[Bldg-sim] Performance Compliance for Buildings FWR question

[Howe, Timothy]

All,
 
The NRC document Performance Compliance for Buildings, states that if the fenestration to wall ratio is greater than 0.4 to use the following formula:
 
Ar = Ap + (1-(0.4/FWR))*Awind
 
Ar = Reference opaque area
Ap = Proposed opaque area
FWR = Fenestration to wall ratio
Awind = Area of windows in proposed design
 
I assumed that the intent was to increase the reference case wall area so that the FWR equals 0.4.  But this calculation does not do that.  I calculated for a proposed design with a FWR of 0.46 and the resulting reference FWR is 0.43???
 
The EE4-CBIP modeling documentation states that the window to wall ratio shall be for the reference case 0.4 and if the proposed case is greater than 0.4 than you must increase the wall area so that the wwr does equal 0.4
 
Any suggestions on what to do?  Does anyone have any experience with the NRC document and why there is a disconnect between the intent of the calc and the results?
 
Thanks.
 
Tim.
 
 
 
Timothy Howe
Mechanical Engineer
Stantec

 
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