| In many modern buildings, the purpose of heating, ventilating, and air conditioning (HVAC) equipment is to maintain a safe and comfortable environment for building occupants. Also, building owners and operators want reliable HVAC systems that have low operating and maintenance costs. To maintain a safe and comfortable environment without wasting energy, it is important to have good control of the HVAC systems. In the HVAC industry, it is common to use proportional-integral (PI) feedback control algorithm. PI control algorithm have two parameters that affect controller performance: proportional gain and integral time and some PI algorithms use the default control parameters shipped with the controller. For some systems, the default control parameters are not appropriate and would lead to poor control performance. Also, many control loops require retiming during the year because a number of HVAC systems have nonlinear and time-varying dynamics and persistent time-varying load disturbances. This paper study a method for automatically adjusting the gain and integral time of proportional-integral (PI) controllers on line ,for adapting to variation of the plant, based upon patterns that characterize the closed-loop response called pattern recognition adaptive controller (PRAC). The algorithm was developed for self-regulating on line systems that can be modeled as first-order plus dead-time systems. The algorithm have been applied to importation (e.g. Johnsoncontrol's DDC in VAV system), but protected by patent so the technique is not published. This paper discusses the implementation and performance of PRAC, and applies the algorithm to pressure loop of supply air duct in VAV system. Simulators and experiments show the algorithm provides near-optimal performance for a range of systems and noise levels, compared with conventional PI controller and optimal PI controller by GA (Genetic Algorithms) setting at one time, adapts to variation of plant characteristic and operating condition. |
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