Re: [TRNSYS-users] Timebase and Trnsys Message 441

[hotline <hotline@Transsolar.com>]

Dear Eva,

the best choice of the time base is:

time base = time step

However, this isn't always possible and you'll receive an error message.

The step of temperature is related to that fact that the time base is larger then the simulation time step. When the wall history is updated based on the time base a step might be encountered.

For control it is recommended to use a component with hysteresis like 
Type 2 and NOT Equations. The "freezing" indicates that a lot of iterations
are performed at this time step in order to reach convergence. 
You should set the max. number of iteration to a considerable number 
like 50 and improve your control in order to achieve convergence.


Marion
Transsolar Software Team

-----Ursprüngliche Nachricht-----
Von: trnsys-users-bounces@cae.wisc.edu [mailto:trnsys-users-bounces@cae.wisc.edu] Im Auftrag von eva.zacekova@fel.cvut.cz
Gesendet: Mittwoch, 5. Februar 2014 12:56
An: trnsys-users@cae.wisc.edu
Betreff: [TRNSYS-users] Timebase and Trnsys Message 441

Dear all,

I have built a small one-zone building with ceiling heating (active  
layer) in Trnsys, however, its behavior looks a little bit strange to  
me.

The first problem is that I am not sure about setting of the timebase  
in building editor. The U-values of external walls are 0.668 while the  
thickness is 0.225. What timebase would you suggest? I tried several  
different values (0.25, 1, 1.5). With 1 and 1.5, the time profile of  
the zone temperature was somehow stairs-like (fast rising at the  
beginning of the sampling period and hardly changing at the end of the  
sampling period; the sampling period is 15 minutes). With 0.25, the  
zone temperature profile was changing very slowly. In trnbuild manual,  
I have found that the higher timebase value, the "slower" the behavior  
is - however, this does not correspond to the behavior of the building  
I have built. Do you have any suggestions/advices for me?

The next problem is with the heating signal. I consider that the  
active layer is placed in ceiling. In case that the heating signal is  
not very smooth (the temperature of the heating water is changing  
rapidly), the simulation gets stuck (and it also gets much slower) for  
and in the list file, the following Trnsys Message occurs:

"TRNSYS Message 441: The inputs to the listed units have not converged  
at this timestep. The values at the last iteration will be used and  
the simulation will proceed."

Is this message related to the fast changes of the heating water? Can  
I solve the problem of freezing simulation while preserving the fast  
changes of the heating water?

Thank you very much in advance.

Best regards,
Eva
-- 

Dipl. Ing. Eva Žáčeková
Czech Technical University in Prague
Faculty of Electrical Engineering
Department of Control Engineering
Prague 2, Karlovo náměstí 13, E-21
+420 22435 7689

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