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# RADIANCE Three-Phase Method - modeling only clear glass

Hi everyone, I have a very simple question about the RADIANCE matrix multiplication methods: Is it correct to go through all the steps of the Five-Phase method to simulate a simple clear glass window? I mean, without any blinds or lighting redirecting device, just clear glass. I thought it would be more accurate because of the sun coefficient calculation, but I’m getting many negative numbers, and also notice that in the tutorial, it is given the example of using clear glass (clear.xml) only in the Three-phase section, for the Three-phase-direct they use already blinds in the example (blinds.xml).

While that would be my main question, I take the opportunity to ask, if for the Sun-Coefficient calculation should be better to use a combination of BSDF (genBSDF), and 'glass material' (like in the tutorial), instead of the blend that we get when adding the 'glass material' using Window LBNL. I ask this because I’ve notice some very high peaks of illuminance (15k + lux), when I use the system created with Window LBNL. This numbers are shown few times in a year-calculation, but are a bit inconsistent with the overall results, and I guess this would be also an issue in images generated for a glare evaluation.

I'd appreciate your help regarding this question Thanks Steph

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Hi Steph,

What is your reason for running a 3-phase (or 5-phase) method in this instance? Are you planning to replace the glazing with different daylighting systems? If not, then you are much better off running a simple Daylight Coefficient (DC or 2-phase) method for annual simulation. This does away with the need for a BSDF, since you simply put the glass in your model and use a single run of rfluxmtx to calculate the interior connection to the sky through the building. This method is described in section 2.2 of Sarith Subramaniam's tutorial https://www.radiance-online.org/learn...

If you do use a BSDF for the window, you might use the "aBSDF" specification, which looks for a view component to result in a more accurate calculation. However, applying a BSDF should always be of necessity, as other methods are more accurate for simple glazings.

Best, -Greg

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