What is the best practice to model an Atrium in EnergyPlus?

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Unfortunately, no current whole-year, whole-building simulation program is able to adequately describe what happens in an atrium. Stacking zones on top of each other will account for some of the effects and create some sort of gradient, but not the right one. In reality, the air is mixed by a large number of vertical mass flows, above each heat source (including patches of sunlight), at each wall surface, by mechanical ventilation jets etc.

Although a CFD model theoretically can describe the air flows involved, it would have to be dynamically fed with boundary conditions from some other tool first, making the study of the truly dynamical situation of an atrium extremely difficult and in every respect time consuming. This is just not practical in every-day design work.

We simply need a new type of zone model in order to describe atria.

I suggest that you split the geometry horizontally by floor, or perhaps in finer granularity, and consider using the ZoneCrossMixing object to capture the stack effect. There is a "Delta Temperature" option that is applicable in this case.

http://bigladdersoftware.com/epx/docs...

1. Just leave it a single zone. It depends how carefully you want model solar and daylighting in the atrium and any spaces with interior windows that open on to it. For example, if you want to model solar distribution on the floor of the atrium, then the IR transparent material is not helpful and should be avoided. I would avoid the approach of splitting the atrium up into horizontal zones. By leaving the zone wide open you can better model daylighting control sensors at the occupant level in the usual way. The solar distribution model will be much more accurate with solar energy penetrating deep into the atrium as it should rather than being stopped in an upper sub-zone. This is because Material:InfraredTranparent does not transmit solar into the zone below it.

2. I wouldn't recommend air walls for horizontal sub-zones but they may be desirable for connecting to adjacent zones when there are open spaces spreading away from the atrium. Use a single, large high-transmission interior window filling the opening between the zones. Only the window model can move solar and daylight from one zone to another. And also mix air between the zones using AirflowNetwork or more simply at some assumed air change rate using ZoneMixing objects.

3. The AirflowNetwork will be simpler with a single zone and can focus on the connections with the outside and adjacent zones.

If you expect a significant temperature gradient in the atrium, then prescribe it using RoomAir:TemperaturePattern:NondimensionalHeight, or similar. This is also how one could make use of results from a CFD model of the atrium, if you have one. As other answers have said, what is missing here is a decent/fast general model that can predict the temperature variations as the simulation runs. But if you are willing to make broad assumptions, in advance, about the resulting temperature variations inside a zone, the implications can be modeled. Obviously this screams out for an approach that brackets the problem by running several models with a range of temperature gradients and return air temperature offsets.

There are a few relevant example files of methods packaged with v8.1. I am using one called AirflowNetwork_Multizone_HorizontalOpening.idf. I am currently applying this example on a project where I have stack flow through a 2 story atrium space. I have a lower level and upper level opening which I am modeling for natrual vent. Seems to be working out well.

Also, for anyone who doesn't know about the E+ sample files, check out the install directory \EnergyPlusV8-1-0\ExampleFiles\ . Also, there is a spreadsheet in that directory that summarizes each file and very handy for keyword searching.