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Material Emissivity - EnergyPlus

asked 2020-04-03 04:16:31 -0500

NCB's avatar

updated 2020-08-19 10:17:40 -0500

I'm trying to modelate a cool roof, but i'm not completely secure that the emissivity of the material it is contemplated in the material properties of EnergyPlus. I'm mistaken? What is the best way to define a cool-roof?

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answered 2020-04-03 12:02:06 -0500

When EnergyPlus performs the heat balance for the outside face of a surface, it assumes that the emissivity is equal to the absorptance. Since the roof is opaque, transmittance is zero, making reflectance = (1 - absorptance).

$$ \alpha = \epsilon$$ $$ \tau = 0$$ $$ \rho = 1- \alpha$$

If you're modeling a cool roof that has high reflectance, you will want to set the absorptance input fields in EnergyPlus to low values. You can read more information in this post and this post.

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Asked: 2020-04-03 04:16:31 -0500

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Last updated: Apr 03 '20