Trane Engineered Smoke Control System Application Manual page 26

Chapter 1 Smoke control overview
14
Note:
Atrium smoke control should not activate on signals from
sprinkler water flow switches or heat detectors. Since the
temperature of a smoke plume decreases with height,
activation by these devices may not provide reliable results.
Beam smoke detectors minimize interference problems created by
stratified hot air under atrium ceilings. On hot days or days with a high
solar load on the atrium roof, a hot layer of air may form under the
ceiling. The layer can exceed 120
fire may not be hot enough to penetrate the layer and reach ceiling-
mounted smoke detectors (Figure 9).
Beam-detector installation typically conforms to one of two
configurations: vertical grid or horizontal grid.
Figure 9: Sample stratification
Vertical grid
The vertical grid is the most common beam detector configuration. A
number of beam detectors, located at different levels under the ceiling,
detect the formation and thickening of a smoke layer. The bottom of the
grid is at the lowest expected smoke stratification level.
Horizontal grid
The horizontal grid is an alternate beam detector configuration A number
of beam detectors, located at different levels under the ceiling, detect the
rising smoke plume. Beam detectors are located:
Below the lowest expected smoke stratification level
•
Close enough to each other to ensure intersection with the plume
•
F (50 C). The smoke from an atrium
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BAS-APG001-EN