November 15, 2001

Mechanical moxie: Innovations at the new Opera House

  • Performing arts hall features rare below-the-seat heat
    CDi Engineers

     Marion Oliver McCaw Hall
    Rendering by LMN Architects
    Marion Oliver McCaw Hall features a curving glass lobby with an adjacent outdoor courtyard. Vertical screen-like “scrims” will display artwork or images from performances under way.

    When the curtain goes up on the Nutcracker Suite and you sit enraptured with the Pacific Northwest Ballet’s pirouettes, the last thing on your mind is the heating, ventilating and air-conditioning (HVAC) system.

    Yet HVAC and other mechanical solutions are important factors in making the Marion Oliver McCaw Hall at Seattle Center a world-class performing hall. Providing enhanced audience and performer safety, environmental sensitivity and overall aesthetic quality, it will be a suitable home for both the Pacific Northwest Ballet and the Seattle Opera for decades to come.

    Originally constructed as the Civic Auditorium in 1927 and remodeled for the 1962 World’s Fair, the Opera House has been in need of seismic and structural upgrades as well as life-safety improvements for many years. Now it is being completely renovated and given a facelift to boot.

    When the McCaw family generously contributed $20 million, the decision was made to name the new performance hall in honor of their mother, Marion Oliver McCaw. The project construction budget is $80 million.

    And under your seats, folks...

    Of special interest to engineering types is a displacement ventilation system for the 2,890-seat auditorium. CDi Engineers, mechanical consultants on the project, designed an air supply system with vents located beneath audience seating. This meant that careful attention had to be given to conditioned air delivery temperatures and velocities. We couldn’t have blasts of hot (or cold) air searing (or freezing) the feet and legs of opera and ballet devotees.

    Would under-seat ventilation be the best solution? It was hard to say in advance, since systems like these are such a rarity. So, CDi staffers for this facility traveled to New Jersey to visit the one U.S. performing arts center that uses a similar system. They also went to Atlanta to conduct testing in a displacement airflow laboratory. They spent several hours in mock theater seats, testing the effects of various air delivery alternatives on their lower extremities.

    The CDi team reported it was very tough work, but someone had to do it. Information gathered from the tests is currently being incorporated into the final design.

    Power in the pit

    The orchestra pit, just below and in front of the stage, is traditionally very difficult to condition in a performance hall. The situation was complicated at McCaw Hall because the design includes a split mobile lift platform that can be moved up to extend the stage, or down to create a larger musician’s pit.

    The mechanical engineering crew came up with a unique answer. Once again, it involved a displacement ventilation system. We created air plenums beneath the movable stage platforms.

    The plenums are served with supply ducts that can accommodate all possible positions of the lifts.

    It was a challenge to coordinate the HVAC system with lift framing, hydraulic lines, stabilizing cables and electrical elements. Figuring that two heads are better than one, we turned to LMN Architects, the project architect, to work out the details. Use of displacement ventilation in the pit is an approach that will influence the design of future performance spaces in North America.

    Here comes the sun

    Sometimes a gorgeous architectural design demands extra creativity from mechanical engineers behind the scenes. This was the case with the hall’s lobby and exterior promenade, where an expanse of clear glazing 200 feet wide and 65 feet high makes a showcase statement. Facing west, it also catches a lot of afternoon sun, causing potential problems with solar heat gain in summer months.

    Traditional HVAC load calculations would require more than 125,000 cfm of conditioned air, an expensive and environmentally inefficient proposition. Instead, a computational fluid dynamics analysis was used to model an interior shade device. The cavity between the shade and the glass is ventilated to remove solar gain before air warms the space. This reduced supply air requirements by more than 40 percent.

    Similarly, the vast lobby glasswork could cause high heating costs in winter. To conserve resources, CDi focused on providing comfortable conditions only where people will congregate. Several hydronic and air heating schemes were examined, but rejected due to either appearance or cost concerns. Instead, we determined that the best solution was to use a hydronic radiant floor, which will heat the ground floor portion of the lobby.

    A firm foundation — fast

    Baugh Construction, who was selected to be the general contractor and construction manager for the project, found there was a need to accelerate foundation work by six months in order to meet an aggressive overall schedule. This would require providing access to the current Opera House building’s basement six months before it was scheduled to be closed for demolition and renovation.

    We discovered there were many mechanical services that were routed through the Opera House basement. And these same services were necessary for providing water, fire, chilled water and steam to the Mercer Arts Arena located next door, where both the opera and ballet will perform for 17 months while their new home is being finished.

    The owner requested CDi document these existing mechanical services in all areas scheduled for early foundation work. We pored through old drawings, and performed field investigations for positive identification.

    Per our recommendations, new dedicated service lines are now being meticulously routed through the lower level of McCaw Hall. Then they can easily be run through a wall and remain undisturbed during hall construction. We are confident that mechanical services will be completely operational for all performances in the arena, despite ongoing activities of numerous subcontractor groups.

    Grand opening of the new Marion Oliver McCaw Hall is slated for mid-2003. Until then, mechanical engineers from CDi will be working hard as part of the project team to make sure everything goes smoothly.

    Perhaps you’ll think of us as unsung heroes for a moment when you enjoy your first performance at McCaw Hall — and take note of the comfy temperature, fresh-smelling air, smooth platform transitions, safe fire systems and luxurious lobby ambience we helped create.

    Norm Brown is an associate at CDi Engineers, a mechanical engineering consulting firm in Lynnwood.

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