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EnergyPlus - Surface Outside Face Sunlit Fraction for Shading Devices

asked 2018-10-03 10:07:02 -0500

updated 2018-10-04 09:42:47 -0500

I am using EnergyPlus in order to calculate the sunlit fraction (by unreflected beam solar radiation, as specified in the Input-Output Reference) of window glazing areas with the presence of external shading devices (e.g. venetian blinds, shades). The output values of Surface Outside Face Sunlit Fraction seem to be unaffected by the presence of these shading devices.

I also tried another case: I removed the shading devices and added an overhang (through the Shading:Building:Detailed object in EnergyPlus). This time I get variable output values of Surface Outside Face Sunlit Fraction, indicating that the overhang was taken into account.

So, is it safe to suppose that, at the moment (at least), EnergyPlus cannot calculate the sunlit area of external surfaces that are shaded by shading devices like blinds, shades, screens etc.(I guess it has to do with the polygon clipping algorithms) ?

Or is there a way that can be calculated in EnergyPlus?

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Just to provide a little more detail are you using WindowProperty:ShadingControl with WindowMaterial:Shade and WindowMaterial:Blind, or you drawing Shading:Building:Detailed similar to your overhang example? If you are not suing shading surfaces then I think your assumption is correct that it won't affect sunlit fraction of window surface, but I don't know that it has anything to do with polygon clipping.

David Goldwasser's avatar David Goldwasser  ( 2018-10-03 12:03:09 -0500 )edit

Hi David! I am defining my shading devices (blinds, shades) using WindowProperty:ShadingControl with WindowMaterial:Shade and WindowMaterial:Blind.

Spyros Akritidis's avatar Spyros Akritidis  ( 2018-10-05 03:52:32 -0500 )edit

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answered 2018-10-12 07:37:44 -0500

This question was also asked on the Bldg-sim list. Repeating the answer from there.

Correct. Sunlit area applies to direct (beam) solar and is the result of the surface (building and shading) shading calculations.

Shading devices (blinds, shades, and screens) are modeled as part of the window system, because there can be more interactions than just impacting sunlit area. There can be inter-reflections between the glazing and the shading device, beam can be changed to diffuse, etc. There are many output variables that report various details of the window system and shading device. Search the RDD output for "Surface Window".

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Asked: 2018-10-03 10:07:02 -0500

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Last updated: Oct 12 '18