Application Of PID Parameters Auto-tuning In Heating Ventilating And Air-conditioning

The Energy consumption of Heating Ventilating and Air-conditioning (HVAC) occupies more than 60 percent of energy consumption of the whole building. Most HVAC controllers are PID controller and the parameters of controllers are invariable. When the load, humidity, the pressure of air, the chilled water temperature and the outer environment change, especially when the humidity and the room load change bigger, the control effect of blaster temperature and pressure is bad. Thus, it is important to study on auto-tuning method of the unit controller of HVAC, which shorten the adjustment time and heighten control precision and stabilization. It is can efficiently reduce the energy consumption in the HVAC system.Firstly the operating process is analyzed. The HVAC system itself has some characteristic, for example, big inertia, long dead time, nonlinearity and time-variety, which make the traditional PID control can't control well. Two continue relay-feed experiments are adopted to identify the actual process model of two-order-plus-deadtime. The PID controller parameters are adjusted in accordance with the amplitude margin and phase margin on line afresh. The auto-tuning PID control can completely satisfy the demand of not only comfortable air conditioning engineering but also high precise air conditioning engineering.The HVAC system' structure is very complex, which has hundreds of control loops even more. Firstly all the control loops are grouped based on equipment and design the performance index of group loops. The bad loops could be found by the performance index. Secondly, from the bad group loops seek for the single loop based on the standard deviation of the control error of single loop.Finally, take the visual C++ 6.0 and SQL Sever 7.0 as the develop tool to develop the unit controller parameters optimization software package and do the test. The result indicates the software works well.