[TRNSYS-users] User-defined CHTC: pane temperature calculation diverging

[David BRADLEY]

Sarah,
   If you are using Type93 for the input value recall please be aware 
that its first output is not delayed; it is the value of the input at 
the current iteration. You need to use the second output in order to get 
the input from the last time step.

   Whether or not the above fixes the problem, I don't think that 
Trnsys3D has anything to do with the issue. Trnsys3D is really just a 
way of getting data into TRNBuild in a more visual manner. You might 
also look at your convection coefficient correlation. The correlations 
that are built in to Type56 raise the surface to air temperature 
difference to a power less than 1 (dampening the effect of the 
temperature difference). It may be that your correlation is too 
sensitive to the temperature difference, leading to convergence problems.
Kind regards,
  David


On 2/25/2013 04:49, Sarah Leenknegt wrote:
> Dear TRNSYS-user,
>
> I have the following problem. I am trying to input a CHTC-correlation in the building model. I am using the input value recall to get the surface and air temperature of one timestep before. I can calculate the CHTC and plot it with an online plotter, but whenever I try to use it as an input, a get the "pane temperature calculation is diverging" warnings from the start of the simulation and the simulation stops. The CHTC is non-zero and positive, and for now, the equation used is simply max(1,2*abs(surftemp-airtemp)). If I calculate a variable CHTC without using the surface and air temperature, the simulation runs without error.
>
> I have used TRNSYS3D to make my one-zone model, including one window facing south-west (TURN = -45°) and 4 air nodes. I am using the detailed radiation model, so all air nodes are combined into one zone. Viewfactors and insolation matrix are generated without problem. I have gone back to the most basic simulation, using only the idf imported in a 3D building project standard template, with a standard Meteonorm Uccle climate.
>
> Following recommendations in previous posts, I have set the CHTC at the window to the standard fixed values for inside and outside. I have also checked if something went wrong when drawing the window in sketch-up, but I do not see any lines that shouldn't be there. Changing to a different glazing doesn't help either.
>
> Can anyone give me some help as to what else I can try? I have done this before without problems, but it is the first time I try it with trnsys3D.
> Please answer to me privately as well, as I am not subscribed to the mailing list.
>
> Kind regards,
>
> Sarah
>
> --
> ir. - arch. Sarah Leenknegt,
> Afdeling Bouwfysica, Dept. Burgerlijke Bouwkunde,
> Faculteit Ingenieurswetenschappen, KULeuven,
> Kasteelpark Arenberg 40 - bus 2447, 3001 Heverlee, België
>
> sarah.leenknegt at bwk.kuleuven.be
> tel. 016 321347
> _______________________________________________
> TRNSYS-users mailing list
> TRNSYS-users at cae.wisc.edu
> https://mailman.cae.wisc.edu/listinfo/trnsys-users
>

-- 
***************************
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

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