New HVAC control by system identification

Abstract Modern air-conditioning systems for commercial buildings commonly employ the concept of a “Central All-Air System” and the VAV system in particular is widely used in Hong Kong and other places around the world for energy conservation. In the lengthy wet summer season of Hong Kong, centralised air-handling units (AHUs) dehumidify and cool down the appropriate mixture of return air and outdoor fresh air to feed a ducting network to various Variable Air Volume Boxes. A good controller for the AHUs is extremely desirable from both human comfort and energy saving points of view. In this paper, a simulation model for a practical air-handling system is presented. Its behaviour under a conventional system of PID controllers is studied. A new controller based on system identification is developed where input and actuating variables are incorporated into a system identification model which can predict the new system status based on past records and suggest the optimal control actions. Computer simulation has proved that such a system identification based controller is superior to the conventional PID controller from at least the following three aspects : adaptation to system change, response rate and energy conservation.