VAV Box Noise Issue

[julylee]

We just added an VAV box in an office to provide addtional cooling air and individual temperature control for the office. However, there's substantial increase of the noise level, about 65 db, especially when the VAV box is fully open. Can anyone advise what's the possible causes and how can we fix it?

Thanks.

 

[texanman]

There are basic rules of VAV installtion and tie-in to the primary air syste. Titus has a good section in their catalog on good engineering practices for installtion and noise reduction guidelines. What is your primary air pressure? Is flex duct used for connections? Are flows under 700 fps?
regards,

 

[Jabba007]

I think he means 700 FPM by the way. 700 FPS is as fast as a SLOW bullet.



Jabba

 

[imok2]

Discharge noise rarely is an issue when a VAV box has hard duct at its inlet, a lined outlet plenum, and flexible duct between its plenum and diffusers. Generally, in accounting for radiated noise, the maximum rating of a VAV box located above a standard acoustical ceiling should be no more than 5-NC higher than the desired room rating. For example, the maximum rating of a VAV box for a general office with a desired NC level of 30 should be no more than NC 35.

Usually, inlet diameter determines VAV-box size. If one VAV box cannot meet noise criteria, consider using two. Two or more VAV boxes can be controlled with one temperature sensor. For more go here:

http://hpac.com/mag/vavbox_selection_code/