R-value of total window assembly for energy model

You could try the LBNL Window 6 free software here to determine the thermal properties of the assembly: http://windows.lbl.gov/software/window/window.html

Perhaps the manufacturer will give you their LBNL Window 6 files for the particular frame profiles used ? You could offer to sign a non-disclosure agreement to protect their intelectual capital.

If you are lucky all you will then have to do then is resize the windows, and add the glass data ...

If they have used custom profiles ( ie frame cross section ) then there is indeed some work to be done.

- make that "intellectual capital" - typing this on a cold autumn morning, keyboard a little sticky :-)

If you want further advice you can approach the NFRC people as well - they use a version of Window 6 in an integrated package called CMAST. Lastly, there is good online 3rd-party training on the use of LBNL's Window 6 from a number of US-based companies.

LBNL Window 7,2 isn't particularly easy to navigate.

It has a list of fixed window sizes (Under "Type" in the window library), with apparently no way to make a new one.

I wonder how one goes about making something resembling the actual window on the project?

I would suggest that it does not have to be exactly the same size to be useful. A size that is relatively close will be likely to only marginally change the U-value.

I finally figured out the only window types that allow you to set a window size are "custom" window types at the bottom of the list.

As Marcus says, it probably isn't important that every single window size is represented, but the Custom window types in LBNL Window 7.2 allows you to get a lot closer to reality than the other 25 default fixed-size windows. 3-4 major window types on a project might be enough. For example I currently have a project with some wood windows, some spandrel glass, and some glass French Doors, all having completely different geometry and frames. But energy models just sum up glass area, so if there is a 48" wood window and a 62" wood window they could all be lumped together as they will have a similar U value.

I asked the helpdesk at EnergyPro if their energy modeling software handles window frames correctly. They said that it did, in fact handle this. They refer to California Energy Code CEC Nonresidential Appendix NA6, which their software complies with. In this case, one would model the window inthe software using the manufacturer's center-of-glass U value, and check the frame type in the window dialog. If "NFRC Rated" is not checked, then the software will use the frame type and a CEC formula to account for window assembly U values. If "NFRC Rated" is checked, use the window assembly U-value calculated using LBNL Window 7 numbers. Perhaps other modeling software also has this capability. If this were questioned by a LEED reviewer, EnergySoft recommends refering them to CEC Nonresidential Appendix NA6 and communications showing they comply. Much simpler to just put in the center-of-glass U-value than messing around with LBNL Window 7.

We generally use eQUEST. It can model the windows either way. We find it easier, simplier and more accurate to model the whole assembly values. We determine these values using Window 6 (now 7 I guess). We are a bit leery of the default frame values. So it is all waht you are used to.

Any of the methods you mention should be acceptable for LEED.