| Concentrated air conditioning systems are usually designed according to peak load,but in the actual operation process,most of the time concentrated air conditionings are not full-load operation,the variable-flow air conditioning system is to solve this problem.Compared with the constant flow air conditioning system,the variable flow air conditioning system can adjust the cooling capacity of the chiller according to the end load change,and change the frequency of the water pump accordingly,and adjust the system flow to match the end load change,not just the flow change of the end device,which reduces pump power consumption.However,at the same time,the decrease in flow rate can also lead to a decrease in the energy efficiency of the operation of the chiller.Therefore,when measuring the energy consumption and energy saving effect of the variable flow system,the changes of the EER,the pump efficiency,the motor efficiency and the inverter efficiency with load should be considered.How to further improve the operational efficiency of various energy-consuming equipment in the water system has always been one of the focuses of the industry,and it is increasingly valued by research,designers and operation managers.The joint optimization design between chillers and pumps and the water system will have a major impact on the quality of the air conditioner,the energy-saving operation of the system and the environmental protection effect.First established the energy consumption model of the chiller and chilled water pump.For the chiller,first analyzed the heat transfer and energy consumption characteristics of components such as compressor,evaporator and condenser,and then jointly set up a chiller common energy consumption model.According to the overall heat transfer characteristics under different control strategies and different ends,the corresponding energy consumption model of the chiller was established respectively.Finally,the main influencing factors of the energy consumption of the chiller in the variable primary flow system were analyzed.For the chilled water pump,firstly,based on the matching of the pump characteristic curve and the pipe network system,the general energy consumption calculation model of the variable speed water pump was established,and then the differential pressure characteristics of the pipe network and the operating law of the pump operating point under different control strategies were analyzed.Finally,the variable speed water pump energy consumption models were established respectly.Then,an experiment table for variable-flow centralized air-conditioning system was set up,with two types of water systems(all on-off control ends and on-off control ends connected with continuous adjustment ends)under two control strategies(the constant trunk pressure difference control strategy and the constant temperature difference control strategy).The experimental research explored the operating characteristics of the chiller and the variable speed water pump,and confirmed with the theoretical analysis.It was found:(1)Different end control forms and different control strategies have different effects on the heat transfer characteristics of the system: under the constant temperature difference control strategy,the chilled water temperature difference is basically 4 ~ 5.5 °C,and the operation effect is good;under the constant trunk pressure difference control strategy,the system of on-off control has “large flow and small temperature difference” phenomenon,and the small temperature difference phenomenon of the system with on-off control and continuous adjustment ends is alleviated;the overall heat transfer characteristics of the system are different from those of a single coil regardless of the end control form and control strategy.(2)The input power of the chiller decreases first and then increases with the decrease of the load rate.When the load rate is greater than 40%,the input power of the chiller decreases with the decrease of the load rate,and the EER of the chiller is relatively stable.However,when the load rate continues to decrease to the experiment1 condition 5(LR < 30%),the input power of the chiller rises,and a "rebound" phenomenon occurs,at which time the EER of the chiller decreases sharply;(3)Different end control forms and different control strategies have different effects on the system overall hydraulic characteristics.Under the constant trunk pressure difference control strategy,the pump operation is relatively stable,the distribution of the pump operating point is in accordance with the control curve,and its distribution under the on-off control and continuous adjustment hybrid system is more uniform and coherent than the on-off control system;Under the constant temperature difference control strategy,the pump operating point is greatly affected by the uniformity of the end load rate distribution,the system pressure difference changes greatly under different working conditions;(4)The input power of the variable speed pump decreases with the decrease of the flow rate,and has a power relationship with the flow rate.Under the control of constant temperature difference in each working condition,the input power of the pump is lower than that of the constant trunk differential pressure control.The difference of energy saving rate of the pump under the two control modes in experiment 2 is smaller than that in experiment 1;(5)By comparing the similarities and differences between the two systems and the comprehensive energy consumption and comprehensive energy saving rate of the chiller and the pump under the two control strategies,it is considered that when measuring the energy saving potential of the primary pump variable flow system,only paying attention to the variable speed pump the energy saving effect may be exaggerated.And the energy saving effect of the constant temperature difference control strategy is not significantly better than the constant trunk pressure difference control strategy.Finally,the design and optimization of the variable primary flow water system were discussed.On the one hand,the main influencing factors of the minimum flow of the system and the method of determining the minimum flow are analyzed.On the other hand,combined with the characteristics of the pipe network and the changing law of the pump operating point,the ideal pump characteristic curve is analyzed to make it better match the pipe network,and the operation is more efficient and energy-saving. |
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