Trying to Keep the (HVAC) Noise Down

October 23, 2006
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When it comes to having noise or a constant rattle inside a building or home, the public usually blames or pinpoints the problem to the HVAC system. It takes an experienced contractor and/or acoustics engineer to determine if the accusations are accurate.

One could argue that the noise culprit is the HVAC system more so than it should be. But, with acoustical panels, plenums, and enclosures available, systems do not have to be loud. Other equipment aimed to put an end to the noise in a system includes specialty air-handling units, stack silencers, industrial fan silencers, HVAC silencers and silencing systems, "floating" floors, and vibration isolation systems. In other words, if there is noise - and it can be pinpointed to the HVAC system - it can be corrected. Or, at the very least, minimized.

SOME COMMON ISSUES

One of the many manufacturers that takes pride in keeping HVAC systems silent is Vibro-Acoustics, with corporate headquarters located in Toronto, Ontario. The company, which has been around for more than 40 years, said it has developed "innovative, yet practical solutions, for some of the most diverse and dynamic projects in the world."

The company can cite 18 com-mon silencing problems, and noted it can provide solutions for each. Among its list of no-nos are limited silencer connection sizes and insufficient straight duct. Regarding the latter, the company said duct layouts are far from ideal in real life applications. Real life systems quite often do not have the recommended spaces required for straight silencers. As a result, silencers located in close proximity (three to five duct diameters, it recommends) to fans, elbows, plenums, fittings, etc. "will result in an increase in silence pressure drop and airflow-generated noise due to aerodynamic system effects." (For a complete look at the company's "18 Common Silencer Problems and Their Solutions," go to www.vibro-acoustics.com.)

SILENT SUB EXHIBIT

Making sure that noise does not ruin a quality HVAC system installation is paramount. Just ask Primera Engineers, a full-service engineering, design, commissioning and construction management firm located in Chicago.

Along with Chicago architect Goettsch Partners, the two were called upon to design a quiet, 35,000-square-foot underground exhibit for the 700-ton U-505, the only World War II German submarine in the United States which had been sitting outside Chicago's Museum of Science and Industry for 50 years.

In this instance, the climate controls and HVAC systems were of critical importance in keeping the sub from further deterioration. The new exhibit needed to be comfortable for visitors, too. In the end, it was imperative that HVAC operations not create any background noise that would interrupt either normal speech or audiovisual programs, which are a part of the visitors' experience.

The acoustical engineers at Shiner and Associates, headquartered in Chicago, specified a range between 30 and 45 NC. In this instance, from the beginning, Primera designed the system based on silencers from IAC America (Bronx, N.Y.)

"The contractors suggested several options," explained Ken Panucci, senior vice president, Primera, "but in the end, no other manufacturer could achieve the combined requirements for both pressure drop and noise control."

In the end, the engineering firm exceeded the specifications for noise criteria, which only made the owners happy.

MORE PROBLEMS WITH SOLUTIONS

Meanwhile, having one of the city's hottest restaurants across the street can be convenient, but not necessarily quiet. Such was the case with Terzo, a San Francisco restaurant, which shot to the top of critics' list shortly after it opened.

Facing apartment buildings' windows, the restaurant's powerful exhaust fans were generating noise of 78 decibels (dB), a substantial problem when the city code is 60 dB. Because of the danger posed by grease, the only silencer to fit the spec was IAC's Packless Silencer, which authorities said succeeded in shaving still another point off the bottom line, controlling the noise to a level of 59 dB.

Philadelphia's Kimmel Center for the Performing Arts is another building that did not want noise in its halls or elsewhere. Spanning a full city block, this center was custom built for the world renowned Philadelphia Orchestra. The concert hall alone seats 2,500 and was designed to be acoustically and architecturally adjustable to suit the size and style of performances. It was the belief of authorities that a world-class orchestra deserved world-class acoustics.

Placement of the mechanical rooms directly under both the concert hall and the recital theater created a noise control challenge. With the close proximity of the mechanical room to these critical spaces, Vibro-Acoustics' systems approach to silencer and acoustic plenum selection and layout was necessary to meet the stringent specified N-1 criteria.

A variety of duct silencers - ranging from rectangular, elbow, circular, transitional cone, to acoustic plenums - were put into place. The air-handling unit silencers were selected by the company to meet the specified criteria at both inlet and discharge. Special attention was given to the air-handling units that supplied the concert hall, which required both a rectangular and an elbow silencer in series. According to the project team, this selection and application saved space and met specified sound power levels.

Publication date: 10/23/2006

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