Glazing materials for Lighting v4+...still some doubts

[spoliti]

Hi everybody, 

I am new to the forum and I've already read most of the topics (really useful BTW)...but still I have some doubts about glazing materials for lighting analysis (specifically ASE/SDA). I'll list them all below: 

- RGB setting for defining Visual Transmission: the only formula to use to determine RGB value is "VT%*255 = RGB", correct? No more tables or spreadsheet here, right? 

- Color RGB when R, G and B are different: I didn't get the purpose of the related formula (VT%= ( 0.2126R + 0.7152 G, 0,0722 B /255)...do I have to use it in case of coloured windows? If this is the case, How do I determine RGB? (It appears to me, to be a linear equation with 3 variables, am I right?

- Thickness and number of glazed panels: this is my greatest doubt. I've read that "thickness of the modelled glass element no longer needs to be considered". What does that mean exactly? In my model, I have windows and curtain walls modelled exactly as they should be in reality: triple glazing with the right thickness for each panel and with an air gap between panels. Now, how should I behave? How do I consider the number of panels and their thickness? Should I set the "Sheet of Glass" parameter in the appearance tab? 

- Linked models: In my case I have three separate models, linked together: one for the internal architecture (walls, floors, ceilings, doors etc., one for the external envelope (windows, curtain walls, facade) and one (the main model) in which I have all the rooms and much other information. Now, I've read that Lighting analysis have to be done in the model where the rooms are set and that it can read the geometry of linked models. My doubt is: can it read also the glazing and opaque materials setting from the linked models? 

Sorry for all these questions but we need to achieve a LEED credit and cannot get this wrong. 

Thank you in advance!

[scheerd · Accepted solution]

Right.  See this post:  https://forums.autodesk.com/t5/lighting-solar-analysis-forum/critical-update-glazing-materials-for-l....

All of this assumes you are using Insight v4.031+

- VT%*255 = RGB is correct for transparency for the 'old' Glazing Appearance assets.  Be cautious that you are not using the 'new' Glazing Appearance assets yet.

- Colored RGB formula is when R != G != B.  Each color has a different weight as to how strongly it affects transparency or reflectivity.  There's no reason to use a color tint for illuminance analysis, as it will not affect the results if the weighted average is the same as a grayscale RGB (R=G=B).  Mainly this is for coordinating with visual renderings.

- Thickness of the modeled pane no longer matters like it used to.  If you are modeling 3 panes of glass, you'll need to define the VT% for each pane rather than the whole assembly.  Normally windows and IGUs are labeled with the performance values of the assembly, so you'll have to disagregate that somehow, or get the performance values of each layer of the assembly from the manufacturer.  For example, if the assembly VT% is 0.30 and you have 3 panes of glass modeled, each pane will be cube-root of 0.30, or 0.67 (0.67 * 0.67 * 0.67 = 0.30).  It's therefore much easier to model the window with a single extrusion (pane). 

- It's fine to have parts of your model in linked docs.  The only things that must be in the main doc are the Rooms and the Floors.  It sounds like you may need to copy some Floors to the main model.  Floors are used to generate analysis points.

[spoliti]

Thank you very much @scheerd !

I've previously read the post you mentioned, that's why I needed some further explanation; and yes, I'm using the v4.031.

I totally got your explanations, I'm just recapping some points as I would like to be 100% sure on them:

- I will cube-root the VT% values of my assemblies then since the model is definitive and it would take too much time and effort to re-model all the glazing materials. Will the results be accurate enough anyway?

- When you speak about "old/new Glazing Appearance assets", you mean the difference between R18 and R19+ appearance tab? I forgot to mention but I'm using Revit 2018.3, and I was following the 'old' Glazing Appearance Assets;

Thank you again, I hope not to bother you again in this

[scheerd · Accepted solution]

First note is that the patches for R19 and R20 are now available and should be installed asap.  After installing the patch, you can use either the 'old' Glazing (with warning symbol on the material thumbnail) and calculate VT from RGB/255, or you can use the 'new' Glazing (no warning symbol, and VT is shown in the UI on the Appearance tab), so no need to calculate using RGB, just change color until you get desired VT.

If there are 3 layers of glass modeled in the IGU, and each layer is assigned the same glazing material, then yes, the cube root of VT(overall) should give you the VT(layer) of each layer.  Then for 'old' Glazing use that to get RGB with VT(layer)*255, or with 'new' Glazing, create a material with VT(layer) shown in the UI on the Appearance tab.  It will be physically accurate for the overall assembly.

For R18, the 'new' Glazing is not available, as it's only in R19 and R20.  R18 and before will only have the 'old' Glazing.