U-Value from Windows to Honeybee


I created a custom window by using WINDOW 7.4 program and import it to GH. However, the U-values that WINDOW generates and the de.construct. component shows is different. I am attaching the related files for you to test.

U-window.gh (95 KB)
Triple Pane with Low E.txt (2.43 KB)
Triple Pane with Low E_Spec.idf (24.4 KB)

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You raise a good point here and it has a logical explanation. WINDOW has functions that compute the resistance of the air gap between the panes of glass depending upon their thickness, gas type, and whether there are low-E coatings on the inner panes of glass. Energyplus also has these functions. However, the Honeybee U-Value calculation is using a simple assumption about this air gap that only takes into account the gas type and assumes a low-e coating with a gap thickness of 1 cm as you see here:


So, long story short, your window construction is going to be simulated correctly by EnergyPlus when you apply it to your HBZones. It’s just being poorly approximated by Honeybee here and it seems that this approximation can be pretty off when you have gap thicknesses less than 1 cm and you do not have low-e coatings. At some point, I’ll try to improve this assumption in Honeybee so that the U-Value displays more correctly. If anyone reads this and can point me to the E+ or LBNL WINDOW documentation that includes these air gap resistance functions, please post here and I’ll add it into Honeybee.


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