Variable Pressure Differential Optimization Control Strategy For Variable Flow Water System In Central Air-conditioning

The energy consumption of air-conditioning water systems in public buildings accounts for about 15%-20%of the total energy consumption.Therefore,the optimal control and stable operation of the air-conditioning cold water system is the key to energy saving.The stability of pipe network system is the key to the healthy and stable operation of air conditioning system.So in this paper,a simulation model of once variable flow primary pump air conditioning of chilled water system is established,several operating conditions of variable flow chilled water system of primary pump with snap-off valve are simulated.This paper studies and analyzes the hydraulic operation characteristics of the pipe network system with the most unfavorable thermal loop and the influence of the position of the differential pressure control point on the operation stability of the system.The results of hydraulic stability evaluation of the pipe network show that when there is no most unfavorable thermal loop in the pipe network,setting the pressure difference control point at the supply and return water main pipe is more conducive to the system stability.When the most unfavorable thermal loop exists in the pipe network,the stability of the system is better if the pressure difference control point is set at the most unfavorable hydraulic terminal.Aiming at the problems existing in the previous methods of constant pressure difference control for supply and return water main pipe,this paper proposes an optimal control strategy of variable pressure difference based on flow rate change.On the premise that the regulating valve at the most unfavorable end is always fully open,when the flow rate of each branch changes synchronously,the total resistance value of the load side pipe network increases by 15.6%when the flow rate of the pipe network changes continuously from 100%to 30%.So in this paper,a pipe network synthetic characteristic curve is synthesized from several characteristic curves of the simulation model system.When the variable pressure difference control strategy is adopted in the chilled water system and the flow rate required by the user is changed,the DP_setwhich is closest to the optimal setting value of the difference in water pressure between supply and return can be directly obtained by applying the comprehensive characteristic curve of the pipe network.Check the flow level on each branch,compared with the design condition,the maximum deviation of flow is 6.3%and the minimum is only 0.1%.At the same time,users with large flow demands should be set on the side close to the cold source as far as possible,good results can be achieved by applying the integrated characteristic curve of the network network to control the variopressure difference of the system.Finally,the optimal control method of variable pressure difference set value based on energy saving is proposed,and the corresponding optimal control strategy of water pump is explored.When the flow ratio of the pipe network is reduced to 30%,the energy saving rate of the pump power consumption can reach 41.1%compared with the constant pressure differential control when single pump frequency conversion+power frequency pump variable number operation is adopted,and when multiple pumps synchronous frequency conversion+number control is adopted,the power of single frequency conversion water pump under the control of the differential pressure can be reduced to 0.68k W,and the energy saving rate can reach 69.9%compared with the constant pressure differential control.Therefore,under the optimal control strategy of variable differential pressure set point proposed in this paper,the overall energy-saving effect is better by using multiple pumps synchronous frequency conversion+number control.The research results show that compared with the constant pressure differential control method,the variable pressure differential optimization control method proposed in this paper has a good reference value for the energy saving operation of air conditioning water system.