2: Abbreviations; Smoke Movement; 1: Stack Effect - Honeywell NOTIFIER SCS Series Operation And Installation Manual

Concepts of Smoke Control
2.1.2 Abbreviations
In order to simplify system configuration discussions and technical illustrations, the following abbreviations are used for control modules
and monitor modules. These are in addition to industry-wide abbreviations already specified in the Definitions section.
Control Module,
Relay Module
Monitor Module
Note: the FDRM-1 acts as both CM or MM, depending on application.

2.2 Smoke Movement

During a fire inside of a building, smoke often flows away from the fire to unwanted areas, threatening life and damaging property. Exit pas-
sageways, stairwells and elevator shafts often become smoke-filled, inhibiting or preventing safe evacuation.
All fires produce smoke and the movement of smoke will follow the same pattern as the overall air movement within a building. Very sim-
ply, a smoke control system must be able to inhibit the flow of smoke within a building. Elements that cause the movement of smoke include
one or more of the following:
• stack effect
• buoyancy of the smoke
• expansion
• wind
• elevator effect
• the HVAC system
Each element is described in the paragraphs below.
2.2.1 Stack Effect
Stack effect is defined as the vertical flow of air due to temperature differences between the interior and exterior of a building. Generally,
there is an upward movement of air within building shafts (stairwells, elevator hoistways, etc.) when the air outside the building is colder
than the air inside. This is referred to as normal stack effect. The air in the building has a tendency to rise because it is warmer and less dense
than the outside air. The taller a building is and the greater the temperature differences between the building interior and exterior are, the
greater the tendency is for air to rise in the shafts. The opposite is true when the outside temperature is warmer than the temperature inside
the building, causing a downward movement of air within building shafts. This is referred to as reverse stack effect. The overall airflow ten-
dencies within a building due to normal and reverse stack effect are shown in Figure 2.1.
The neutral plane of a building is defined as the elevation where the hydrostatic pressure inside the building equals that outside. Normally
the neutral plane is located at the midpoint of the building, but can occur at any floor and depends upon building design. The neutral plane of
a building should be determined before design of the smoke control system. Refer to the ASHRAE publication Design of Smoke Manage-
ment Systems for information on calculating the neutral plane of a building.
Another factor involved in determining stack effect is the temperature of the
smoke. Reverse stack effect, as described below, reacts only with relatively
cool smoke caused as a result of smoldering fires. Relatively hot smoke, the
result of fast burning fires, will still have a tendency to rise into the shaft
against reverse stack effect due to the effects of buoyancy. Normal stack
effect reacts with both hot and cool smoke.
In a building with normal stack effect, smoke from a fire will follow the air-
flow into the shaft. If the source of the fire is below the neutral plane, the
smoke will flow up the building shaft until after it crosses the neutral plane.
Once the smoke crosses the neutral plane, its tendency will be to flow into
the floors above the neutral plane. The effects of buoyancy can also add to
the upward movement of smoke due to the temperature of the smoke, as
described in the next section.
14
Table 2.1 Chart of Abbreviations
Code
Term Used in
Manual
CM Control modules:
Relay modules:
MM FMM-1, FMM-101, FDM-1, XPM, XP5-M, MMX-1, FZM-1
Part Number
FCM-1, XPC, XP5-C, CMX-1, CMX-2
FRM-1, XPR, CMX-1 (relay configuration),
CMX-2 (relay configuration)
Normal Stack Effect
arrows indicate direction of air movement
Figure 2.1 Air Flow Due to Stack Effect
SCS Series Manual — P/N 15712:L 7/18/16
Smoke Movement
Reverse Stack
Effect
Neutral
Plane