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McCaw Hall's efficient HVAC system keeps patrons (and staff accountants) breathing easy
By NORM BROWN
CDi Engineers
Photo courtesy of CDi Engineers
Special low-velocity ducts in McCaw Hall restrict noise and enhance energy efficiency.
"The best acoustics in the world."
That was the goal of Speight Jenkins, general director of the Seattle Opera, when the Opera House was being transformed into Marion Oliver McCaw Hall.
"LEED silver certification for exemplary energy efficiency."
That was what the city of Seattle wanted for the hall, helping the municipality achieve its sustainable-building goals.
Mechanical engineers worked to attain both of these ambitious goals: an ultraquiet and energy-efficient HVAC system that has only been adopted in a couple of other performing arts centers in the nation, and a host of design innovations that is expected to help earn the project a LEED silver rating later this year.
Ductwork that whispers
Noisy blasts from the heating and air conditioning system are the last things operagoers want to hear.
The new hall features low-velocity air supplied to acoustically sensitive spaces through sheet-metal rectangular ducts, sized larger than normal to meet restrictive allowable noise levels. A special duct liner absorbs unwanted crosstalk, equipment and air rush sounds.
Energy economies
Designers created distinct HVAC zoning for the orchestra, first and second balcony levels in the auditorium. Air flow and temperature in these areas can be regulated separately, allowing operators a great deal of flexibility for making minor adjustments for comfort levels.
The system also permits energy savings by throttling when a performance has less than a full house, since air flow can be throttled to match the number of people in attendance.
The auditorium system has an unusual specialized heat-recovery system that should help contribute to LEED silver certification. During a performance, all of the auditorium's air comes from the outside to provide superior air quality to the occupants, and is filtered and heated (or cooled) before delivery.
But in winter it can be expensive to heat vast quantities of fresh air. The recovery system captures heat from air that is being exhausted to the outside after use, stores it in a coil, and transfers it to the fresh air coming in. This reduces the building's heating energy costs by about 15 percent.
Super-clean ducts
LEED requirements focus heavily on indoor air quality. To ensure that the air-delivery system remained as clean as possible, McCaw Hall's engineering project team specified that ductwork be maintained in pristine condition from the sheet-metal fabrication shop during transportation and storage at the site, and during installation.
A rotary-based fiberglass liner with a moisture-resistant surface enhancement contained an EPA-registered antimicrobial agent to reduce possible microbial growth.
In addition, all ductwork was sealed with visqueen at both ends during fabrication. The visqueen stayed in place until each piece was ready to be erected, and was then removed on one end when the ductwork was placed.
In this way, the building's duct system always remained hermetically sealed, preventing construction dust from contaminating the duct's liner.
Trimming air-flow
The lobby and exterior promenade of McCaw Hall boast huge expanses of glazing, which catch afternoon sun. Upper levels would normally require extensive cooling in summer. Even with a specially designed shading device in place, the upper balcony will require extensive cooling on a warm day.
The engineering team installed a control damper on the air supply to the conditioning system for the second balcony zone. During most of the year, sensors throttle the fans back so that upper levels are not over-chilled. Only on the hottest summer days does the system function at full capacity, cutting energy consumption by about $4,000 per year.
Also in the lobby, a radiant heat system will provide warmth in the ground-level entry space during chilly winter evenings. Although used relatively infrequently in commercial construction, the application in McCaw Hall was a natural.
The radiant floors will provide heating comfort to only the ground-floor portion of the lobby rather than all of the air throughout the large foyer. Radiant heat slabs work especially well in transition spaces, where doors are constantly opening and air is passing in and out, saving about 10 percent in heating energy for the lobby.
Cooking and flushing
McCaw Hall has a full kitchen in its basement. Industrial kitchens typically waste energy with hood ventilation systems that stay on full speed whenever the kitchen is occupied. McCaw Hall's kitchen features a Melink system for hood vents, which uses optical and temperature sensors to detect when the grill or burners are in use.
When no one is cooking, the system throttles fans for both the exhaust and inflow air systems, working at full capacity only when necessary.
Female visitors to McCaw Hall will probably never appreciate (or even see) one of its more remarkable resource-saving innovations — namely, the waterless urinals. These use a fluid that is lighter than urine to create a seal between waste and the atmosphere. McCaw Hall is the largest public project to date to implement waterless urinal technology.
When the project is granted LEED silver status, as anticipated, it will be one of the first large projects in Seattle to achieve this coveted rating. And the sustainable building practices incorporated in its design will be instrumental in helping the city cement its reputation as one of the most energy-efficient municipalities in the nation.
Norm Brown is an associate at CDi Engineers, a mechanical engineering consulting firm in Lynnwood.
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