Car park ventilation and impulse fans
I'd like to get the opinion of car park designers on the following point:
Impulse fan manufacturers claims that the instalation of impulse fans reduces dramaticaly the flow rates of exhaust and supply fans of the car park.
My model consistently showed that the tunnel analogy doesn't work in a car park and the CO concentration is very much set by the average air velocity throughout the carpark created by the exhaust/supply velocity in a car park of rectangular shapes with exhaust on one side and supply on the opposite side. The higher velocities created in the fan areas are only mixing the pollution, create recirculation zones, and destroy the vertical stratification of CO concentration.
In my opinion, impulse fans are only usefull for smoke dilution in the case of a rectangular car park. They can help with CO only when there are stagnation areas in car park with a complex shape (by bringing some fresher air in the stagnation area) or when the sides of the carpark are open and thus the impulse fans set the average velocity of the air through the car park (tunnel analogy is valid in this case).
Anybody to agree or disagree?
Re: Car park ventilation and impulse fans
A well designed Jet thrust system will ventilate an are in both pollution and smoke modes. You are correct in the fact that the air change rate within the are is achieved with the main extract fans and this will not change from a ducted system, however where a ducted system has both high and low level grilles placed evenly around the car park, the jet thrust system uses impulse fans to distribute the air.
The advantages of a Jet thrust system is that the main extract fans have far less resistance to overcome due to not having associated duct work, and therefore have smaller motors, have to do less work and in turn consume less power, the volume flow rate remains the same.
Jet fans also have the advantage of being directional. this allows individual areas, also known as zones, to be defined, allowing selective oporation of jet fans in polluted areas. This methodology also translates into an emergency scenario where fans can be run strategicaly depending on the location of the fire, allowing the smoke to be directed to the closest extract point within the car park, helping tto keep the rest of the area free of smoke to allow fire fighters to tackle the fire safely.
I want to simulate in fluent Combustion of polyurethane with power of combustion of 4 MW. the area of the source of combustion is 2mX5m.
The time of combustion is 20 min. The use of this simulation is for carpark ventilation system.
It will be fine if some can help me to estimate the visibility as well.
THank you .
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