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Chapter 1 Smoke control overview
8 BAS-APG001-EN
If the technique employs modulated supply airflow, a fan provides at least
minimum pressure when all stairwell access doors are open. Either a
single-speed fan with modulating bypass dampers or a variable frequency
drive varies the flow of air into the stairwell to compensate for pressure
changes.
If the technique employs over-pressure relief, a damper or fan relieves air
to the outside to maintain constant pressure in the stairwell. The amount
of air relieved depends on the air pressure in the stairwell. A barometric
damper, a motor-operated damper, or an exhaust fan can be used to
maintain the air pressure.
Non-compensated pressurization technique
The non-compensated pressurization technique provides a constant
volume of pressurization air. The level of pressurization depends on the
state of the stairwell access doors. When access doors open, the pressure
in the stairwell lowers. When access doors close, the pressure raises. One
or more single-speed fans provide pressurization air (
Figure 5).
Non-compensated stairwell pressurization works best when:
• Stairwells are in a lightly populated building (for example: telephone
exchanges and luxury apartments).
• Stairwell access doors are usually closed, but when used, remain open
only a few seconds.
Figure 5: Sample non-compensated system