Optimal Control Research On Variable Air Volume (VAV) Air Conditioning System

After the oil crisis emerged in the eruamerican countries in the1960s and1970s,the world began to realize the importance of energy and began to pay attention to thedevelopment and the use of energy-saving technologies in various fields. In the HVACarea, the variable air volume (VAV) air-conditioning system came into being, andsoon got a rapid development and widely application.VAV air conditioning system is relative to the constant air volume (CAV) airconditioning systems, its main feature is that it, according to the changes of indoorload, can change the air supply to meet the indoor thermal comfort requirements bycontrolling the air handling units (AHU) fan’s speed automatically and real-timely.Especially in partial load, it reduces the fan ‘s speed to meet the air flow requirements,so it can avoid energy wasting caused by hot offset in CAV air conditioning system.Therefore, VAV air conditioning system has great energy-saving potential.The study of the optimal control of VAV air conditioning system in this paperincludes two parts-the optimal control of supply air static pressure and supply airtemperature in air handling unit, namely, in order to control the air handling units,theset points of supply air static pressure and supply air temperature can be changedaccording to changes of indoor load.Different from the past study based on simulative experiment, this study bases on acentral air-conditioning system of a real office building in Hong Kong-CambridgeHouse. Data including VAVBox and AHU was obtained from the SQL database by thecommunication system,the optimal control strategies were proposed after analysingthe VAVBox’s air flow and the damper position. A software—OCAHU developed wasapplied to the building management systems (BMS) in Cambridge House, it can sendthe optimized set points to the controller to control AHU automatically andreal-timely. Through the on site tests with several control schemes and analysis withthe data, an optimal control scheme was determined ultimately.From the analysis of the results, the optimal control scheme used in this thesis canreduce the AHU fan energy consumption to achieve the energy-saving purposes aswell as improve the indoor thermal comfort.