[Greenbuilding] apples, oranges, and u values

John Straube jfstraube at uwaterloo.ca
Mon Apr 16 10:46:27 CDT 2012


The Europeans DO measured U-value differently.
They measure at an outdoor temperature of 32 F.  The result is slightly higher R-value / lower U-values and slightly wider optimum air gaps.  They also design their hollow frames with larger voids as convection does not set in as quickly.
As a rule of thumb, I derate their R-values by 10% relative to NFRC, but it varies on the window.
A
Similar situation with HRVs. They dont rate them at -10F like they do in Canada at least.  I hear that 2 manufacturers from Germany tried to get their products approved, and they not only had low efficiencies, they plain failed the test (they frost up, something we discovered 25 years or more ago).  For warmer places, like Kentucky, say, or drier, like Denver, they should work OK.
  

On 12-04-16 11:06 AM, Alan Abrams wrote:
> I appreciate all the perspectives, but the question remains, do the Europeans measure window performance differently, U for U, or R for R, than we do here in the colonies? (or are energy stimulated molecules less excitable here in the new world, than they are, in say, Gay Paree?)
>
> -a
>
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-- 
Prof. John Straube, Ph.D., P.Eng.
Faculty of Engineering
Dept of Civil Engineering / School of Architecture

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