[TRNSYS-users] Error creating transfer function coefficients

[Kim Goethals <kim.goethals@ugent.be>]

Hello,

I found the following message. My model suffers from the same problem. Isn't there an easier way to simulate
a very thick insulated wall? I tried the following: I splitted the wall with for example 5 layers in two walls,
respectively with 2 and 3 layers. I define the same surface, orientation and the same CHTC's. I only incorporate
the window in one of the two walls. From comparing the simulations of both test cases, I conclude that
this option doesn't work. Please some feedback and hopefully a solution.

Thanks in advance,

best regards.





Dimitris,

Unfortunately, I am not sure that there is a simple workaround to your 
problem. The algorithm that TRNBuild uses to choose the coefficients to 
describe the wall does not work for very thick or in some cases, very 
high capacitance walls. The only solution that I can think of off hand 
is to write your own model for the very thick wall (probably using a 
method similar to the way that storage tanks and the rock bed thermal 
storage models are written). This model could then be attached to a 
Type56 boundary wall that represents the inside surface of your wall. 
Your wall model would take the inside wall surface temperature 
(calculated by Type56) and would return the temperature at the interface 
between the Type56 boundary wall and the wall in your model. If you 
would like to send me your .bui file, I would be happy to take a look at 
it and comment if there are other possible workarounds to your problem.

Kind regards,
david


At 08:23 11/25/2005, Dimitris Anastaselos wrote:

   Hi all!!
     

   I would like to model very thick walls. In the case I am working I
   have walls around 6m! For this case, TRNSYS (i.e. TRNBuild) cannot
   calculate the transfer coefficients. I have created new walls with
   40cm thickness and keeping the U-value constant by changing the
   thermal conductivity.

   When I save the project, the following message is shown:

   Error creating the wall transfer function coefficient:

   Stability criteria not fullfield

   Check layer definition (thickness, ratio of conductivity/density)

   Please check the INF-file for further information


     

   When I check the INF-file the same message is shown: Stability
   criteria not fullfield

   I have changed the TIMEBASE from 1 to 2 but the problem still remained.

     

   The same was when I set TIMEBASE=3 or 4 or 5 or 6. Only when the
   TIMEBASE is 7 the problem is solved but then the following message
   is shown:

   * *

   Error creating the wall transfet function coefficients:

   Unable to find a root after indication that a root exists.

   Maybe the timebase is too small.

   Please, check the INF-file for further information

   * *

   If I set the TIMEBASE around 100 the above message still remain.


   What can I do to work around this problem?

   --
   Anastaselos Dimitris
   Dipl. Mechanical Engineer
   Laboratory of Heat Transfer and
   Environmental Engineering
   Aristotle University Thessaloniki
   Box 483 54124 Thessaloniki, GREECE
   Tel: + 30 2310 996048
   Fax: + 30 2310 996012
   e-mail: [EMAIL PROTECTED]
   URL: http://aix.meng.auth.gr
     

--
kim goethals
engineer-architect
department of architecture and urban planning
faculty of engineering
university of ghent
t + 32 (0)9 264 78 61
f + 32 (0)9 264 41 85
www.architectuur.ugent.be

begin:vcard
fn:Kim Goethals
n:Goethals;Kim
org:Universiteit Gent;Vakgroep Architectuur & Stedenbouw
adr;quoted-printable:;;Plateaustraat 22;Gent;Oost-Vlaanderen;9000;Belgi=C3=AB
title:ir.-arch.
tel;work:092647861
tel;fax:092644185
url:www.architectuur.ugent.be
version:2.1
end:vcard