Exterior opening (what is the right way of modelling)

[Edin Mer]

Hello!
Can somebody tell me if the exterior opening of aluminium frame (transom) should be modelled as "Frame cavity slightly ventilated NFRC 100" or just left empty and then apply "NFRC 100-2010 Exterior" boundary condition? 

See attached screenshot. I am asking this because it is a pretty big area.

Thanks,

Edin

[Robin Mitchell]

Edin

 

See page Section 6.3.7, page 6-13 of the THERM/WINDOW NFRC Simulation Manual for guidance on modeling slightly ventilated cavities.

 

http://windows.lbl.gov/software/NFRC/SimMan/NFRCSim6.3-2013-07-Manual.pdf

 

***

Robin Mitchell

Building Technology and Energy Systems

Lawrence Berkeley National Laboratory

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[Edin Mer]

Thanks for your answer, Robin.

But "Slightly ventilated exterior cavities" are only for cavities between 2 and 10mm. In my case the size is 21mm (see attached picture). 

In Figure 6-11 (Ch. 6.3.7) it is written "For cavities > 10mm, do not model a frame cavity". 

So I guess I shouldn't model it (as in attached picture) - just apply Exterior boundary condition. 

Am I correct?

[Jose Li]

literally, this cavity is not "slightly ventilated cavity".

But normally there are gaskets in this 21mm area for water-proof  or better insulation.

[D. Charlie Curcija/LBNL]

This is correct. However, when gasket is present it needs to be modeled. If indeed there is opening greater than 10 mm, it is trrated not as cavity but as exterior BC (i.e., boundary goes inside the cavity).