Extremum seeking control for efficient and reliable operation of air-side economizers

Economizers have been recognized as a class of energy-saving devices for heating, ventilating and air conditioning (HVAC) systems that may increase the energy efficiency by taking advantage of outdoor air during cool or cold weather. There has been a tremendous demand for reducing energy consumption of HVAC systems in commercial buildings. However, many economizers do not operate in the expected manner and waste even more energy than before installation, mostly traceable to the unreliable sensors and actuators in practice. In this paper, an extremum seeking control (ESC) based self-optimizing strategy is proposed to minimize the energy consumption. Rather than depending on the unreliable temperature and humidity measurements, the proposed strategy is based on the feedback of chilled-water supply command. The mechanical cooling load is minimized by seeking the optimal outdoor-air damper opening in real time. Such scheme does not need temperature and humidity sensors and depends much less on the knowledge of the economizer model. Simulation was performed on a Modelica based transient model of a single-duct air-handling unit (AHU) developed with Dymola and the AirConditioning Library. The simulation results demonstrated the potential of using ESC to achieve minimal mechanical cooling load in a self-optimizing manner. In addition, an anti-windup ESC scheme is proposed to overcome the ESC windup issue due to actuator (damper) saturation. The simulation results validated the effectiveness of the proposed anti-windup ESC.