[Bldg-sim] Performance Compliance for Buildings FWR question

[Brian Fountain]

Check sentence 2) of section 5.3.5.5 Windows -- it defines the reference 
building window size by setting the reference  FWR as the lesser of the 
proposed building FWR or 0.4.  This defines the reference building 
window area.

The sentence you are quoting increases the reference building wall 
area.  Given that your FWR is 0.46, this formula calculates the wall 
area to give the reference building the 0.4 FWR.  It worked for me (see 
attached spreadsheet).  If your Ap = 540 and your Awind = 460, FWR = 
0.46,t solves for Ar = 600 giving a reference FWR of 0.4.

Cheers,
Brian


Howe, Timothy wrote:
> 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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