[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
RE: [EnergyPlus_Support] Window5 data vs IDF dimension
Frames play important role in window heat transfer and unless their
properties are very close to the glazing they need to be specified fairly
precisely. This is especially true for commercial fenestration, where
framing material is typically Aluminum (thermally broken or not). E+
anomaly to treat single lite windows different than multiple lite windows is
something that we had to deal with for our EFEN program. Because it is very
inconvenient to have to model every size of window in WINDOW program for
dual lite windows (where E+ takes dimensions from the WINDOW report file and
ignores IDF file), we have developed procedure that converts dual lite
window report file into the equivalent single lite report file, preserving
all of the parameters of the original dual lite window. This allows user to
model standard size dual lite window in WINDOW program and to use that same
file for other sizes that may be given in IDF file. The procedure is
explained in the following document:
www.designbuildersoftware.com/docs/transfer/Conversion_multi-glazing-windows
.doc.
The warning when dimensions in IDF file are different more than 10% than
dimensions in WINDOW report file can be completely ignored because the
resulting error is very small and is well within any other uncertainty
associated with window modeling. It would be best if that warning message
was removed because it is meaningless. On the other hand the error
associated with the use of WINDOW report dimensions for dual lite windows
(i.e., good number of users will not even realize that their IDF dimensions
are ignored) is huge and its relevance is completely lost in the current
warning message. If windows were small contributor to the overall load and
energy transfer, this would not be big deal, but windows are credited on
average with 25% of the overall energy transfer in a building, which makes
their treatment extremely important, whether you are analyzing effects of
daylighting or not. Theoretically, the use of WINDOW report file should
result in similar simulation run time whether you are modeling hundreds of
windows or a single window, because their properties are pre-calculated in
WINDOW, so no further calculations are necessary, however it seems that run
time in E+ increases substantially for larger number of windows. This is
something that needs to be addressed and resolved in future versions of E+.
Charlie Curcija
DesignBuilder Software
_____
From: Rob Hitchcock [mailto:RJHitchcock@xxxxxxx]
Sent: Friday, June 15, 2007 1:40 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Window5 data vs IDF dimension
You are correct that the dimensions of your window as input in the IDF will
take precedence over the dimensions of the window in the Window5 data file,
*UNLESS* the window in the Window5 data file contains two sections that have
different glazing systems, in which case the Window5 dimensions will be
used. See details of this under "Importing Windows from Window 5" in the
"Group - Thermal Zone Description/Geometry" section of the Input/Output
Reference.
The frame that is part of the Window 5 data file will be used to create a
WindowFrameAndDivider object that will be assigned to the window for
EnergyPlus analysis. EnergyPlus will generate a warning if the dimensions of
the window in your IDF differ from the Window5 dimensions by more than 10%.
This warning indicates that some inaccuracy may result because of the
different area and perimeter relationships between the glass area and the
frame. Unless you are especially concerned with the frame effects, you
should create a simple narrow frame in your Window5 file to reduce these
differences. It is not possible to create a Window5 window system for export
to EnergyPlus without including some type of frame.
The importance of modeling your windows precisely depends on what you are
trying to analyze. If you are interested in daylighting effects, then it is
important to model the windows accurately. If you are only looking for
general thermal effects, then this is not as important.
Rob Hitchcock
----- Original Message -----
From: Ery Djunaedy <ery@djunaedy. <mailto:ery%40djunaedy.com> com>
Date: Thursday, June 14, 2007 10:41 pm
Subject: [EnergyPlus_Support] Window5 data vs IDF dimension
To: EnergyPlus_Support@ <mailto:EnergyPlus_Support%40yahoogroups.com>
yahoogroups.com
> All,
>
> I use Window5 data file for my windows properties, and I would like to
> know is the best strategy to model the window (detail vs accuracy vs
> time).
>
> In IDF file, I modelled the windows as a long continuous horizontal
> stripe in the external wall. However in Windows5 I modelled the
> windows in the correct dimensions (glass+frame).
>
> I initially thought that the Window5 data will take precedence over
> the IDF dimension. But referring to the manual, this is not true. When
> there is a discrepancy in the dimension between IDF and Window5, then
> IDF dimension will take precedence.
>
> The glass properties will be taken from Window5, but the dimension
> will be from IDF file.
>
> But what about the frame? The manual does not mention anything about
> the frame, will the properties be taken from the Window5 file or from
> IDF?
>
> This brings the question on what is the best way to model the window.
> If we want to justify, for example, that a certain window is so good
> that we do not need the perimeter heating, then we need to model the
> frame as detail as possible.
>
> Do we really need to model every window exactly as the dimension is?
> This will make the simulation time increased tremendously.
>
> Any suggestion is very welcome.
>
> Thanks,
>
> Ery
>
[Non-text portions of this message have been removed]
The primary EnergyPlus web site is found at:
http://www.energyplus.gov
The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/
Attachments are not allowed -- please post any files to the appropriate folder in the Files area of the Support Web Site.
EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/EnergyPlus_Support/
<*> Your email settings:
Individual Email | Traditional
<*> To change settings online go to:
http://groups.yahoo.com/group/EnergyPlus_Support/join
(Yahoo! ID required)
<*> To change settings via email:
mailto:EnergyPlus_Support-digest@xxxxxxxxxxxxxxx
mailto:EnergyPlus_Support-fullfeatured@xxxxxxxxxxxxxxx
<*> To unsubscribe from this group, send an email to:
EnergyPlus_Support-unsubscribe@xxxxxxxxxxxxxxx
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/