I’m running into some unexpected behaviour when using AirBoundaries in Honeybee models.
When setting an Air Boundary, Honeybee automatically adds ZoneMixing objects between the connected zones, assuming an air speed of 0.1 m/s.
In my tests with two identical, unconditioned zones and no internal loads, I found that once the wall is set as an AirBoundary, the temperature profiles of the two rooms become somewhat flattened. If I manually remove the ZoneMixing object from the IDF, the temperature profiles start to make more sense, representing an average of the two zones’ conditions before they were connected, and the results also match those of a merged single-zone model. With zone mixing assigned, I would have expected just a faster averaging between the zones, not such a dampening of their peaks.
What seems like an incorrect balancing in the airflows when using ZoneMixing may actually be more of an EnergyPlus issue than a Honeybee one, that’s why I first posted about it here on Unmet Hours.
However, since AirBoundaries are commonly used in Honeybee, and since ZoneMixing is automatically assigned to them, I thought I’d ask here in case others have noticed similar results.
This also reminds me of another issue I looked into a while ago involving CO₂ dilution with ZoneMixing. There too, the exchanged air appeared to distort the mass balance showing strange results in terms of CO₂ concentration. That post is here.
Would love to hear your thoughts.