By Amy Silverman
By Olivia LaVecchia
By Monica Alonzo and Stephen Lemons
By Chris Parker
By Michael Lacey
By Weston Phippen
"Montreal didn't work. Toronto did," says Bank One Ballpark's chief roof engineer Felim McCaffrey of Hatch Associates in Toronto. "We are batting .500. The question is, does it go up to .667, or does it go down to .333?"
McCaffrey and everyone else associated with the project are praying the average goes up.
McCaffrey doesn't expect to disappoint anyone.
"I don't have a major concern about it not working," he says. "We feel very confident."
Optimism runs high because the design of the retractable roof is based on applications used for 100 years in shipyards and heavy industry.
"We are transferring heavy industrial equipment from a factory or steel works and putting it on top of a sports facility," McCaffrey says.
The roof will be supported by two steel trusses that are, essentially, elevated railroad tracks. The retractable portion of the roof will be mounted on wheels similar to railroad cars and divided into six panels.
Three panels will be pulled to the east side of the stadium, and three to the west side, where they will stack on top of each other. An elaborate array of steel cables, winches, pulleys and gears, powered by a 150-horsepower electric motor, will open or close the roof in as little as five minutes.
McCaffrey says the 5.25-acre opening created when the roof is fully retracted can be constantly adjusted to minimize heat buildup in the stadium seating areas. Opening or closing one side of the roof can throw shadows on seating areas.
This may prove to be an essential feature in realizing a second unusual but fundamental feature of the ballpark. Designers want to keep the roof open as much as possible to provide sunlight for a natural-grass field.
Summertime sunlight obviously creates very high temperatures in the seating areas. The Diamondbacks plan to close the dome three to four hours before game time and then use a powerful cooling system to lower summertime temperatures inside the stadium from 115 degrees or more to about 78 degrees before the first pitch.
The solution to the problem is brute force--8,000 tons of water-chilled coolers.
"There really is no magic or cutting-edge technology," says cooling engineer Robert Barrett, of ME Engineers, Inc., of Denver. "It's pretty basic. We will throw a lot of cooling at it, and it will do the job."
The stadium's electrical system will draw up to 14 megawatts of power, most of it associated with cooling the building. That's enough energy to meet the electrical needs of 1,700 homes.
APS obviously is happy to have the stadium on its grid. The ballpark will rate as one of the utility's 200 largest customers. But electrical costs are not now expected to be as high as first feared. The industrial rate structure offered by APS "eliminates much of the penalty associated with the ballpark's large electrical demand load," Barrett says.
Cool air will only be circulated on the concourse and above the seating areas of the stadium. The air will be blown across the top of the stands from vents located along the perimeter of the upper and lower concourses. The cool air is expected to cascade across spectators and toward the field.
Temperatures in the seats will differ by as much as ten degrees from the 78-degree target, with the coolest seats closest to the field and warmest seats in the upper reaches of the stadium.
The playing field will be the warmest spot in the stadium, with temperatures expected to be around 88 degrees when the roof is closed.
Even though designers express confidence in the cooling system, it has the Diamondbacks nervous.
"One of the scariest things about this whole project is the AC," says Diamondbacks president Rich Dozer. "I'm on edge," he continues. "That's just a big risk factor, air conditioning that place."
And the Diamondbacks are responsible for the operating costs of the stadium--including the cooling.
Colangelo has always insisted that Bank One Ballpark will be a natural-grass field. But no domed or retractable-roof stadium has been able to keep a living field.
Turf scientists at the University of California at Riverside claim they have found a solution. Steve Cockerham, superintendent of agricultural operations, has led a summerlong experiment, testing several different grass varieties to see which types can tolerate long periods of shade and are tough enough to be used as an athletic playing surface.
Cockerham believes one of the grasses he tested, a hybrid zoysia grass called DeAnza, which has been used in golf courses since 1982, will meet the needs of the ballpark.
"I don't think it's going to be great, but it is going to be a damn good grass," Cockerham says.
In testing, the DeAnza kept growing even when it was repeatedly subjected to complete shade for up to eight days, Cockerham says.
The grass exceeds the team's expectations. The Diamondbacks were hoping to find a grass that could survive for three or four days--the maximum length of time the stadium roof is expected to be closed during home stands.
There are a couple of drawbacks to zoysia grass as a baseball surface. The turf doesn't mend itself as quickly as the Bermuda grasses generally used in Major League Baseball fields in warmer climates. And there is a tendency for zoysia grass to cause a baseball to zigzag as it rolls. This effect can be diminished or eliminated if the grass is cut short, turf experts say.