Under the hood E+ settings for AirBoundary construction

I am using LBT 1.2.0 to model 2 zones that are connected with each other (open boundary), so I am modelling the boundary surface between the zones as an AirBoundary. I need to make sure that both beam and diffuse solar and daylight are transmitted through the Airboundary, that long-wave heat exchange between surfaces occurs through the AirBoundary, and that the air between the 2 zones is mixed. So I am wondering what are the E+ options that are selected by LBT when the surface construction is set to AirBoundary:

  1. Solar and Daylight Method → Is this set to GroupedZones or to InteriorWindow?
  2. Radiant Exchange Method → Is this set to GroupedZones or to IRTSurface?
  3. Air Exchange Method → Is this set to None or to SimpleMixing?
    Also, are there maybe LBT fields where I can set these options?

Hi @IasonBournas ,

Yes, they are both set to GroupedZones. Also, EnergyPlus got rid of the other options in E+ 9.6 (LBT 1.4) such that GroupedZones is now the only option. So you’ll always get complete radiant and solar heat exchange across the AirBoundary.

For air mixing, we took a different approach since the option available on the EnergyPlus Construction:AirBoundary is too simple for most cases. So we always set the Construction:AirBoundary Air Exchange Method to None and then we use ZoneMixing objects to set up the cross-mixing between the rooms that have the air boundary adjacency. By default, we mix the air at a rate of 0.1 m3/s per square meter of AirBoundary surface area. So larger air boundary surfaces will get higher air flow rates as you expect. It’s possible to change this by creating your own custom AirBoundaryConstruction with the honeybee-energy SDK. I should also clarify that all of these simple assumptions about air flow are ignored when you set up your Model to run using the AirFlowNetwork with the HB Airflow Newtwork component. In this case, we don’t write any ZoneMixing objects and we account for the AirBoundary surface in the AFN by using an AirflowNetwork:MultiZone:Surface. And we just use a very large crack factor that is correlated to the the AirBoundary surface area (I believe this is derived from Bernoulli’s equation but you can check the honeybee-energy source code).

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Thanks for the very informative answer @chris ! Looks like Honeybee is super capable of modelling these conditions. Much appreciated!

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