RE: [EnergyPlus_Support] Interior Shade

[Peter G Loutzenhiser <post@xxxxxxxxxxx>]

Charlie,

Thanks for your explanation.  I guess I understand how the shade (I 
am talking a diffuse shading screen here and not a blind) is 
modeled.  But from the manual, it appears that a diffuse assumption - 
hemispherical transmittance - is being employed for the initial 
transmission of beam radiation through the glass as well as the shade 
to arrive at an overall transmittance for the glass/shade.  I wanted 
to confirm that this is not correct and that, for an interior shade, 
the transmittance through the glass initially is angular dependent - 
and then - of course - based on the diffuse model assumption - the 
first transmittance through the shade and the back reflectance are diffuse.



Thanks for further clarification.

Peter



At 00:03 18.03.2006, you wrote:
>Peter,
>
>The diffuse assumption applies only to shade material (i.e., shade material,
>like venetian blind slats are assumed to reflect purely diffusely).
>However, there is still beam component of solar radiation that goes through
>the shades undisturbed (e.g., open or partially open venetian blinds).  Even
>if nothing is directly transmitted through the shade, there is beam and
>diffuse incident radiation, which becomes all diffuse after the solar beam
>hits the shade.  Therefore, simulation takes into account both direct and
>diffuse.  The simplifying assumption here is diffuse (Lambertian)
>reflectance of shading material, which for some highly specular materials
>(i.e., metallic venetian blinds) may be oversimplifying, but at the time
>there is no correction for specularity of material.
>
>Charlie
>
>-----Original Message-----
>From: Peter G Loutzenhiser [mailto:post@xxxxxxxxxxx]
>Sent: Thursday, March 16, 2006 7:15 AM
>To: EnergyPlus_Support@xxxxxxxxxxxxxxx
>Subject: [EnergyPlus_Support] Interior Shade
>
>Dear All,
>
>When EnergyPlus simulates an interior shades for windows, is the initial
>beam radiation component transmitted through the glazing unit/window
>angular dependent and then a geometric series used assuming infinitely long
>flat plates.  The Engineering manual leads me to believe that only diffuse
>solar transmittances and reflectances are used to calculate the overall
>transmittance of the blind+glazing unit/window , but I am unsure.
>
>Regards,
>Peter
>
>
>
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