System Sensor FAAST Comprehensive - Manual (Page 33)

open AreA proTeCTion
Ceiling Sampling
In typical ceiling installations, the pipe network is suspended from 1 in. to 1
ft. (25 mm to 300 mm) below the ceiling level in the protected area. This type
of installation is the most common installation. It could be used in offices,
warehouses, equipment rooms and a variety of other types of installations.
The pipes and hence the air sampling holes are exposed to the protected envi-
ronment. The PipeIQ software can also provide guidance for the design.
Concealed pipe networks
Capillary tubes are typically used for concealed pipe networks. This type of
network is normally used for either aesthetic or security purposes. The main
pipe network is installed in a ceiling void and capillary tubes are branched off
at regular intervals. These capillary tubes are used to monitor the protected
area by projecting through the ceiling covering while the main pipe network
remains hidden.
inter-Beam Sampling
When large ceiling beams are used in construction, pockets of space are
created between the beams. In normal circumstances, the pipe network is
mounted on the bottom of the beams and does not sample the large spaces be-
tween the beams. If it is necessary to cover this space, a rigid pipe in the shape
of an inverted “L” can be extended vertically from the pipe network up into
the area between the beams so that the pipe reaches up towards the ceiling in
these locations. The sampling hole should be drilled just before the end cap
on the horizontal portion of the pipe. The ends of these sampling pipes should
be capped with an end cap. The end cap may or may not have a sample hole,
depending on the pipe network design.
unDer Floor proTeCTion
Floor void Sampling
The FAAST system is well suited to protect concealed voids, either in the ceil-
ing or under the floor. Some locations use either ceiling and/or under floor
voids as return air plenums (ducts). To monitor the return air in these areas, a
pipe network must be designed to monitor the flow through these areas. Some
ceiling and floor voids are used for cable runs or for small equipment instal-
lation. Monitoring of these areas must be done using a pipe network designed
for operation in these areas. When installing pipe in a floor void, keep in mind
that the air sampling holes are still located at the bottom of the pipe. This
means that the pipe would be located towards the upper portion of the void.
oBJeCT proTeCTion
Cabinet Sampling
Equipment cabinet sampling may be accomplished in two ways: pipe net-
works and sampling points can be installed directly inside the equipment cab-
inet or directly over the equipment cabinets being monitored, if the cabinets
have ventilation grills.
in-Cabinet Sampling
For in-cabinet sampling, capillary tubes can be used to enter the equipment
cabinet. The capillary tube is connected to the pipe network via a tee connec-
tion with an adapter. The maximum length of these capillary tubes is 26 ft. (8
m). PipeIQ can help create an appropriate design.
An alternative to capillary tubes is a rigid drop tube. In this application, the
pipe network is run over a row of cabinets and drop tubes are run down to
each cabinet. This tube or pipe should be less than or equal to the network
pipe diameter and is connected to the top of the cabinet and to the pipe net-
work via a tee connection. Or the pipe could come up from under a floor void
into the cabinet.
Cabinets with extractor fans may cause sampling problems when the sample
point is on top of the cabinet. The extractor fan creates a low pressure area
within the cabinet that can stop air from being drawn into the detector system
at the sampling point. This type of installation must be checked carefully for
proper sampling operation. This can be accomplished using canned smoke at
the sample point location.
Above Cabinet Sampling
In above cabinet sampling, the pipe network should be installed directly over
the cabinets that will be protected. Sampling holes are placed over the cabinet
ventilation grills. Holes should be oriented so that they face into the air stream
coming from the cabinet. If there is more than one exhaust from a cabinet, a
sampling hole should be installed over each opening.
NOTE: With either application it is best to locate the sampling hole in the path
of the air flow, near the top of the cabinet.
lArGe AreA proTeCTion
Large volume areas and areas with high ceilings require special design con-
siderations for the pipe network design. Stratification occurs when smoke is
heated by smoldering or burning materials and becomes less dense than the
surrounding cooler air. The smoke rises until there is no longer a difference in
temperature between the smoke and the surrounding air. (See NFPA 72-2007,
A.5.7.1.10.) Stratification, therefore, may occur in areas where air tempera-
ture may be elevated at the ceiling level, especially where there is a lack of
ventilation. When stratification is likely to occur, conventional pipe network
sampling may not be effective.
One method to overcome the stratification problem is to create a vertical sam-
pling pipe in addition to the horizontal pipe network on the ceiling. The verti-
cal sampling pipe has sampling holes at various heights to sample within any
stratification layers present in the area, as shown in Figure 1.
FiGure 1. verTiCAl SAmplinG pipe
ColD AreA proTeCTion
The FAAST detector is approved for operating temperatures ranging from
32°F (0°C) to 100°F (38°C) and sampled air temperatures ranging from -4°F
(-20°C) to 140°F (60°C). However, special considerations should be taken
when operating at the extreme end of these ranges, especially the cold end.
Refer to the section titled The Pipe System for recommendations on handling
the pipe itself in cold environments.
The temperature in a cold area is typically just at or above 32°F (0°C). In
designing a pipe system, the pipes should be kept out of the immediate airflow
from a chiller unit, if used, as its air is often significantly colder than the room
itself, in order to maintain the correct temperature. In a cold room application
it is not usually necessary to use a heater element, but only a water trap to
remove condensation. For more information see the cold storage white paper
at systemsensor.com/faast.
Smoke Stratification Layer
Sampling Pipes
Aspirating
Detector
Sampling Holes
ASP-35
SS-400-007 34 E56-3621-003
Application and Design