calling 'calculate_derivatives_thermal' once

[SimonRubenDrauz]

• Just calling 'calculate_derivatives_thermal' once instead of calling it for each component seperately
• renaming TINIT and T_OUT in TINIT and TOUTINIT in branch

[codecov]

Codecov Report

Attention: 17 lines in your changes are missing coverage. Please review.

Comparison is base (6a87439) 85.23% compared to head (2aae8dc) 85.06%.
Report is 11 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #563      +/-   ##
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- Coverage    85.23%   85.06%   -0.17%     
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  Files           90       90              
  Lines         6202     6181      -21     
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- Hits          5286     5258      -28     
- Misses         916      923       +7     

Files	Coverage Δ
...component_models/abstract_models/base_component.py	92.30% <100.00%> (+1.92%)	⬆️
.../component_models/abstract_models/branch_models.py	83.67% <100.00%> (-4.94%)	⬇️
...odels/abstract_models/branch_w_internals_models.py	91.15% <100.00%> (+0.07%)	⬆️
...dels/abstract_models/branch_wo_internals_models.py	85.45% <100.00%> (+0.26%)	⬆️
...mponent_models/abstract_models/circulation_pump.py	90.62% <ø> (+1.07%)	⬆️
...omponent_models/circulation_pump_mass_component.py	100.00% <ø> (ø)
...nent_models/circulation_pump_pressure_component.py	100.00% <ø> (ø)
...dapipes/component_models/flow_control_component.py	100.00% <100.00%> (ø)
...pipes/component_models/heat_exchanger_component.py	98.00% <100.00%> (-0.12%)	⬇️
pandapipes/component_models/pipe_component.py	84.81% <ø> (-0.47%)	⬇️
... and 11 more

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[dlohmeier]

In general, I like this whole approach and it's about time to put together all branches when calculating the thermal derivatives. One thing that strikes me is the variable TINIT / TINIT_IN that we define in branch_idx and that you rename here. This is not a solver variable, so I would suggest to throw out this variable fully. It leads to confusion, because "the branch temperature" is not defined. It would make more sense to me to always define which temperatures precisely I need in what constellation. If I want the intermediate of the two neighboring junctions, I have to get from_nodes and to_nodes beforehand.

[SimonRubenDrauz]

@dlohmeier: What I do not understand: What do you mean by throwing out the variable? Shall we rename it? I wouldn't throw it out completely because we use it in different functions.

[dlohmeier]

Yes, it is used, but it can be replaced by a call like

from_nodes = branch_pit[:, FROM_NODE].astype(np.int32)
to_nodes = branch_pit[:, TO_NODE].astype(np.int32)
t_init = (node_pit[from_nodes, T_INIT] + node_pit[to_nodes, T_INIT]) / 2

The advantage is that there is more control over what value really is needed in the specific case. If we assume that a fluid property of a branch element depends on the branch temperature, it makes sense to rethink how the temperature of this branch should be calculated. In case of thermal calculation, we would definitely need to change the above statement to:

from_nodes = branch_pit[:, FROM_NODE].astype(np.int32)
t_init = (node_pit[from_nodes, T_INIT] + branch_pit[:, T_OUT]) / 2

but in case of hydraulic simulation, T_OUT might not be properly initialized. We have to check this again, but I think that it is more useful to assume that the temperature is a very local (point) variable that cannot be a branch variable and each time you need "the temperature" of a branch, you have to define it yourself.

[dlohmeier]

This now looks good to me.

[SimonRubenDrauz]

@dlohmeier: I just checked how T_OUT is initialized in a pipe. Actually it is exactly what you described above:

Thus, both equations above should get the same result in the hyadraulics calculation. So we could use this definition:

t_init = (node_pit[from_nodes, T_INIT] + branch_pit[:, T_OUT]) / 2

to always calculate the correct temperature:

[SimonRubenDrauz]

I reconsidered your point and decided to throw out TINIT completely. I agree that it is really misleading and causes confusion. And the result is that I found something what really confuses me.
In some files we use the branch temperature combined with p_from/p_to. You can find this in the pump_component, result_extraction for example where we determine v_mean/v_from/v_to. I also apated it. I guess, it was a mistake. What do you think?

[dlohmeier]

Wouldn't it make more sense to import this? Less error prone...

[dlohmeier]

I like the adjustments here. Guess we have to look at the pump again, but it seems that you were able to fix a few error prone implementations here.

[SimonRubenDrauz]

@dlohmeier, can we merge this PR. All changes have been realized which you recommended.

[dlohmeier]

Looks really good to me. This should improve performance and be a great preparation of using numba for thermal simulation as well, and we got rid of yet another branch variable. :-D