Air Velocity in Parking Exhaust Duct 1

[EnOm]

Hi
What is the maximum acceptable design velocity for air inside the ducts in a small parking about 6 ft below ground level?
I'm talking with respect to acceptable noise levels/acceptable pressure drop.

The main duct riser will then rise up to the roof of the building through a shaft between apartments.
The shaft is surrounded by kitchens and toilets.
The walls of the shaft are made of 200mm hollow concrete blocks. No sound attenuating materials are to going to be added to the walls.
Do I need to reduce the velocity from that used in the parking lot to reduce the noise further since now the shaft is passing in close proximity with the habitable parts of the building? Or will the walls provide enough sound attenuation?

Best Regards

 

[317069]

What is the relationship between sound velocity in the air and air pressure,
Do you mean if we use 3500fpm in a 10" duct with 2" static pressure we will have a sound issue, but is we add more dampers to same duct and make it with let say 10" static pressure we will not have a sound issue,
Or in other word, if we consider same air velocity in both return and supply duct of a system, would be a difference in sound velocity between the supply side and the return side of the same system in this case they have the same air velocity , but different pressure

 

[EnOm]

I kept postponing responding to this, so I apologize.

willard3,
Thank you for your response. You are right again. But sometimes nobody is willing to listen. I would elaborate more, but since I am posting from work that might not be the best of ideas, and I don't want to end up venting non-technical related matters on here.

SAK9,
Thank you for your response. That is very valuable information. I will keep that in mind.

cry22,
Thank you for your response. I am quite doubtful about 2000 fpm being quiet enough for a residence. In a factory setting maybe, but I haven't come across velocities that high in residential before.

cdxx139,
Thank you for your response.

sprinkler1000,
I think that up to 1200 might be O.K, but I would not want bear the risk since it's outside my specialty.

317069,
Thank you for the response.

 

[dynamo78]

Enom! If I am in your situation, I would make the decision first of the type of ventilation system,like what is the preferred set up for this, Is it induce draft or force draft? this will be a big part of your logic,mind you. then the sketch and then do the math. HTH

 

[EnOm]

dynamo78,
Thanks for your response. I've already finished the project and submitted it, but thanks for the tips regardless

Best Regards

 

[dynamo78]

@Enom, If I may ask what type of fan did you used? was the system forced or draft?

Thanks for the response

 

[EnOm]

dynamo78,
Actually I had two very similar projects. I did one as induced draft, and the other was forced draft. In one of them there was no place for a shaft for the duct to go up to the roof so I had to place the fan in the parking in a noise-isolating cabinet, and let the air out at an empty space at backside of the building. I don't really have a lot of information on this issue actually. I would be grateful if you could explain some of the implications of each type of system. Thanks.

Regards