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Re: [EnergyPlus_Support] U-values in E+



As you know, the surface details report (report, surfaces, details;) gives U-
values with and without film coefficients.  The construction report (report, 
construction;) reports a thermal conductance without film coefficients, which 
should be the same value as the "Nominal U (w/o film coefs)".

For the "Nominal U (with film coefs)", there is a table of film coefficients 
given in the "Output Details and Examples" document, p. 26 (pdf p. 32).  I see 
that this table is in I-P units.  Here are the values in S-I units (which we 
will add to the document, but it might be too late to add for the 1.3 release). 
 These values are directly from the source code:

Surface type, Interior film, Exterior film {m2-K/W}

Wall, 0.1197548 , 0.0299387

Floor, 0.1620212 , 0.0810106

Ceiling/Roof, 0.1074271 , 0.0810106


Would you please repeat your hand calculations using the above values and 
confirm if this agrees with the reported "Nominal U (with film coefs)"?

Mike



On 20 Apr 2006 at 13:03, Clarice Bleil de Souza wrote:

> Hi Everybody,
>    
>   I am trying to run some simulations with different U-values to check the
> sensitivity of the results and I was wondering, how does E+ calculates the
> U-values. 
>   I have some material compositions that gives me 0.5w/m2K calculated by hand
> (using Rso = 0.055 and Rsi = 0.123 - using the inverse sum of the
> resistivities in series) and E+ gives me 0.55 which is near. Once I look for a
> more conductive material with a hand calculated value of 3 w/m2K, Energy Plus
> gives me a value of 6.5W/m2K. I could not understand why this is happenning. I
> know the U-values won't be used by E+ but I want to be sure that results will
> be somehow equivalent. Can you please let me know how E+ calculates the
> U-values? I couldn't find anything about it in the documentation.
>    
>   Thanks a lot for your attention and hope hearing from you soon,
>    
>   Regards,
>    
>   Clarice
>    
>    
> 
> 		
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========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support      
EnergyPlus-Support@xxxxxxxx





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