title: How do I avoid circular equality errors in a closed media circuit? (modelica)
body: <p>I'm attempting to build a model of a pumped water heat exchange loop in modelica using thermal.fluid library components (doing my compiling in OpenModelica). The inlet of the constant-volume pump connects to a flow port from a heated pipe component, which is ostensibly the "last" stage in the circuit which is driven by the pump, and so the loop is completed. </p>
  
  <p>This system worked when my media flowed from an ambient source, through the pump, through the system, and out to an ambient sink, but now that I've "completed the circuit," the simulation fails and I receive "circular equality" errors. This makes a modicum of sense physically, as pressure-type variables need a baseline to reference, but it seems that the friction-based elements in my system would create pressure losses through the system, and the pump would operate normally, as pressures would arrive at zero in the piping leading up to the pump. </p>
  
  <p>Any ideas on how to clear these "circular equality" errors, or particular pitfalls I should be looking out for? Could it be that the constant-volume pump operation is interfering with the pressure calculations, and I should use the ideal pump library component?</p>
  
  <p>Thanks for your thoughts!</p>