[TRNSYS-users] tank and glycol.

[David BRADLEY]

Dear Fernando,
   I have had some troubles with the stability of the Type60 heat 
exchanger model too. I think that the algorithm for the natural 
convection heat transfer coefficient on the outside of the exchanger is 
at fault. One workaround would be to use Type534 from the TESS Storage 
Tank library in place of Type60 if you have access to it. You might also 
try changing the Type60 internal time step. Lastly, check carefully over 
your tank and heat exchanger configuration to make sure that they are 
correct. Putting a very big heat exchanger into a small tank can cause 
the kind of instability in calculating the heat exchanger UA.

   The answer to your question about freezing depends on the component. 
Some components may deal with freezing phenomena while others do not. 
None of the solar water heating components in the standard TRNSYS 
library account for freezing of the working fluid. Having done some 
research work on it, I can tell you that it is enormously difficult to 
predict when freezing will become a problem because it has almost 
everything to do with how the system is installed, not how the system is 
designed.
Best,
  David


On 11/12/2010 09:59, Sancho,Fernando wrote:
>  Dear Trnsys-users,
> Im using Type 60 as a Tank  and have a convergence problem with the 
> solar heat exchanger just when I use glycol in it.
> error *non convergences for Hx 1. Final UAHx value =* 345.adjfhadgfg
> That is a reported problem in the list, the solutions indicated were 
> normally  about "adding pipes in the solar loops", to be sure that 
>   in a certain time step  a portion of fluid is not going in and out 
> the pump or similar problems. Or decresing  the internal time steps of 
> the tank.
> I tried a wide rate of values for both variables  but it didn´t work. 
> And that happens just not always in the same time step, it depends on 
> the limit of my simulation, i find that strange as well.
> So i´m getting into the "physics behind" during the weekend, but 
> ...hat anyone any advice?
> And, about the same situation , with water in der solar loop 
> everything runs with no problems...but can someone explains to me how  
> deals TRNSYS with a freezed fluid in the collector?
> Thanks a lot!!! Enjoy the weekend
> (David, thank you, I added my new type succesfully after testing)
>
>
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-- 
***************************
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

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

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