| With respect to "double-carbon" goal,there is a long way to go for building energy saving potential since air-conditioning energy consumption accounts for over 45% of total building energy consumption,thus it is imperative to reduce air-conditioning energy consumption.VAV(Variable Air Volume)air conditioning system has attracted much attention due to its advantages of energy saving and thermal comfort.However,some problems are encountered in the operation practice,such as complicated internal components,high non-linearity,large time-varying and strong coupling,which lead to inaccurate control and difficult tune,especially when the system is utilized to a large space,the traditional control method easily results in energy waste and local over-cooling or over-heating,therefore thermal comfort of indoor people are deteriorated.In order to solve the aforementioned problems in VAV air conditioning system,this paper focuses on VAV air conditioning system,aiming to investigate the control algorithm and control strategy of VAV air conditioning system by means of control simulation modeling and experimental verification,etc.Firstly,the mathematical models of various components of central air-conditioning system are summarized,and some transfer function expressions are given,which provide theoretical basis for the modeling of air-conditioning system in the following chapters.Next,taking an actual air-conditioning system as an example,the operation data of the air-conditioning system are sorted and analyzed,common problems existed in air-conditioning system,e.g.,insufficient control precision,temperature inhomogenous distribution in space.Then,to address the above issues,the terminal control of air conditioning system is modeled by Matlab/Simulink,and the control effectiveness of three different control algorithms,namely PID(proportional,integral,derivative),fuzzy PID and MPC(Model Predictive Control),are compared.The results show that MPC control algorithm can respond smoothly and promptly to adapt complex and changeable indoor cooling loads,reduce the frequency on/off control,improve the stability and control accuracy of the system,and finally enhance indoor thermal comfort.In order to handle the problem of local over-cooling and over-heating in large space,TRNSYS(Transient System Simulation Program)and Matlab/Simulink software are used to model a large space air conditioning system,in which the whole space is divided into several sub-areas without physical partition.for the purpose of achieving more practical control results,the CONTAM(Contamination transport)program and TRNSYS are added to co-simulation.In this paper,CONTAM is applied to calculate the airflow coupling between adjacent areas,and TRNSYS regulates the supply air flow rate to track the zonal temperature set-point with regular PID controllers.In order to further reduce energy consumption,the zonal demand control strategy is optimized,which adjusts the zonal temperature set-point in real time on the basis of the current cooling load demand to avoid unnecessary energy waste.Finally,The simulation results showed the zonal demand model could alleviate the over-cooling or over-heating phenomenon in conventional temperature control.Thermal comfort performance was also improved by considering the zonal temperature demand.Moreover,it contributed to 18% reduction in fan power consumption compared to the benchmark model. |
