2- Speed Fans ( Car Park )

[Rumananoor]

Hi All,

I have a query regarding car park fans for exhaust and on emergency use.
If a fan is designed for car park normal day to day smoke exhaust of 12000 cfm (normal speed) for a given area. How much ratio to be considered in case of emergency smoke exhaust running on (high speed).


Kindly ignore if my question doesn’t seems to be technical well.

Regards,

 

[Drazen]

firstly, you should make clear difference between smoke exhaust, carbon monoxide emergency exhaust and regular ventilation rate.

each demand should be calculated separately, and as they are not directly dependent on each other, establishing arbitrary rate among them is quite meaningless in my opinion.

 

[sherifheity]

Actually car park ventilation & Smoke extraction work in three modes:

1-Normal ventilation (normally at 3 ACH (Air change Per Hour)
2-CO detection (fans will jump to do 6 ACH)
3-Smoke/Fire detection (Fans will work at max. speed to do 10 ACH).

ideally the selection of the fans should be done to achieve the 10 ACH.

Also you have to check your car park if it has jet fans & Main extraction fans (which is the most common practice) the detailed sequence of operation will be as follow:

1-@ 3 ACH: jet fans will be on (1st speed) , main extraction fans will be off.
2-@ 6 ACH : Jet fans will be on (2nd speed (normally it`s double speed), Main extraction fans will be on at 1st speed.
3-@ 10 ACH: Jet fans will be on (2nd speed), Main extraction fans will be on at 2nd speed.

Hence your jet fans and main extraction fans should be ordered fire rated with double speed motor.

hope it`s useful.

Sherif Abulfetuh

 

[cry22]

Where does it say (code) that parking garages need smoke control systems?
OK, structure below grade, more than 30 feet deep require smoke control per IBC. But if your parking is less than 30 feet deep, why do you provide smoke control?
I also noticed that most people use ducted smoke control with low exhaust points, this defeats the purpose of smoke removal, as the exhaust is enabled, it will pull the air DOWN to the floor instead of having a plume or layer build-up at ceiling which leaves time for people to crawl out of the space instead of having a buoyant smoke all over teh place.
I also see make-up air fans provided in garages that are 2 floors below grade. Why can't the ramp be used as make-up air?

1. we do not provide smoke control for parking less than 30 feet deep
2. we do not provide make-up air fans for parkings that are standard size (say about 120 feet long), air comes form the ramp - for long parkings, we provide intake shafts and/or jet fans.
3. Actually, we do not provide ducted parking exhaust neither, we just provide several exhaust fans connecting to exhaust shafts.