[TRNSYS-users] (no subject)

[David BRADLEY]

Weihua,

  First, if you are using Trnsys18 then I would recommend that you work 
your way through some of the tutorials that are in the 09-Tutorials.pdf 
(..\Trnsys18\Documentation). There are a lot of issues in your email 
that are very fundamental to the correct use of Trnsys and that would be 
worth understanding well.

  The warnings that you refer to are probably warnings about timesteps 
when the simulated system did not converge. TRNSYS has a limit so that 
if more than a certain number of warnings are generated, the simulation 
will terminate with an error. You can adjust the allowable number of 
warnings before the error but I would not recommend you do so; non 
convergence issues should be corrected.

  It is hard to tell you how to solve convergence problems; it depends 
on what you're simulating. The usual problems are that you do not have 
any enough thermal mass in the loops of a system. For instance if you 
have a Type1 solar collector, pump and heat exchanger model in a loop 
then those are all quasi steady state models and there is no thermal 
mass. The models will react unrealistically fast to external changes and 
may result in convergence problems. The other typical problem is too 
long a time step. Trnsys can only make one control decision per time 
step. If you are controlling a system with a 1 hour time step then the 
system will likely be unstable and have problems converging. I recommend 
using something between a 1 and 5 minute timestep.

  For your question about the active layer I would recommend that you 
refer to the Type56 manual to understand the limitations on the model.

kind regards,

  David



On 08/08/2018 19:48, 吕伟华 via TRNSYS-users wrote:
> hello,I am student, I use TRNSYS to do some simulation works. I have 
> some confusion during my work. I conducted a simulation system of a 
> new air conditioning system on the pletform of TRNSYS. the type56 was 
> used to build the building model and the active layer was used to 
> simulate the pipe-embedded wall.
> My questions are:
> 1) I have built the simualtion model and it can run successfully. but 
> when I change the weather data from one city to another city, and 
> change the envelope insulation(U value), other things keep the same. 
> then I ran the simulation again, it began to work, but after a period 
> running, it breaked and the message shows that"the maximum number of 
> warnings allowed per simulation has been exceeded". I donnot know why. 
> Can you explain this situation for me? and how should i do ?
> 2) similarly, in some simulation, when I set the timestep one hour, it 
> can run successfully, but if I set the time step 30 minutes, or less 
> time, it began to run but then occur the same error as "the maximum 
> number of warnings allowed per simulation has been exceeded". can you 
> help me with this question?
> 3) for the parameter of the active layer,when I change the pipe wall 
> conductivity value,the allowed minimum water flow will change. the 
> default value is 0.792kJ/hmk，if i change this value to 1.56 kJ/hmk, 
> the allowed minimum water flow willincrease, bigger than 13 kg/h.m2. 
> what is the relation between the pipe wall conductivity and the water 
> flow rate? can you help me with this phenomenon?
>   looking forword for your reply. many thanks!
> Best wishes!
> Weihua
>
>
>
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-- 
***************************
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

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