Resistance minimization control for a secondary pumploop in air conditioning systems

This paper presents the resistance minimization control method of the variable water volume for the secondary pump loop in air conditioning systems, as well as methods of the constant terminal differential pressure control and the variable terminal differential pressure control. As the earliest variable water volume control method for the secondary pump loop, the constant terminal differential pressure control suffers from several drawbacks such as difficulty in selecting the measuring position for terminal differential pressure, uncertainty in determining the setpoint and an increased local resistance at control valves when the flow decreases. The variable terminal differential pressure control achieves better energy saving but is complex to implement. In contrast, the resistance minimization control leverages the monitoring capabilities of the building automation system (BAS) and adjusts the secondary pump speed based on the opening degree of the control valves. This method effectively resolves the limitations of the traditional differential pressure control methods while offering a simpler and more energy-efficient solution.