Research On Operation Control Strategy Of Liquid Desiccant Fresh Air Handling Unit Driven By Heat Pump

The liquid desiccant fresh air handling unit driven by heat pump has become a potential air dehumidifier because of its high efficiency,energy saving,health and comfort.Aiming at the liquid desiccant fresh air handling unit driven by heat pump,this paper divides the corresponding operation model of unit under different conditions in hot summer and cold winter zone,and puts forward the most reasonable adjustment control scheme of unit under different operation models through simulation analysis,and designs an unit automatic control system based on PLC to provide reference and basis for the research on operation control strategy of unit.Firstly,the mathematical models of basic physical properties module and core subsystem module are established by the modular modeling method.On this foundation,the simulation model of liquid desiccant fresh air handling unit is established by the MATLAB/Simulink software,which is composed of the basic physical properties calculation module,the number of mass transfer units NTU_m calculation module,the solution outlet parameters calculation module and the air outlet parameters calculation module.The experimental results are compared with the simulation results,and the comparative results show that the relative error between the test value and the simulation value is less than 10%,so the simulation model has a high accuracy.Secondly,the hourly meteorological parameters of typical meteorological year in Nanjing are selected to divide the whole outdoor meteorological area into five regions,and it is concluded that the unit operates in three modes of dehumidification,air supply and humidification under different regions.Based on the simulation model of the liquid desiccant fresh air handling unit,the most reasonable adjustment control schemes under three operation modes are explored.The results show that the unit should give priority to adjusting the fresh air flow and solution concentration when it operates in dehumidification I region.However,the temperature and moisture content of outdoor fresh air in I region are too high.It is difficult for the unit to deal with fresh air to meet the set requirement of supply air moisture content.Therefore,the fresh air should be pre-treated by high temperature cold water before it is sent to the unit.In addition,the unit should give priority to adjusting the solution temperature and concentration when it operates in dehumidification II region,and give priority to adjusting the fresh air flow rate and solution temperature when it operates in humidification V region.In addition,when the unit operates in the supply air III and IV region,only the fan is turned on and all other units are turned off.And the fresh air is directly sent into the room through the fan to improve the indoor air quality.The main regulating parameter of the unit under the supply air mode is the supply air volume,and it is determined by the indoor latent heat load under the premise of guaranteeing the minimum fresh air volume.Finally,using PLC as the control core,the control system of the liquid desiccant fresh air handling unit driven by heat pump is designed.In addition,the overall structure of the control system is composed of the upper computer touch screen and the lower computer PLC.The touch screen reads the running status and data parameters of the unit collected and stored by the lower computer through RS485 or Ethernet communication.The lower computer PLC receives the data information uploaded by the sensor and the operation fault information of unit,and the executing agency and driving devices in the control system are controlled according to the control signal sent by the upper computer.Furthermore,the whole control system has13 digital input points,10 digital output points,14 analog input points and 4 analog output points.