A New Northwest Passage

Despite its being a major hub of the nation's fourth-largest airline, Northwest Airlines, Detroit's Metropolitan Airport had long lagged on services and support compared to other such flagship facilities. Cramped spaces and limited concessions made travel both inconvenient and unpleasant.

But the McNamara Terminal/Northwest WorldGateway, which opened last February, goes a long way toward addressing these shortcomings. The new $1.2 billion terminal includes almost 2 million sq. ft. in three concourses, bringing world-class amenities to a formerly down-at-its-heels airport and earning its SmithGroup designers a CSE ARC Award for institutional building.

The terminal's 97 gates, 80 shops and restaurants and 1.5 miles of moving walkway are spread over two major structures and a connecting tunnel. The main concourse—A—is nearly a mile long with 67 gates and an internal tram. The sister "B" structure—with only eight gates—sits some 800 ft. away, joined to its "sibling" by an underground passenger tunnel. The final concourse—C—includes 25 gates for regional and commuter aircraft.

Planning for the project began in 1996. Under a unique public/private partnership, Wayne County, the terminal's owner, oversaw construction of related airfield improvements and developed the concessions program, while delegating oversight of the terminal itself to Northwest Airlines, the facility's primary tenant. Detroit-based SmithGroup began its design efforts in early 1997, with construction crews breaking ground in late 1998.

Ironically, for a project so large, space constraints posed the biggest challenges for mechanical and electrical engineers. Expansive glass walls—reaching 36 ft. high in some spots—and low, tarmac-level luggage-handling areas limited the space available for both air and electrical distribution.

Complications began for mechanical designers when architects started fashioning the signature roofline. The stainless-steel roof structure is formed of seamless panels that swoop like the abstract wings in a child's drawing of seagulls to cover both terminal structures—some 675,000 sq. ft. in the case of Concourse A. Visual interruptions became verboten as plans were formalized.

"It kind of evolved over time," says Jack Yorke, senior design engineer in SmithGroup's mechanical department. "The designers didn't want the stainless-steel, curvilinear roof to be penetrated. There's no ventilation piping—nothing that penetrates."

Instead, engineers shoehorned a series of mechanical rooms into existing service cores housing, among other things, vertical transportation, retail concessions and restrooms. These rooms are serviced by a new central energy plant. SmithGroup provided specifications for this plant, which was designed by another vendor.

The plant houses an 8,300-ton chiller, with chilled-water distributed via utility tunnels to the 13 mechanical rooms. Perhaps bucking current design trends, SmithGroup designers specified triplex constant-speed pumps, instead of variable-speed models, to circulate the water over the cooling coils of the 45 air-handling units (AHUs). Each of the three pumps can be operated alone or in parallel, providing any necessary variability. However, the pumps were sized to ensure maximum efficiency, given the 16°F delta-T of the chilled-water system.

"They're relatively small pumps," Yorke says. "The base loads were pretty much always there."

To boost energy savings, all AHUs are equipped with air-side economizers with 100% outside air capability, limiting chiller requirements during Detroit's notoriously cold winters. Two-stage filtration, including activated-charcoal filters for gate-level intakes, helps maintain air quality.

Window design has also helped limit cooling needs. Glass is a major architectural element in the new terminal, providing soaring views of, well, soaring aircraft. Conversations between engineers and architects aimed at limiting the efficiency impact of these open expanses brought the design team to the solution of fritted glass. This product sandwiches tiny plastic disks between two panes of glass to block solar rays. The disks, which can only be seen up close, reduced solar loads by 40%, according to SmithGroup calculations.

Heating also raised design challenges. HVAC planners turned to radiant options to keep both passengers and luggage handlers warm.

During winter months, the central plant produces 350°F water that is distributed under pressure to the 13 mechanical rooms. Here, the water is stepped down to 200°F and distributed to a total of two miles of radiant panels installed along the ceiling's perimeter, as well as to pre-heat coils, unit heaters and VAV-box reheat coils. This approach is intended to help keep glass surfaces warm so temperatures remain consistent throughout the facility.

The luggage-handling area is another beneficiary of radiant technology. This large, warehouse-like space, interrupted by a series of conveyors and carousels, would be almost impossible to heat with a forced-air system. Cold air regularly rushes in when workers transporting baggage to and from waiting aircraft open the area's large bay doors. Even if a distributed-air approach had been feasible, the low ceiling heights required to allow the gates above to line up with parked jetliners would have made ductwork placement difficult.

So, instead, engineers specified more than 90 natural-gas-fired infrared heaters throughout the space. The units are on manually controlled timers that luggage handlers can activate as needed. Because radiant appliances heat surfaces, not air, Yorke says this approach best meets this application's demands.

"You can't just heat the air, because it's constantly being replaced with cold air every time the doors open," he says. Now, workers "have a warm surrounding environment, even though the air around them is cold. I think this is one of the most unique solutions in any airport," the engineer speculates.

Tight quarters in vast spaces also posed problems for electrical designers, according to Tony Tomaino, SmithGroup's senior electrical engineer on the project.

"I think the biggest challenge was just the sheer size of the project," he says. "To get the power distributed throughout that facility was a real challenge."

Designers were most concerned about voltage drops, especially in Concourse A, which is nearly a mile long and spread out over three major levels. The solution: a series of substations incorporated into the facility about 400 ft. apart, and about 4 ft. below the grade of the flight apron. This placement was required to allow sufficient clearance without raising the level of the gate areas above.

Power is delivered to the substations through a utility-tunnel network running from the central power facility. To ensure redundancy in case of equipment failure, each substation incorporates a double-ended design, with two buses connected by a tie breaker. Though each bus typically carries half the substation's intended load, both have the capacity to carry the full load if one fails.

Emergency power is supplied by a series of six 400-kW diesel generators, each having localized fuel storage. Uninterruptible power-supply systems are in place to cover critical operations during the brief delay that would occur while generators started up.

Power quality, itself, has been addressed at specific receptacles, rather than at the panel level, as the project's scope made the latter prohibitively expensive, according to Tomaino.

The scope of the new terminal also posed challenges for fire/life-safety engineers. First, all 2 million sq. ft. had to be tied into a single, networked system. Next, measures had to be taken to prevent any localized situation triggering a generalized evacuation.

The new network now comprises panels in the four main fire-control rooms as well as 59 additional remote panels, according to Greg Spence, director of engineering at St. Louis-based Ross & Baruzzini, the project's fire and life-safety consultant. The panels are tied together with a six-strand, diverse-path fiber loop. The diverse-path design, with six strands entering and exiting each panel, helps ensure a single panel failure doesn't disrupt network operations as a whole.

For alarm purposes, the two concourse buildings have been divided into 15 evacuation zones. In an emergency, only the affected zone—along with the zones adjacent on either end—are evacuated.

Security and life safety took on even greater importance in the wake of the Sept. 11, 2001, terrorist attacks. The new terminal was nearly complete, but the failings uncovered by the incident forced the engineering team to immediately reevaluate designs long thought finalized. Where feasible, these efforts were incorporated into construction plans before operations began in February; others are ongoing.

And as security plans continue to develop, such as installing explosive-detection devices (see "Airports in a Post-9/11 World," CSE 09/02 p. 30), other systems will likely be affected with cooling-system adjustments the likely result.

Better news, however, is that airline business changes also are generating renovation plans. With primary tenant Northwest Airlines recognizing growth opportunities in increasing its regional service, Concourses B and C are now slated for expansion just eight months after they opened.