Material Emissivity
Posted by Richard Raustad, Last modified by Linda Lawrie on 04 June 2010 12:08 AM
Q: I would like to know how E+ is calculating the emissivity of materials (not the glazing ones). I am guessing it is an indirect proceedure, as there is no specific input field for this subject.

A: In EnergyPlus input there are three different wavelength bands for absorptance – thermal, solar, and visible. Assuming that by "emissivity" you are referring to an average for longwave thermal radiation, then in EnergyPlus, emissivity is “calculated” to be the same as the value you enter in the field called Thermal Absorptance in the Material object. The material located at the outer or inner layer in the Construction provide the surface property data for all surfaces that use that Construction.

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