Enclosed Car park Ventilation 1

[Buildtech2]

The total area of enclosed carpark is 47817 sq.ft. As per client requirement, the ventilation to this car park shall be based on NFPA 88A standard which is 1 cfm per sq.ft. Therefore the total ventilation air required would be 47817 cfm.

Since the total area of my basement car park is 47817 sq.ft. and CO sensor location requirement is every 5000 q.ft. I am unable to take a decision whether I should go for ducted intake and exhaust system or wall mounted intake and exhaust system with several jet fans which will be interlocked with CO sensors.

As an option, we can propose a main exhaust intake fan and supply fan (both with VFD) with capacity of 47817 cfm and in addition to this, there will be several jet fans which will be interlocked with co sensors. I have selected 18 jet fans of maximum air flow of 2669 cfm and minimum air flow of 1356 cfm.

Questions:

1. Is it required to run the main exhaust and supply fans continuously at low speed under normal operation even if there is no requirement of any jet fan to be operated based on CO sensor..


2. Do we need to consult a supplier for CFD analysis and calculation for car park ventilation.

3. Imagine if only 4 jet fans runs at a particular time at low speed, the air flow of these fan will not be equal to the main exhaust fan and supply fan even at low speed. How can we balance it.

 

[cdxx139]

Its been a while since Ive done a garage but will take a shot.

IBC/IMC also has cfm requirements. If they are your code, you must meet them in your design. I thought there was a regular OA requirement, then a CO alarm cfm requirement.
Ypur CO sensor locations are a function of the sensor and manufacturer info. My recollection was a 50 foot radius, so we drew 100 foot circles, and made sure they covered all parts of the garage.
This sounds like a large facility. I never ducted a garage. I provide supply and exhaust fans at strategic points, and added transfer fans where needed to help confirm fresh air gets to every part of the garage, especially corners.

1. I believe so, your applicable code will tell you. Where are you?
2. I never used CFD
3. The jet fans are transfer fans? I wouldn't be worried.

knowledge is power

 

[chicopee]

I would say that you should increase you calculated CFM by at least 20%. 1CFM/sq.ft. is the minimum. Have you read the NFPA 88A code in its entirety and have you paid attention to the scopes?

 

[mab1119]

I agree with cdxx139, you should check the code to meet the requirement. for your questions,

1. Yes, you should be running the main intake exhaust & supply fan at normal conditions.

2. CFD are needed for us to know if the location of the jet fans will perform as intended when there is smoke / or fire in the carpark.

3. If you need to balance the supply & intake condition at a particular time, it will be dependent on the BMS. which it will be for the BMS engineer task. But to keep it simple, you should run your main intake exhaust & supply fan at normal conditions to meet the client requirement & you're jet fans will function only when there is fire/smoke or when the CO sensor sense large quantity of CO in that particular area.

 

[Buildtech2]

Thank you everybody for your valuable comments.
Ventilation to the enclosed basement car parking floor si complying to NFPA 88A. In fact, the ventilation has been designed with min. 6 ACH which exceeds the NFPA minimum requirement (65000 cfm). The supply and exhaust fans will be normally running at 6 ACH (which exceeds NFPA requirement). The impulse jet fans was also considered which eliminates the ductwork. For fire condition, the ventilation was considered with 10 ACH with 2 pre-set fan speeds of supply and exhaust fans.

System sequence of operation for the car parking ventilation during normal and high co level concentration:

A. When co level <30 ppm, it will be considered as normal ventilation mode

1. Jet fan are not in operation
2. Main extract and supply fans will operate at low speed to maintain 1 cfm /ft² or 6 ach.

B. When co level >30 ppm but < 50 ppm
1. Required number of jet fans will operate at low speed based on the demand of co sensors.
2. Main extract and supply fans will operate at low speed

C. When co level >50 ppm
1. Required number of jet fans will operate at high speed based on the demand of co sensors.
2. Main extract and supply fans will operate at low speed
3. After 15 minutes if co level is still >50 ppm, main extract and supply fans will operate at high speed.

System sequence of operation for the car parking ventilation in case of fire:
In the event of fire when sprinkler system operates, after 3 minutes a signal goes to the addressable fire alarm system which is interface with car park ventilation system, sends signal to the ventilation system and accordingly the exhaust and supply fans will work at high speed and also the manual cap point in car park area and smoke detector in the lift lobby area can initiate fire alarm signal to the addressable fire alarm panel in case of fire.

 

[Buildtech2]

Anybody would like to comment on my above sequence of operation for car park ventilation system.

 

[DRWeig]

I seem to remember a requirement in the mechanical code to also run the fans based on occupancy sensors. That is, whenever anyone is walking in the garage. You might take a look to be sure.

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies