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

asked 2014-09-07 13:57:32 -0500

updated 2014-09-19 12:22:46 -0500

I have seen multiple discussions on EnergyPlus email list about modeling atrium (without using CFD) however I still don't have a clear idea what is the best way of modeling an atrium. I am looking for recommendations on:

  1. Preparing geometry: Should we split the atrium horizontally in each floor? or should the segments on the top of the atrium should be shorter to capture the stack effect. Is that even make sense considering the EnergyPlus will transfer the radiation as diffuse radiation between the zones?

  2. Air walls/surfaces: Assuming that there will be some sort of geometry split, what is the best suggestion for the construction of surface between the geometries?

  3. Air flow network: Again assuming that there will be some sort of geometry split, what is the best practice to set up the airflow between the atrium zones?

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answered 2014-09-11 05:29:14 -0500

Per Sahlin's avatar

updated 2014-09-11 05:35:43 -0500

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.

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"We simply need a new type of zone model in order to describe atria." I so agree with this. I think there should be some template zone types for architectural elements such as Atrium, DSF, etc.

Mostapha Roudsari's avatar Mostapha Roudsari  ( 2014-09-19 12:14:11 -0500 )edit

answered 2014-09-10 12:58:20 -0500

updated 2014-09-19 12:21:59 -0500

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.

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Thanks Kyle, I asked Dan to add a wish to OpenStudio measures so we can have one that takes a zone as and input and set it up as an atrium similar to what you mentioned up there. Any thoughts on that?

Mostapha Roudsari's avatar Mostapha Roudsari  ( 2014-09-19 12:15:54 -0500 )edit

Anytime you divide an open space into multiple thermal zones, you must include interior windows between the zones if you want to transmit sunlight from one zone to the next. If you are using FullInterior solar distribution, all solar will be diffuse once if passes through an interior window.

MJWitte's avatar MJWitte  ( 2014-10-29 09:48:40 -0500 )edit

answered 2014-09-15 09:53:58 -0500

Archmage's avatar
  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.

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answered 2014-09-10 22:30:20 -0500

Jeff Landreth's avatar

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.

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There are actually two spreadsheet files indexing the EnergyPlus example files, ExampleFiles.xls has one row per example file (as @Jeff Landreth mentioned above) and ExampleFiles-ObjectsLink.xls which has one row per object type and lists the first two or three example files which use that object.

MJWitte's avatar MJWitte  ( 2014-10-29 09:46:45 -0500 )edit

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Asked: 2014-09-07 13:57:32 -0500

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Last updated: Sep 19 '14