I am building a honeybee model of a large open space (a train station). I would like to account for vertical air stratification in my model, but I’ve seen conflicting advice about what is and isn’t best practice, although some posts are quite dated.
Since the release of LBT 1.0 back on 2020, air boundaries have not blocked radiation for EnergyPlus simulations. Sometime a little bit before then, EnergyPlus added a Construction:AirBoundary object that permits that transmission of both shortwave solar and longwave radiant heat transfer. So, for the last 6 years or so, using air boundaries has been a decent way to understand air temperature differences across different parts of a building that are open to one another.
However, a critical consideration for your case here is that EnergyPlus still does not offer any robust solutions for modeling air stratification in an atrium. Granted, the AirflowNetwork models buoyancy driven flows across the network, meaning that the flow of cool outdoor air in the lower floors of a building and then out the top of the upper floors is likely to all be pretty true to the physics of a real building.
However, figuring out a stratification height through the balance of buoyancy-driven and inertial flows is a different type of question, which is at a finer level of detail than what the EnergyPlus Airflow Network is capable of modeling.
The best that E+ currently offers for stratification at the moment are some very simple models that attempt to account for stratification in displacement ventilation systems like RoomAirSettings:ThreeNodeDisplacementVentilation. We have not exposed these in Honeybee so you would need to add them with additional strings or postprocessing of the OpenStudio model. But they aren’t really designed for the case of stratification in an atrium anyway.
So, if you really need to understand where the stratification height is going to be under different conditions in order to design some type of system to automatically maintain a given flow rate in the atrium (like in displacement ventilation), your best bet is going to be to run a series of CFD simulations.
Otherwise, if your not actually designing a ventilation system to hit a certain airflow rate and you just need to understand generally how having an open atrium is going to affect the temperatures of different rooms across a naturally ventilated building, using the E+ AFN should be good enough. If you want to split the atirum into one zone-per-floor connected by air boundaries, this should be fine in terms of the overall functioning of the AFN. Just don’t expect it to compute an accurate stratification height for you in the atrium.
I’m not modelling any HVAC, and there are no adjoining rooms (at least in this early model), it’s just a big naturally ventilated space (around 30 m tall). I really just wanted to see the temperature in the occupied level as bulking the whole temperature together would give me a higher value than reality, and now I’m seeing a temperature difference up to around 4C.
If your main focus is on ventilation system design, especially the airflow velocity, temperature distribution, and vertical temperature stratification at different locations within the station, you should use CFD software such as OpenFOAM as a more suitable tool for this type of analysis.