Have A 39 story building with two stairwells. Each stairwell has one constant volume fan and one freq. drive controlled fan. We will be holding a set pressure with the freq. drive to adjust for doors opening and closing. Where should we put the static pressure sensors? I'm thinking one in each stairwell around the 14th floor. Fans are on the roof. Thanks.
"if" it is critical then why not 2 or more and average with some fail safe logic, should one sensor crap out?
Are you looking for pressure control during smoke purge?
Local 30 New York, New York Operating Engineer
Yes. I should clarify that this is for life safety and tied into the fire alarm system.
Originally Posted by kdocsr05
Assuming we are talking about a life safety stairwell pressurization system with the modulating fan an element of the building smoke purge system, I offer the following.
With positive pressure relationships in the stairwells and potentially negative pressure relationships established on the fire floor by the ‘purge fans’ used to control smoke, forces required to open a door to the stairwell becomes significant. The concern is that someone might not be able to open the door against the pressure differential induced force, and thus would be unable to enter the stairwell. Our local codes restrict this force, which requires that a pressure control system be provided for the stairwell. Inspectors often want this stairwell pressure control system to be demonstrated as a condition of acceptance, selecting the fire floor and doors to test at random. The problem is the required amount of force to open a door has no definition and is left to the inspectors discretion.
I do not think you will find an application standard here. The verification process may involve setting up the ‘pressure sandwich’ on every floor and then testing all doors, then repositioning the sensor as adjustments become necessary which can be time-consuming.
Smoke purge and stairwell pressurization are evolving post 911 and it has become almost impossible to keep up with all the changes. We are put in a situation were you learn as you go with little or no direction. Then during commissioning all the big shots show up and everything changes.
I have been involved with commissioning smoke purge and pressurization at the NYC Port Authority Bus Terminal for ten weeks, worked there today on a pre-inspection and my head is spinning. We had a different designer today than last week, who has a new interpretation of the local fire code.
Local 30 New York, New York Operating Engineer
Just to add my two cents.
Kd has detailed described the issues that may arise...
I am not based in US so i dont have to deal with local codes, but i have recently involved on a high security US building and the presurization control is a nightmare...
Get ready for a serious period of not ending living hell....
In order to build and maintain a pressure stack you would need two things...
1. A good design that takes into consideration building pressure stack and builts it in normal operation lets say "by default".
2. A well commissioned and programed "reaction" mechanism that shall pull back pressure stack in design values when this ones goes off.
Not having a clear view of the whole design i would recommend to test in an aproprieate manner what happens on normal mode when everything is settled, in othe words crosscheck the design and find possible flaws...
You may experience that a potential door opening shall collapse your stack and then you need to chase once again and re-built stack etc...
After that you can spot with a critical eye where are points of best monitoring space pressure..., with light hart I could say one sensor at low rise, one at mid and one at high rise... observation will lead you on definition of low mid high (by the way you need to have installed sensors on the beginning and start recording..)
Second (again without knowing the mechanical design), the two fans may create you a slight problem maintaining the pressure even with a good design..
Just to have an idea I had space DPs in ALL critical spaces, with modulating dampers and VFD fans... and still the damn pressure stack some times collapse and then you need a serious amount of time to rebuilt it..
Anyway extensive tests (trial and error sequence) only lead to the desirable result..
I hope that all the above worth two cents...
Biggest obstacle you have is getting someone to SAY where and how much differential you have to maintain.
If I had to guess I'd bet you have to maintain your differential relative to the basic building envelope but no one told you where to reference it right.
Do you reference the 19th floor ?, the 39th floor ?, the 1st floor ?
The last one I was involved in we had to maintain .01" relative to the basic building envelope, Referenced center of the building, during "Normal Operation". In "Fire Mode" we had to keep it (stairway) neutral to floors above and below (both positive to floor involved) floor involved, which was in full evacuation mode (negative to everything else) but stairway could never be negative to floor involved. It proved to be quite tricky to keep ALL of the presure relationships correct but we were only working a 10 story with 3 parking levels below.
You have your work cut out for you. I hope someone in a position of authority gives you a definitive target to aim for
If sense were so common everyone would have it !
All opinions expressed are my own. Any advice provided is based on personal experience, generally accepted fact or publicly available information. As such, it is worth exactly what you paid for it, not a penny more not a penny less !!
There is also the configuration of the VFD that must be looked at for life saftey operations. Some VFD has an Override function that must be used when doing stairwell pressurization. This override mode wil disable the keypad for external control, eliminate response to certain faults and warnings within the drive and acknoledge and disregard certain safties that are wired to the drive. I have been told by many contractors that use our drives for this very situation that the setpoint and sensors used are dependent on the local code. Some use high/low select, averaging and mutiple sensors. The internals of our VFD can do the stated above. BUt as this is life saftey please check with your local requirements.