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[EnergyPlus_Support] Re: Window U values in HTML vs idf

There is a knowledge base article on the support website about this, I think. SHGC is only measured at one angle, but epluse needs to know how the energy transfer is at many angles during the day. To do this it uses a backwards recontruction to create a complex glazing system from the entered SHGC, Tvis and U-value and has a complicated way for specifying a best fit based on standard double glazing. After having recontructed the complex glazing, it calculates the SHGC.

The best fit is based on real glazing. If you have an unrealistic glazing like ASHRAE 90.1 Climate Zone 1 A with SHGC of .4 together with U-value 6.81 (which can't be done with real glass, then the calculated SHGC and U-values of the reverse engineered complex glazing will be quite a bit off target.

As for the film coeffs...NFRC method used for calculation of standard SHGC and U-values inludes for a film coeff based on inside and outside convection rates as well as radiation exchange, so I can only assue that it is included. This should be somewhere in the engineering ref. It should also include frame and edge of glass effects. 

Hope this helps.  





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