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-   -   Car park ventilation and impulse fans (http://www.cfd-online.com/Forums/phoenics/52263-car-park-ventilation-impulse-fans.html)

guillaume May 11, 2008 20:00

Car park ventilation and impulse fans
 
Hi

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?

Peter March 5, 2009 16:45

Re: Car park ventilation and impulse fans
 
I think it is possible using fans to make the situation worse when it introduces recirculation zones. At the same time I think fans in general are very useful to avoid recirculation and therefore enhance ventilation. You can think of an almost closed zone in a car park where without the use of fans large recirculation will occur. Also it helps to guide the air in proper directions (when properly used).

Koolifant March 16, 2009 07:46

Quote:

Originally Posted by guillaume
;161425
Impulse fan manufacturers claims that the instalation of impulse fans reduces dramaticaly the flow rates of exhaust and supply fans of the car park.

I wouldn't think so. The exhaust fan has to match the flow of the impuls fans otherwise indeed backflow occurs. I think the main use is to give the air extra momentum. But i think backflow can mostly not completely be avoided because the fans create an low- and highpressure area and the air at the outlet would alway more or less be drawn back to the low pressure area. But perhaps with exhaust fans with enough capacity this effect will be minimal. I've done too few impulsfan studies to be sure.

MarekM July 2, 2009 03:42

Car fire modelling based on various carfire courves and principles
 
I made hundreds of jetfan projects and CFDs.
My conclusions are:
1. Jetfans are suitable when day-to-day ventilation is required. Also jetfan smoke control system is very smart system when there is no sprinklers requirement and if you need reversible smoke control system to help fire fighters to enter the garage, locate and put-out fire.
Jetfans smoke extract/control system can not be design if people evacuation is a principle. If you design smoke control system you need huge air volume extract and supply. More important is to have huge extract and air supply then how much jetfans you have. You can play with jetfan thrust and quantity but you can not oversize this because you speed up to much air and smoke extract shafts will not be be able to suck this air volume. Be sure of that. Smoke will flow backward and all carpark will be filled with smoke. If smoke is spreading in all region of carpark please try to increase extract volume and supply, first. If does not help, please try to split carpark in more virtual zones or fire compartments with fire gates or add extra smoke extract shafts. Increasing quantity of jetfan will not help.
2. I hesiate to use fire curve proposed by TNO when I check if people can evacuate. When I use fire curve from TNO (1999y) for 1 car, and I use smoke potential 400m2/kg, I see that smoke dencity is growing too fast and visibity (SLR= sight reflecting length) in 120sec is lower then 10m. It means that people can not evacuate even in 120 sec. This dense smoke appeares before people are able to react for comments released by voice speaker system and before smoke extract system is able to start extracting smoke, even. So this hard to design good system to extract air from carpark because smoke density is growing faster then fresh air is able to dillute smoke in first stage of fire (till 5 minute).
My conclusion was that smoke potential shuold be between 100 and 200 m2/kg which values are mentioned for car fires till 5th minute (mentioned in figures from tests in TNO raport). After 5th minute smoke potential grows from value=100-200m2/kg till value of 300-600m2/kg in 5-20 minute in TNO tests.
Smoke potential 400m2/kg must be considered when car is full in fire after 10 minute. When fire grows much slower than "design fire" the smoke productions is much more relalistic in the begining (till 5 minute) in my CFDs.
I made a lot of modelling based on car fire curve from TNO and f.e. in 90 sec from start smoke extract is not working yet but people already can not evacuate because of smoke and SLR is less then 10m, friendly speeking. This is horrible.
I made a lot of modelling also based on other courves. This gives me realistic smoke density and visibility and poeple are able to evacuate till 3 -4 minute. I used also model of smoke potential= 200m2/kg. I used TNO carfire courve and 400m2/kg when smoke control system for fire fighters is required and I check conditions in 15-16 minute after break-out the fire.
Did you hear about other car fire curves?
3. When I do "nothing" with smoke extract (f.e. minimum smoke extract = 1 or 2 ACH) I have better visibility condition in carpark for people for evacuation, in most "evacuation worst case scenarios". I now really belive that for evacuation we shouldn't design smoke extract system at all, or we should shut down this systems if applied and restart again after people has evacuate. System shall clean carpark from smoke and high temperature for firefighters.
4. I am focused on evacuation organization (max route distance shall be 40m and I require more exit doors than it is mentioned in local building regulations).
What dou you think?

Koolifant July 2, 2009 04:35

Good story, Marek

Quote:

Originally Posted by MarekM (Post 221166)
I am really belive that for evacuation we shouldn't design smoke extract system at all, or we should shut down this systems of applied and start again after people has evacuate.

A Dutch guideline indeed states that the ventilation system should be turned off upon fire detection swiched on again after 3 minutes. An other (newer but not yet approved) guideline states that only trustventilaton should temporarily be turned off but exhausts be turned on upon detection. I think turning of trust ventilation is definetely a good thing but turning on the exaust might be less of a problem as long as flow speeds are not too high. You agree?

MarekM July 2, 2009 05:30

reply for: I think turning of trust ventilation is definetely a good thing but turning on the exaust might be less of a problem as long as flow speeds are not too high.

Hi, I am happy about your oppinion. I agree entirely. Moreover, I check the effect that when I turn on extract shafts automatically by the smoke detections sytem, The Available Evacutaion Time was decreased drammatically fast in regions between fire and extract shafts. So I proved with CFDs, also, that poeple were surrounded by smoke and were no be able to escape. And it does not care if you apply thrust ventilation or ductwork system or piston ventilation or slowly growing fires or fast growing. So best way is to wait with starting extract shafts till min. 5 or 6 minute acc. to evacuation organization and garage layout.

Abbas September 13, 2009 02:00

Quote:

Originally Posted by MarekM (Post 221166)
I made hundreds of jetfan projects and CFDs.
My conclusions are:
1. Jetfans are suitable when day-to-day ventilation is required. Also jetfan smoke control system is very smart system when there is no sprinklers requirement and if you need reversible smoke control system to help fire fighters to enter the garage, locate and put-out fire.
Jetfans smoke extract/control system can not be design if people evacuation is a principle. If you design smoke control system you need huge air volume extract and supply. More important is to have huge extract and air supply then how much jetfans you have. You can play with jetfan thrust and quantity but you can not oversize this because you speed up to much air and smoke extract shafts will not be be able to suck this air volume. Be sure of that. Smoke will flow backward and all carpark will be filled with smoke. If smoke is spreading in all region of carpark please try to increase extract volume and supply, first. If does not help, please try to split carpark in more virtual zones or fire compartments with fire gates or add extra smoke extract shafts. Increasing quantity of jetfan will not help.
2. I hesiate to use fire curve proposed by TNO when I check if people can evacuate. When I use fire curve from TNO (1999y) for 1 car, and I use smoke potential 400m2/kg, I see that smoke dencity is growing too fast and visibity (SLR= sight reflecting length) in 120sec is lower then 10m. It means that people can not evacuate even in 120 sec. This dense smoke appeares before people are able to react for comments released by voice speaker system and before smoke extract system is able to start extracting smoke, even. So this hard to design good system to extract air from carpark because smoke density is growing faster then fresh air is able to dillute smoke in first stage of fire (till 5 minute).
My conclusion was that smoke potential shuold be between 100 and 200 m2/kg which values are mentioned for car fires till 5th minute (mentioned in figures from tests in TNO raport). After 5th minute smoke potential grows from value=100-200m2/kg till value of 300-600m2/kg in 5-20 minute in TNO tests.
Smoke potential 400m2/kg must be considered when car is full in fire after 10 minute. When fire grows much slower than "design fire" the smoke productions is much more relalistic in the begining (till 5 minute) in my CFDs.
I made a lot of modelling based on car fire curve from TNO and f.e. in 90 sec from start smoke extract is not working yet but people already can not evacuate because of smoke and SLR is less then 10m, friendly speeking. This is horrible.
I made a lot of modelling also based on other courves. This gives me realistic smoke density and visibility and poeple are able to evacuate till 3 -4 minute. I used also model of smoke potential= 200m2/kg. I used TNO carfire courve and 400m2/kg when smoke control system for fire fighters is required and I check conditions in 15-16 minute after break-out the fire.
Did you hear about other car fire curves?
3. When I do "nothing" with smoke extract (f.e. minimum smoke extract = 1 or 2 ACH) I have better visibility condition in carpark for people for evacuation, in most "evacuation worst case scenarios". I now really belive that for evacuation we shouldn't design smoke extract system at all, or we should shut down this systems if applied and restart again after people has evacuate. System shall clean carpark from smoke and high temperature for firefighters.
4. I am focused on evacuation organization (max route distance shall be 40m and I require more exit doors than it is mentioned in local building regulations).
What dou you think?

Hi

I am working on jet fan simulation by Gambit & Fluent software,according to your experience, can you help me about these questions:

1-what is the equation for jet fan in the fluent?
2-In the Gambit ,which of the subtract or split commond should be used in combing jetfan in parking?

this is my email:khani1349@yahoo.com

thanks

2- In the

Koolifant September 14, 2009 03:47

Quote:

Originally Posted by Abbas (Post 229347)
Hi

I am working on jet fan simulation by Gambit & Fluent software,

Hum I think you're on the wrong forum, Abbas.. this is the Phoenics forum

ilyas_mufeen03 February 8, 2013 02:29

Reg co simulation
 
Quote:

Originally Posted by MarekM (Post 221166)
I made hundreds of jetfan projects and CFDs.
My conclusions are:
1. Jetfans are suitable when day-to-day ventilation is required. Also jetfan smoke control system is very smart system when there is no sprinklers requirement and if you need reversible smoke control system to help fire fighters to enter the garage, locate and put-out fire.
Jetfans smoke extract/control system can not be design if people evacuation is a principle. If you design smoke control system you need huge air volume extract and supply. More important is to have huge extract and air supply then how much jetfans you have. You can play with jetfan thrust and quantity but you can not oversize this because you speed up to much air and smoke extract shafts will not be be able to suck this air volume. Be sure of that. Smoke will flow backward and all carpark will be filled with smoke. If smoke is spreading in all region of carpark please try to increase extract volume and supply, first. If does not help, please try to split carpark in more virtual zones or fire compartments with fire gates or add extra smoke extract shafts. Increasing quantity of jetfan will not help.
2. I hesiate to use fire curve proposed by TNO when I check if people can evacuate. When I use fire curve from TNO (1999y) for 1 car, and I use smoke potential 400m2/kg, I see that smoke dencity is growing too fast and visibity (SLR= sight reflecting length) in 120sec is lower then 10m. It means that people can not evacuate even in 120 sec. This dense smoke appeares before people are able to react for comments released by voice speaker system and before smoke extract system is able to start extracting smoke, even. So this hard to design good system to extract air from carpark because smoke density is growing faster then fresh air is able to dillute smoke in first stage of fire (till 5 minute).
My conclusion was that smoke potential shuold be between 100 and 200 m2/kg which values are mentioned for car fires till 5th minute (mentioned in figures from tests in TNO raport). After 5th minute smoke potential grows from value=100-200m2/kg till value of 300-600m2/kg in 5-20 minute in TNO tests.
Smoke potential 400m2/kg must be considered when car is full in fire after 10 minute. When fire grows much slower than "design fire" the smoke productions is much more relalistic in the begining (till 5 minute) in my CFDs.
I made a lot of modelling based on car fire curve from TNO and f.e. in 90 sec from start smoke extract is not working yet but people already can not evacuate because of smoke and SLR is less then 10m, friendly speeking. This is horrible.
I made a lot of modelling also based on other courves. This gives me realistic smoke density and visibility and poeple are able to evacuate till 3 -4 minute. I used also model of smoke potential= 200m2/kg. I used TNO carfire courve and 400m2/kg when smoke control system for fire fighters is required and I check conditions in 15-16 minute after break-out the fire.
Did you hear about other car fire curves?
3. When I do "nothing" with smoke extract (f.e. minimum smoke extract = 1 or 2 ACH) I have better visibility condition in carpark for people for evacuation, in most "evacuation worst case scenarios". I now really belive that for evacuation we shouldn't design smoke extract system at all, or we should shut down this systems if applied and restart again after people has evacuate. System shall clean carpark from smoke and high temperature for firefighters.
4. I am focused on evacuation organization (max route distance shall be 40m and I require more exit doors than it is mentioned in local building regulations).
What dou you think?

Hi,

If possible can you guide me how to do CO simulation of car park in PHOENICS

prom October 27, 2015 06:57

Hi,

Is it required to model columns and place cars in parking lot for simulation?


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