Flow imbalance remain after balance the airflows

felipeduran · Posts: 26

Dear All,
I have a problem with the cfd boundary conditions. Firstly I e import the from the E+ simulation and it give a message that the flow is not balance -1.3 l/s (6351,621 and 6350,251) difference. Ive selected an opening and I have corrected the problem.

But, when I open the CFD module, and press the "update calculated data" it shows me the grid statistics telling me that there is a flow imbalance, inflow=7.574 m3/s, Outflow = 7.583 m3/s and I can not conduct the CFD analysis.

¿How can I fix the problem?

I am using the last DesignBuilder version (300092).

Felipe Duran

Steve Potter · Posts: 572 Location: newcastle

Hi Felipe,

Could you upload your model (without results) to the forum so that we can try to identify what is causing the problem? Perhaps you could also let us know the period for which you are importing E+ results.

Regards,

Steve

felipeduran · Posts: 26

Hi Steve,

Thank you very much for your reply. I am attaching you the model.
I am trying to conduct a CFD analysis for the 23 of june at 11:00. The airflow numbers are different than the ones I gave you on my previous email. That model it´s corrupted but I have the same problem with this model.

Kind Regards,

Felipe

Steve Potter · Posts: 572 Location: newcastle

Hi Felipe,

We have found out what was causing the flow imbalance with your model. A tolerance within the software was preventing the very narrow vents that you have defined from being transferred to the CFD grid. We have modified this process to prevent this from happening in the future. The modification/fix will be available in the next update of the software (3.0.0.096) which you should be able to obtain within the next few days.

I should advise you that you will need to make sure that the grid merge tolerance that you use when creating the CFD project should be less than the minimum vent dimension - the minimum vent dimension is 0.05m so a merge tolerance of 0.03m should be fine.

I hope this problem hasn't caused you too much inconvenience.

Regards,

Steve

felipeduran · Posts: 26

Hi Steve,

Thank you very much for your reply. I will wait for the 3.0.0.096 release.
What is the minimum vent dimension that can be use with the current release?

Kind Regards,

Felipe

Steve Potter · Posts: 572 Location: newcastle

There is no actual limit on the minimum dimension that can be specified for an opening (vent) but in practice it will be limited by the resulting grid cell maximum aspect ratio. Consequently, for smaller opening dimensions, you may need to increase the grid resolution (decrease default grid spacing) in order to arrive at a reasonable maximum cell aspect ratio.

The important point to bear in mind is that the grid line merge tolerance must be less than the minimum opening dimension used.

Regards,

Steve

felipeduran · Posts: 26

Hi Steve,

I have downloaded the 3.0.0.096 version and the problem about air flow imbalance was solved.

The problem is when the CFD is initialising boundary conditions it gives me the following message:

"-2147417848, Automation error
The object invoked was disconnected from its clients. , Design Builder"

Do you know what does it means and how to solve it?

Many Thanks,

Felipe

Steve Potter · Posts: 572 Location: newcastle

Hi Felipe,

Apologies for this. We discovered that your model was still causing a problem with the boundary condition routine. We have fixed this and the fix will be incorporated in the next available update of DB (3.0.0.097) which should be available later today.

Regards,

Steve

felipeduran · Posts: 26

Thank you very much Steve, now its working fine

thibautvitte · Posts: 3

Dear all,

I have the exact same problem, and am using 3.0.0.097 version.
The difference is big, (49 968 in / 33 984 out), but my boundary limits are OK. I've tried many grids configurations, but these figures do not change.

Thx in advance.

Steve Potter · Posts: 572 Location: newcastle

Please upload your model to the forum so that we can try to figure out what is going wrong with it. If you first save the model without results and also, if you are importing boundary conditions from an E+ simulation, let us know the hour selected for the import.

Regards,

Steve

thibautvitte · Posts: 3

Dear Steve,

Please see enclosed my model. Boundary conditions are not to be imported from E+ simulation. Please note that we made a different simulation with all extractions replaced by one big extraction, and we still have the same problem.

Regards,

Steve Potter · Posts: 572 Location: newcastle

Hi,

We have now fixed this problem and the fix will be available in the next release version (following version 3.0.0.097) which should be available later this week.

Regards,

Steve

thibautvitte · Posts: 3

Thanks a lot.

Regards.

Thibaut

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