A robust sequencing control strategy for air-handling units

Abstract

The controllers of air-handling units (AHU) should exploit split-range sequencing control strategies to determine the most economic way to use the AHU components to maintain the outlet air temperature at the set point. The control instability during the transition regions between different control modes as well as the problems in tuning the control loop(s) involving processes of different dynamic parameters are among the major diffculties when utilizing AHU sequencing control strategies in applications. A three PIs split-range sequencing control strategy with ‘freezing’ and gain scheduling schemes (SRFG) is developed addressing these problems. ‘Freezing’ means that the PI output is xed at zero or one together with its integral term. SRFG is evaluated in various simulation tests and by comparing with conventional three PIs split-range sequencing control strategies. Test results demonstrate that SRFG strategy allows stable and robust AHU control.