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

[Sarah Leenknegt]

Hi Marion,

That was a very interesting suggestion, thank you. I am using type93 for 
the input value recall, and placing it in front of type56 did indeed 
stop the convergence problem.

Kind regards,

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 2/26/2013 8:40 AM, Marion Hiller schreef:
> 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
>
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>
>   
>
> -----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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