Study On Temperature And Humidity Decoupling Control For CC&AC Control System

In order to control the room temperature and relative humidity, variable machine dew point control method is needed in Contamination Control & Air-Conditioning system. As the temperature and humidity control channel are coupling so it is difficult to control. In practically the phenomena of the cooling valve, heating valve and add humid valve opening at the same time is present commenly which results in the energy wastes. So decoupling control is an effective method in multivariable control system.An automatic control system which consists of PC and PLC was designed for a constant air volume and four-pipe water CC&AC system. A temperature and humidity decoupling control method in this variable dew point control CC&AC system was presented in this paper to resolve the coupling problem between temperature and humidity.Two input and two output transfer function matrix model was established by combining the theoretical analysis with the data analysis of experiment. By introducing absolute humidity as an intermediate variable to control the relative humidity, the coupling channel between heating valve and room relative humidity was decoupled; and a feedforward compensator was designed to decouple the channel coupling between cooling valve and room temperature. A control system consisting of feedforward compensator and PID control was designed. The simulation based on MATLAB results demonstrated that this method is effectiveness and it is also the effective method to control temperature and humidity system.