separated hydraulic and heat calculation causes unexpected behavior

[SimonRubenDrauz]

feature request
Currently, conducting a heat calculation, a hydraulic calculation is done beforehand. This calculation is done independently from the heat calculation. This can cause unexpected behaviour.

possible solutions
A solution is to couple the heat and hydraulic calcuation. Setting a flag would enable to choose between different options. I see three options:

1. ) Seperated: Keep it like this. heat and hydraulic calcuations are seperated.
2. ) Iterative: The results of the heat calculation are passed back to the hydraulic calculation and the entire calculation is repeated.
3. ) Integrative: heat and hydraulic calculation are done combined.

alternatives
Keep it like this, however, adapt the documentation, so that a user understand the corresponding behaviour.