Sound Insulation

[ub313]

Hi
Can some one suggest any non-fibrous insulation material for cold supply air ducts.
Is it true, polyolefin liners have good noise absorption properties as claimed by the manufacturers?
Any industry experience?
Thanks

 

[CarolinaPE]

Some liners of equipment is now available as "foil faced" and meets certain standards for being anti-microbial, etc. I have not heard of a duct liner though that meets these standards. Have you considered using perforated wall liners on the air handler? We have found that quiets them down considerably. Also, if you are "smart" about how you route the ductwork you can prevent "crosstalk" and other noise issues. Just make sure you design it so that there is not a direct path between adjacent spaces. You might check manufacturer websites such as Knauf, etc for liner materials.

 

[stanlsimon]

If you need to attenuate fan noise it is easier to spec a silencer. They are available in various configurations and with materials acceptable for medical applications.

Don't route ducts directly from room to room. Locate the main in the corridor and extend small runouts to each room.

The problem with liners is the fine dust that accumulates on the surface. The liner itself doesn't support microbial growth but the dust layer is a fertile medium for pathological organisms, especially if the humidity is high in the duct. Then when the time comes to clean the duct,the cleaner has to be careful that the cleaning device doesn't chew into the liner.

 

[amorrison]

Try "Google Images" using acoustic absorption -fiber

http://images.google.ca/images?q=acoustic+absorption+-fiber&svnum=10&hl=en&lr=&start=40&sa=N

 

[tombmech]

Duct liner should be banned.

Stanlsimon is correct. Silencers are better - assuming that you have the room. Even if you don't, you're better off accepting the noise. As for the other statement, it is better to state it this way:

"... even if the cleaner is careful, the cleaning device will chew into the liner."

Most duct with liner more than a decade old might as well be completely replaced; the decomposition of the material is so bad and pervasive. In advanced stages, whole areas can receive a daily deposit of black particles - because of the liner decomposition. In worse cases, people are actually breathing it.

That doesn't even account for the possible microbial potential. Industries as diverse as heavy industrial to ultra-precision measurement and bio labs have been increasingly banning the practice for the last 20 years.

The Engineering community (ASHRAE?) should take a more proactive stance and ban it alltogether.

 

[ub313]

Thank you for your answers.

I accept controlling noise at source or attenuating in Plant room/AHU is the best way to tackle.
and i infer that there is no Non fibrous liner for duct work.

Does any one know, why the Active silencer technology (Microphone-speaker combo) was never succcesful

 

[CarolinaPE]

There is some "silencer" technology available. A rep came by our office the other day and gave a presentation. Basically you give them a set of inputs to the design and general duct routing and they configure the silencers. I do not remember their name but will post later at work when I can look at the brochure again.

 

[tlhoo]

http://www.jm.com/insulation/technical_info/media_3020.htm

Discussion of non-fibrous liner alternatives. They're out there, the VAV box manufacturer's also offer a non-fibrous liner in addition to the foil faced option.

 

[CarolinaPE]

It is "Vibro-Acoustics" (see my post above).

 

[stanlsimon]

There was a firm in Wisconsin that was selling an active attenuation system, they wanted about $7000 per air handler. The price seemed prohibitive. It seems like if Bose can put that technology in headphones for much less $ someone should be able to mass produce a canned system for HVAC applications.