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guillaume May 11, 2008 19:58

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?

jdc May 12, 2008 19:31

Re: Car park ventilation and impulse fans

So far, our modelling have shown similar conclusions to the ones you mention:

1) Impulse fans help with local stagnation area; 2) Impulse fans help natural ventilation; 3) For mechanically ventilated car park, we have not found a consistent way to position the impulse fans that clearly demonstrate an improvement in CO concentration (and potentially reduce ventilation flow rates).

My understanding is that the impulse fans should work by improving the mixing, i.e. smoothing inhomogeneities in CO. We were not able to get this behavior in the models.

How are you modelling the fans and what kind of throw pattern do you get?

guillaume May 12, 2008 20:31

Re: Car park ventilation and impulse fans
Hi I am modelling the fans as a velocity inlet with a 20 deg downward. I didn't take into account the small angle sidewards due to the centrifugal fan, that's negligeable. The throw pattern look perfectly normal, if you send me your email, I'll send you a picture.

jdc May 13, 2008 00:23

Re: Car park ventilation and impulse fans
Hi Guillaume,

I received the pictures and specifications. I noticed that you are modelling the fan using a forced outlet bc (at the bottom of the fan) and a inlet. Do you couple the CO between the two conditions?

The throw pattern of the fan looks good. I had a specification sheet for the fantech CPC-100N model that indicates a throw length of approximately 90m.

As I explained earlier I have had difficulties finding the right pattern to ensure that the fan arrays works efficiently. But believing the hype and the fact that these are installed in Europe (haven't had any occasion to check them in operation) they should work.

Regards Julien

guillaume May 13, 2008 00:43

Re: Car park ventilation and impulse fans
Hi julien

Yes the CO concentration of the air flow that exits the domain through the fan outlet comes back in through the inlet. A throw of 90m probably correponds to a throw without any obstacle (No cars). I doubt you get that throw in a full car park...

jdc May 13, 2008 01:02

Re: Car park ventilation and impulse fans

I was wondering about the impact of these fans on pedestrian comfort.

guillaume May 13, 2008 01:22

Re: Car park ventilation and impulse fans
Not comparable to a standard system with a average air velocity below 0.5m/sec...

guillaume May 13, 2008 01:24

Re: Car park ventilation and impulse fans
The other thing is that there is no variable speed drive on those fans, so it bumps up your energy consumption compared to a standard central exhaust and fresh air intake.

andy2O May 13, 2008 04:15

Re: Car park ventilation and impulse fans

I'm just about to update a fan model which uses an inlet and an outlet to model a fan (but not for a car park!). I need to make the inlet concentration depend on the outlet concentration. So I am pleased to hear that you have already got this working in CFX.

Did you just use CEL expressions to work out the mass flow of CO at the outlet, and manipulate this in CEL to specify the inlet concentration? Or did you need to use Fortran? Was it straightforward? Or were there any tricks you had to use?

If you feel able to provide any brief pointers about this I would be very grateful. Even just to know whether it was easy or hard for you would help remove a little uncertainty from my work plan....

Oh, and good luck with your own study too!

Best regards, andy

andy2O May 13, 2008 04:24

Re: Car park ventilation and impulse fans
PS: I saw you post in the CFX forum about this topic, and I summized that you are using CFX for this model. If not, then please ignore my post, and apologies for the noise on this list!


guillaume May 13, 2008 18:51

Re: Car park ventilation and impulse fans
Sorry Andy I did that on Star CCM+, It's very straight forward: you define a report that reads the mass flow averaged CO concentration, then you create a field function that is equal to that report and you define the CO concentration at the inlet as equal to the field function.

I used CFX only for two months, I can't remenber if you can do it in the same way in CFX.

Nissim Nissimoff June 13, 2008 16:54

Re: Car park ventilation and impulse fans
Does anyone whether there are Japanese manufacturers of impulse and induction fans and who are they?

Is there software for designing impulse and induction ventilation in car parks.


Nissim Nissimoff

trulytrue June 27, 2011 11:16

Dear ALL.
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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