As far as I know, you don't, but that depends on your model. In the MSL they are using "acceptable" values in types and then use these types.

Modelica tools will prioritize start values that are set via modifications close to the top level in the instance hierarchy.
So, if you have issues set the start values via variable modifications in your top model.
Also, most tools can tell you which variables are used as iteration variabels via some flags.

To make matters worse tools use different variables as iteration variables so models working in one tool (because of proper start values) will not initialize in another.

Let's take ThermoSysPro as an example, in ThermoSysPro, it deals with the initialization problem as @adrpo said, liked showed in the following screenshot which is from the example model shipped with ThermoSyspro, but when I try to use the same method, I really can't find which variable I should set values to, cause I don't know which variable causes the initialization failure in a big system.



Here is another method from Thermal Power Library developed by Modelon, in this library, each component seems to transfer the values layer by layer until to the iteration variables, but again, I am not sure which variables are chosen as iteration variables in advance, so I have to modify the code after an initialization failure.

Here is a similar question on StackOverflow.

https://stackoverflow.com/questions/609 … ica-models