water source VCC activation

[MatNif]

Describe the bug In the cooling resource activation script of the optimisation algorithm (cea/optimization/slave/cooling_resource_activation.py), the water source vapour compression chillers are not always activated to their fullest potential:

The general layout assumed by the scripts is the following:

If the temperature of the water body allows it, the VCC is bypassed and the water is used for free cooling. And if the cooling demand is larger than the capacity of the cooling components the thermal storage is discharged, otherwise it is charged.

However, this second condition uses min(Q_wb;C_VCC) to determine if the cooling energy provided is sufficient. This leads to an underutilisation of free cooling from the water body in case Q_wb > C_VCC and T_wb < T_DC - 2K. And it also leads to a underutilisation of the VCC in case C_VCC > Q_wb and T_wb > T_DC - 2K.

Expected behaviour I would suggest changing the conditions so that these two cases are handled adequately.

[MatNif]

Here is a more detailed description of what I would suggest as a solution:

It is important to note that the thermal efficiency is strictly speaking dependent on the VCC and its operating point.

Assuming that all the heat from the VCC is absorbed by the cold water cycle (water body) and none of it is dissipated in the air, the following holds true under the 2. law of thermodynamics:

Therefore,

Since the real COP is hard to determine and the current model to calculate it seems faulty, I would suggest using an approximation of it for now. The real value of the thermal efficiency has to lie somewhere between 0 and Carnot efficiency:

Assuming it to be close to Carnot efficiency will lead to an overestimation of the energy that can be withdrawn from the water body, however, seeing how rarely this case will probable appear, it might still be a good first approximation.