Can you put a light shelf on the inside?

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I've never seen or heard of such a thing, but it seems that it might work much the same as one on the exterior. The historical building folk think it's a bad idea to add these on the exterior of a building that never had shading elements - and that's one of my modeling projects, so I'm brainstorming for energy saving ideas.

If you think it will work, I can't think how to model it (in EnergyPlus), so I'd love some ideas about how to do that.