Stairwell Pressurization

[Jabba007]

Just digging into this. Can't convince the architect NOT to do it. There seems to be some misunderstanding about what's required. The way I read the code, I need to provide enough ventilation air to the stairwell to provide .05" - .15" in the stairwell even when "X" number of doors are open. That is a VERY big fan, on the order of 13,000 CFM per open door, plus what escapes thru building cracks.

The architect insists that we need only supply enough air to pressurize when there are no doors open.

Anyone out there have any real world experience in this arena?

Thanks in advance!

Jabba

 

[friartuck]

Depend which country your in

Get BS5588 which confirms your figures. If all you needed was to pressurise the stairs with the doors closed, you would need a tiny fan (60l/sec per door)

If you can design the system out by putting the stairs on the outside wall, then that would be better



Friar Tuck of Sherwood

 

[garnerengr]

Here in Houston (International Building Code), the rule is that you need a defined minimum air velocity (measured at several places across the door area and then averaged. I am not at my office and I can't remember that exact number) across the door on the floor of the fire with the stair doors of the floor above and below and the ground floor (4 total doors) open. Depending upon the number of floors, it ends up being quite a large number indeed.

The requirement and the test procedure is usually listed in the local fire code. Call your Fire Marshall for exact rules and procedures in your area. Don't let the architect's stubbornness and lack of knowledge get you into trouble.

 

[ChasBean1]

Jabba007, don't design cfm of any fan to maintain a pressure with any open doorways. Trust me on this.

The pressure range for the pressurized stairs is 0.15-0.35 in. w.c. ONE stairwell (the one that transverses the building height and drops to the bottom of the basement, has to be a smokeproof enclosure and not a pressurized stair. This enclosure, the firefighters' main stair, has to be positive to each floor's vestibule by 0.1 in. w.c.

There can be much more said on this subject and I'll invite any questions and will try to respond in reasonable time.

Regards, -CB

 

[Jabba007]

I am in Indiana.

The architect directed me to IBC 909.20.5 "Stair Pressurization Alternative".

Paraphrasing... .15"-.35" in the shaft, relative to the building with all doors closed under maximum anticipated stack pressures.

Hmmm. Seems we can do it that way. Still gonna be a fair sized fan I think, but at least an order of magnitude smaller than the 4 doors open method. Wow! That would have been 75,000 CFM.

Thanks guys. I invite any further discussion as well.

Jabba

 

[ozmosis]

You may wish to have a look at the Australian Standard AS1668 for some advice and good common sense information on this subject.
I work in the VFD business in product development and have been working on the subject of Fire Mode/Essential Service Mode within drives and how they should be designed with smoke spill and stairwell pressurisation in mind. Looked at many standards around the world (I'm involved in the development of a global HVAC drive)and I must say that AS1668 is quite a useful document, even though you (or I)are not in Australia.