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<DIV dir=ltr align=left><SPAN class=998554407-02072010></SPAN><SPAN
class=998554407-02072010><FONT face=Arial color=#0000ff size=2><SPAN
class=451585007-02072010>Hi all,</SPAN></FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=998554407-02072010><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=998554407-02072010><FONT face=Arial><FONT
color=#0000ff><FONT size=2>in order to avoid these problems with thick and
lightweighted walls, there are another methodes to calculate the heat transfer
through walls, so called finite difference methods.<SPAN
class=451585007-02072010>Es</SPAN>pecially the crank-nicholson method is a very
good <SPAN class=451585007-02072010>possibility to to that. Our first
experiences with a CN-Type are positive. Moreover this method seems to
allow the simulation of pcm-materials.</SPAN></FONT></FONT></FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=998554407-02072010><FONT face=Arial><FONT
color=#0000ff><FONT size=2><SPAN
class=451585007-02072010></SPAN></FONT></FONT></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=998554407-02072010><FONT face=Arial><FONT
color=#0000ff><FONT size=2><SPAN
class=451585007-02072010>best</SPAN></FONT></FONT></FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=998554407-02072010><FONT face=Arial><FONT
color=#0000ff><FONT size=2><SPAN
class=451585007-02072010></SPAN></FONT></FONT></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=998554407-02072010><FONT face=Arial><FONT
color=#0000ff><FONT size=2><SPAN
class=451585007-02072010>Hans-Jürgen</SPAN></FONT></FONT></FONT></SPAN></DIV>
<DIV><FONT face=Arial color=#0000ff size=2></FONT> </DIV></DIV>
<DIV> </DIV>
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<P class=MsoNormal><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">GN
Bauphysik Ingenieurgesellschaft mbH<BR><SPAN class=SpellE>Bahnhofstr</SPAN>.
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<FONT face=Tahoma size=2><B>Von:</B> David Bradley [mailto:bradley@tess-inc.com]
<BR><B>Gesendet:</B> Donnerstag, 1. Juli 2010 17:21<BR><B>An:</B>
gossard@cict.fr<BR><B>Cc:</B> trnsys-users@cae.wisc.edu<BR><B>Betreff:</B> Re:
[TRNSYS-users] Stability criteria.<BR></FONT><BR></DIV>
<DIV></DIV>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.
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</PRE></BLOCKQUOTE><BR><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>
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