This is a model for an indirect district heating substation. Its main components are a heat exchanger, a flow regulating valve/pump, an expansion vessel and controller that maintains the temperature at the secondary side by setting the position of the flow regulating valve/pump. The supply temperature setpoint at the secondary side can thereby be set to a constant or can be changed depending on the outside temperature.
A mismatch between the setpoint and the actual value of the secondary supply temperature can have different reasons:
Redimensioning the substation, e.g., by using a more efficient heat exchanger or a higher differential pressure at the primary side, might solve these issues.