CO Concentration in Carpark Ventilation System Design

[Buildtech2]

We have designed carpark ventilation system with 6 ACH at normal mode and 12 ACH at fire mode which is in line with NFPA and local regulations. However, following is also mentioned in NFPA 5000.

As per life safety code, NFPA 5000, (Ch. 49 CL.49.2.2.5) which specifies - Enclosed parking structure shall have a ventilation system designed to limit the concentration of carbon monoxide to not more than 35 parts per million of air when measured between 36 in. and 48 in. (915 mm and 1220 mm) from
the floor”.


We need to justify to our client that the ventilation system so designed will attain above code
requirement. Appreciate, if anybody can guide me on this.

 

[EnergyProfessional]

IMC 404 requires 0.75 cfm/ft²
You should check if that is more stringent than what you quoted.

I think calculating a specific ppm is a fool's errand. what vehicles and what usage scenario can you guarantee to be used? and do you personally guarantee that each car's emission control system works properly? Better to follow the code-prescribed ventilation rates.

 

[Buildtech2]

I need to justify to my client that proposed 6 ACH at normal mode which is in line with NFPA and local regulations can limit the co concentration in basement carparks to less than 35 ppm. Since design is already completed, it is difficult to change at this stage. Please advise.

 

[EnergyProfessional]

Design isn't completed until JHA approved it.
Does IMC not apply to your jurisdiction?

 

[Buildtech2]

Yes, you are right. Design is incomplete until it is approved by JHA. We have to comply local regulations here which are in line with NFPA codes. IMS is not followed here.

 

[chicopee]

You need to figure out the generation rate of CO in order to determine make up air flow rate. So to estimate, figure the maximum number of vehicles that would be operated in the idle mode during the busy hours, that is when either vehicles are coming in or leaving the parking area, then you can estimate the amount of CO within the volume established at the height recommended by the NFPA 5000. The fresh air flow rate should be based between the maximum concentration and the allowable concentration of CO. Your biggest obstacle will be to determine an acceptable CO generation rate. For reference to the equations needed to determine fresh air flow rates, I suggest "Ventilation for Control of the Work Environment by William A. Burgess, Michael J. Ellenbecker and Robert D. Treitman, chapter 4.2 and equation 4.5.

 

[EnergyProfessional]

whatever you do, assume the worst and perform the most conservative calculation.

I still would use IMC as a guideline unless you come up with more stringent ventilation rates. Later on, when you have to testify in court or in front of the licensing board, you have a better reason why you came up with the flowrates you did.

I don't recall which NFPA exactly (it isn't adopted in my jurisdiction), but one of those requires 1 cfm/ft². so you should check that too if that applies. Remember, there are several codes/standards to follow and they are not necessarily coordinated. you need to follow the most stringent.

 

[Buildtech2]

Please see attached ventilation calculations to achieve 15ppm CO concentration in enclosed basement carpark as per ASHRAE guidelines. please see if this is acceptable.