Research On Pipeline Network Characteristics And Energy Saving Operation Of District Air Conditioning Distributed Secondary Pump System

In China,due to the rapid development of urbanization,district air-conditioning systems have received extensive attention with integrated energy.Achieving the hydraulic balance while reducing the energy consumption of transportation is a hotspot and a difficult point.This paper proposes a district air conditioning distributed secondary pump system,expected to improve the transmission efficiency and the stability of the pipeline network by changing the power distribution.Based on the modeling and simulation of the system,this paper analyzes the influencing factors of the energy consumption and the operation characteristics of the pipeline network,and studies the appropriate operation control strategy.This paper is based on the graph theory,using the basic loop analysis method for pipeline network solution.Based on the black box MDOE-2 model,the mathematical model of the energy consumption of the centrifugal chiller is established.Based on the working principle,the mathematical model of the variable frequency pump is established,and the pump operating range is obtained by integrating the maximum flow rate and the minimum speed ratio.Through the least squares method,the system model is parameterized and a system simulation model is established.Verifying the accuracy of the model,the consistency between the actual value and the simulated value is very high.Based on the system model,the influence of the position of the zero pressure difference,the load rate and the non-uniform distribution of the load space on the energy consumption of the system is studied.The calculation results show that the zero pressure difference is set between the cold source and the critical point,and there is no need to add a valve,where the transport coefficient is up to 37.1,and the chilled water transport economy is the best;.When the load rate is 70%,the highest energy saving rate of the distributed system is 50.8%.The spatial distribution of load has no effect on the centralized system.By comparing four typical spatial load non-uniform distribution schemes,the pump system of the second scheme where the load is concentrated on the nearest end of the pipeline network is the most energy efficient.The sensitivity method was used to study the influence of power form,pump characteristics and zero pressure difference position on the stability of the distributed secondary pump system.The front-end users of the pipeline network have better stability with centralized power,while the users at the far end of the pipe network have better stability with distributed power.The pump characteristic curve can be divided into steep type and flat type,the source side primary pump is flat type,and the branch secondary pump is steep type combination system has the best stability.When the zero pressure difference is selected at the middle of the pipe network,the overall stability of the system is the best.The hydraulic imbalance characteristics of the system are analyzed by hydraulic imbalance method,and the hydraulic misalignment and hydraulic stability coefficients are calculated to solve the hydraulic imbalance problem.Based on a district cooling and heating project in Nanjing,the operation control strategy of the distributed secondary pump system was analyzed,including the unit number control strategy and the pump frequency conversion control strategy.According to the system servicing for office and residential,combined with the hourly cooling load coefficient,analyze its load characteristics.The loading/unloading strategy of the heat pump unit and the corresponding primary pump is studied.The control strategy of the secondary pump frequency conversion and the number of variables is analyzed.At the same time,the secondary pump should be set to the lowest flow operation mode,and the minimum flow rate should be maintained by bypass connection or mixed water connection to increase the efficiency of the secondary pump.By calculating the energy consumption of the system during the typical summer day and cooling seasons,compared with the centralized system,the energy saving rate of the distributed secondary pump system under typical summer day is 17.4%,the energy saving rate during the whole cooling season is 18.1%,showing the energy saving effect is obvious.