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a gap between two zones or with the shade surface

asked 2024-09-26 08:43:42 -0500

RobinCris's avatar

updated 2024-09-27 15:45:12 -0500

as recommended here, I used the internal coordinates of the floor to give the zone geometry. same as the walls.

I look at the model in visualization under OpenStuio, and as expected, there is a gap between two floors and between two zones or between two zones in the same floor. there is also a gap between an external wall and the shade surface next to it.

When I run the model, is the sun go trough this gaps? Hope it is not stupid question image description

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@RobinCris can you add an image to your post to show these gaps?

Aaron Boranian's avatar Aaron Boranian  ( 2024-09-26 09:41:17 -0500 )edit

@Aaron Boranian Yes.Of course. Sorry for forgetting. I just edited the original post

RobinCris's avatar RobinCris  ( 2024-09-26 09:47:33 -0500 )edit

"When I run the model, is the sun go trough this gaps?" No, it won't. The sun will only go through windows, skylights, etc.

shorowit's avatar shorowit  ( 2024-09-26 12:43:06 -0500 )edit

@shorowit How can I know? Even with the shade?? How sure are you?

RobinCris's avatar RobinCris  ( 2024-09-27 03:52:39 -0500 )edit

The EnergyPlus Engineering Reference clearly states that e.g. beam solar radiation enters a zone through exterior windows (i.e. not through opaque surfaces or gaps between surfaces), as mentioned by @shorowit. Here, "window" is generic for any fenestrated subsurface (e.g. skylight, glass door).

Denis Bourgeois's avatar Denis Bourgeois  ( 2024-09-27 06:24:05 -0500 )edit

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answered 2024-09-26 11:28:02 -0500

updated 2024-09-27 07:46:01 -0500

(edited answer, in response to your comment below).

Re-reading your initial post, you indeed asked a single, specific question on potential solar contribution from gaps in your model. @shorowit provided the answer, while mine did not help with that - sorry for the confusion.

I took your question as a more general one: "any challenges when using interior dimensions only and having gaps between zones"? When zooming in the image, more precisely surface intersections along the horizontal and vertical gaps between the 2 top-floor spaces, there seems to be missing interzone surfaces between them. There's also a gap between wall and floor. This may create 2 potential issues:


Adjacencies: In your comment, you allude to setting boundary conditions of 2 (near) parallel interzone surfaces, just as one would do if both shared the same 3D plane. I haven't tested this in years, but I found it nice at the time that EnergyPlus allows 2 fairly distant (yet parallel) surfaces to be considered adjacent, by reciprocally setting their boundary condition to each other. This is what I meant by:

I have seen imported IFC models where gaps do exist between otherwise enclosed spaces, which generally require resorting to adiabatic boundary conditions for nearly interzone surfaces. Not ideal, but should work.

Instead of setting their boundary conditions to adiabatic, one can also specify that they are adjacent to each other (as you mention). Nonetheless, you may want to check the run/eplusout.err file for info or warning messages to that effect. You seem to have found a suitable solution - good.


Enclosure: Spaces do not appear hermetic (i.e. not enclosed) in the image. EnergyPlus is typically unable to auto calculate volumes when zones are not properly enclosed, which triggers an assignment of 10m3 for that zone. Check the run/eplusout.err file. The solution is straightforward: explicitly set space and zone volumes. Maybe do the same for zone height, and so on. This is extra work with larger models, yet manageable for smaller ones. This is why the general recommendation is to ensure spaces are enclosed, ideally with interzone surfaces shared between adjacent spaces - no gaps.


More of an FYI. Building energy codes/standards do indeed have different requirements when it comes to space geometry delineations. For instance, 90.1 requires that spaces shall be (in part) defined by the outside face of exterior walls. Other codes instead require the inside face of exterior walls. Yet most codes would require interzone walls (i.e. common to 2 adjacent spaces) to be drawn along the centreline of shared partitions (i.e. no gaps). Same with floors: should be modelled along the top of the floor slab - the adjacent ceiling below should be a mirrored copy of the floor surface (i.e. no gaps, ignoring slab thickness). Again, the solution (you allude to) also works.

Hope this helps.

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I do not really understand and if what you saying is right, I must have doing something wrong. I know there are few ways to for describing the geometry of building surfaces in EnergyPlus. Inside, Outside or Centerline. In this case I used the inside (For zone volume and floor area to be real) as an interzone and point to the other side surface and it gave me no errors. is that sou

what you are suggesting is to use the use outside dimensions for exterior surfaces, and centerline dimensions for interior surfaces and overridden by entering values for zone volume and floor area in the Zone object

RobinCris's avatar RobinCris  ( 2024-09-27 03:50:24 -0500 )edit

@RobinCris : Sorry for the confusion, not my intent. I strongly edited my initial answer in response to your comment. Hope this is clearer.

Denis Bourgeois's avatar Denis Bourgeois  ( 2024-09-27 07:25:48 -0500 )edit

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Asked: 2024-09-26 08:43:42 -0500

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Last updated: Sep 27