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How to enable air stratification in EnergyPlus?

asked 2021-03-15 23:55:53 -0600

Wolfgang Kaiser gravatar image

updated 2021-03-16 09:05:50 -0600

Hello, does anyone know how we can enable air stratification in EnergyPlus?

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answered 2021-03-16 05:58:36 -0600

... this may only be a partial answer - others might have additional or better suggestions.

It depends on what you're after. If you're interested in modelling stack effects in tall buildings in cold climates (for instance), then EnergyPlus' Airflow Network (AFN) Model is well suited. Note that the AFN doesn't generate stratified air layers within zones (only between zones). If instead you're interested in buoyancy effects linked to displacement ventilation, then EnergyPlus' in-house 3-node solution is pretty handy. There's a nice explanation here. More complex cases will push you towards CFD-coupled solutions, such as described here.

If you search for "CFD", "displacement", etc. using UnmetHours' search bar, you'll find plenty of past discussions on the topic.

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@Denis Bourgeois, Thank you so much Denis! So I have two scenarios. One is a double facade that uses glass. I guess the 3 node thing works in this case. But how about those with something like chimneys that cause natural ventilation in the building? Should we use airflow for that?

Wolfgang Kaiser gravatar image Wolfgang Kaiser  ( 2021-03-16 13:59:32 -0600 )edit
Wolfgang Kaiser gravatar image Wolfgang Kaiser  ( 2021-03-16 14:01:42 -0600 )edit

Both cases you describe are particularly challenging to model/simulate, and I would say neither are well suited for EnergyPlus' displacement ventilation models (i.e. outside their scope). I suggest you consult section 7.8.10 Solving for Gap Airflow and Temperature in the Engineering Reference, which may be useful for your first scenario. You may want to consult the literature on these (an example).

Denis Bourgeois gravatar image Denis Bourgeois  ( 2021-03-16 14:46:26 -0600 )edit

For your second scenario, although it is possible to approximate your case using the AFN, uncertainty in opening discharge coefficients and static pressure distribution is significant. You're probably better off with CFD-based solutions (e.g., wind-driven static pressure distribution, coupled CFD/E+ for indoor buoyancy effects). I guess my point is that E+ does offer you options, but a fair amount of expertise is required to harness them to generate meaningful results. Best of luck.

Denis Bourgeois gravatar image Denis Bourgeois  ( 2021-03-16 14:54:41 -0600 )edit

@Denis Bourgeois Thank you so much for the detailed information

Wolfgang Kaiser gravatar image Wolfgang Kaiser  ( 2021-03-16 15:33:45 -0600 )edit

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Asked: 2021-03-15 23:55:53 -0600

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Last updated: Mar 16 '21