[Equest-users] Question regarding "U-EFFECTIVE" value

[Joe Huang]

Chris,

Your intuition is correct, but your equation is incorrect.  The idea of 
an "U-EFFECTIVE" is to modify (generally reduce) the conductivity of an 
underground surface from what it would be based on the input material 
properties. Since the compliance requirements for foundations are given 
in F-factors, which are conductivities per foot of exposed perimeter, 
you should set the U-EFFECTIVE to produce the same total conductance, i.e.,

      U-EFFECTIVE x (Area of Underground Surface) = F-Factor x (Length 
of exposed perimeter)

Thus, in your example, the total conductance is 21.97/h-F, and the 
U-EFFECTIVE will be 21.97/(Area of the underground surface).

There is another technical detail that I need to mention, though. Back 
in the early 1990's, FSEC pointed out that using the U-EFFECTIVE 
produced an inconsistency in the Weighting Factor, so that a significant 
amount of the heat flow into the space was being lost.  In response, 
Fred Winklemann and I (we were both at LBNL at that time) have 
recommended against using U-EFFECTIVE, but rather to add a fictitious 
resistance layer to the outside of the underground surface so that its 
conductivity equals the U-EFFECTIVE. This was all written up in an old 
DOE-2 User News article, but I don't have the link handy.  I also don't 
know whether the U-EFFECTIVE in eQUEST is the same as in DOE-2.1E, or 
has automated the procedure described in the Winklemann article.

Joe

Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
yjhuang at whiteboxtechnologies.com
http://weather.whiteboxtechnologies.com for simulation-ready weather data
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On 7/20/2014 1:29 PM, Chris Baker wrote:
>
> I am having some trouble running my compliance anlaysis.  The cause is 
> apparently a floor system modeled with an underground wall.
>
> When I went back and looked at the properties of the affected floors, 
> "U-EFFECTIVE" value has been left blank.
>
> My question is, wouldn't you be able to figure "U-Effective" by 
> multiplying the two compliance inputs together.
>
> In this instance ...  42.25 (ft) X 0.52 (Btu/h-ft-F) = 21.97 (Btu/h-ft2-F)
>
> Thus U-effective should show "21.97" instead of being blank.  Is this 
> a correct assumption?
>
> I'm not sure if this is the cause for the compliance analysis error 
> but if I try to manually change "U-Effective" to zero, it sais
>
> *Range Checking Violation for Underground Wall 'EL5 Flr (G.SSW1.U1)' 
> U-EFFECTIVE: Error: Input must be > 0.0001*
>
> **
>
> Thus being blank would be causing the compliance errors, would it not?
>
> (Because there is no value for the DOE2 engine to factor into the 
> calculations when you run the analysis.)
>
> Chris Baker
> CCI CAD Drafter
>
>
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