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

[Marion Hiller]

Sarah,

in general, very low CHTC values cause convergence errors in all 
simulation programs. Therefore, the min. values is often fixed to value 
of 1W/m² = 3.6 kJ/h. 
If the min. value is very low and the initial surface temperatures are 
set equal to the initial zone temperature convergence problems like pane 
temperature diverging may occur.

I'm not sure but do you use Type93 for input recall or not?

In addition, I have in mind that the component order could help with 
convergence problems. You may check both orders  Type93 before and 
after Type 56.

Marion



Dipl.-Ing. Marion Hiller 
TRANSSOLAR: KlimaEngineering - Technologien für energieeffizientes Bauen 
und Nutzerkomfort in Gebäude 
Munich - New York - Stuttgart + 49.711.67976.0 

Transsolar Energietechnik GmbH, Curiestrasse 2, 70563 Stuttgart 
Amtsgericht Stuttgart - HRB 23347, Steuernummer 99073/00911, USt-IdNr.: 
DE152272639
Geschäftsführer: Dipl.Ing. Matthias Schuler, Dipl.Ing. Thomas Auer, 
Dipl.Phys. Stefan Holst, Prof. Dipl.-Ing. Bleicher 

 

-----Ursprüngliche Nachricht-----
Von: Sarah Leenknegt [mailto:sarah.leenknegt at bwk.kuleuven.be] 
Gesendet: Montag, 25. Februar 2013 19:03
An: David BRADLEY
Cc: trnsys-users at cae.wisc.edu
Betreff: Re: [TRNSYS-users] User-defined CHTC: pane temperature 
calculation diverging

Dear David,

Thank you for your answer. I know about Type93, in fact I have tried 
with one or four time steps, did not make a difference. About the 
correlation, I have manually tried several variable or constant values, 
which I would expect would challenge convergence, but as long as I did 
not use the input value recall, the simulation would run.
In the meantime, I was experimenting a bit, and found the following 
strange solution. The first equation does work, the second one doesn't..
(1) max(0.01,2*abs(surftemp-airtemp)**0.31 + 0*time)
(2) max(0.01,2*abs(surftemp-airtemp)**0.31)

I can accept this as a workaround, but would like to understand why it 
is needed..

Thanks,

Sarah

ir. arch. Sarah Leenknegt - KU Leuven - Building Physics Section - 
Department of Civil Engineering - Kasteelpark Arenberg 40, bus 2447 - 
B-3001 Heverlee, Belgium - tel. +32(0)16321347

Op 2/25/2013 6:49 PM, David BRADLEY schreef:
> 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
>>
>

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