Research On Temperature And Humidity Independent Control Strategy Of VRF-VAV Composite Air Conditioning System

VRF(Variable Refrigerant Volume)system-variable refrigerant flow multi system,that is,the control of refrigerant flow and through the direct evaporation of refrigerant or direct condensation to achieve refrigeration or heating air conditioning system.VRF system has many advantages such as energy saving,comfort,smooth operation,and the rooms can be independently adjusted to meet the different air conditioning load needs.Because of the good performance of the VRF system,it has been widely used in commercial air conditioning systems.Due to the lack of fresh air,the VRF system itself can only meet the room temperature requirements and seriously affect the room air quality.The VRF system can’t achieve the control of the temperature and humidity at the same time.It is difficult to meet the requirements of high temperature and humidity requirements or human comfort requirements when ignore the room humidity adjustment.Under this situation,a VRF and VAV(Variable Air Volume)composite control system is proposed,which not only solves the problem of VRF air conditioning system,but also solves the problem of room temperature and humidity control at the same time.Introduce the characteristics of VRF and VAV system,and establish the composite air conditioning system.Respectively,proposed VRF and VAV control logic.Based on the simulation platform,VRF-VAV composite air conditioning system can be set up for independent control of temperature and humidity.In order to verify the accuracy of VRF model,the simulation model of VRF subsystem is established,and the corresponding experimental platform is set up to verify the operating characteristics of VRF subsystem model.The simulation results are in good agreement with the experimental results,indicating the rationality and accuracy of the VRF subsystem model.In order to realize the independent control of indoor temperature and humidity,the VAV air temperature control strategy is studied.Respectively regard the outdoor fresh air moisture content or indoor relative humidity as the input signal control method,and establish the model.From the aspects of energy saving potential and humidity control,the two control strategies are simulated and compared.The simulation results show that it is more reasonable to select the indoor relative humidity as the input signal of indoor humidity independent control.Based on the simulation platform,the relationship between the air supply temperature of VAV and the relative humidity of the room is studied.On this basis,the independent control strategy of temperature and humidity is proposed.In order to verify the effectiveness of the independent control strategy of temperature and humidity,two cases were proposed,which are the influence of room wet load change and different outdoor weather parameters on temperature and humidity independent control strategy.Room wet load changes include high humidity load,low humidity load and mutation humidity load.Different outdoor weather parameters include high temperature and humidity and high temperature and low humidity two different situations.The simulation results show that the independent control strategy of temperature and humidity has good effect for different cases.In order to control the relative humidity of the room more precisely,optimize the VAV air supply temperature,introduce the genetic algorithm,and propose the independent control strategy of temperature and humidity based on genetic algorithm.First,the indoor relative humidity prediction model is established according to the air supply temperature of VAV.Then the cost function is established,that is,the deviation of the relative humidity between the indoor humidity and the relative humidity obtained from the forecast of the air supply temperature,and the optimized value of the VAV air supply temperature is obtained by minimizing the cost function.According to the VAV side of the new air supply air temperature control loop,adjust the electronic expansion valve opening of VAV,to achieve the control of the air supply temperature.The simulation results show that the temperature and humidity of the room can meet the setting requirements under the control of the independent control strategy of temperature and humidity based on genetic algorithm.In this paper,the temperature and humidity independent control strategy for VRF-VAV composite air conditioning system can solve the problem about relative humidity,and realize the independent control of the room temperature and humidity.