Interplay Of Ventilation Plant And Smoke And Heat Extraction In The Event Of Fire - Siemens SED2 Application Manual

Siemens
Building Technologies
3.3 Interplay of ventilation plant and smoke and
heat extraction in the event of fire
The illustration below shows a possible scenario in the event of fire and the inter-
play between ventilation plant and smoke and heat extraction. According to the
scenario chosen, a fire broke out on the floor in the middle of the building. In prin-
ciple, the change from ventilation mode (comfort mode) to fire mode (smoke ex-
traction mode) can take place automatically via the fire alarm center, or through a
key switch on the fire alarm panel.
In both cases, the ventilation plant in section 2 will be shut down first of all. Both
fire protection and smoke extraction dampers will be closed or opened as shown.
Then, the fume gas fan (smoke extraction) in section 3 will be activated. The hot
and usually toxic fumes will thus be vented to atmosphere. The resupply air duct
and the open damper ensure that the space will be adequately vented.
The fire protection dampers on the respective floor prevent smoke from reaching
the other floors via the supply and extract air ducts. However, open doors, passage
ways or other openings between the floors and the stairwell or lift shaft allow
smoke to spread. In order to keep escape routes and the other floors free from
smoke as long as possible, ventilation plant in these zones will purposely be oper-
ated under overpressure.
In zone 1 (stairwell), overpressure of 50 to 100 Pa is produced with the help of a
differential pressure sensor and a speed-controlled fan (using a PID controller).
Overpressure prevents smoke from entering the stairwell. Pressure changes
caused by the opening and closing of doors are compensated by the control sys-
tem, which also ensures that doors can still be opened in case pressure differen-
tials exceed a certain level.
The supply air fan in zone 2 will also be activated, producing overpressure like in
the stairwell. Naturally, differential pressure control could also be employed. But in
most cases, the fan operates at a fixed speed.
The interplay of smoke and heat extraction and ventilation plant pursues the follow-
ing targets:
• To minimize the amount of smoke and heat, the fume gases produced by the fire
shall be conducted to atmosphere as quickly as possible.
• Overpressure operation of the ventilation plant shall ensure that escape routes
and neighboring spaces will be kept free from smoke as long as possible.
Functioning principle of smoke and heat extraction and ventilation plant in the
event of fire:
Escape and
emergency route
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Application Guide «Fire Mode»
Introduction
Air handling
system
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CM1A5192en_01
23.10.2007