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

[a8304506 at graduate.hku.hk]

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