Research On Control Strategy Of Variable Primary Flow System

With the rapid development of China’s economy and society, the building energy consumption in the proportion of the total energy consumption of society is growing. It has increased from 24.5% in 2007 to 32% in 2012, the large public building energy consumption accounts for 22% of the total building energy consumption, centralized air-conditioning system power consumption accounted for 50% to 60% of total electricity consumption of large public buildings. Centralized air-conditioning system will become the focus of building energy efficiency. As one of the most effective energy saving measures, central air conditioning research and application of variable primary flow system gradually attention has been paid. But we found that it often fail to be frequency-conversion pump in accordance with the design requirements in actual projects, it is also less than ideal energy-saving effect. I studied the control methods and control strategy of variable primary flow system, including the following:In this paper some of basic theories and control system of variable primary flow system are expatiated first,then several key problems in variable primary-flow system’s application are proposed.The hydraulic condition of variable primary-flow system under different control modes are analyzed and compared, discussed the applicable conditions of different control modes and energy saving effect. Several control methods for the energy-saving effect: Temperature Difference > Variable Pressure Difference > Terminal Pressure Difference > Trunk Pressure Difference. In addition analyzed the practical engineering problems existing analyzes which could provides a reference for designers.Then we study an office building in Chongqing, and test the ground source heat pump and chilled water pumps. Through data analysis, we found that "a large flow of small temperature difference" problem in water systems is existed and chilled water pumps are not in accordance with the design variable flow operation. The main reason for this problem is caused by the control strategy did not play a real regulatory role.Then according to the analysis of the situation of water systems tested,I have two recommendations for improvements to the building control strategies: I suggest the temperature control and valve position control for improvement aim to the terminal pressure control method.Through the detailed analysis of the control principle, I pointed out that the control method has the advantages of good energy saving and stable control. And gives the specific regulation strategies.I proposed the calculation method of the valve opening for the fan coil in the end of the office building, and calculated the equivalent valve opening degree with 11 story office building as an example; I conventional PID control strategy proposed fuzzy PID control algorithm based on fuzzy self-tuning strategy. I set up to simplify the transfer function model through the 11-storey building with a room as an example.By comparing the simulation software simulink I found that when the system model changes or there are disturbances, and the initial PID parameter values unchanged, Fuzzy self-tuning PID control are better than conventional PID control with overshoot volume, adjust the time, anti-interference ability and other performance indicatorsIn fully considered the impact of variable flow water system of the various factors,based on detailed design and build the experiment platform of air conditioning water system, To provide the experimental basis for the comprehensive study of the control mode and control strategy of the variable flow water system.