The Corrective Control Of AHU Operation In Central Air Conditioning System Based On The Actual Characteristics Of The Equipments

At present,the energy consumption of the centralized air-conditioning system accounts for a large proportion of the total energy consumption of the building.Under the background of energy-saving and emission-reduction,how to optimize the operation of the centralized air-conditioning system and reduce its energy consumption has become a research hotspot in the industry.The AHU is an important air-handling unit of a centralized air-conditioning system.The operation of the AHU will greatly affect the energy consumption of the centralized air-conditioning system and the stability of the room temperature and humidity parameters.Simulation is a powerful tool to study the control of AHU.At present,most of the simulations on AHU operation control strategies do not focus on the actual working characteristics of devices in AHU.The equipment models such as air and water valves often use theoretical simplified models.This will cause the control strategy deviate from the ideal situation which applied in the actual AHU model.Therefore,this article study the control deviation of the AHU based on the actual characteristics of the air valve and water valve.This article first built a AHU control bench,test the water valve,fan,air valve,to get its actual operating characteristics.Secondly,a simulation model of the AHU and its control system was established based on the mathematical model of each device of the AHU in MATLAB/Simulink.In order to get heat transfer effect law of the cooling coil,the influence of different import parameters on the heat transfer of the cooling coil and the temperature and humidity parameters of the outlet air was studied.In PI control system,the setting of the parameters K_p and K_i plays a crucial role in the operation of the AHU.The AHU is operated according to the outdoor air ratio designed by the ideal characteristic model of the air valve,which will lead to the deviation of the actual outdoor air volume,mixed air temperature and heat exchange amount,and the heat exchange efficiency of the cooling coil is reduced.Based on the actual operating characteristics of the air valve,an opening correction link is added in the control loop and the values of parameters K_p and K_i were reduced in the meantime to adjust wind loop parameters meet the ideal conditions.For a system that adopts return air temperature control method,the PI parameters which adjusted by the ideal model applied to an actual AHU model will cause frequent water valve oscillations,large fluctuations in the supply air temperature,and eventually cause room temperature oscillations and overshoots.Based on the actual operating characteristics of the water valve,when the water valve operates at a relatively high degree of opening for most of the time,the values of K_p and K_i must be properly reduced to reduce the system oscillation;when the water valve operates at a lower level for most of the time.The values of K_p and K_i must be adjusted to values smaller than those in the former case,since the small change in the opening degree at this time causes a large fluctuation in the heat exchange amount of the cooling coil.When the water valve changes largely during most of the time,the variable air volume should be used to control the room temperature.The water valve is used to control the supply air temperature and increase the Kp value appropriately to increase the corresponding speed.After the adjustment,the actual operation of the water valve and the room temperature become stable.The research results of this paper show that the actual operating characteristics of the AHU equipments are often different from the theoretical characteristics,resulting in the deviation of the actual operation of the system from the ideal operating conditions.It is particularly necessary to conduct a site-testing on the equipment and formulate a corresponding control scheme based on its actual operating characteristics.