Sizing Carpark Exhaust Shaft

[Ogsray]

Hi guys.

I am currently doing design on Carpark Ventilation, the building has 6 basement Carpark floors.
Can I consider a diversity at the shaft's total airflow in sizing the shaft itself?if yes, how much diversity can I use?
what maximum velocity can I consider in sizing the shaft?

 

[Emrelug84]

Hi Ogsray,

Is there possibility to fill all 6 basement carpark floors at a time? If it is so, diversity does not work to size shafts. I think shaft is sized according to the max air flow rate and you can put more than one fan with frequency drive. Therefore, you can fulfill the full air flow condition at max condition and with frequency fans, you can arrange air flow rate with respect to the part load condition. Please also check which one is critical smoke exhaust flow rate or normal exhaust flow rate.

Regards,
Emre

 

[Ogsray]

Hi Emre,

Thanks for the reply and I agree with you on the"I think shaft is sized according to the max air flow rate".
Basically I am having 4 exhaust risers connected with 1 axial fan each riser and each floor. And I am coming up with a velocity at shaft of 12m/s considering maximum airflow. Is this velocity too much? What velocity can I use?
For the Smoke Control at Carpark, what standard can I look into for the rate(ACH)?

Thanks

 

[Emrelug84]

Ventilation rate is given as roughly 7.5L/s-m2 for parking garages according to Table E-2 from ASHRAE Standard 62-2001 Addendum n. (please note that exhaust not required if two or more sides comprise walls that are least 50% open to the outside) However, It is 300L/min for min. according to NFPA 88A. For more accurate calculation if needed, you need to have the number of cars in operation and the emission quantites. (i think you can decrease investment cost by making detail calculation since standard values give more than necessary)
For your interest:

https://www.academia.edu/28614713/Ventilation_for_Enclosed_Parking_Garages

I think velocity is optimum at 10-12 m/s for normal condition and 15m-18m/s for smoke exhaust condition.
You can look into NFPA standards for smoke control at carpark.
Regards,
Emre