[TRNSYS-users] Type 952 - Convergence and flow/temperature drop

[David BRADLEY via TRNSYS-users]

Hélène,

   I would go back to the version that has all Type31s then replace one 
of those Type31s with a 952. Put an online plotter that shows the 
temperature and flow rate of liquid into and out of the Type952. Go 
carefully through the parameters and make sure that they are all 
reasonable values and that there isn't something like a very low deep 
earth temperatures.  Hopefully the results will make sense at which 
point you should replace a second Type31. Type65 can be a very powerful 
debugging tool to make sure that the system is operating as expected.

  Have a look also at the time step and the flow rate through the pipes. 
If you have a long time step and a short pipe then it may be that the 
convergence problems are because liquid flows through the pipe network 
multiple times per timestep and causes numerical instability in the results.

kind regards,

  David



On 09/12/2017 04:56, Hélène THIEBLEMONT via TRNSYS-users wrote:
>
> Good morning everybody,
>
> I am modeling a district heating and cooling system. Therefore, in 
> order to model the pipes, I am using the Type 952 from TESS.
>
> However, after a comparison with the use of a simple pipe (Type 31), I 
> have two problems:
>
>   * First, I have a significant period of my simulation that does not
>     convergence. To give you an example, if I change only 5 pipes from
>     Type 31 to 952 my simulation does not converge 34% of the time and
>     if I change all of them my simulation does not converge 100% of
>     the time, even in reducing the time step to 0.1hr. Is there
>     anything to do that may help TRNSYS to converge in that situation?
>   * Secondly, and what is particularly strange to me: when I replace
>     my types 31 by 952, the results become completely crazy. I’ve
>     attached two files with the temperatures and flow that go in and
>     out, with the type 31 and the type 952. As you can see, the
>     results are logical with the type 31, and the flow and the
>     temperature drop close to 0 with the type 952 without any reason.
>     Do you have any idea of what may cause this kind of problems?
>
> Thank you very much for your time and help,
>
> Sincerely
>
> Hélène
>
>
>
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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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