Auto-Tuning of PID Controller and Robustness Assessment under Variable Disturbances for Electric Heat Pump-Air Handling Unit with Variable Air Volume System

This paper deals with auto-tuning of proportional-integral-derivative (PID) controller gains for a first-order system with dead time under ON/OFF operation and examines the control performance of a tuned PID under various disturbances. Taking thermal noise and heat load into account, an effective auto-tuning and control method for a PID controller of a supply air fan in a direct-expansion type air handling unit (AHU) was proposed. Experiments were conducted under various conditions using a calorimeter as an experimental device instead of using an actual AHU system. The validity of the proposed method was verified by confirming precise control of the indoor temperature to the set value through experiments conducted under various disturbance conditions and operating points. Moreover, the stability and repeatability of the tuned PID controller were verified through analysis of the pole position of the PID closed control system based on the transfer function obtained from the dynamical characteristic experiment. The PID controller with tuned gains demonstrated desirable control performance by maintaining the indoor temperature within the desired range of 24℃ ± 0.3℃.