Bosch FAS-420-TM, Operation Manual, Page: 52 / 104

52 en | Planning FAS-420-TM Aspirating Smoke Detector
F.01U.088.878 | 4.1 | 2010.11 Operation Guide Bosch Sicherheitssysteme GmbH
3.9 Planning for forced airflow
Monitoring the air-conditioning ducts
Air-conditioning units are broken down into low and high-speed units (see table below). The
details provided in this chapter apply only to low-speed units. There are no adequate
empirical values available for high-speed units. Hence, smoke trials must be executed for air-
conditioning ducts with flow speeds above 10 m/s, in order to determine optimal response
behavior.
The speed distribution in an air-conditioning duct appears as follows:
Limiting values Min. distance FAS-420-TM – last T-fitting 2 m
Max. distance FAS-420-TM – last T-fitting 20 m
Max. branch length 12.5 m
Max. total pipe length per pipe system
– Pipe Ø 25 mm
– Additional pipe Ø 12 mm
50 m
8 x 3 m
Max. total pipe length per pipe system for a fan voltage
< 10.5 V
– Pipe Ø 25 mm
– Additional pipe Ø 12 mm
40 m
8 x 3 m
Max. number of air sampling openings (n) per pipe
system
8 units
Min. distance between 2 air sampling openings 0.1 m
Max. distance between 2 air sampling openings 4 m
Double U-pipe system Number of air sampling openings
4 8
Ø of air sampling openings in
mm
a
4.4 3.0
a
Punch diameter of the aspiration reducing film sheet
Air-conditioning
ducts
Low-speed units High-speed units
Flow speed Maximum 6 to 10 m/s > 10 m/s
Duct cross-section Large Small
Difference pressures along
the flow direction
Low High
Figure 3.15 Speed distribution in an air-conditioning duct
1 Air-conditioning duct
V
1
- V
4
Flow speed
1
v
1
v
1 >
v
2 >
v
3 >
v
4
v
2
v
3
v
4