Stability analysis on air conditioning system

Room air temperature control of a single zone space is studied. In air conditioning systems, no matter what the forcing -a step or impulse in setpoint or slight disturbance-, the loop can easily get into huntings. Variable air volume (VAV) control is very common for air distribution in air conditioning system today. The supply air flowrates to the room can be controlled by damper or by fan speed control. Such a VAV system is assumed to be essentially to the source of huntings. To explore the possible existence of huntings, a dynamical system model is formulated as a bilinear model with time-delayed feedback (by P or PI control actions), and a parametric analysis of the stability region is presented. Results are given showing the stability region affected by the selection of setpoint values and control parameters. This analysis is conducted to help us tune the PID controllers for achieving good control performance.