VESDA VLF-500 Product Guide
VESDA by Xtralis
22
www.xtralis.com
3.3
Return air sampling (return grilles)
The VESDA VLF is suitable for air sampling across return air grilles of Air Handling Units. The recommended
coverage of the VESDA VLF is 0.4 m² (4 sq. ft.) per sampling hole. This should be considered in conjunction
with local codes and standards.
Note:
Rotate the air sampling hole approximately 45° away from the direction of the incoming airflow and
towards the grille surface. This will minimize the risk of a Low Flow Fault being recorded in
situations where air flow changes (e.g. where the Air Handling Unit is turned off).
Some points to consider for setting up a pipe network are:
l
sampling holes should be evenly spaced (within 20% of the separation distance to each other)
l
an un-vented end cap should be fitted to the end of the sampling pipe
l
during installation, consideration should be given to the future maintenance requirements of the air
handling unit. Access to filters should not be restricted and pipe network should be easily removable by
the use of socket unions
For full details concerning return air grille sampling pipe network design, consult the VESDA System Design
Manual.
The table below shows the appropriate hole sizes for pre-engineered designs for return air grille set ups.
Return Air Sampling – U Shaped design with equal holes on each side
Sampling Holes
ID 21 mm Pipe Hole Size (mm)
IPS ¾ in. Pipe Hole Size (in.)
8
3.0 – 4.5
–
10
3.0 – 4.0
–
12
3.0 – 3.5
14
3.0
Table 3-3: Return air sampling pipe hole numbers and sizes
*For code-specific information, refer to Codes and Standards Information for Air Sampling Smoke Detection on page iii.
Legend
A
Sampling pipe
С
Return grille
B
Sampling hole
В
End cap (no hole)
Figure 3-5: Return air sampling over an air handling unit grille