Bibliography. Honeywell AUTOMATIC CONTROL SI Edition

SMOKE MANAGEMENT FUNDAMENTALS

Another consideration in zone pressurization is that bringing in outdoor air at low temperatures can cause serious freeze damage. Provision should be made to prevent damage when using outdoor air, such as providing emergency preheat and minimizing the quantity of outdoor air used.

Testing of smoke control strategies should include not only verification of acceptable pressures but also confirmation that interaction with other systems creates no problems, such as excessive door pull in a stairwell pressurization system (refer to American with Disabilities Act).

Typical Operation for Zone Pressurization System (Fig. 6):

1. Smoke detector(s) initiate alarm in specific zone.

2. System switches to smoke control mode as determined in remote control panel.

3. System turns on pressurization fans if not already on.

4. System allows pressurization fans to continue running if supply duct smoke detector is not in alarm or manual override is not activated.

5. System enables damper operation as appropriate for smoke control mode.

6. Operator verifies operation as appropriate (e.g., action of differential pressure switch).

7. Operator cancels smoke control mode as long as initiating panel is not in alarm and FSCS is not in manual override.

complex system to modulate dampers or fans at multiple injection points (Fig. 9) in response to differential pressure measurements at these points.

STAIRWELL

ROOF

LEVEL

BAROMETRIC

PRESSURE

DAMPER

C5151

Fig. 8. Stairwell Pressurization with Barometric

Pressure Damper to Vent to the Outside.

ROOF

LEVEL

STAIRWELL

EXTERIOR

WALL

OUTDOOR

AIR

INTAKE

STAIRWELL PRESSURIZATION CONTROL

The objective of stairwell pressurization is to provide an acceptable environment within a stairwell, in the event of a fire, to furnish an egress route for occupants and a staging area for firefighters. On the fire floor, a pressure difference must be maintained across the closed stair tower door to ensure that smoke infiltration is limited. Also, adequate purging must be provided to limit smoke density caused by temporary door openings on the fire floor.

To ensure proper stairwell pressurization system design, a means should be included to modulate either the supply or the exhaust/relief dampers. Also, a means should be included to provide multiple supply injection points at a minimum of every three floors (unless design analysis can justify a greater spacing) to provide uniform pressurization.

According to NFPA 92A, Recommended Practice for Smoke

Control Systems, the intake of supply air should be isolated from smoke shafts, roof smoke and heat vents, and other building openings that might expel smoke from the building in a fire. Wind shields should be considered at fan intakes.

Open-loop control of pressurization is seldom acceptable because of significant pressure differences caused by door openings. Closed loop or modulation provides the ability to control pressurization within acceptable limits. Closed loop control can be as simple as a barometric pressure damper

(Fig. 8) to relieve pressure at the top of a stairwell or a more

MODULATING

DAMPER

(4 PLACES)

DUCT

SHAFT

DUCT

CENTRIFUGAL

FAN

C5152

Fig. 9. Stairwell Pressurization with Modulating Dampers and Multiple Injection Points to Regulate Pressure.

Testing of stairwell pressurization systems should be conducted with agreed on conditions including:

— Number and location of doors held open

— Outside pressure conditions known

— Maximum door pull force allowed

Typical Operation for Stairwell Pressurization (Fig. 6):

1. Any fire alarm initiates smoke control mode.

2. System turns on pressurization fans.

3. System allows pressurization fans to continue running if supply duct smoke detector is not in alarm or manual override is not activated.

180 ENGINEERING MANUAL OF AUTOMATIC CONTROL