Simulation Research On Cascade Control Of Temperature And Humidity In VAV System

To solve the problem with the CAV(constant air volume) air conditioning system that it is unable to change the volume of the supply air according to the change of outdoor temperature, which leads to the overcooling of air conditioned building and a waste of energy, the VAV(variable air volume) air conditioning system reduces the airflow when the cooling load drops while keeping the difference between the supply air temperature and the ambient temperature as a constant. In order to accomplish the designing goal, the VAV system should have excellent controlling capacity.The paper begins with an analysis of the operation scheme of the VAV system, then builds up mathematic models of main elements of the system based on the findings of the analysis. Then the paper analyses the dynamic mechanism of four basic controlling units of the VAV system, which are the control of AHU (air handling unit), the combined control of supply air system and return air system, the control of terminal devices and that of the airflow of fresh air sucked into the VAV system. Furthermore, the paper proposes two cascade control systems, one for the control of indoor temperature and the other for the control of indoor relative humidity. The result of simulation experiments proves that the designed cascade systems are able to keep indoor thermal parameters in set points and the control performance is satisfying.The paper combines the theory of neural network with classical PID control theory to design a NN-PID controller which tunes core parameters of the PID controller, which areδ, T_I and T_D , using the BP neural network algorithm. The results of simulation experiments demonstrate that the NN-PID controller is better than the classical PID controller and it has good self-adaptive capacity.