BY ROBERT P. MADER
Of CONTRACTOR’s staff
PITTSBURGH — Architect Rafael Vinoly took his inspiration from the Allegheny River and three nearby suspension bridges when he designed the new David L. Lawrence Convention Center here, creating a boat-like structure with a cable-suspended roof that resembles a sail.
Limbach Facility Services and numerous mechanical subcontractors are in the middle of the convention center project that is scheduled to finish in March 2003.
Though sustainable features such as natural ventilation and daylight are widely used in European exhibit halls, Pittsburgh’s new facility is the first time an American convention center will implement these features, said Dave Linamen from consulting engineer Burt Hill Kosar Rittelmann Associates.
The shape and height of the roof encourage natural cross ventilation of the main exhibit space, drawing outdoor air from all four sides of the facility and relieving it through the peak of the roof. Natural ventilation will provide almost all the cooling for the main exhibit hall when outdoor temperatures are between 50°F and 60°F.
The cooling system for the 250,000-sq.-ft. exhibit hall uses a low-temperature air supply. The 38°F primary air reduces the volume flow rate of air required to cool the space, thereby minimizing duct sizes and reducing energy consumption by reducing fan capacity requirements.
Water use for the facility is minimized by water recycling, as well as by use of water from a local well for replacement of evaporated water for the building’s cooling towers and for a fountain feature on the street that passes beneath the main exhibit hall. The water recycling system purifies the water to a clear and odorless condition and returns it to the facility for toilet and urinal flushing. Overall water use is reduced by more than half.
The natural ventilation system is the most significant design element of the building and greatly affected the mechanical plans.
The building will have a weather station near the roof, which will measure air temperature, humidity, wind speed and direction, explained Mike Hall of controls contractor Control Solutions. When conditions are right, between 50°F and 60°F, the 20 air-handling units serving the exhibit hall will turn off. Dampers will close and direct the outside air, pushed solely by wind velocity, through the return ducts and into the exhibit area.
“It’s the first time anyone has ever made a whole exhibit hall a mixed-air plenum,” Hall said. Louvers near the roof will modulate to exhaust the air and keep the convention center at a slight positive pressure of 0.005 w.c. The pressure can’t be any higher because the roof is cable-suspended fabric.
Because the building looks so much like a boat, it’s referred to in nautical terms. The front of the building on the north side is the bow, explained Limbach project manager Rich Snead. The mechanical room in the bow is on the ground floor. In the stern, the mechanical room is in a fifth-floor penthouse.
The building has three floors in the bow and five in the stern. The mast area is the demarcation point between the stern with the exhibit halls taking up three-quarters of the bow and the rest of the space occupied by meeting rooms and pre-function areas such as ticket offices. The main entrance is also in the bow.
There are meeting rooms in the third and fourth floors of the stern. All delivery areas are in the stern with storage on the first and second floors.
Chilled water for the building is provided by NORESCO, the energy services arm of utility holding company Equitable Resources, which is selling chilled water to the facility under a long-term contract. NORESCO furnished and installed four Trane 1,500-ton chillers, which have excess capacity for a hotel that will be built nearby, explained Mark Johnson, manager of the chilled water facility for NORESCO.
Trane provided the condenser water pump skids and chilled water pump skids and the controls. The chilled water pumps are controlled by a variable frequency drive. Johnson’s job is to “push chilled water out the wall at 34°F at 80 lb.”
Steam for the building will be provided by local utility Pittsburgh Allegheny County Thermal, Snead said. Many of the air-handling units mix 38°F primary air with return air and then reheat with steam if needed. Smaller AHUs for pre-function areas, fan-powered boxes and VAV boxes use hot water reheat, provided by running the steam through a heat exchanger.
Because the roof is suspended fabric and the primary air is 38°F, metal duct would have had to have been heavily insulated or double-walled, with either choice too heavy for the roof structure. Consequently, all ductwork in the exhibit halls is a fabric air-dispersion system manufactured by DuctSox.
The DuctSox, in various lengths and arched along the roofline of the building, measure 32 in. and 34 in. in diameter, and move 5,000-6,000 cfm each, said Limbach’s sheet metal foreman Mike Gunning.
Gunning’s crew also has fabricated 2.5 million lb. of ductwork for the more conventional parts of the building, with some of the ductwork 528 in. wide.
The fabric roof will create a heating problem in winter, Snead said. Consequently, Limbach will install what he described as “monstrous” Runtal steel tube heaters near the roofline for air tempering.
The gray water system is the most unique aspect of the plumbing system, said Sauer Inc. project manager Ron Rombach. The building will recycle about 50% of its water. The wastewater will pass through a digestive process and submicron filtration and come out clear and odorless, explained consulting engineer Linamen.
Water supplied to food services, however, will be conventional city-supplied water because of the danger of viruses. Sauer is piping the water treatment facility.
Sauer is fabricating all toilet rooms in the shop, Rombach said, including all lavatories, water closets, urinal carriers and water line headers.
“We send them down, bolt them in and they’re done,” Rombach said. “I think we most probably saved 35% to 40% on labor on the fabrication of the toilet rooms.”
The building will have about 24 restrooms. Fixtures are American Standard and faucets and flush valves are Sloan sensor types.
Rombach’s crew is installing about two-dozen Bradford White water heaters, from 50-gal. to 80-gal., to serve restroom and food service areas.
The constantly flexing roof posed a problem for fire protection contractor S.A. Communale as well because conventional sprinklers couldn’t be hung from the roof of the exhibit halls.
Consequently, Mark Communale selected Monitors, also known as Piranha Water Cannons, made by Equipment Specialties Co.
The 25 Monitors, which Communale described as giant squirt guns, will protect the four exhibit halls. They are mounted at the ends of the halls about 15 ft. above the floor.
If ever called upon, each Monitor will oscillate in a 60-degree arc, firing 500 to 600 gpm of water 300 ft.
Communale installed a VESDA (very early smoke detection and actuation) system and an infrared system to detect the location of a flame. When both systems are actuated, they send a signal to a control panel that opens a solenoid that releases water to the Monitor closest to the fire. The system is designed to operate up to three Monitors at a time, although the 2,500-gpm fire pump gives them extra capacity. A 16-in. main feeds the fire pump from the city water supply; 8-in. feeds run to each bank of Monitors with 4-in. pipe to each water cannon.
The rest of the convention center, such as meeting rooms, is protected with a standard sprinkler system using black Schedule 10 and Schedule 40 steel pipe joined with cast-iron grooved fittings. About 12 dry systems will protect parking garages and loading docks.