Open Brep after windows

Hello everyone,

I am trying to simulate indoor microclimate to assess nat ventilation effectivity on open office spaces scattered around various levels of a 3 story atrium. It is quite a complex zone, but I´m interested in taking into account the air movement all around. I manage to produce a closed brep for the atrium, but as soon as I add any window, the result is an open Brep. I have rebuilt the zone several times without success. I would greatly appreciate any help!.

Best Arturo (601.3 KB)


Your geometry is mostly not gonna run correctly in EnergyPlus for “Natural Ventilation”.
Modeling rule No.1 in EnergyPlus: do not model concave zones.

I think in your case, you might need to run real CFD.
EnergyPlus is just not built for this task.

Hi @MingboPeng
I ended up dividing the zone in 3, and connected them trough air walls. Seems to have run without errors. Should I not trust the simulation?.

Hi @LUISARTUROREYESVALEN, energyPlus can give you air flow rate from the openings in the ballpark, which I think that’d be good enough for your comfort study.
Unless you are designing the spaces based on the air flow rate, then you will need a CFD study. If you are evaluating operative temperature, you should be fine.

I think this might not be it @LUISARTUROREYESVALEN. HoneyBee’s first back-end is OpenStudio. OpenStudio airwalls are a construct built for Radiance simulations, and do not have to do anything with air transfer at all.

Following @MingboPeng post, EnergyPlus Modeling rule No.2 is “the air within a zone is well-stirred”. Take a look at the exact situation you are trying to model in the Engineering reference. If you want to account for air moving, I will say you should look into CFD.

Sorry to say, but this is not necessarily true. Air walls can be used definitely in energy simulations. Done it myself quite a few times.
Saying the OpenStudio provides constructions for Radiance is also not completely true. OS is a sophisticated interface for Energy+, hence for energy simulations.

@AbrahamYezioro Hmm, really? Here is the previous code in the OpenStudio’s EnergyPlus Forward Translator that processes the AirWallMaterial objects. As you can see, it only replaces it for a gyp board.

In fact, work has been done in 2.9.0 to create a more complex object ConstructionAirBoundary to represent air surfaces with some pre-selected air exchange (but still not free-flowing “natural” airflow) but has not been fully implemented yet. Feel free to elaborate.

I’m not aware of the developments of OS2.9.
@chris can provide a better explanation of the use of air walls in energy simulations. Still i used them for internal comfort studies, mainly based on some hydra examples (Ex1, Ex2). I remember vaguely @chris’s explanations about the convenience of using air walls for those purposes (until the air netflow will be implemented). BTW, his thesis uses extensively Air Walls (can’t find right now the link to it, but you can look for it).
Also used them for such cases of thermal zones which have more than 1 orientation and is probable that the other ones can affect the simulated performance. Like dividing this zone in smaller zones while the separation between them is an Air Wall.
You can also check the explanations of them at the I/O manual.

Interesting thread, though.

Follow up development. Someone on UnmetHours has posted a question about this topic and went into details about the developments of EnergyPlus 9.2.

Maybe is worth to try to convert a file with air wall material to 9.2 to see how it looks like in this version … This instead of trying to understand this from scratch.