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Roofs shading other roofs?

asked 2014-11-19 09:21:17 -0500

hodor's avatar

updated 2015-07-10 09:03:47 -0500

I have another question about EnergyPlus. I made a study with a stair stepped roof, the lower steps seemed to be shaded. Then I deleted all the wall surfaces leaving only roof surfaces and the lower steps were no longer shaded. Can roof surfaces shade other roof surfaces in EnergyPlus?


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answered 2014-11-21 15:32:39 -0500

EnergyPlus surfaces only cast shadows in the direction of their outward facing normal. Roofs face up, so they do now shade anything below them. Shading surfaces are mirrored by default so they cast shadows in all directions. When the building surfaces form an enclosure, all of the expected shading should occur since there will be either vertical walls or downward facing overhangs or soffits to shade surfaces below.

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Thanks for those details, I had it backwards.

David Goldwasser's avatar David Goldwasser  ( 2014-11-21 17:48:24 -0500 )edit

answered 2014-11-21 15:10:25 -0500

updated 2014-11-21 15:22:26 -0500

I'm not sure if heat transfer surfaces in EnergyPlus block the sun from both sides by default. Just to confirm it is not an issue you might want to make sure the surface normal isn't reversed on the roof. Also, even if your roofs are correct, when the sun is behind the high end of the roof but at a low angle it would sneak in under the higher roof to hit the lower roof.

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Asked: 2014-11-19 09:21:17 -0500

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Last updated: Nov 21 '14