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Designing a smoke evacuation system by a jet fan
A jet fan is a fan of fresh air injected into the parking lot completely to all points of the parking lot and provides a harmonic current to eventually pollute the carbon monoxide by smoke evacuating fans called Drainage fans are called to be driven out of the parking lot and evacuated.
In order to obtain accurate results in designing a smoke evacuation system by a jet-fan, it is necessary to carefully check the parking conditions. The use of CFD analysis can be used to validate design results. Sometimes it’s necessary to remove a number of fans from the circuit or add another group to the circuit, depending on the situation. In some cases, it is also necessary to change the orientation of the fans. For each parking lot, a drainage system can be designed according to its conditions. Before designing the system, the design of the system requires identification.
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Exploring Parking Geometry: Given the parking geometry, it is important to identify the entry points of fresh air and air discharge points in such a way that the airway is in harmony with the natural airway and the air travels effectively along the parking lot to the exit point Be guided. The features of a design in its effectiveness will be very important. Note:
For system with linear flow, it is better to enter the fresh air and air intake points in the garage.
Fresh air inlets should include access ramps.
The design of the drainage system should not conflict with the flow of natural air.
Number of Jet Fans: To obtain the number of jet fans, at least 5 Newtons of Trust should be considered in the normal condition for every 100 square meters of parking space. Note that using a smaller jet fan with a higher truster will be less costly than using a larger jet fan with a thrust. Although for parking lots with unusual shape and geometry, it is necessary to select more fans with the same thrust.
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Features of the ceiling: For more efficiency, the system must fit the jets of the fans to the roof rails. If it is not possible to put the jets in the direction of the beams (perpendicular to the beams), their impact will be less and we will probably need more fans.
It should be noted that fan jets must be installed at an elevation that has enough vertical space to the floor of the parking lot and has the maximum flexibility in design. Placing jet fans between the roof rails can minimize the height of the system.
If there is a need to install a jet fan in front of the beams or any other obstacle, the jets must be fitted in a sufficient distance. Normally the gap is equal to 8 times the height of the obstacle. The presence of nozzles and the downward angle of the jet outlet of the fans is designed for this purpose. The position of the jet fans relative to the mechanical equipment and other components such as sprinkler, pipes, panels and … should be such that the equipment is outside the scope of the pattern Fan outlet jets. An example of this is shown in the figure below.
Fans Distance: Fans should be installed at a maximum distance of one second, so that the air speed of a jet fan does not exceed 0.2 m / s when entering the next jet fan. Also, the appropriate distance is considered to be that the air velocity of most air conditioners is greater than 1 m / s. By numerical analysis, it can be ensured that this is achieved. In some parking lots with ideal design conditions, maximum distances can be considered.
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Parking air evacuation systems can work with two different philosophies during and after the fire:
After the fire is completely extinguished by the firefighter, the air drain system will start and, according to the agreed standard, will smoke out of the environment and prepare it for use as soon as possible. In this capability, at the time of fire and diagnosis The flame in the parking space is switched off by the sensors of the whole system and preventing the mixing of smoke in the vicinity of the ceiling with other air layers. Damper parking lots are open or closed according to the dictation policy of the fire department. The possibility of commissioning and using the jet-fans of the system is provided manually for firefighters so that the firefighter can, if necessary, according to his wishes Use the appliance.
The Smoke clearance feature does not require any additional equipment than the devices used for evacuation of contaminated air caused by the traffic of cars, so it is recommended to use this feature in parking spaces of non-utilized buildings where economic discussion is more important.
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In this feature, during the fire and detection of flames in the parking area by sensors, the entire system is shut off for 3 to 5 minutes, so that hot smoke is near the ceiling and prevents people from leaving the parking lot. After this time, all system devices will work at their maximum power. The system planning will be such that the parking environment is separated into different zones and the system operates so that only one polluted zone will smoke and other zones remain clean. This feature may begin at the incident before the firefighter arrives, but can be manually controlled at the time of fire.
Given that the Smoke Control capability requires additional equipment than the equipment used for evacuation of contaminated air caused by the car traffic, and it will be economically more expensive for the employer, so it will only be used in parking lots of special buildings such as the Treasury of the Bank Museums and important political buildings and high towers are proposed