[TRNSYS-users] Difficulty with convergency

[David BRADLEY]

Behzad,

   You have caught the most common error (too long a time step) and I 
must admit that I am not sure why reducing the timestep so far did not 
make the simulation start converging again. The reason that reducing the 
time step helps is that if you have pumps (or fans) that are pushing a 
greater volume of fluid around a loop in one time step than the devices 
that have thermal capacitance can hold then the problem can become 
numerically unstable. Devices that have thermal capacitance are storage 
tanks, pipes, and the building (if there is one).

   I think you'll need to use the TRACE tool (the icon with the foot 
prints in the toolbar on the left of the simulation studio). Activate 
TRACE on the components that are being flagged as not converging in the 
error/warning log. What TRACE does is to write the values of all the 
parameters, inputs, and outputs for each of the activated components to 
the *.lst file at every iteration. By looking at the outputs and inputs 
from one iteration to the next, you can tell specifically which one(s) 
are causing problems. Unfortunately TRACE writes a lot of information to 
the *.lst file and it can be a bit hard to find what you are looking 
for. However, it is a handy tool in cases like this.

kind regards,

  David


On 12/10/2018 08:17, up201700037 via TRNSYS-users wrote:
> Dear Users,
>
> I am simulating a building which is cooled or heated by heat generated 
> by sollar collectors and stored in Stratified tank type4. The 
> simulation goes well with 6oo liters volume of the tank. Then i 
> decided to reduced the size of the tank to reach an optimum volume. I 
> tried for the cases of 500 to 100 liters and got the results but when 
> reducing the volume to 50 liters the simulation diverges because of 
> many warnings stating that many types in the simulation did not 
> converge at this time step(30s). Therefore, i decided to decrease the 
> timestep. I repeated the simulation even for the least time stem 
> defined in trnsys but it did not converge. I also tried to change the 
> relaxation factor but didnt work. I read that some people suggest that 
> if i increase the convergence criteria or the limit number for 
> warnings in the control cards, it will converge but it is not solving 
> the problem. Actually it seems like cheating. Please help me to solve 
> the problem.
>
> Best regards,
> Behzad shahzamanian sichani
> _______________________________________________
> TRNSYS-users mailing list
> 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
F:+1.608.278.1475
d.bradley at tess-inc.com

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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/trnsys-users-onebuilding.org/attachments/20181210/13f7755f/attachment.html>