Re: [TRNSYS-users] Strange error when using the equation proforma

[a8304506@graduate.hku.hk]

Hello, David.

Thank you for your reply, but do you mean that the simulation does not start at
the first component as indicated in the input file?  Moreover, does the error
only occur for the wrong equations within the same equation proforma?

Best Regards
LEE, Chun Kwong
City University of Hong Kong

Quoting David BRADLEY <d.bradley@tess-inc.com>:

> 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 and therefore can't be resolved.
> 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
> 
> P:+1.608.274.2577
> F:+1.608.278.1475
> d.bradley@tess-inc.com
> 
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> http://www.trnsys.com
> 
>