.Buildings.Fluid.HydronicConfigurations.ActiveNetworks.Examples.InjectionTwoWayVariable .Buildings.Fluid.HydronicConfigurations.ActiveNetworks.Examples.InjectionTwoWayVariableThis model is almost similar to Buildings.Fluid.HydronicConfigurations.ActiveNetworks.Examples.InjectionTwoWayConstant except that a cooling system is represented, and the consumer circuit is a variable flow circuit with a variable speed pump and two-way valves. The pump speed is modulated to track a constant pressure differential at the boundaries of the remote terminal unit.
For this circuit to operate as intended, it is critical that the
secondary supply temperature set point be different from the primary
supply temperature.
Otherwise, the tracking error does not change sign and there is no
overshoot that can desaturate the integral term of the PI controller.
In other words, the controller output is fixed as soon as the measured
value equals the set point.
Therefore, the equilibrium point typically differs from the control
intent which is a primary flow rate varying with the load.
One can observe that behavior by setting
TLiqSup_nominal=TLiqEnt_nominal and
have_resT2=false.
Such setting yields a fixed valve position with a primary recirculation
and a flow reversal in the bypass whereas the control intent would
be a slightly closer position ensuring a positive flow in the bypass.
Note that this is nearly invisible from an operating standpoint
since the set point and the loads are met.
However, this is definitely detrimental to the overall performance
as the primary circuit is operated at a higher flow rate and lower
ΔT than needed.
The system practically behaves as there was no control valve installed
on the primary return line.
The fact that the load seems unmet at partial load (see plot #4) is due to the load model that does not guarantee a linear variation of the load with the input signal in cooling mode, see Buildings.Fluid.HydronicConfigurations.ActiveNetworks.Examples.BaseClasses.Load.