Xtralis VESDA E-Series, Manual

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VESDA Pipe Network Design Guide VESDA by Xtralis
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4.6.2 HVAC System
HVAC protection is implemented for both return side and supply side to protect the HVAC fan and filter.
Additionally, detectors may be placed in the outdoor air supply in order to identify whether external pollutants
are being drawn into the system from outside of the building.
A B
C
D
E F
G
H I
J
K
F
Legend
A Exhaust Damper
B Return Air Sampling
C Return Air
D Supply Air
E Supply Air Sampling
(Fan, Filter Fire)
F Fan
G Filter Bank
H Supply Air Damper
I Outside Air Monitor
J Fresh Air Intake
K Return Air Damper
Figure 4-23: HVAC System
4.7 Large Area Sampling
Areas such as atria and warehouses with high ceilings require special variations of the pipe network design
rules. Stratification is a process where due to hot air layers closer to the ceiling, smoke loses its thermal
energy, stops rising and levels out horizontally at a certain height. Stratification layers may be formed at
different heights, restricting the smoke’s ability to rise and reach the sampling pipe network. Factors such as
temperature, ventilation, and roof height, all affect the degree of stratification and the level to which the smoke
will rise. Changes in the above mentioned factors result in different stratification effects on a site. Where
stratification is likely to occur, conventionally designed pipe networks may not be effective.
Legend
A Detail of sampling hole
B Stratified smoke layer
C Vertical sampling holes
Figure 4-24: Sampling air from areas with high ceilings
To overcome the stratification effect, a vertical sampling pipe may be installed in addition to the standard pipe
on the ceiling. The vertical sampling pipe penetrates the stratification layers at different heights and samples
the air at multiple levels. Follow local codes and standards for dimensioning. Heights exceeding value
specified by local codes and standards should adhere to a performance-based design approach.
4.8 Dilution
If smoke concentrations occur at the extreme end of the sample pipe run, a smoke-laden air sample must
pass a number of other sampling points, all of which are supplying only slightly polluted samples (if they are
near the fire source) or completely clean samples (if they are far away from the fire source). The net result is