The Fundementals of Smoke Control
1-20 Infinity Smoke Control Guide
TOC
There are also a number of ways a compensated stairtower smoke control
system can get rid of excess air pressure, to ensure that the doors leading into
the stairtower can open properly. One or more vents to the building’s
exterior (with dampers) can be used in the stairtower to release excess
pressure. These dampers can be barometrically controlled (being forced
open by the excess air pressure) or controlled by electric motors or
pneumatics as in conventional HVAC systems. In both cases, the dampers
must be placed far enough away from the air supply to prevent venting of
air that has not yet been able to disperse through the stairtower. Vents can
also lead into the building, but you should consider carefully the impact of
venting extra pressure into the building before using this type of vent.
In some cases, a ground-level stairtower door can be used in place of
dampers. This door automatically opens and closes to maintain the
proper amount of pressure in the stairtower. The door is usually locked,
for security reasons. During an emergency, the smoke control system
has to be able to override the lock. Using a door in this manner has its
problems, since wind effects close to the base of a building could
prevent the air from escaping through the door.
Figure 1-9. Methods of Controlling Stairtower Pressure
You can also use an exhaust fan to vent the excess pressure from the
stairtower. Such a fan should be designed to operate only when the
stairtower is overpressurized. It should never be on when the pressure
differential between the building and the stairtower is below the lowest
limit.
Roof-mounted Exhaust Fan
Automatic Door Used to Vent Pressure
Vent to Outside with Barometrically
or Automatically Controlled Dampers
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