Study Of The Energy Saving Control Strategy Of Air Conditioning Terminal Equipment Based On Constant Temperature Difference Of Chilled Water

With the improvement of people’s living standards,China’s building energy consumption has continued to grow,and building energy conservation challenges are enormous.In buildings with central air conditioning,central air conditioning operates at very high energy levels,exceeding 60%of the building’s total energy consumption.With the rapid development of modernization,the energy problem becomes more and more tense,which will restrict the sustainable development of economy.Saving central air conditioning energy consumption in public buildings is imminent.The central air conditioning system serves the end users,and the terminal equipment is the main component of the central air conditioning system.Relevant data shows that the operating energy consumption of the terminal equipment is higher than the transmission energy consumption of the system,accounting for about 30%of the energy consumption of the central air conditioning system.In the central air conditioning system,the heat exchange capacity of the surface heat exchanger can be changed by adjusting the chilled water flow rate and air volume of the end equipment to meet the demand for load changes.Due to the extreme load considerations of the air conditioning system design,coupled with the reliability requirements of the project and the fact that most of the end equipment does not have the function of continuously adjusting the water flow,the chilled water of the end equipment often has a phenomenon of"large flow and small temperature difference".And because of the difference of user load,the temperature difference of the chilled water of each terminal device is also uneven,especially the air conditioning system based on fan coil is particularly obvious.When using the chilled water pump frequency conversion adjustment,no matter the fixed temperature difference adjustment or the constant pressure difference adjustment,it is based on the concentrated effect of the main pipe,which is quite different from the actual operation state of the terminal equipment,and the adjustment effect is restricted.In addition,in the current research on energy-saving of air-conditioning systems,the energy saving of the end-fans is often ignored,and the attention to energy consumption of the air supply system of the terminal equipment is insufficient.In fact,the influence of the fan control method on the room temperature and energy consumption cannot be ignored.To meet the indoor comfort and further reduce the energy consumption of the air conditioning system,it is of great significance to adopt more effective control methods for the end equipment.The heat and moisture exchange in the surface heat exchanger is a complex and multivariable process.The chilled water flow and air flow through the surface heat exchanger have strong coupling to the heat exchange capacity of he surface heat exchanger,the air outlet temperature and the chilled water discharge temperature.The degree of coupling between the variables is high,and the decoupling is difficult.How to adjust the flow rate of chilled water and the air flow rate at the same time,so that the air-conditioned room can reduce the energy consumption of the fan and pump under the premise of achieving comfort,which is an urgent problem to be solvedBased on the above considerations,the mechanism of the surface heat exchanger is deeply studied in this paper.According to the working principle and the classical theoretical formula of the surface heat exchanger,the physical models of the end components of the central air conditioning system are established in detail.Furthermore,the corresponding simulation model is established through the Simulink function block in Matlab.The influence of the flow rate of frozen water and air volume on the heat transfer performance of surface heat exchanger and the temperature of outlet water of frozen water is studied by simulation in order to seek the law of the change of parameters affecting the heat transfer process,and the regulation method of wind-water coupling of surface heat exchanger is obtained.A control strategy based on constant temperature difference control for surface heat exchanger of air conditioning terminal equipment is proposed.The correctness of the control strategy is verified by system simulation.On the basis of this,the fan-coil experiment system is built,and the corresponding controller is designed and developed.The correctness,feasibility and energy conservation of the control strategy of wind-water control is verified by the experiment.The experimental results are in good agreement with the simulation study.The adjustment method of wind-water coupling for surface heat exchanger can be used in practical engineering.It can not only meet the requirements of room temperature and the temperature difference of the chilled water at the same time,but also have a good control effect and stability.When all the terminal equipment of the central air conditioning system are adjusted,the temperature difference of the chilled water system can be guaranteed,the system can obtain good regulation characteristics,and the energy consumption of the fan and water pump can be reduced.At present,the control strategy of the surface heat exchanger proposed in this paper has applied for invention patent and has been tested in practice.