Kidde VM-1 Manual page 26

Chapter 1: Fire geometry and smoke movement in buildings
Since both absorption and scattering of light cause a
reduction in the light sensed at the receiver, projected
beam detectors work well for both smoldering and fast-
flaming fires.
Projected-beam detectors are normally installed parallel
and within 20 in. (0.508 m) of the ceiling except when
high ceilings or smoke stratification are a design
consideration. Projected beam detectors have an
operating range of 30 to 330 ft. (9.1 to 100.6 m).
Manual pull stations
Manual pull stations are placed in buildings for occupant
use in reporting fires and notifying other occupants.
Manual pull stations are not normally used to activate
smoke control systems, but may be used for stairwell
pressurization systems. With manual pull stations there
is a greater likelihood of a person signaling an alarm
from a station outside the smoke zone in which the fire is
occurring and thereby pressuring and venting the wrong
areas.
Automatic sprinkler and specialized extinguishing
systems
The same criteria that dictate the installation of a smoke
control system are likely to also dictate the installation of
an automatic extinguishing system. Most model codes
will require automatic sprinklers for large or tall buildings.
In the design of the smoke control systems, the size of
the expected fire must be determined in order to
establish exhaust flows for the smoke generated.
Automatic sprinkler systems are designed to contain or
control fires, thus limiting the size of an expected fire and
the amount of smoke generated. Smoke control system
designers utilize the limiting of fire size and spread due
to automatic sprinklers as an important element in sizing
HVAC systems and fans for smoke control.
Automatic sprinkler systems can be utilized to activate a
smoke control zone, provided the flow switch for the
sprinkler system serves only fire sprinklers in the smoke
control zone. For new buildings, the coverage areas of
sprinkler systems must be coordinated with smoke zone
areas to ensure applicability.
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Manual controls
For smoke control, manual activation or deactivation
refers to the means available to an authorized person to
activate one of the smoke control functions. Manual fire
alarm pull stations are not in this category. Manual
controls will be at the FSCS in a location directed by the
AHJ.
Smoke control output circuits
Smoke control system output circuits may contain some
of the same output modules and devices found in a
standard VM-1 fire alarm system. Output commands for
a smoke control zone include the startup or shutdown of
fans, damper operation, vent or louver operation, and
door or barrier operation. Sequencing of each action is
critical in the proper functioning of a smoke control
system. Dampers may need to reach fully open or fully
closed position prior to fan startup. Fans may also need
to rundown or stop prior to damper movement.
Fans
HVAC fans are classified as either centrifugal or axial.
Fan performance and economics are major factors in the
type of fan for an application. Forward-curved fans are
used for low-pressure applications including residential
furnaces and packaged air-conditioning equipment.
Airfoil and backward-curved fans are used for general-
purpose HVAC applications, and airfoil fans are usually
limited to large systems where the energy savings are
significant. Radial fans are used when high pressures
are needed. New building installations using fans for
smoke control will consider the emergency operation
parameters when selecting the HVAC system fans.
Centrifugal fans: Centrifugal fans (see Figure 18) are
subdivided into forward-curved, backward-curved, and
airfoil. Forward-curved centrifugal fans rotate at a
relatively low speed. They are generally used to produce
high flow rates and low static pressures. Backward-
curved fans rotate at about twice the speed of forward-
curved fans and have a higher efficiency. Both forward-
curved and backward-curved impeller blades are single-
width blades.
VM-1 Smoke Management Application Guide