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Didier,<br>
Type56 uses something called the conduction transfer function (CTF)
method for determining the energy transfer through walls. The
(admittedly oversimplified) idea of the CTF method is that a series of
weighted averages going back in time is developed to tell how important
the temperature difference across the wall is now, how important it was
an hour ago, how important it was two hours ago, etc. The size of the
step back in time is called a time base and it doesn't have to be one
hour; you can set it in the TRNBuild "outputs" window . There are also
a number of other factors (such as the history of the energy transfer
through the wall) for which there are also weighted averages
determined. Type56 and TRNBuild are limited to using the first 20
coefficients determined.<br>
<br>
If you have a wall that is too massive or not massive enough then
TRNBuild has a hard time determining the CTF coefficients. For example,
if you have a thick stone wall, the conditions of that wall more than
20 hours ago may matter quite a lot to the energy transfer now (in
other words, there isn't enough there aren't enough CTF coefficiencts
developed). If you have a very lightweight wall (like a metal door)
then all the conditions that matter to the energy transfer across that
wall occur right now (in other words the time base is too big).
TRNBuild generates the "failed to fulfill stability criteria" error.
You can tell which wall caused the problem by looking in the *.inf
file. Look first near the bottom and the inf file will show you the
coefficients that it generated for each wall. Note the name of the last
wall for which it generated coefficients then scroll up to the top of
the file. The wall AFTER the one that successfully generated in the
list of walls is the one that caused the problem.<br>
<br>
If it is a lightweight wall that caused the problem, simply treat it
as a "resistance only" in other words, that wall should be made up only
of a massless layer.<br>
<br>
If it is a very massive wall that caused the problem you can increase
the time base.<br>
Best,<br>
david<br>
<br>
<br>
<br>
<br>
On 6/30/2010 08:48, <a class="moz-txt-link-abbreviated" href="mailto:gossard@cict.fr">gossard@cict.fr</a> wrote:
<blockquote cite="mid:20100630154839.ba6sfrwq8s88ggoc@webmail.cict.fr"
type="cite">Hi all,
<br>
<br>
I'm working with TRNSYS 16 with Type56. TRNBuild suddenly stops with
the following error message :
<br>
<br>
"Error creating the wall transfer function coefficients :
<br>
<br>
Stability criteria not fullfilled
<br>
<br>
Check layer definition (thickness, ratio of conductivity/density)
<br>
<br>
Please, check the INF-file for further information."
<br>
<br>
What is this "stability criteria" ?
<br>
<br>
Please find enclosed the INF and BUI-files.
<br>
<br>
Best regards,
<br>
Didier.
<br>
<br>
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<pre class="moz-signature" cols="72">--
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI 53703 USA
P:+1.608.274.2577
F:+1.608.278.1475
<a class="moz-txt-link-abbreviated" href="mailto:bradley@tess-inc.com">bradley@tess-inc.com</a>
<a class="moz-txt-link-freetext" href="http://www.tess-inc.com">http://www.tess-inc.com</a>
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