Research And Implement Of Variable Flow Control System In Central Air-Condition For Energy Efficiency

The central air-condition consume a high percent (about 50%) energy of a building. But the most time building air-condition run under the low load operation condition. The reason is that the design standard of building air-condition is according to most disadvantageous operation condition, and the load calculation of building air-condition use the approximate method. In china, the most building air-condition are the constant flow system. They can not adjust the flux to the actual load of air condition and the pumps always run under the rated load. Therefore the chiller and the pumps capacity always exceeded the actual requirement. The operation cost has become heavy burden of building manage.Variable flow hydraulic system is an effective energy-saving measure, which could adjust the flux to the load of central air condition. To solve the problems in the design and operation of constant flow hydraulic system, this thesis suggested that convert constant flow into variable flow. In this thesis, the situation about variable flow hydraulic system used in china was introduced, and the significance of variable flow for energy efficiency was illuminated. From the analysis results of pump's characteristics, evaporator and condenser's thermodynamic characteristics and the performance influence of the variable flow conversion to chiller, the feasibility of the conversion was proved.This thesis is on the basis of actual object that the hydraulic system of Qing-Tai edifice was converted into variable flow hydraulic system. Condenser water system and chilled water system were converted after analyzes of the original hydraulic. Variable flow system used constant temperature differential control method, and adopts transducer to adjust the speed of pump. To solve the long dead-time of hydraulic system, single neuron with Smith predictor controller was applied in the temperature control. Hardwires structure and connecting mode was presented; software's structure, flow of program and user-interfaces were introduced in this thesis. The conversion only changed or added a few devices in the original hydraulic system. The result of test running proved that this system is concise and reliable. Not only save the running charge largely, but also reduce the work of operator.