Wind coefficient problems when changing data for stack ventilation


I think I may have detected a problem.

While working with stack ventilation I’ve noticed that the data in the “opening effectiveness” does not get refreshed in the following runs.

The open effectiveness, as explained in the big ladder manual is related to the wind discharge coefficient, if I’m right.
If no data is input in the wind coefficient the “opening effectiveness” appears as “autocalculated”, if a value is input it is calculated by a formula.

My problem is that if I create an IDF for a wind coefficient of whatever value the open effectiveness appears as a number. In my next run I don’t input any value, so in the idf the open effectiveness should appear as “autocalculated”, but it appears with the same value as the previous run. It only changes if I re-run it for natural ventilation and then again stack ventilation. I tried also changing the name of the run and it didn’t work for me.

Am I doing something wrong or is it an issue?


1 Like

@JuliaT ,
I think I’m going to need a bit more information to understand your question. Are you running a custom wind and stack object or window based natural ventilation? A GH file that recreates your issue would be very helpful.

Hi Chris,

I will upload the GH as soon as I can, it is extremely messy.

I’m trying to model an atrium. I have at the moment 1 zone with the inlet at the GF and the outlet 7 floors above with windows. In the future I was planning to test the linear stratification that you used on your thesis, but I’m not yet at that stage.

At the moment I was testing the impact of the wind coefficient. After running different tests I saw that 0 WC, 1WC or nothing input in the WC were giving me the same values. Checking the big ladder manual I spotted that what that is changing is the opening effectiveness. The problem was that when I change just the WC from one run to the next one this data is not overwritten in the idf, I have to go to no ventilation or to delete the idf and then re-run.

In the image attached you have 2 idf, on the left the idf with WC=0 and on the right with the WC empty. That is what is not changing if I don’t delete the idf

this is the gh file, its still quite messy, but hope you will understand it. I’m using the Porto epw from energy+ web (706.9 KB)

@JuliaT ,

Thanks for letting me know about this. It was a bug left over from a time when I simplified the default window-based natural ventilation so that people didn’t end up with bogus results (I originally underestimated the amount of people anxious to model natural ventilation without changing the inputs to the wind and stack equations :slight_smile: ). I’m glad we have experts like yourself changing the defaults and checking the advanced workflows

The bug has been fixed here:

And in your file here: (711.5 KB)

Thanks again!

Thanks! and happy to help :slight_smile: