[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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