Silencer Location? Before or After Fan 1

[scythe13]

Hi,
What are the parameters to select silencer location (before or after fan)?

For a commercial building project, there are several AHUs and as I have provided in the attached drawings in some AHUs, silencer is located before the fans and in the other cases it's located after the fans...Can you help me to find what are the criteria?

 

[Zesti]

I have not looked at the drawings (can't open the file) but my guess is that all attenuators are on the the building-side of the fans.

For an AHU supplying air to the building this would mean the attenuator is after the fan.
For an AHU extracting air from the building this would mean the attenuator is before the fan.

Apparently in your case the soundlevels to the outside is not that important and no attenuators are needed on that side.

However, it could also be that attenuators are planned in the ductwork connecting to the AHU's.

Sound is very important in ventilation-design.

Be sure to know what the requirements are and how to design the system accordingly!

 

[willard3]

Put the sound attenuator between the fan and the area you want to protect.

 

[houseman20]

I can't download the file at work.

Most of the time, you won't need sound attenuators especially if your ahu is on a different floor than the conditioned space. In most cases, standard acoustic lining 30 feet upstream/downstream of fans works fine. To start analysis you need to get sound power levels of the fan/ahu/acu. You need to have room criteria(acoustic) defined for the critical spaces. And the duct configuration and number of diffusers in the room may also be part of the analysis.

This work is often done by acoustic consultants. They'll prepare a report with their recommendations.

 

[Falah7582]

Dear your file is not downloading, however get yourself an acoustic engineer to measure up and gives you recommendation if you are on execution phase and if on design it depends on how the return and supply ducts are and total CFM of AHU plus its configuration there is a lot of things you should determine to give the right solution.
Cases:
1- free return, coil in front of fan, ducted and lined supply, low noise motor, medium static pressure fan; use attenuator at return side (suction).
2-free return, coil behind of fan, ducted supply, low noise motor, Hi static pressure fan; use attenuator at return side (suction)and attenuation at the back.
What I mean to say there are many cases to build a system, so we need to take a look at your configuration drawing.