AHU smoke dampers 1

[remp]

I'm installing and AHU to serve 3 floors of production area.
There is a smoke damper on the inlet and discharge side of the AHU, to shut down in fire mode. The inlet of the AHU takes air from a fresh air plenum in another fire compartment. The consultant reckons we need these dampers to shut in fire mode, which is fair enough, but he wants to put a smoke detector at the inlet and another one at the outlet. I think this is a waste, and one would do at the outlet. He reckons because of the presence of filters including a HEPA filter smoke at one end would not reach the other, which I think is incorrect. What do you think/ The consultant keeps on refering to NFPA 90 too. Is he correct?

 

[friartuck]

blimey, you must be using really efficient filters. (I think he must be smoking something)

Unless you are using HEPA filters I cant see snoke being filtered out.



Friar Tuck of Sherwood

 

[quark]

NFPA 90A(4-4.2) guides the location of smoke detectors to be downstream of filters and before any branch takeoff. But this is application specific in my opinion. Most HEPA filters used in air conditioning system can't withstand higher temperatures and they give off near bonding(there are special HEPAs which can withstand 300⁰C that are used in sterilization tunnels. If you are using smoke detector to activate fire dampers, I prefer it to be in the fan suction side so that you can save your AHU.

Regards,

 

[DRWeig]

Say Billy,

Maybe I'm missing something, but if your AHU is more than 15000 CFM (I'm assuming it is, since you say it covers three floors), doesn't the Mechanical Code require smokes in both supply and return?

The one at the discharge is to detect components of the AHU which may be afire.

Just my take on it...

Old Dave

 

[KweziV3]

Say Billy
HEPA filtration as we all know, is defined by 99.97% removal of 3 micron particles and bigger. smoke is in the order of 0.01-1 microns. so your HEPA will not stop them getting to detector. But you do need to stop AHU produced smoke (i.e. That fan that blows), so HP side protection is definately required. So in short I have to agree with the Consultant
Justin and the consultants

 

[remp]

KeweziV3,

But thats my arguement, the consultant want smoke detection upstram and down stram of the HEPA filters because he thinks the filters will filter out the smoke. so why do you agree with that since you admit that the smoke particles are to small to be captured by the HEPA filters.
Does HP side mean High pressure side?

 

[SAK9]

In my opinion one detector in the fan chamber will do the job.This can be before the HEPA and after the fan.This will take care ofa motor burnout as well.Further down the HEPA there is no component which can cause fire so a detector there would not make any sense.If the system is 100 % exhaust, you may need to interlock the AHU and the exhaust fans