Extracted from HPAC.COM
By: STEPHANIE AYERS, Evonik Foams Inc., Allen, Texas; JEFFREY L. FULLERTON, INCE Bd. Cert., LEED AP BD+C, Acentech Inc., Boston, Mass.; and STEVEN H. MILLER, CDT, Chusid Associates, Tarzana, Calif., Jan 1, 2012.
"There are two basic types of duct liner: fibrous and foam.
Figure 1 compares the sound-absorption efficiencies of fiber-glass, polyimide-foam, and elastomeric-foam duct liners. Testing was performed per ASTM C423, Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method.
Lastly, a note on FibreGlass duct liners, from HPAC.COM:
|According to the North American Insulation Manufacturers Association (NAIMA), fiberglass insulation is “inorganic and inert and does not support mold growth or act as nutrients for mold growth.”1|
Fiberglass duct liners also are resistant to microbial attack, as described in ASTM C1338, Standard Test Method for Determining Fungi Resistance of Insulation Materials and Facings, and required by Standard 62.1 for HVAC air-stream surfaces. The duct liners also are in accordance with ASTM G21-96, Standard Practice for Determining Resistance of Synthetic Polymeric Materials to Fungi, and ASTM G22-76, Standard Practice for Determining Resistance of Plastics to Bacteria, as required by ASTM C 1071, Standard Specification for Fibrous Glass Duct Lining Insulation (Thermal and Sound Absorbing Material).
How much liner is enough?
For general environments (e.g., an office or a classroom), acceptable noise reduction often requires the lining of the first 10 to 20 ft of ducts adjoining a fan system. An engineer calculates how much lining is needed by determining an acceptable noise level for the application, using the documented noise output of the fans and the known acoustic properties of the lining material.
For spaces with exacting sound requirements, lining an entire duct for maximum noise control may be desirable.
Some work is done by the bends in the ducts itself..
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1.NAIMA. (2002). Insulation facts 34: The facts about mold growth. Alexandria, VA: North American Insulation Manufacturers Association.
1. Engineering Guidelines by Carrier
2. ASHRAE JOURNAL 2014