Design-PH Shading Calculation Alignment to Honeybee-PH

Hey Ed and everyone,
What is the best practice for calculating shading in PHPP? Should I wait to perform the shading calculations when I remodel the building using Design-PH, or is there a way to align HB-Radiance’s shading calculations with those in Design-PH? Additionally, I’m concerned that using an EPW file may not provide verifiable results (since PHPP uses Meteonorm data).

After analysing your “Shading Factor Settings” component and using the “window mesh setting” input, I believe I was able to align the analysis points with how Design-PH calculates them. However, I am still uncertain about how to calculate the “Shading mask resolution.” I experimented with some of the sky matrix components to increase the sky patch density, but I am unsure how this is affecting my results.

Additionally, I encountered another issue with my script: it was incorrectly lumping window reveals, install depth, and shading into a single calculation for the “Additional Shading Reduction Factor” cells.

Could you provide some insight into how you set up your script to accurately calculate shading for PHPP?


HoneyBee-PH To PHPP.3dm (1.0 MB)

HoneyBee-PH To PHPP_Example.gh (196.3 KB)

This sounds like a good one for @edpmay

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Hi @Luke

Happy to provide some background here:

  1. For ‘Certified’ Passive House projects working in the PHI protocol and PHPP, as far as I am aware it is currently not allowed to use any program other than DesignPH to calculate shading factors. So if your project is achieving PHI-Certification, then as far as I know the rules (right now) lock you into only that software. When we do Certified projects, we model in Rhino, then export a model to DesignPH, calculate the shading over there, and bring those values back into the Rhino model. We have a component which can read in those values from DesignPH (you just copy the shading factors from DesignPH and paste into a GH-panel)

  2. Currently the ‘Shading Factor’ tools included in HBPH are only for ‘design-phase’ analysis, visualization, and assessment. Because of the above rule, we cannot use these tools for Certification calculations right now.

  3. In principle of course, there is no reason that we cannot match the DesignPH process in Rhino though. The challenge is mostly just that the DesignPH implementation is not open-source, nor documented or published - so we cannot match their calculation process exactly. But as you say, by working through test-cases and reviewing the results, we can see that we can get the Rhino results to align very closely.

  4. For background, the implementation we came up with for HBPH is to use the ladybug ‘Incident Radiation’ solver to calculate the actual radiation on the windows. We do this for each window twice: once WITH all the shading context, and again WITHOUT the shading context - then simply divide one radiation result by the other in order to get the shading factor as a % value. You can see the exact implementation at honeybee_grasshopper_ph/honeybee_ph_rhino/gh_compo_io/shade_solve_LBT_rad.py

  5. One key input to set in Rhino is the ‘_window_mesh_settings’

    which will control the number of analysis points. DesignPH limits the analysis points to a fairly low number, and so you would want to match that in Rhino in order to get aligned results.

  6. The main actual difference between the Ladybug Incident Radiation method and DesignPH (as far as we can tell) is how they deal with reflected radiation (reflected from occluding objects). I believe the LBT solver ignores ALL reflected radiation, while the DesignPH method adds in a constant value to account for an approximate reflected radiation. So because of this, in DesignPH if you have a window ‘inside’ something like a garage (fully closed / covered) it will still show a small amount of radiation. This discrepancy will cause some small divergence between the results when comparing them.

all the best,
@edpmay

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Thanks for the clarification. The workaround you’ve described sounds solid, and the point about reflected radiation is definitely something to watch out for. I still think I will try and align the results for quick prelim assessments. Thanks again!

Best, Luke