IAQ
Air Should Be Felt and Not Heard

A new high school auditorium honors student musicians by giving them a quiet HVAC system

By Stephanie H. Ayers and Steven H. Miller, CDT

When the audience settles down in the newly renovated auditorium at Houlton Jr./Sr. High School in Houlton, Maine, it can get very quiet. You can hear the performers beautifully. One thing you can’t hear is the heating, ventilation and air conditioning (HVAC) system… which is just as it should be.

“We had three major concerts in our auditorium in December and the air exchange system could not be heard, only felt,” relates Joe Fagnant, President of the Houlton Community Arts Center Council (HCACC) that spearheaded the project, and also chair of the Houlton High School Music Department. “It was encouraging to have an air handling system that did not interfere with the acoustics of the space nor interfere with the performance taking place.”

Sound is probably a subject of keen awareness for many who come to the new auditorium, since the inspiration to build it was the community’s pride in the school’s music program. It had very high participation, with 13 different musical ensembles. In addition, nearly twenty community organizations made use of the meeting and performance space in the Houlton High arts wing. The existing space, therefore, was badly over-subscribed as well as being outdated. The community decided to build a facility “to match the caliber of our musicians,” as Joe Fagnant wrote on the HCACC’s website.

Serving both school and community, it was named the Houlton Community Arts Center. It was designed by Carla Haskell of the Design Group Collaborative, Ellsworth, ME, with acoustical consultation from Acentech, Boston, MA. The HVAC system was designed by Jeff Armstrong, Armstrong Engineering, Fort Fairfield, ME and fabricated and installed Ross Sheet Metal, Houton, ME.

The project was budgeted at $5 million, half raised by a bond referendum, the other half by donations. That was a sacrifice for a town of 6,000, so it’s understandable if they’re all ears now when attending a concert.
The excellent acoustic performance of the HVAC system is in part the result of a cutting edge material - polyimide foam – used to provide both acoustic damping and thermal insulation inside the ductwork. It’s a material that is used in projects where a concern about indoor air quality (IAQ) has ruled out the use of common fiberglass insulation.

Insulation and Indoor Air Quality

IAQ is increasingly on the minds of building owners and managers, architects, and HVAC engineers. It is considered critical in buildings whose occupants are deemed especially sensitive or vulnerable, including children and those with weakened immune systems.

Fiberglass has become one focus of concern. It is widely used to insulate ductwork for thermal efficiency, often wrapped on the outside of ducts. It is also used on the inside – called duct liner - to provide noise reduction along with thermal insulation. It does these jobs effectively, but some people are concerned that glass fibers could get loose in the HVAC system – an effect called “dusting” - and either be harmful to breathe or carry harmful microbial growth. The potential for dusting is tacitly acknowledged in the published best practice of applying edge sealer on cut edges of fiberglass duct liner to help stabilize the fibers. Most fiberglass products include a binder to help keep fibers from coming loose. However, these binders often contain urea-formaldehyde (UF), a known health risk. (See Sidebar “The Fiberglass Question”)

In facilities where fiberglass is not acceptable, either because of health issues or for “clean-room” applications such as laboratories, polyimide foam duct liners have proved equally effective.

As demand for non-fibrous liners has arisen, several different types of foams have been tried including products made from polyimide, polyolefin, and elastomeric foams. Of these, polyimide foam provides the best combination of acoustic performance and stability under high heat. Open-cell polyimide foam can equal or exceed the sound-absorbing performance of similar thicknesses of fiberglass.

Originally developed by NASA for use in space vehicles, polyimide foam is lightweight and has excellent fire-, smoke- and heat-resistance. Polyimide foam liners meet the same performance criteria as fiberglass in terms of response to heat and flame. The material was tested according to UL 723/ASTM E 84/NFPA 255 and can be used up to 121 C (250 F). It is almost as efficient in thermal resistance as fiberglass of similar thickness.

“Because of concerns about fibrous liners delaminating in the airflow, the idea of nonfibrous is often attractive,” explains Ben Markham, LEED AP, Senior Acoustic Consultant with Acentech, Boston, MA, the acoustic consultants for the Houlton project. “There are certain kinds of projects, schools and hospitals for example, where any kind of liner is prohibited unless it is encapsulated. But that encapsulation, unless done with great care, often negates acoustical performance of the liner, even though it may be fine thermally. When a product comes along that satisfies criteria about fibers in the airstream and also satisfies our criteria for acoustical performance, as polyimide foam does, that makes it an attractive option.”

Return on Investment

Polyimide foam duct-liner is a high tech material that costs more than fiberglass. In the case of Houlton High School, where fundraising for the project is on-going, cost was a serious consideration, but the Council decided that it was a worthwhile investment.

“I was there when the demolition was started in June, 2009,” recalls Fagnant. “The old fiberglass liner had completely collapsed down the length of the ducts. I saw all the dirt in it, and how the batts were falling apart, and I suddenly said, ‘Now the idea of using foam makes sense.’ I also saw the foam being installed, and I could tell that it wasn’t going to have any issues.”

The first phase of the program, now completed, includes the remodeled auditorium with the addition of a new balcony, a new entry vestibule outside the auditorium, and renovation of the gymnasium, kitchen and cafeteria. The second phase will add 13,000 square feet including a band room, chorus room, theater/dance space, and an art room. Polyimide foam will be used throughout.

Final judgment on the result of their investment is positive. “I am very happy with the product and the installation,” says Fagnant. “It is a great asset to the auditorium. With our old system, there was no air exchange. It would reach 85 degrees in there with an audience present. And you could hear the heat kick on and off, hear the fans making noise. With the new system, it feels much more pleasant and you don’t hear a thing. We had our first performance in November - Damn Yankees - and the auditorium was sold out. People could hear things differently. They were very positive in their response.”


Authors:
Stephanie H. Ayers is marketing manager for Evonik Foams Inc., an Allen, Texas-based manufacturer of SOLCOUSTIC®, a non-fibrous coated polyimide foam duct liner. She can be contacted via email at stephanie.ayers@evonik.com.

Steven H. Miller, CDT, is an award-winning writer and photographer specializing in issues of the construction industry, and Creative Director for Chusid Associates, a technical and marketing consultant to makers of advanced building products. Miller can be reached via www.chusid.com.

SIDEBAR: The Fiberglass Question

Fiberglass manufacturers maintain that their product is safe.

Sheet metal workers who fabricate ducts and install insulation, and have high exposure to fiberglass, routinely protect themselves when installing it by wearing eye protection, particle-resistant masks or respirators, gloves, and long-sleeved shirts. The Sheet Metal Occupational Health Institute Trust (SMOHIT) was established in 1986 for the purpose of studying the rates among sheet metal workers of disease and other occupational illnesses related to asbestos. It found that sheet metal workers who had high exposure to synthetic vitrous fibers, such as fiberglass, were diagnosed with more bronchitis and obstructive lung disease, compared to workers who were not exposed.

It is beyond the scope of this article to determine what health hazard, if any, fiberglass may pose. However, the “facts on the ground” are that some facilities are forbidding its use in new construction or remodels.

SIDEBAR:

Ducts And Acoustics

Most of the noise from an HVAC system comes from the cooling compressors and large fans that move the air through the building. The HVAC unit can be placed in a soundproofed room or outside the building to acoustically isolate it, but there is still a route for fan noise to get into the rest of the building: the ducts carrying the air form a potential noise highway.

Ducts are essentially tubes, and noise moves through them much as the sound of your heartbeat travels through the tubes of a doctor’s stethoscope. Sound waves are reflected off the inner sides of the tube, zigzagging down its length, and finally emerging at the vent openings with much of their original volume.

HVAC engineers combat this noise by lining part or all of the ducts with acoustical material. Noise reduction is achieved by two types of action:

• scattering (i.e. redirecting of sound waves from their original direction by use of reflection); and

• absorption (i.e. converting sound to other forms of energy, generally a small amount of heat).

In other words, liners don’t contain noise or filter it out, but break it up and weaken its force. How much sound they can break up depends on how much surface area of acoustic material is exposed to the sound waves. This means that the more length of duct that is lined, the more noise is reduced.

For general environments – an office or a classroom - acceptable noise reduction often requires lining only the first 10 to 20 feet of ducts adjoining the fan system. Limited lining of this kind reduces fan noise, but usually will not eliminate it completely. The engineer calculates how much lining is needed by determining an acceptable noise level for the application, and using the documented noise output of the fans and the known acoustic properties of the lining material. That noise calculation becomes part of a larger set of choices about the acoustic needs of each room in the building.

For spaces with exacting sound requirements (e.g. performance spaces or sound studios), it may be desirable to line the entire duct length. The Houlton High School Auditorium system was lined along its entire length for maximum noise control.

Duct liners are also employed to prevent ducts from becoming conduits carrying noise from one room of the building to another. Ducts joining two rooms can be designed in a U-shape and lined, which effectively dissipates room-to-room transmission and protects speech privacy.

Duct lining materials must have certain properties:
• sound absorption;
• minimal thickness, so the liner does not significantly reduce the open pathway for airflow;
• heat resistance;
• flame spread and smoke-developed limits; and
• mold resistance.

(See Table 1 for detailed duct liner performance standards)

Both fiberglass and polyimide foam meet these criteria. The foam is generally coated on at least one surface with an acrylic product serving as a protective barrier against dust and moisture, and helping resist mold growth. Polyimide is a low-emitting product in terms of volatile organic compounds (VOCs), enhancing its ability to be used in applications with sensitive indoor air quality (IAQ) requirements. Due to its performance with regard to IAQ, it has been certified under the Greenguard Children & Schools program.

Installation of polyimide foam is similar to standard fiberglass rigid plenum liner board, so contractors experienced in installing these products already possess the basic knowledge to install foam. The biggest difference is that workers installing foam generally do not feel the need to wear the dust masks, respirators, gloves, or long sleeves that they wear when handling fiberglass.

Table 1: Duct Liner Performance Standards

ASTM C 1071, Standard Specification for Fibrous Glass Duct Lining Insulation (Thermal and Sound-absorbing Material), the performance standard for fibrous duct liners, is frequently referenced when contrasting the performance of both fibrous and non-fibrous liners.

Photo by Stephanie H. Ayers, used courtesy of Evonik Foams
One important element of the renovation was a new HVAC system. Because it is a performance space, special care was taken to eliminate fan noise by using polyimide foam acoustic lining throughout the length of the ductwork. (The yellow edge of the foam can be seen in the open ends of unfinished ducts at top and bottom.)

Photos by Steven H. Miller, used courtesy of Evonik Foams
Fiberglass insulation (left) and polyimide foam (right). Polyimide foam is a lightweight, fire-resistant material used as duct liner in applications where fibrous materials are not desirable. The dark acrylic coating serves as a protective barrier against dust and moisture, helping resist mold growth. An inch of polyimide foam has a noise reduction coefficient (NRC) equal to or exceeding that of an inch of most fiberglass duct liners.

Photo by Stephanie H. Ayers, used courtesy of Evonik Foams
The auditorium project was a community undertaking. Here, John Ross (left), the sheet metal fabricator who built and installed the ductwork of the new HVAC system, makes a donation to help pay for the building. It’s gratefully received by Joe Fagnant (right), President of the Houlton Community Arts Center Council (HCACC), Chair of the Houlton High School Music Department, and project manager of the renovation and expansion.

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