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Difference between Infrared/Thermal radiation material properties

asked 2025-09-04 12:37:38 -0500

updated 2025-09-04 13:12:05 -0500

Hello, My doubt is very straightforward :

For materials, it is need to specify :

Semi-transparent : Solar/Visible/Infrared Transmitance/Reflectance and Hemispherical Emissivity and for

Opaque : Thermal/Solar/Visible Absorptance

From the point of view of the OpenStudio calculation engine, Are there any difference between Thermal and Infrared ?

I am confused, because some literature considers the Sun spectra with Visible and Infrared wavelenghts, and with Direct and Diffuse components.

Any thoughts about are very welcome thanks.

Other doubt : Way is not need to specify the emissivity for opaque surfaces?

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@amscosta what simulation tool are you using? Please mention it in the title or body of your post, as well as add a tag so that others can provide better help.

Aaron Boranian's avatar Aaron Boranian  ( 2025-09-04 13:11:07 -0500 )edit

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answered 2025-09-04 14:29:05 -0500

OpenStudio's calculation engine is EnergyPlus.

For opaque materials, go over the wavelength differences explained in the EnergyPlus IO Reference:


For instance, on solar absorptance:

[...] Solar radiation (0.3 to 2.537 μm) includes the visible spectrum as well as infrared and ultraviolet wavelengths.


On thermal absorptance vs emittance/emissivity:

For long wavelength radiant exchange, thermal emissivity and thermal emittance are equal to thermal absorptance.


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Asked: 2025-09-04 12:35:30 -0500

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