BSDF has negative thickness

Hi, I have generated a BSDF for shading by using genBSDF through a python code in grasshopper. When I import the file to LBL Window to extract SHGC and other thermal properties to report to BSDF-IDF format for honeybee energy plus simulation, the BSDF gives a negative thickness (i.e. -1.00) while the going through the xml file in text editor the thickness parameter is correct (i.e. approx 11 inches).

This crashes the LBL Window if i try to calculate values with negative thickness. Any help would be greatly appreciated. Thank you.

Hey Rio,

As long as your dimensions are in the acceptable range (not too big) it should be fine (check the Window manual document). Window has limitations in terms of convective heat exchange if you use a big element.

Just head’s up… about other parameters such as ThermalConductivity, Emissivity front and back, and TIR. As you know, without adjusting those numbers, you wouldn’t get a correct SHGC.
see below one how I did it once:


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Hi fazel
Many thanks for your response and more so for the head’s up. It is very helpful.

The issue of “negative thickness” turned out to be due to units. It gets solved when I change the units to “millimeters” or “meters” which seems strange to me but imports correct values.
But still when I press “calculate” for the shading system the LBL Window crashes saying some problem occurred
I am still looking for (could not find yet) the dimension’s range (as u mentioned) to see if there is the issue :worried:

Its been days of trying to work out the file but in vain. Here is the issue, I need to report a “BSDF-IDF” file of my glazing system from “lbnl window” for energy simulation in “honeybee open-studio” but “lbnl window” crashes when I press "calc"button when trying to calculate the glazing system properties with shading layer of assigned BSDF (created with gen-BSDF).Thickness is not the issue anymore but calculating SHGC etc is the problem now. I am attaching the file so if any learned member could check it on lbl window and point out any mistake I may have made or any error or problem with the file.
Thanks and Regards.
Membrane genBSDF.xml (426.2 KB)

Hi Rio,

if you are sure about your inputs and the units in SI (e.g. ThermalConductivity 0.168 sounds low to me…) I recommend you to post your questions in LBNL WINDOW Forum.

Also keep in mind that you should always use the latest version to avoid any already fixed bugs in the software.

Good luck.

Hi fazel,
Thankyou for the help. I rechecked that the values are correct and software versions are latest.
For anyone interested or having same problems here is how it worked. The issue with thickness is resolved by changing units while the issue of crashing in “calc” is resolved by increasing -ab, -ad values while reducing the -st threshold lower. I also added both +b and +f to the calculation (all these i didn’t for test run to lower simulation time).
Again many thanks.