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How do you treat floor openings in EnergyPlus?

asked 2015-08-10 04:33:59 -0500

updated 2015-11-12 14:59:35 -0500

I'm modeling a new construction building that is going to be a Mall. The center area is a concourse, 2-story high (about 30 feet total). There's a skylight at the very top. There are also numerous floor openings.

Here's what you could see when looking from above through the skylight.

View from above through the skylight

I need to say that I will look into daylight sensors.

I'm wondering whether I should just model one big zone encompassing both floors, or if I should model each floor separately.

What I think my problem is that if I model one zone I'll be able to make sure that I have the same internal temperature, but I will likely overestimate daylighting going to the space because there won't be any light-blocking materials in there. If I model two zones I'm afraid I'll make the top one too hot compared to the bottom one.

(I'm not even talking about the square footage problems I'll have with LEED (too much if two floors, too little if one), or correctly adding lighting power and occupant density.)

Any advice?

Also, if modeling separately, how should I model the floor openings? I know that Air Walls do not let light pass (if using E+ daylight object at least... I think Radiance might be able to do it), while interior windows don't let air pass. I do have mechanical supply of conditioned (cooled) air at both level, so my boundary conditions if I define some kind of interior skylight will be the same. I could also make the conductivity very high just in case, and set the window property so I don't have any reflection. So I'm thinking I would use a window?

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I'm not sure where I should put this comment, so I'll leave it here. You should probably not use AirflowNetwork for the big openings in your picture. Pressure network methods (like AirflowNetwork) are not particularly good at this sort of situation without a great deal of effort. This is more of a job for CFD.

Jason DeGraw gravatar imageJason DeGraw ( 2015-08-11 11:39:23 -0500 )edit

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answered 2015-08-10 11:19:52 -0500

updated 2015-08-10 11:24:42 -0500

This isn't a complete answer, but just a collection of things to think about.

  1. If you do model as two zones, you can flag the upper zone to be excluded from the building floor area.
  2. If you use internal windows keep in mind that while light passes through them, that light is diffuse. It won't behave exactly the same the same as if you modeled it as one thermal zone with only exterior windows to pass through.
  3. If you use Radiance via OpenStudio then light will pass through air walls.
  4. If you model the upper and lower atrium as two seperate spaces in OpenStudio and include them in a single thermal zone, The area from the upper space won't be included in the building Floor Area. OpenStudio does this for any interzone floor/ceiling surfaces whether they have an air wall construction or not. That is what you want in this case, but wouldn't be what you wanted if you modeled a multi-story stair well where you wanted an LPD for each story. You may want to model the atrium as two spaces. That would keep the option open to model as two zones or one. There is an issue filed that would look at the construction to determine if inter-zone floor/ceiling should contribute to floor area.
  5. However you model it make sure to keep the sides where there is a concourse (and not open floor) as a separate zone.
  6. OpenStudio will have zone mixing and simple ventilation in 1.9.0 but will require measures to access it. If you want to use AirflowNetwork you would have to add EnergyPlus measure to accomplish that. I'm not aware of any AirflowNetwork measures that have been written yet.

image description
Typical mall profile with 5 spaces across (store,concourse,atrium,concourse,store) on each story.

image description
Render by zone shown with multi-story zoning option. Note how 2nd floor concourse still has its own zones. You could optionally do this on the first floor as well.

image description
Render by zone shown with separate zone for each story of atrium.

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answered 2015-08-10 08:02:15 -0500

I would suggest modelling two zones with openable glass doors in an AirflowNetwork. Maybe my answer to this question on onpenable windows can help modelling the air exchange.

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Asked: 2015-08-10 04:33:59 -0500

Seen: 363 times

Last updated: Aug 10 '15