Implementing exceptions for special configurations of circulation pumps

[dcronbach]

Using the current implementation of circulation pumps, there are some configurations in combination with external grids and sinks which might not work.

We can

a) either change the concept of the circulation pump. Probably related issue: vgl. auch Issue 214 auf GitHub #214

b) identify these configurations and implement exceptions for them.

Both alternatives are time-consuming.

[SimonRubenDrauz]

At the moment I think of three different concepts:

• pumps which determine the pressure lift beetwen two junctions: No matter what the input and output absolut pressure value is, only the pressure lift itself is determined.
• pressurce controller are components which are able to set the pressure at one/two specific junctions.
• ext_grids like pressure controller are able to control the pressure at one junction and are able the balance the mass flow within one system.