[TRNSYS-users] Unknown unit number + negative flow rate errors

[David BRADLEY]

Damien,
   As far as your question 2/ is concerned, my guess is that the time 
step in question did not converge. When components do not converge after 
a certain number of iterations, TRNSYS stops iterating and makes the 
"end of time step" call, then goes on to the next time step. In earlier 
versions of TRNSYS, this was referred to as the "post convergence" call 
but really that is poorly named since that call is made whether or not 
convergence was reached.

   Check to make sure that there is some thermal capacitance in your 
flow loop and that your time step is not too big. If you have simplified 
the loop by omitting the piping or if you are using too long a time step 
convergence of the controls becomes very challenging.
Kind regards,
  David


On 5/7/2013 06:27, Damien Casetta wrote:
> Hi,
>
> Thanks Ciarán for your help. However, the .lst file doesn't say much 
> more about the errors.
>
> 1/ The unit number (24) is not written on the input file. Plus, the 
> associated type changes (and is not in the current simulation in most 
> cases) each time I get this error. Let's forget about this then.
>
> 2/ The second error ("a negative flow rate was encountered") has 
> retained my attention (first of all because it stops the simulation) 
> and I would be glad if I could draw your attention on this issue. 
> Please find attached the TRNSYS model and refer to it for unit and 
> type numbers. As you can see I have traced the critical components to 
> better understand the error. Here is what happens :
> - During post-convergence call, mass balance is not achieved through 
> the first tee piece (Type 11, Unit 55). Input flow rates are 339,8 
> kg/hr and 0 kg/hr whereas output flow rate is 339,6 kg/hr (equal to 
> iteration 0 and 1 of the current time step and to the converged value 
> of the previous time step). Right after this, in the lst file, a fatal 
> error is detected (no unit specified), as attached in my previous 
> message. Does it occur at iteration 0 of the next time step? Why is it 
> post-convergence call (current time step) if a simple mass balance is 
> not checked?
>
> Feel free to ask if you need more info about the project,
>
> Thanks a lot for helping me on this,
>
> Have a nice day,
>
> *Damien Casetta*
>
> *INSA Lyon* Génie Énergétique et Environnement
> +33.6.71.78.03.75
>
>
> On 3 May 2013 16:41, Flynn Ciaran <ciaran.flynn at aalto.fi 
> <mailto:ciaran.flynn at aalto.fi>> wrote:
>
>     Hey Damien,
>
>     Click on the "Lst file..." tab, you can see it from the screenshot
>     you took. This will open your lst file and when you scroll to the
>     bottom of it you will get more information about the type of
>     errors you are getting.
>     (Note that to access this file directly, go to the same directory
>     as your trnsys file and it's the text file in the same name)
>
>     Hope this helps,
>
>     Bon wkd,
>
>     Ciarán
>
>
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>
>
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-- 
***************************
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
d.bradley at tess-inc.com

http://www.tess-inc.com
http://www.trnsys.com

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