Difference between shades and blinds in EnergyPlus

asked 2020-02-12 10:17:49 -0600

Marios gravatar image

updated 2020-02-12 17:25:34 -0600

Going through the general description of the Optical Properties of Window Shading Devices in the Engineering Reference of EnergyPlus, it seems that, when speaking about external shading, "Shades" are assumed to be perfect diffusers, while the optical properties of the "Blinds" are strongly dependent on angle of incidence. Copying from the original text on page 298:

“Shades” are assumed to be perfect diffusers. This means that direct radiation incident on the shade is reflected and transmitted as hemispherically uniform diffuse radiation: there is no direct component of transmitted radiation.

“Blinds” in EnergyPlus are slat-type devices such as venetian blinds. Unlike shades, the optical properties of blinds are strongly dependent on angle of incidence. Also, depending on slat angle and the profile angle of incident direct radiation, some of the direct radiation may pass between the slats, giving a direct component of transmitted radiation.

However, in the detailed description of the "Blinds" on page 304 it is stated that:

The slats are perfect diffusers. They have a perfectly matte finish so that reflection from a slat is isotropic (hemispherically uniform) and independent of angle of incidence, i.e., the reflection has no specular component. This also means that absorption by the slats is hemispherically uniform with no incidence angle dependence. If the transmittance of a slat is non-zero, the transmitted radiation is isotropic and the transmittance is independent of angle of incidence.

Does anyone know what is the difference between the optical properties of the two?

edit retag flag offensive close merge delete