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This provides efficient air circulation when outdoor temperatures are between 45°F and 65 degrees Fahrenheit (7 and 18 degrees Centigrade), about one-third of the time in Pittsburgh. The building has a weather station near the roof to measure air temperature, humidity, and wind speed and direction. When conditions are right, the 20 air-handling units serving the exhibit halls shut off, the vents open, and outside air flows into the exhibit area.

The convention center also uses natural ventilation to flush air from the exhibit halls at night during warmer periods, which further reduces the time during which the conventional cooling system is needed. Natural ventilation saves 3.8 million kWh of electricity a year.

Fabric Ducts

One of the more innovative elements of this system is the fabric ductwork. Burt Hill had been considering low-temperature air for the HVAC system to reduce the total airflow and fan energy requirements. By reducing the air requirements, such a system would also reduce the required duct sizes.

We further recognized that we could reduce the duct sizes even more by using two ducts at each bay, one on either side of the bottom cord of the truss, and by feeding the ducts from both ends. In addition to contributing to the aesthetic that Viñoly was trying to achieve, the low-temperature air system reduced duct costs and fan energy by approximately 40 percent.

As the design progressed, it became clear that there would be considerable movement in the building structure, especially in the roof. Another complication was that even the smaller ducts were quite heavy because double-wall duct insulation was being considered for appearance and to avoid condensation. It was also difficult to find diffusers that would deliver low-temperature air and meet aesthetic expectations.

We realized that fabric ducts would solve several of these problems because of their lower weight and because they can easily flex with building movement. Moreover, they can be designed with a specific porosity allowing them to "bleed" a controlled volume of air. This bleeding creates a microclimate around the duct that prevents condensation.

The fabric duct manufacturer designed a hole pattern for delivering supply air to the space, in an even distribution without drafts. The manufacturer provided a computational model to demonstrate this performance. Their solution reduced the cost of structural support, sheet metal, and diffusers.

When the lighting designers, Lam Partners, saw the fabric ducts, they decided to develop a lighting scheme that would highlight the translucent fabric, further enhancing the visual effect. The architect then designed a support system for the fabric ducts and the lighting.

Natural Lighting

Clerestory windows where the walls and roof meet and long, 6-foot- (1.8-meter) wide ribbon skylights covering 10 percent of the roof area provide daylight for 75 percent of the convention center's exhibition space. This glazing is projected to save 9.5 million kilowatthours of electricity per year.

In addition to its aesthetic appeal, daylight can boost business. A recent study by the Heschong Mahone Group for the Pacific Gas and Electric Company suggests that using daylighting in trade or commercial exhibits can increase sales on a convention floor by about 40 percent.

Water Efficiency

The Lawrence Convention Center taps Pittsburgh's "fourth river," the aquifer that runs beneath downtown. This source provides make-up water for the convention center's refrigeration system cooling towers, reducing the demand for water from the city water system.

Pulsed-power treatment of the cooling-tower water to eliminate bacteria without chemicals further reduces the demand for city water. This design will save an estimated 1.8 million gallons (6.8 million liters) of water annually.

The convention center uses recycled water for toilet and urinal flushing. The water is conditioned by an aerobic digestion and sub-micron filtration system. The effluent is totally colorless and odorless. With final ultraviolet light treatment, the effluent has been treated for everything but viruses. The system recycles 50 percent of the building's water and will save an estimated 6.4 million gallons (24 million liters) annually.

In November, 2003, the convention center will be the site — and a focus of attention — of the Greenbuild International Conference and Expo, which will bring thousands of green building professionals from around the world to take a close look at the center's design.

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David Linamen, an engineer, and Harry Gordon, an architect, are directors of Burt Hill Kosar Rittelmann Associates, which provided engineering and sustainable design services for the David L. Lawrence Convention Center.

Lobby of the David L. Lawrence Convention Center in Pittsburgh, Pennsylvania, designed by Rafael Viñoly and Burt Hill Kosar Rittelmann Associates. Photo: Hedrich Blessing Photographers The sweeping roof with skylights designed for ventilation and daylighting within the building. Photo: Hedrich Blessing Photographers The fabric ducts curve below the fabric ceiling. Photo: Hedrich Blessing Photographers The direct/ indirect illumination system consists of fluorescent sources running between the pair of parallel fabric ducts. The ducts diffuse and baffle the direct illumination of the fluorescent tubes to create a large scale luminaire. Photo: Hedrich Blessing Photographers Second floor plan, David L. Lawrence Convention Center. Image: Greater Pittsburgh Convention and Visitors Bureau Third floor plan, David L. Lawrence Convention Center. Image: Greater Pittsburgh Convention and Visitors Bureau The ballroom has track lighting with conical downlights. The "ceiling" is a dark blue mesh that conceals the roof deck and mechanicals. Photo: Hedrich Blessing Photographers Pedestrian bridge. Photo: Hedrich Blessing Photographers   Click on thumbnail images to view full-size pictures.