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[EnergyPlus_Support] Optical properties of glazing

   Looking the Engineering Document, I have a question: for EnergyPlus, what is
the difference between Reflectance and Reflectivity? Or Transmittance and

   Studying the manual, I concluded that the difference is that reflectivity is
the term used to account the angular dependence, while reflectance is used to
express normal incidence.

   Searching on the net, i found the following definitions:

- Transmittance is the ratio of the total radiant or luminous flux transmitted
by a transparent object to the incident flux, usually given for normal

- Transmissivity is the ratio of the directly transmitted light after passing
through one unit of a participating medium (atmosphere, dust, fog) to the
amount of light that would have passed the same distance through a vacuum. It
is the amount of light that remains after the absorption coefficient and the
scattering coefficient (together the extinction coefficient) are accounted for.

- Reflectance is the ratio of incident luminous flux upon a surface which is
reradiated in the visual spectrum.

   Can I use this definitions for EnergyPlus?

   Thank you!

 Engº Fábyo Luiz Pereira
 UFRGS - Laboratório de Vapor e Refrigeração
 Rua Sarmento Leite, 425 - Sala 203 - Centro - 90050-170
 Fone / Fax: +55 51 3316-3167 / 3316-3355
 Porto Alegre - RS - BRASIL

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