Closed aperture behavior with AFN

AndyKobe · July 3, 2025, 10:19am

Hi all

I am facing and issue with closed aperture in my model.
I assigned some aperture as “operable” and “non operable” for the closed ones.
But when i monitored the Node volume flow rate, there were values for all the aperture even for the closed one.
I appears that in the idf file, the opening factor for the operable aperture is the value i specified but for the closed aperture it is 1 instead of 0.

You can see below some extract of the idf file

and the operable fraction specified in the model

How can i change the default value for the closed aperture?

Best regards.

Andy

chris · July 8, 2025, 12:36am

Yes. Even closed windows have infiltration through them, which the EnergyPlus AFN accounts for.

To change the infiltration through the closed windows, you can change the flow_coefficient_closed and the flow_exponent_closed on the VentilationOpening object inside of a GHPython component:

github.com

ladybug-tools/honeybee-energy/blob/master/honeybee_energy/ventcool/opening.py#L37-L53


      
          flow_coefficient_closed: A number in kg/s-m, at 1 Pa per meter of crack
              length, used to calculate the mass flow rate when the opening is closed;
              only used in an AirflowNetwork simulation. Some common values for this
              coefficient (from the DesignBuilder Cracks template) include the following:
          
              * 0.00001 - Tight, low-leakage closed external window
              * 0.003 - Very poor, high-leakage closed external window
          
              (Default: 0, indicates the VentilationOpening object will not participate
              in the AirflowNetwork simulation).
          flow_exponent_closed: An optional dimensionless number between 0.5 and
              1 used to calculate the mass flow rate when the opening is closed; required
              to run an AirflowNetwork simulation. This value represents the leak geometry
              impact on airflow, with 0.5 generally corresponding to turbulent orifice flow
              and 1 generally corresponding to laminar flow. (Default: 0.65,
              representative of many cases of wall and window leakage, used when the
              exponent cannot be measured).

AndyKobe · July 8, 2025, 6:58am

Thanks @chris for your answer. The thing is that the air flow rate is higher through the closed aperture than opened one while flow_coefficient_closed is set to 0.0014. The probleme is coming from the default opening factor in the EMS part of the idf file. While all operable aperture have the value i gave to them, non operable aperture have an opening factor of 1. It is that defaut value i want to overide without manualy changing it in the idf file.
Best regards,
Andy

chris · July 8, 2025, 7:51pm

Ah, thank you for brining this up, @AndyKobe .

It looks like I introduced this bug 3 months ago when I was putting together the new honeybee-openstudio Python translators to replace the Ruby ones that we had been using:

The line of code that I added was correct and it was helping work around this fatal error that EnergyPlus throws if you set the SimpleOpening object up to have a zero openable area:

However, I put the line of code in the wrong place such that it was also causing the EMS program to set the window opening to 1 instead of zero (and the EMS program always overwrites whatever is specified on the SimpleOpening object).

I just pushed a change here to put the line of code in the right place:

… and I verified that it writes the correct EMS program for inoperable windows and doors:

You can get the fix on your end now with the LB Versioner and I also just updated the Food4Rhino installer with the fix since it’s a pretty substantial bug that affects any AFN model with inoperable windows.

Thanks again for reporting the issue, @AndyKobe!

AndyKobe · July 8, 2025, 8:52pm

Thanks @chris and all LBT team for your amazing job.
Andy