Chun Kwong,
You are correct in your understanding of how TRNSYS iterates to
solve. However, it has to have somewhere to start so TRNSYS performs
a check on all the equations before starting the simulation to make
sure that it can solve them. If you wrote a set of equations that
said:
EQUATIONS 2
A = B
B = A
there would be no way that TRNSYS could ever solve because it would
have nowhere to begin the iteration. My guess is that your T_CHWS
and T_CHWR equations are too interdependent.
Best,
david
On 12/13/2010 20:38, a8304506@graduate.hku.hk wrote:
Hello, everyone.
I am trying to simulate a chiller plant with primary and secondary chilled water
pump systems. I use to equation proforma to calculate the chilled water flow
and temperature at the supply and return header. However, I get the following
error messages:
*** Fatal Error at time : 0.000000
Generated by Unit : Not applicable or not available
Generated by Type : Not applicable or not available
TRNSYS Message 420 : The following variable defined in an EQUATIONs or
CONSTANTs card could not be solved as this variable depends on either an
undefined EQUATION or CONSTANT name or depends on another EQUATION or CONSTANT
that cannot be solved. For example A=B and B=A would trigger this error
Reported information : T_CHWS
*** Fatal Error at time : 0.000000
Generated by Unit : Not applicable or not available
Generated by Type : Not applicable or not available
TRNSYS Message 420 : The following variable defined in an EQUATIONs or
CONSTANTs card could not be solved as this variable depends on either an
undefined EQUATION or CONSTANT name or depends on another EQUATION or CONSTANT
that cannot be solved. For example A=B and B=A would trigger this error
Reported information : T_CHWR
I am a little bit confused. My understanding is that Trnsys performs the
calculation in the equation proforma based on the input and the sequence of the
equations as typed in the proforma, and the system performance at each time step
is determined component by component which follow the order as indicated in the
input file. Hence, should there be any improper formulation, the consequence
should generally be non-convergence. Is my interpretation wrong, and how can I
solve the problem? Please advise. Thank you!
Best Regards
LEE, Chun Kwong
City University of Hong Knog
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David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI 53703 USA
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d.bradley@tess-inc.com
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