Quantitative Evaluation On Stability Of Variable Water Volume Air-conditioning System

In the design of air-conditioning system,the quality of the water system will directly affect its comfort and energy-saving effect.Therefore,it is very necessary to improve the hydraulic stability of the air-conditioning water system.The traditional hydraulic calculation of air conditioning system only depends on the selection of pipe diameter and reversed return layout to obtain the limited,local and static balance,but there is no effective measure for the comprehensive,accurate and dynamic balance of the system.Therefore,choosing appropriate control method in the process of dynamic adjustment of variable water volume air-conditioning system,which achieve dynamic hydraulic balance and improve its hydraulic stability,can not only satisfies the requirements of air conditioning comfort but also realize the purpose of energy saving.It has become a topic of concern for many scholars.In order to quantitatively study the hydraulic stability during the adjustment of the variable water volume air-conditioning system,first,a series of experimental studies were carried out to analyze the dynamic changes of the pipe network under pump non-control and constant differential pressure control,and its influence on the hydraulic stability and energy-saving.Secondly,the corresponding simulation model was established by TRNSYS simulation software.The simulation model was composed of pump,valve and other components with hydraulic characteristics,which was built according to the logical relationship of pressure,water volume and impedance.Thus it can overcome TRNSYS software shortcomings of only considering heat characteristics while neglecting the hydraulic characteristics.Then the simulation model of the system was dynamically verified to prove its reliability.Finally,the dynamic changes of the pipe network under variable pressure difference control is studied through the simulation model,combined with strategies of pump non-control and constant pressure difference control,the changes of the hydraulic characteristics of each passive branch during the active branch adjustment were comprehensively studied under the three different control strategies.Based on the quantitative data of hydraulic stability and energy-saving effect of the pump,the advantages and disadvantages of each control strategy are evaluated.The results show that the effect of pressure difference control is obvious in the process of variable water volume regulation from the aspects of hydraulic stability and energy saving,and the effect of variable pressure difference control is better than that of constant pressure difference control.The coefficient of hydraulic misalignment of the pipe network is 0.072 under variable pressure difference control,which is reduced by 0.442 compared with pump non-control.The energy saving of the pump can reach 27.1% under variable pressure difference control while closing the valve of any branch.