positioned at 20-ft. intervals. Installers followed the sled down the field, walking on the same plywood planks and manually snapping the tubing into place on the rails.
Althoff’s Bennett estimates that the sled cut in half the time it took to run a loop of tubing from end zone to end zone.
“We did the first two loops manually, and it probably took us 10 minutes just to walk it down and back, 410 ft. each way,” he recalls. “With the sled, the roundtrip was five minutes, max, and with a lot less physical labor. This innovation makes our installers’ jobs easier, while meeting our client’s need to stick to a very tight construction schedule.”
Even as it shortened installation time, the sled enabled Althoff to use fewer workers. Instead of the normal 20 installers manually passing tubing down the field, the Althoff crew numbered only 12, Bennett says.
The Wirsbo PEX-Rail Tracking System also spared the crew from the conventional but time-consuming chore of manually tying the tube to mesh screening covering the entire playing surface. A gridiron the size of Soldier Field (roughly 100,000 sq. ft.) would typically require 20,000 wire ties.
Bennett confirms that his crew came close to its initial goal of completing the installation within three eight-hour shifts, despite the brief disruption caused by heavy winds one evening after the first 50,000 ft. of tubing was in place.
“From the initial contact to the estimation phase through sales and installation, it was a team effort at Althoff, and we’re very happy with the way the project came together,” Bennett says. “Of course, that’s a byproduct of the many hours we spent with Ken Mrock and the Chicago Bears doing our homework on this job - including visits to other fields and investigating alternative turf-conditioning systems before choosing Wirsbo. The Bears wanted to make absolutely sure that once the tubing was buried in the turf, the system would perform at a superior level for a long, long time.”