NC Level of Garage Ventilation Ducting 1

[walz]

I am designing the ventilation system of parking garage in two basements. The allowable NC level is 45. Ashrae HB for applications says that with 45 level of NC, the maximum velocity of the duct is 2000 FPM. I have to have the duct mounted fans in the high level of these basements. NC level mentioned is for the ductwork only. i have to keep some margin for the fan also. Now i have to reduce my velocity in this ductwork from 2000 FPM down to some number so that NC level of Fan plus duct air velocity dont exceed NC level of 45. Waht could be the way to do so?

or if somebody has another aproach, a standard or done something similar to this. Also what could be the maximum velocity for ducts inside the shafts.

 

[ChrisConley]

You have to convert the sound power from the fan into NC for it to be useful. The path that the sound takes from the fan to the listener has to be calculated so an NC can be generated. This is much more important in calculating NC than duct velocity.

The ASHRAE HB acoustics chapter lays out fairly well how to do this, but I recommend using software.

You can get free acoustic software from a variety of silencer manufacturers. I like and use Vibro Acoustics

http://www.vibro-acoustics.com/

McQuay and VAW also have functional sound software.

 

[walz]

Thanks CC

I will look into this and may come back to u, if needed.