VESDA by Xtralis VESDA PipeNetwork Design Guide
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4.4.3 Return Air Grille Sampling
The sampling pipe is placed over the return air grille of a duct or an Air Handling Unit (AHU). Figure 4-8
illustrates pipe mounting over the return air grille. The number of AHUs that can be covered by different
detectors is dependent on the suction power of the AHU and also on the size of the return air grille.
Recommendations:
l a VESDA VLP or VESDA VLS detector should not monitor more than four AHUs
l a VESDA VLC should not monitor more than two AHUs,
l a VESDA VLF should not monitor more than one AHU.
l the detectors should be in close proximity to the AHUs.
l transport time should be less than 60 seconds.
l sampling hole sensitivities should be maintained.
Legend
A Sampling pipe
B Return grill
C End cap without hole
D Sampling hole
Figure 4-8: Return air sampling over a return air grille
Note: Socket unions are also used where it is important to have correct orientation of sampling holes.
4.4.4 Hot - Cold Aisle Sampling
In hot - cold aisle systems, the cabinets are adjoined into a series of rows, resting on a raised floor. The fronts
of the racks face each other and become cold aisles, due to the front-to-back heat dissipation of rack servers.
Hot - cold aisle protocol can be implemented with underfloor, overhead, horizontal displacement, or local air
distribution systems.
Figure 4-9: Hot - Cold Aisle System
l Primary Sampling: Rear of racks, Air-return grills (CRAC, Ceiling)
l Secondary Sampling: ceiling.
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