Check mass flows/pressure drops in singlezone_commercial_hydronic

[icupeiro]

I think that the mass flow rates in the singlezone_commercial_hydronic testcase should be revised.

We have unsuccessfully tried to do an identification in this model, and the main issue we saw is that the 3-way valve positions (even in the peak period) are always near to be closed (around 1% opening) with the baseline controller. This makes the identification process highly difficult due to the lack of excitation.

Having done a deep dive in the model, I observed that there is only one speed controlled pump, but the pressure drops of the circuit are in the order of a few thousands of Pascals, which seem a bit unrealistic to me looking at the performance curves of the pump model: the resulting mass flow rates in fully open conditions are very very large and represent an idealistic case more than a real case. Therefore, the valve has to work almost closed to produce a large pressure drop and adapt the flow to the set-point.

I would suggest to increase the fixed pressure drops in the circuit to avoid this behavior. An idea is to adapt these to have a resulting mass flow rate at open conditions m_nom = Q_nom/c_p/dT_nom, based on the DH heat exchanger.

[dhblum]

Another issue @haraldwalnum reported is that the pump operation may be inconsistent with valve operation. He reports that currently the main pump is running at constant speed, but the valves operate based on a variable flow system (fixed pressure difference), so that when there is no heat demand, the pump runs full power against a closed system. @Mathadon offered to potentially take a closer look.