WINDOW BDSF .idf file into Energyplus Problems

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Hi, I have developed a vacuum glazing system in WINDOW7.8 and have generated a .idf BDSF file for my E+ simulation. When I integrate the generated objects into my E+ master file and run the simulation the generated u-factor is significantly different to the one generated in WINDOW (e.g. for this vacuum window I am getting a u-factor of >5!).

Why would this be?

I have not changed any other classes apart from the FenestrationSurface to the new vacuum construction.

This is shown in my results through extortionate losses and heat gains, so any help would be greatly appreciated. Please forgive me as I am new to E+.

Thank you in advance