[bldg-sim] EQuest handling of window conductance?

Mahabir Bhandari bhandari at fenestration.com
Tue Oct 25 07:08:09 PDT 2005


John,

 

NFRC U factor is always calculated at the winter condition.  If you input
the NFRC U factor, SHGC and VT, eQuest converts U factor to Glass-Conduct
and SHGC to Shading-Coeff.

 

e.g if you input NFRC U-Factor as 0.4 and SHGC as 0.2, VT as 0.3 (From the
NFRC label), eQuest will convert the values as follows: 

 

"Window Type #1 GT" = GLASS-TYPE

     TYPE             = SHADING-COEF

     SHADING-COEF     = 0.229885

     GLASS-CONDUCT    = 0.434216

     VIS-TRANS        = 0.3



It uses the formula from the table you mentioned to convert the U-factor
into conductance. I agree with you that there is a difference in U factor
input and eQuest and the resultant window U-value in the LV-D report. My
recollection from my conversation with the developer is that there was a bug
in the reporting in LV-D though the program uses the accurate value for the
simulation.

 

In this case, it assumes frame width as 0.0. You will notice it in your .inp
file.

 

"North Win (G.N3.E3.W2)" = WINDOW          

   GLASS-TYPE       = "Window Type #1 GT"

   FRAME-WIDTH      = 0

   X                = 60.64

   Y                = 3

   HEIGHT           = 5.22

   WIDTH            = 8.11057

   FRAME-CONDUCT    = 2.781

   ..

 

I hope it helps..

 

Mahabir

 

 

 

Mahabir Bhandari, Ph.D.
Senior Energy Analyst
Carli Inc.
Tel:  (413) 256 4647
Fax: (413) 256 4823

 Web:  <http://www.fenestration.com> www.fenestration.com







 

  _____  

From: John Weale [mailto:jweale at gmail.com] 
Sent: Monday, October 24, 2005 6:12 PM
To: bldg-sim at gard.com
Subject: [bldg-sim] EQuest handling of window conductance?

 

Hello,

I am doing some modeling with EQuest 3.55 and am trying to understand two
things: How to input an NFRC window U-value, and how the DOE2.2 engine deals
with window conductance.  

For inputting an NFRC window U-value, the help file offers Table 2.5 under
Glass Conductance to convert between "manufacturer's U-Value and DOE-2 glass
conductance."  However, the conversion is different between summer and
winter, and conductance is a single input, not a seasonal one.  Is it really
a matter of doing a weighted average of the converted Summer and Winter
U-values?  I am leaving the emissivity at its default 0.84.

Once the conductance is fed in (1), the resultant window U-value in the LV-D
report does not match the conductance. I assume that Table 2.5 is intended
to add the air film, and I am not modeling any frame (2).  Does
DOE2.2/EQuest assume a frame of some sort by default?

Thank you for any insights,

John Weale


(1) "GLASS-0.470-0.563" = GLASS-TYPE      
   TYPE             = SHADING-COEF
   SHADING-COEF     = 0.5635
   GLASS-CONDUCT    = 0.531

(2) A typical window definition:
"WINDOW3" = WINDOW          
   GLASS-TYPE       = "GLASS-0.470-0.563"
   SHADING-SCHEDULE = "DEFAULT-SHADE"
   MULTIPLIER       = 1
   HEIGHT           = 13.86
   WIDTH            = 13.86
   MAX-SOLAR-SCH    = "SHADE-CTRL"
   ..



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