[BLDG-SIM] Bug in Window 5.2

Mahabir Bhandari bhandari at fenestration.com
Fri Jun 17 07:57:02 PDT 2005


Michael,

 

Thanks for pointing this out. This is a known bug in WINDOW5.  However, you
can still use WINDOW5 with a little modification. The methodology for
calculating inside heat transfer coefficient was changed in WINDOW5 where
radiative and convective part of film coefficients are calculated separately
but the DOE2 output report from WINDOW5 only reports convective part. I saw
this bug a long time back and asked Jeff Hirsch about the clarifications, I
would like to share his reply with the group:

 

Mahabir Bhandari

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




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The problem is an issue with Window 5 ouput that eQUEST cannot fix;

Window 5's ouput for the hrout, hcout , and (hcrin + hcin) reported

at the bottom of the ouput is inconsistent with the reported u-center.

For example (here is a W5 ouput table for u-center)

 

Overall and Center of Glass Ig U-values (W/m2-K)
Outdoor Temperature                 -17.8 C      15.6 C      26.7 C
37.8 C
Solar      WdSpd  hcout hrout  hin
(W/m2)     (m/s)     (W/m2-K)
   0        0.00   4.00  3.54  2.77  3.63 3.63  3.67 3.67  3.75 3.75  4.11
4.11 
   0        6.71  30.84  3.30  3.13  5.88 5.88  5.51 5.51  5.52 5.52  6.22
6.22 
 783        0.00   4.00  3.64  2.59  3.63 3.63  3.67 3.67  3.75 3.75  4.11
4.11 
 783        6.71  30.84  3.33  3.08  5.88 5.88  5.51 5.51  5.52 5.52  6.22
6.22

 

Where the same glass from W4 would produce

 

Overall and Center of Glass Window U-values (W/m2-C)
Outdoor Temperature                 -17.8 C      15.6 C      26.7 C
37.8 C
Solar      WdSpd  hcout hrout  hin
(W/m2)     (m/s)     (W/m2-C)
   0        0.00  12.25  3.43  8.23  5.10 5.30  4.83 4.98  4.82 4.97  5.33
5.57 
   0        6.71  25.47  3.33  8.30  5.95 6.31  5.49 5.76  5.46 5.72  6.13
6.51 
 783        0.00  12.25  3.48  8.17  5.09 5.28  4.56 4.66  5.06 5.25  5.43
5.69 
 783        6.71  25.47  3.37  8.27  5.94 6.29  5.34 5.58  5.67 5.97  6.22
6.61 

 

The three film coefficient should be input into the FILMS-COND

keyword in the GLASS-TYPE-CODE command. For the above

window 4 library entry the values would be:

 

     FILMS-COND=  (25.47, 3.33, 8.30)

These values are in agreement with the window 4 report u-center's in the
table, but the

above window 5 value for the last film coeff is not correct (it does not
include both radiative

and convective components) as it does not allow the reproduction of the
reported u-center's

of the table.

 

eQUEST, at this time, does not put a FILMS-COND keyword into the
glass-type-code command

due to this W5 probelm; we will decide what to do at some point (we were
waiting for the W5 group to

fix this problem/bug in their output)

 

For now you could insert a films-cond keyword using the first two values
reported by

W5 and replacing the third with a value you calculate to get the right
u-center based

upon the glass the the other two values reported by W5 (or just approx with
8.3,

but then LS-D will not be correct)

 

 

  _____  

From: Mike Tillou [mailto:miket at etcgrp.com] 
Sent: Friday, June 17, 2005 9:02 AM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] Bug in Window 5.2

 

Hi All, 

Anyone using Window 5 (any version) to create custom glazing for DOE2
simulations should be very careful.  There is a bug in the output feature of
Window 5 that incorrectly reports the window film coefficients used to
calculate the center of glass U-value.  If you use this data in a DOE 2
simulation the calculated center of glass U-value may be off by as much as
40%.  BE CAREFUL and check the output reports to verify glazing performance
if you are importing Window 5 performance data.  Apparently Window 4 does
not have this problem, it worked fine when I tried it.  

I have been told that LBNL is aware of the problem but to date has not
resolved the issue.  

I have only heard one side of the story (and would be happy to hear the
other) but it seems like this is another chapter in the ongoing saga of DOE2
vs Energy Plus.  I am not saying this is the case, but it is disturbing to
think that software bugs in publicly funded software are not getting fixed
for political reasons.

Unfortunately those of us trying to use these tools and can't because of
issues like this suffer most. 

Sincerely, 

Disgruntled Modeler. 

 

Michael Tillou, PE
etc Group, Inc.
PO Box 7, Williamstown, MA 01267
ph. (413) 458-9870  fx. (413) 458-9875

  

 
 
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