Quiet Operation

According to CertainTeed Corporation, the opera house is known for its excellent acoustics. With this in mind, the designers of the project were determined to not only retain that reputation, but also improve upon it with an ultra-quiet HVAC system design.

The mechanical engineering firm of CDi Engineers was engaged to design a new mechanical system, the centerpiece which is an upgraded and more responsive HVAC system. Several elements of the project, undertaken by MacDonald-Miller Facility Solutions, set it apart from other performing art center renovations.

To preserve the acoustic quality of the opera house, a number of requirements were necessary, including the installation of a low-velocity HVAC system lined with CertainTeed ToughGard® duct liner with moisture-repellant surface.

McDonald-Miller’s mechanical contract for its work at the hall is valued at $13 million, much of which is devoted to the new HVAC system, which supplies 250,000 cfm of air. Low-velocity air is supplied to the acoustically sensitive spaces through sheet metal rectangular duct that ranges in size from 6 by 6 inches, to 12 feet wide. The duct is sized larger than normal in some cases in order to meet the restrictive allowable noise level.

The duct liner chosen for the application, CertainTeed ToughGard, absorbs crosstalk, equipment, and air rush noise.

Importance Of IAQ

Because the building owner was very concerned about ensuring high indoor air quality for the entire HVAC system, an IAQ specialist was hired. Operating under stringent rules, MacDonald-Miller employees took precautions to protect every piece of lined ductwork from moisture and other contaminants. The goal was to avoid collection of fine dust and minimize any risk of mold growth due to the combination of dust and moisture during the production, transportation, and installation phases.

“We had to keep all duct liner wrapped in our shop,” said Ray Burdine, purchasing manager for MacDonald-Miller. “Once it was applied to the sheet metal, we had to seal each end with plastic to prevent dust and moisture from entering. Sealed duct sections were shipped on our trucks and were checked by inspectors to make sure each arrived in good condition.”

A New Approach

The underfloor displacement ventilation system, which was also an important part of the overall system, is based on the same system used at the Newark (New Jersey) Performing Arts Center, the only other arts center to use such a system. In traditional performance halls, air is supplied overhead and air returns are through grilles located either under the seats or positioned low on the side wall. With the McCaw Hall system, conditioned air is supplied from underneath the seats. There are 8-inch supply air diffusers spaced at approximately every other seat that allow a relatively small amount of air to pass at a very low velocity. According to the designers, this keeps the moving air noise at a minimum.

“There are several advantages to designing a system like this,” explained CDi’s Norm Brown, P.E. “One, you’re delivering the conditioned air right where the people are located, so you’re giving them superior air quality in terms of ventilation. Two, since the air is delivered where the people are, it can be delivered at a slightly higher temperature than traditional overhead systems, which contributes to energy savings and efficiency. The point is that we’re conditioning the air where it is needed. We’re not conditioning the entire space.”

Publication date: 04/28/2003