Sanity check on daylight results with a translucent glass material

grasshopper honeybee
1

I need to simulate the effect of switching from a regular glazing material of 60% VLT, to a translucent (i.e. frosted) glazing material - also with 60% VLT. I’m only interested in the daylight levels inside the room.

This is how I’ve defined the two materials:

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Was I correct in assigning 0.6 for the diffuse transmission, in order to represent 60% VLT? For the diffuse reflectance, I was assuming it must be 0.4 so that the numbers add up to 1, but this does not seem to be the case judging by other examples I’ve seen? Will that value have any impact on my indoor daylighting conditions or don’t I have to worry about it?

Here are the results I’m getting:

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I’m a bit surprised about how the results show much better daylighting conditions with the frosted glass, though I guess it makes sense that the scattering would lead to much more uniform results, and therefore higher daylighting towards the back of the room than with clear glazing.

Just hoping someone on the forum who has more experience with this can confirm that the results look alright and that I’m simulating it correctly?

2

Hey @MaxMarschall ,

The way that you have created your trans material means that all of the transmitted light is diffusely transmitted, which is very different than the way clear glass behaves. So your trans material is much more like some diffusing material like Kalwall than glass. If you want your trans material to be closer to your glass material, you should be setting the _spec_trans_ to be close to your glass transmittance (and the _diff_trans close to zero).

3

Hi @chris, I’m trying to create something like this:
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I feel like that window is closer to Kalwall than to clear glass but get your point that specular transmission should be above 0. Do you know a resource where I could find indicative values?

Also, do diff_ref, diff_trans, and spec_trans need to add up to 1?

4

I guess they don’t have to add up to 1 since some of the energy gets absorbed by the material.

It would still be good to know a resource or calculation method to come up with a realistic assumption for the split between diff_trans and spec_trans though, if anyone has one?