The Control Study Of Compressor And Electronic Expansion Valve In Ground-source Water-cooled VRV System

The ground-source water-cooled multi-connection system is a new type of air-conditioning system which integrates the sustainable development of ground-source heat pump technology and Variable Refrigerant Volume Air Conditionings system(VRV system)technology.Unlike air cooling system,ground-source heat pump technology are not susceptible to external environmental interference,and the VRV system integrates a variety of technologies,such as multi-split technology,frequency conversion technology,networked control,energy saving and so on.Within a few years,the VRV system has been developing rapidly based on its own energy efficiency.And it has taken a place in the air conditioning market.In recent years,it begun to develop small family VRV system.However,in this rapid development process,there are still some problems in the ground-source water-cooled VRV system,especially the overall control of the VRV system and the energy saving of the ground-source water-cooled VRV system.The contents and results of this study are as follows:(1)Taking the summer cooling as an example,the mechanism of the components in the VRV system was studied,mainly including the electronic expansion valve(EEV),the evaporator,and the compressor,and their mathematical models were established.The coupling relationship between the components was discussed.It was found that the opening degree of the electronic expansion valve was linear with the flow rate,and the first-order inertia plus lagging transfer function between the superheat and the inlet flow of the evaporator was established.(2)Using the Simulink in MATLAB to establish the negative feedback controlsystem of superheat in the evaporator,in which the electronic expansion valve is the actuator,the evaporator is the controlled object,and the superheat of the evaporator is the controlled variable.The controller uses the PI control algorithm,and the optimum superheat response curve was obtained by setting the PI parameters.And by changing the initial value of the system,observing the response curves.It is found that the output response curve does not fluctuate greatly when faced with different initial values,indicating that the established regulation system has good regulation.(3)Taking a room in a certain building in Shenyang as the research object,and a mathematic model of the room was established.The cascade control system with room temperature as the controlled variable was put forward,in which the room temperature is the main parameter and the superheat is the sub parameter.At the same time,the single-loop feedback control system based on the room temperature as the controlled variable was established.Using simulink simulations to compare the two model.(4)According to the drawbacks of the existing compressor control scheme,a coordinated control scheme of compressor-electronic expansion valve was put forward from the integrity and dynamics of the system.It is verified by examples that although this numerical values was different due to the different of the equipment types and operation conditions,but this method was universal.At the same time,the feedforward + feedback complex control system of compressor-electronic expansion valve was put forward on the basis of coordinated control.The coordinated control was used as feedforward adjustment and suction pressure control as feedback regulation,thus the compressor and electronic expansion valve in the VRV system were more accurately controlled.(5)Taking a building in Shenyang area as the research object,the dynamic load simulation model of building was built by using TRNBuild in TRNSYS.Then to build a water-water heat pump system through TRNSYS,simulate the annual hourly energy consumption of the system,and calculate the COP of the heat pump unit.Under the assumption that the operating conditions of ground source heat pump,building load and heat pump unit COP of the water-refrigerant heat pump systemwere equal with the water-water heat pump system.Comparing the energy consumption of the two model,it was concluded that under the same COP value,the power saving rate of the ground-source heat pump+VRV system was 12% than that of the ground-source heat pump + fan coil system,and the annual system coefficient of performance(TASCOP)was higher 14.29%..Above research,the control scheme of VRV system was perfected from the whole,and the phenomenon of system stability and pidity caused by the original independent control logic was solved.Through simulation,it was found that the ground-source water-cooled VRV system has good energy saving.