The Fundementals of Smoke Control
1-18 Infinity Smoke Control Guide
TOC
Controlling Pressure in a Stairtower
Stairtower smoke control systems are divided into two categories—
noncompensated and compensated. Noncompensated systems simply
turn on a fan to pressurize the stairtower. The fan’s speed does not
change to compensate for doors opening and closing. The more doors
that are open, the more the pressure differential between the stairwell
and the building drops.
Figure 1-6. Compensated and Noncompensated Stairtower
Systems
A compensated system adjusts the airflow to make up for pressure lost
through open doors. It can use dampers to relieve excess pressure in the
stairtower to ensure that the pressure does not go over the maximum
limit.
There are a number of ways compensated stairtower smoke control
systems can control pressurization. In a basic system with a roof-
mounted fan blowing air into the stairtower, pressure can be regulated by
varying the speed of the fan, the pitch of the fan’s blade, the inlet vanes,
or the number of fans operating (assuming there is more than one).
More sophisticated systems use ducts to deliver air to several points in
the stairtower. The dampers can be controlled to maintain the
appropriate pressure in their zone.
Vent
Variable-
Speed
Fan
Constant
Fan
Speed
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