NatLabRockies / NatLabRockies/EnergyPlus

PixelCounting also doesn't seem to handle reflections

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#10,366 4 comments 0 reactions 1 assignee View on GitHub

@nealkruis is already working on this.

Since Jan 11, 2024.

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Description

Issue overview

Running a model with shading surfaces around the windows and the solar distribution set to FullExteriorWithReflections I found significant differences in results between the PixelCounting and PolygonClipping shadow calculation algorithms.

Testing found that the reason for these differences was that with PixelCounting there appears to be no reflected solar radiation. When using PolygonClipping I observe expected non-zero outputs for Surface Outside Face Incident Sky Diffuse Surface Reflected Solar Radiation Rate per Area and Surface Outside Face Incident Beam To Diffuse Surface Reflected Solar Radiation Rate per Area, and, as we would expect, if the shading reflectance is increased from 10% to 90% the reflected solar on the window also increases.

Using PixelCounting all the values for these outputs are 0, and the resulting zone temperatures are noticeably colder and are unaffected by ShadingProperty:Reflectance inputs.

This suggests that further warnings need to be added around the use of PixelCounting following the previously identified issues with it and transparency (#9653). Though now this is more an unconditional "if you have significant shading reflections then PixelCounting may significantly underestimate your solar gains and this point I'm not sure anyone should even consider using it".

Details

Some additional details for this issue (if relevant):

  • Windows 10
  • EnergyPlus v22.1.0
  • Unmethours link or helpdesk ticket number
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