Research On Energy Saving Of Central Air-conditioning Water System Based On Segmental Speed Regulation And Thermostatic Control

The central air conditioning system has a large proportion of energy consumption in modern building automation equipment,and it has the characteristics of large lag and high equipment coupling,which makes the conventional control effect not ideal.Therefore,this paper takes the central air conditioning water system in service as the optimization object,and takes reducing the overall energy consumption of the system as the optimization goal,puts forward the variable flow group control strategy of central air conditioning based on the segmented speed and constant temperature control based on PLC(Programmable Logic Controller).(1)The experimental bench of intelligent variable flow central air-conditioning system was designed and built.This paper analyzes the working principle of the existing central air-conditioning system and the necessity of variable flow rate transformation,introduces the selection and installation of intelligent detection instruments such as temperature,pressure,flow rate and electric power,and puts forward an energy metering control system composed of three layers: data acquisition layer,control layer and equipment layer.(2)The control requirements were analyzed and the hardware configuration based on PLC was designed.Hardware devices includ CPU module,analog input module,analog output module,and frequency converter,etc.Then the device parameters were set and the communication connection was established to provide the hardware foundation for the formation of remote visual intelligent control.(3)The variable flow control schemes of central air conditioning water system were designed.Analyzing the operation characteristics of the water system test bed by the experiment,the optimized PID constant temperature control program was designed,and an automatic control scheme of segmental speed regulation which was simpler and more efficient was proposed.The control trapezoid diagram was designed and written by GX Works software,and the human-computer interaction interface designed by the Force Control was used to realize the remote terminal control.(4)The experiment verified the rationality of the variable flow control scheme and the energy-saving effects under different loads.The rationality of PID constant temperature control and segmental speed regulation automatic control scheme was verified by whether the temperature difference of heat exchange can be achieved and the length of stable time.,and the variable flow group control strategy of compressor,refrigerating water pump and cooling water pump under different loads was obtained according to the experiment.Then,the parameters of circulation flow,temperature difference of heat exchange,energy efficiency ratio and energy saving rate of the water system under the two control modes and the constant flow rate were compared.The experimental results showed that the designed control schemes had a good energy-saving effects,in the range of 40%～95% experimental load,under the control of segmental speed regulation,the average energy saving rate of the chilled water pump was 68.9%,while the cooling water pump was 58.5%,and the total energy saving rate of the system was 33.1%.Under PID constant temperature control,the average energy saving rate of the chilled water pump was 69.8%,while the cooling water pump was 59.3%,and the total energy saving rate of the system was 33.3%.