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Solar gain distribution between zones in Solar enclosures (Construction: Airboundary)

asked 2022-12-01 05:58:56 -0600

updated 2022-12-02 09:28:20 -0600

Hi all,

Does anyone know how the solar gain is distributed between the different Zones that compose a Solar enclosure (one or more surfaces defined as Construction: Airboundary)?

We are making tests with a thermal model for a space for which we have temperature recordings. The space is a large hall, which is connected to some other adjacent space with Airboundaries.

Surprisingly, the resulting air temperature from the Model is only close to the recordings if we eliminate the Airboundary between the spaces. When we add the Air boundary, temperature drops by 4-5ºC in the relevant space - which is making me think that the solar gains are not being distributed correctly between the zones that compose the Solar enclosure. Is this possible?

I´d greatly apreciate if anyone could throw some light on this. Best, Rafael

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Which solar distribution algorithm are you using?

shorowit's avatar shorowit  ( 2022-12-01 08:37:26 -0600 )edit

good question, I just realised it is FullExterior - we are making a test with Full Exterior and Interior and I'll report back

rafael.alonso's avatar rafael.alonso  ( 2022-12-01 08:46:05 -0600 )edit

we just ran the model changing the solar distribution to "FullInteriorAndExteriorWithReflections" and the temperature surprisingly didn't change.

rafael.alonso's avatar rafael.alonso  ( 2022-12-01 12:25:38 -0600 )edit

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answered 2022-12-01 14:09:55 -0600

updated 2023-01-03 12:41:59 -0600

The zones which are connected by Construction:Airboundary become one continuous enclosure for solar and radiant exchange. You should be able to compare Output:Variables such as "Surface Inside Face Solar Radiation Heat Gain Rate per Area" and "Surface Inside Face Net Surface Thermal Radiation Heat Gain Rate per Area" with air boundary vs an interior window to see the impact.

If the openings are large relative to the connected zones or spaces (such as the air boundary between perimeter and core office spaces) then Construction:AirBoundary is a good option. If the openings are small, relative to the zone volumes, then an interior window is probably a better model. because the interior solar distribution algorithm is not able to model the impact of opaque surfaces within the enclosure which may block solar from other surfaces when using the default PolygonClipping ShadowCalculation method. The PixelCounting method will account for the initial solar distribution (if using FullInteriorAndExterior Solar Distribution).

However the radiant exchange algorithm and distribution of reflected interior solar use very simple rules: all surfaces in the same enclosure can "see" each other unless they are facing the same direction.

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Thanks for the detailed reply.

When you say because the interior solar distribution algorithm is not able to model the impact of opaque surfaces within the enclosure which may block solar from other surfaces.,

does that mean the solar distribution algorithm doesn't see internal walls as obstructions between the zones? How does it distribute the solar gains, say, between two connected zones that form an L shape? (I thought Pixel Counting would overcome this limitation with non-convex zones/enclosures).

Happy to give more details if needed.

rafael.alonso's avatar rafael.alonso  ( 2022-12-02 02:52:30 -0600 )edit

You are correct that PixelCounting will handle the solar properly (if using FullInteriorAndExterior solar distribution), but interior radiant and reflected solar distribution also need to be considered. I will edit the answer above.

MJWitte's avatar MJWitte  ( 2023-01-03 12:39:20 -0600 )edit

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Asked: 2022-12-01 05:58:56 -0600

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Last updated: Jan 03 '23