Baseline for curtain wall

Opaque spandrel panels within a curtain wall system are considered wall area.

Marcus,

  Am following up on Francessco's question here... Does the U-value of Table 5.5- Metal framing (curtainwall/storefront) include both the transparent parts and the opaque parts?  I've read that with mullions and spandrels the R-12 value  is the most most efficiency you can get... how does this relate to this table Table 5.5- Metal framing as well?

For a spandrel, you're compared to the opaque wall, because the definition of "fenestration" in Section 3.2 is an area that "lets in light", and spandrels don't. So for example, in climate zone 4A, the glazed panels + frame are compared against U-0.50; whereas the spandrel panels + frame on the same curtainwall system will be compared to the much more stringent U-0.064. That's the figure in Table 5.5 that you need to use for the model for spandrel panels areas. 

So, you can say that overindulging in spandrel panels in pursuit of a certain architectural aesthetic will penalize the project energy wise. You can recommend adding insulation behind the spandrel, but you'll need to account for the thermal bridging of the frame too. Kawneer has charts for some of their systems when tested according to AAMA 507 for various levels of spnandrel insulation. 

Waleed,

  Thank you, I understand better how to deduce U-Factor of U-0.064 (Steel-Framed Above Grade Wall) under Climate Zone 4 for the spandrel area considered/treated as a wall area because it does not let in light within a curtain wall VS. the Curtain Wall area with Glazing within the same Climate Zone would be U-0.50 for the Base Building. But am assuming that curtain wall should have an overall area weighted average U-Factor of both the spandrell and glazing combined (U-0.50 and  U-0.064) which will be inputted into the baseline building model, is this correct?  

Just a side note: we are using YKK AP America Inc's  curtain wall unit which apparently calculates thermal performance per AAMA 507. I will see if the product data sheet shows that the testing accounted for various levels of spandrel insulation

But for the Proposed Building, because we do not have NFRC labeled fenestration, I am using the values under the  Unlabelled Fenestration Table 8A.2 under Frame Tpe "Metal and other frame types Double Glazing" U-0.90 for both Tinted and Clear Glass? Does this approach make sense?

Just read this from the user manual "When a building has more than one class of construction that falls within the same space-conditioning categories, area-weighted averaging can be performed using the U-factor, C-factor, or F-factor, compliance option. Area-weighted averaging is not allowed for R-value compliance. Area-weighted averaging enables one construction assembly within the class to fail to meet the criteria as long as other constructions within the class exceed the requirement. However, the area-weighted average of all constructions within the class must be less than the U-factor, C-factor, or F-factor criteria.  When doing area-weighted averaging, up to one percent of openings due to recessed equipment can be ignored. If the openings are greater than one percent, they need to be accounted for in the area-weighted average."

I think what you input in the model is a combination of what the tool allows you to do and being a judgment call. If I were to model it, I'd model spandrels as an actual wall not a curtain wall, and only model the vision glazing as a curtain wall if that makes sense. That way I can troubleshoot easier. That also makes sense because a wall doesn't take a SHGC value and a glazing does. If you're modeling daylight dimming that's a third thing to average. So I just avoid that and model them separately as opaque wall and transparent glazing, where spanrels will be categorized as opaque wall. U-factor averaging is certainly acceptable in many scenarios, and that's essentially what we do when accounting for thermal bridging. 

That excerpt from user manual seems to refer to class of construction though, as in above/below grade walls, or mass wall with some steel stud portions, etc. 

As for the proposed U-factor, I recall LEED might allow you to model the glazing using WINDOW if you don't have an NFRC label? I'm not sure. But a baseline of U-0.5 against a proposed case of U-0.9 seems like a steep penalty.