The main task of ventilation systems is to take in, heat or cool the fresh air, and to expel the polluted air. Besides this task, fire escapes and emergency elevators will be used for evacuation purposes, positive pressure is needed to accommodate clean air, and therefore pressurization systems are used in the event of a possible fire in buildings.
Smoke resulting from the fire inside the building can be transported to non-fire areas through ventilation ducts. However, it is also possible for smoke resulting from a fire outside to be taken into the building by the air handling units or the pressurization system. To prevent this situation, which is extremely dangerous with potentially serious consequences, it is important to place detectors to provide early detection in the ventilation duct.
One of the preferred devices is the UG-7 ventilation sampling device. This is because the smoke detection of the device is sensitive and reliable. Besides detection of fire, fire dampers and other devices must be controlled so that smoke does not disperse into the air ducts from inside and outside the building.
Smoke detection and management in ventilation ducts
Fire and gas detection systems, which must be installed in buildings according to the regulations, and duct-type smoke detectors installed in ventilation ducts are located in the same loop line, and all necessary controls are made according to cause-effect scenarios through relay modules.
It is extremely important to follow the guidelines of the standards and regulations. For example, according to fire guidelines, when the duct direction changes, a duct-type smoke detector should be used at a distance of five times the hydraulic duct diameter of this change point. If the damper is close to the filter device, this ratio should be three times.
According to the standards on the Installation of air conditioning and ventilation systems, the following items should be considered when determining the positions of duct-type smoke detectors to be used in air distribution systems.
- For duct installations to automatically stop supply fans in systems above 2,000 cubic feet per minute (cfm); duct-type smoke detectors should be installed at a suitable point in the main supply duct under the filters.
- For systems above 15,000cfm, additional duct-type detectors are required at the common return entry point in the return system of each floor
- To detect whether smoke is drawn into the system from outside the building, duct-type detectors are required close to the outdoor air supply. Thanks to warning signals coming from duct-type detectors, the outside air damper of the HVAC system will be closed.
In the example of an HVAC system, when it detects smoke in any channel:
- By turning off the fan system and switching all the dampers shown to off position, it will be possible to prevent the distribution of smoke over the air handling unit to unaffected areas of a building.
- Alternatively, the air-supply fan is turned off, fan continues to run, the outside air damper and the air mixing damper are closed. At those moment, if exhaust damper is opened, smoke will occur.
Smoke detection and management in pressurization ducts
In fire stairs and emergency elevators which are used for emergency evacuation in buildings the presence of smoke is prevented by providing controlled overpressure with permanently installed pressure devices.
Smoke evacuation is important in an emergency for fire exits and rescue points. When pressure systems are designed:
- When the doors are closed, the pressure difference between the protected and unprotected area ≤100N corresponds to the maximum door opening force.
- When the doors are opened, air flow has to be between 1m/s and 2m/s for air exit channel.
A pressure evacuation damper is a device that evacuates excess compressed air in an overpressure area (stairwell) and will usually be located at the top of the stairwell.
When in control mode (stairwell is closed), excess air must be discharged to atmosphere through the pressure evacuation damper. Mechanical or motorized pressure controls are possible.
Special shafts and facade openings can be used to escape hot smoke from the living area of the building or another area of the building that is not under pressure.
Generated smoke can be evacuated through the smoke evacuation shaft or through the facade opening in the living space.
To minimize flow and pressure losses in the stairwell, outdoor air is blown from shaft at various levels (for example, every three floors) for tall buildings.
The Smoke Damper Module developed by Mavili Elektronik operates optimal an integrated operation of ventilation systems and fire alarm systems.
The Maxlogic Smoke Damper Module can perform multiple tasks by having a single address in intelligent addressable fire alarm systems.
In the event of a fire, in order to analyse the event more clearly, it is possible to view the messages coming to the exchange by transferring them to the computer environment with an interface and software. As can be seen in Figure 5, all information generated in the fire alarm system panel can be transferred to the graphical monitoring and management software via RS232 and RS485 interfaces directly over the cable at close distances, and via communication methods such TCP/IP and GPRS at long distances.
In the Regulation on the Protection of Buildings from Fire it is stated that if smoke control and pressurization systems are installed in a building, the fault and position change signals related to these systems can be managed by fire-alarm systems. The location information of the smoke control and pressurization systems can be monitored and controlled on a second monitor to which the graphic monitoring and management software is connected, as shown in Figure 6.
As a result, in the protection of the air taken in by the ventilation systems in the buildings against the ingress of smoke, flammable gases and steam; duct-type smoke detectors should be used. It should be noted that these detectors can alarm in a possible danger depending on the fire-alarm system. In order to prevent loss of life or property, in line with the cause-effect scenarios, the dampers should be controlled through the modules included in the fire-alarm system.
For more information, go to www.mavili.com.tr/en
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