If I’m designing a stairwell pressurization system. How do i know what the height limit is for the fans?
I am not into fans or high rise buildings
I am thinking there is no hieght limit on fans?
More of a calculation design thing.
OHHH I am not an engineer, so you can discount my reply if you want, and I cannot do math.
Section 220.127.116.11.2 of the 2018 NFPA 92 requires a design analysis to be conducted for all single bottom-injection system and for all other single-injection system for stairwell exceeding 100 ft in height.
The annex A.18.104.22.168.2 has some guidelines on the location of the single-injection point where doors may remain open much of the time.
Otherwise, good design practice dictates that a stairwell pressurization fan can be located anywhere, but since the entry/exit doors at ground level will remain open during emergency for fire personnel entry as well refuge escape operations, the top location is preferred to avoid the short circuiting of the air. Fans shall be positioned to avoid introducing smoke and toxic gases into the stair especially when located at high level.
• There should be two air intakes facing different directions in order not to be affected by the same source of smoke.• Each air intake shall be protected by a smoke control damper operated independently via a smoke detector in such a way that if one damper closes due to smoke contamination, the other air intake will supply the air requirements of the system without interruption.• The air intakes should be ducted to the fan inlet. This measure is necessary to prevent the pressurization fan reducing the pressure in the fan room below atmospheric pressure and hence inducing flow from the building towards the fan room.• Each inlet shall be independently capable of providing the full air requirements of the system.• The air intake shall not be less than 16 ft (5 m) horizontally from any exhaust discharge opening and be independent from wind speed and direction.
For high-rise buildings the preferred distribution arrangement is a vertical duct running adjacent to the pressurized spaces. Distributing to these areas can be achieved by:
Stairwell pressurization systems are accompanied with a vent system. The purpose of the vent is to relieve excess pressures in the stair when doors are opened and closed. When a door is opened, the pressure in the stair is reduced and the relief vent closes, thereby diverting the excess air to the open door. When the door closes, the vent serves as a relief for excess pressures in the stair to reduce door-opening forces.
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