Design Of Refrigerating Machine Sets Supervising System Of Central Air-conditioning Based On SIMATIC

Four lithium bromide absorption refrigerating machines are used for concentratedcooling in airconditioning system of certain tobacco plant. Opeartion and control ofEach refrigerating machine is independent by manual mode, which is backward andinefficient, cannot meet the requirement of product supply and system energy saving.On the basis of analysing the principle of double-effect LiBr absorption chiller, thetechnics process of circulatory water system including colling water, colling tower andchilled water, an automatic controlling scheme for four refrigerating machinesparalleled is presented, which used Siemens S7-300PLC and Profibus-DP. The paperdesign a parameter self-tuning fuzzy PID controller to realize the closed-loop controlfor circulating water pumps and fans. Meanwhlie, an software based on SiemensWINCC is designed for the upper PC, it realized a centralized supervisory to wholecolling ststem.Syetem hardware based on Siemens S7PLC is designed, it is configurated bymeans of Field Bus. System software structuralized programming complete the controlto refrigerating machine stes by mutual calling among various function blocks. Thispaper presents network structure to control industrial field equipment withPROFIBUS-DP, Industrial Ethernet and MPI network. The paper use group control wayto control refrigerating machines’7colling pumps and6fans of cooling tower, whichaiming at colling water inlet and outlet temperature, utilize1converter to enable morepumps (or fans) respectively and adjust frequency automatically to control one ofthem.With fuzzy-PID control algorithm, the system performs optimizing closed-loopcontrol by real-time parameter adjustment. Furthermore, the number of operatingrefrigerating machines depend on control algorithm program about the range of coldload. These designing economize energy effectively, greatiy enhance the stability of thesystem and reduce project costs.After implementing this project, muti-machine paralleled can be control throughthree ways: automatic control, remote network control, local control. Furthermore, theresult shows that system has strongly control function, high reliability, convenientdebugging and maintence, it’s electricity energy-saving effect reach above20%.