[TRNSYS-users] Convergence problem for the internal regulation

[David BRADLEY]

Hugo,

   This kind of problem is not uncommon, especially when doing combined 
airflow/thermal simulations. I have not run into the problem of 
convergence problems inside of Type56, which is a little surprising. I 
thought that I had gotten all of the possible TRNSYS errors at least 
once! The solution I usually use is to implement a short time step (1 
minute perhaps) and then to put a delay component (like Type661 or 
Type150) between Type56's output temperatures and Type98's inputs. It is 
a bit of a cheat but I think with a short timestep it is realistic 
enough. We assume that air entering a Type56 zone immediately mixes 
thermally with the zone air and that thermostats react immediately. When 
you add the automatic heating/cooling that Type56 can do you are further 
assuming that the mechanical systems can react instantaneously and 
provide exactly the right amount of heating and cooling. I don't think 
it is unreasonable to introduce back a small time delay in order to get 
the whole thing to converge.

kind regards,

  David


On 01/07/2021 09:05, Hugo GEOFFROY via TRNSYS-users wrote:
>
> Hello,
>
> We need to modelize a few stories building in a cosimulation 
> TRNSYS/CONTAM.
>
> The thermal part is handled by TRNSYS with a Type 56 and the aeraulic 
> part by CONTAM with a Type 98.
>
> The model works but encounters several convergence problems as noticed 
> in the *.lst file. The model includes daily windows openings that 
> coincide with the convergence problem occurrences. Furthermore, most 
> of the rooms are heated with an ideal system of which power is limited 
> to 100 W.m-2. The setpoint temperature is fixed thanks to a schedule 
> in the "Heating type manager"
>
> Removing this heating resolves the convergence problem, but these 
> convergence faults cannot be fixed by reducing the time step, 
> modifying the number of iterations, or convergence tolerance of 
> Simulation Studio. The following error message shows that the faults 
> are not directly generated in the "simulation studio" calculation but 
> by Type 56 and are indeed a consequence of the heating of the building 
> Type 56 model.
>
> --------------------------------------------------------
>
> *** Notice at time        :       130.000000
>
>     Generated by Unit     :    56
>
>     Generated by Type     :    56
>
>     Message               :  TIME =     130.000  More than 6 
> iterations for internal regulation HEATING/COOLING
>
> *** Warning at time       :       130.000000
>
>     Generated by Unit     :    56
>
>     Generated by Type     :    56
>
>     Message               :  TIME =     130.000  CONVERGENCE NOT 
> ATTAINED USING INTERNAL REGULATION FOR HEATING/COOLING
>
> -------------------------------------------------------
>
> This fault appears while the *.dck maximal iteration is fixed to 500.
>
> Has somebody already encountered this problem in Simulation studio ?
>
> Is it possible and if yes, how the numerical parameters (tolerance of 
> convergence, number of iterations, …) of Type56 can be modified? Do 
> you have any idea for another solution to solve this problem?
>
> Thank you
>
>
> _______________________________________________
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> TRNSYS-users at lists.onebuilding.org
> http://lists.onebuilding.org/listinfo.cgi/trnsys-users-onebuilding.org

-- 
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
3 North Pinckney Street - suite 202
Madison, WI  53703 USA

P:+1.608.274.2577
d.bradley at tess-inc.com

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

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