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

[Damien Casetta]

David,

Thanks for your answer.

As you can see from the attached screenshot, there is, to me, enough
thermal capacitance in the loop (actually it is modelling an existing
system, pipe length and tank volume are known). Simulation time step is 10
min and input data time step is also 10 min.

Thanks in advance for your help,

Have a good day,

*Damien Casetta*

*INSA Lyon* Génie Énergétique et Environnement
**
+33.6.71.78.03.75


On 7 May 2013 22:09, David BRADLEY <d.bradley at tess-inc.com> wrote:

>  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> 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
>>
>>
>>
>> _______________________________________________
>> TRNSYS-users mailing list
>> TRNSYS-users at cae.wisc.edu
>> https://mailman.cae.wisc.edu/listinfo/trnsys-users
>>
>>
>
>
> _______________________________________________
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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:+1.608.278.1475d.bradley at tess-inc.com
> http://www.tess-inc.comhttp://www.trnsys.com
>
>
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