Hi again, I should also tell you that the proposed equation is
C_c = sum(abs (T node_i^m - T node_i^m-1) / nx),
where nx stands for the number of nodes.
The reason of changing "abs(sum...)" for "sum(abs...)", is that we
think the form abs(sum...) (as it is stated in the source code) could
not sum up properly, or carry out the substractions between the levels
or iteration of the nodes temperatures correctly.
Regards,
Miguel Casas
-------------------------
DE: saleh saadi <salehsnjsaadi404@xxxxxxxxx>
PARA: "EnergyPlus_Support@xxxxxxxxxxxxxxx"
<EnergyPlus_Support@xxxxxxxxxxxxxxx>
ENVIADO: Viernes, 24 de mayo, 2013 19:51:57
ASUNTO: Re: [EnergyPlus_Support] Why does E+ lose accuracy for lower
values of the space discretization constant?
Based on my previous check of the E+ code (version 7), the
convergence criteria is calculated as such:
C_c = abs(sum (T node_i^m- T node_i^m-1) / sum(T node_i^m) ), where m
stands for iteration level.
As the number of nodes increases, it is good to use small convergence
criteria as well as small time step. This seems to work well for me
when Gauss-Seidell solver is used with the equation of convergence
criteria mentioned above .
Are you modeling Phase Change Materials (PCM) or massive structure?
If you are not modeling any of these structures, then go for CTF
algorithm.
regards
Saleh
-------------------------
FROM: Miguel Casas <miguelcasasarredondo@xxxxxxxxx>
TO: "EnergyPlus_Support@xxxxxxxxxxxxxxx"
<EnergyPlus_Support@xxxxxxxxxxxxxxx>
SENT: Friday, May 24, 2013 5:37 PM
SUBJECT: Re: [EnergyPlus_Support] Why does E+ lose accuracy for
lower values of the space discretization constant?
Hi Saleh. I am glad you answered.
Yes, I am sure the number of nodes increase by decreasing the Space
Discretization Constant (C). I quote from the Engineering Reference
Documentation: "Lower values for the Space Discretization Constant
yield more nodes, with higher values yield fewer nodes".
I already modified the Convergence Criteria, using the lowest value.
My results got better, but still, the same tendecy came out: lower
values for C would generate lower accuracy. Why could this be
happening?
When I read the Engineering Reference Documentation I found kind of a
definition for the Convergence Criteria. I quote:
Because the solution is implicit... The Gauss-Seidell iteration loop
is the inner-most solver and is called for each surface. It is limited
to 30 iterations but will exit early when the sum of all the node
temperatures changes between the last call and the current call,
normalized by the sum of the temperature values, is below 0.000001C.
This convergence criteria is typically met after 3 iterations...
From what I understood, the Convergence Criteria is given by
C_c = sum^i (T node_i^t - T node_i^t-1) / number of nodes.
Is this equation correct? Am I interpreting this parameter correctly?
-------------------------
FROM: Miguel Casas <miguelcasasarredondo@xxxxxxxxx>
TO: "EnergyPlus_Support@xxxxxxxxxxxxxxx"
<EnergyPlus_Support@xxxxxxxxxxxxxxx>
SENT: Wednesday, May 22, 2013 3:37 PM
SUBJECT: [EnergyPlus_Support] Why does E+ lose accuracy for lower
values of the space discretization constant?
¿ENERGY PLUS: WHY DOES THIS SOFTWARE LOSE ACCURACY FOR LOWER VALUES
OF THE SPACE DISCRETIZATION CONSTANT?
I am using Energy Plus to simulate a cubic test hut without air
conditioning in a hot climate. When I modify the Space Discretization
Constant (C), set as default as 3, awkard results come out. I was
expecting that lower values for C would yield more accurate results.
Nonetheless, when I use low values for C, the results tend to lose
accuracy. The fully implicit finite difference scheme was used with
the default convergence criteria.
Miguel Casas Arredondo
52 (777) 2245453
Insituto de Energías Renovables
UNAM
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