| Considering the characteristics of large building volume and intensive personnel activities in public buildings,the central air-conditioning systems are generally used to create comfortable indoor environments.Due to lack of adaptation and control for different heat-humidity loads of the central air-conditioning system in some public buildings,the phenomenons of high energy consumption,low energy efficiency,and deterioration of hydraulic conditions were encountered in operational conditions,among them,the central air conditioning water system accounts for the highest proportion in the total energy consumption of the air conditioning system.Therefore,there are great significances to research the energy-saving strategy of the central air-conditioning water system and the hydraulic conditions for achieving energy saving in buildings.This paper adopted the central air-conditioning water system of a shopping mall in Yuzhong District,Chongqing City as the research object,and researched its working conditions of the cold source equipment,energy consumption,hydraulic conditions by actual measurement.Afterwards,using DeST to simulate the building air-conditioning load of the mall,and imported the calculation results into the original central air-conditioning water system energy consumption simulation platform established by TRNSYS.Accroding to the comparison results between measured datas and simulated datas under average working day in summer,the energy consumption simulation method adopted was reliable.In addition,the SPSS had carried out a stepwise multiple regression analysis of the load and building disturbance parameters to establish a load forecasting model.Then,in view of the problems found in the actual measurement research,this paper proposed the optimization schemes of integrating constant pressure differential variable flow control for the chilled water system,constant temperature differential variable flow control for the cooling water system,and variable air volume for the cooling tower,based on the energy-saving mechanism and adaptability analysis of various variable flow control strategies.Simultaneously,this paper analyzed the effectiveness,efficiency-economy of the integrated-optimization schemes proposed by comparing its TRNSYS simulation results with the simulation results of the pre-optimization system,then summarized the changing law of the flow and temperature difference of the variable flow system during the cooling season.Finally,this paper adopted Flowmaster to establish the hydraulic condition simulation platform of the air conditioning chilled water system of the mall.After verifying the reliabilities of the simulation,in order to obtain the optimized energy-saving programme for better hydraulic conditions,this paper researched the hydraulic conditions of different constant pressure difference control modes under variable load conditions based on the integrated-optimization programme which has been proposed.The conclusions of the research as follows:(1)The actual measurement research found that if the water pump and cooling tower fans operated in the control mode with the minimum operating frequency settings,when the overall building air conditioning loads were low and fluctuated nearby the minimum setting conditions,the pumps and cooling towers started and stopped frequently,which was likely to cause more motor loss;when the overall building air conditioning loads were overall higher than the minimum setting conditions,the water pumps and cooling tower fans operated at a fixed frequency,which would cause the energy consumptions rose.(2)The actual measurement results showed that the energy consumption of the chiller and pump accounted for about 88% of overall energy consumption in the original air conditioning system,which brought a large potential for energy saving.However,the COP values of the chiller within each actual measurement day flactuated from 3 to 4,which was less than the limit of relevant standards.The phenomenon indicated that the system had low energy utilization efficiency.The temperature differences between the supply and return water of the chilled water system and the cooling water system within each actual measurement day were lower than the design temperature difference(5°C),which caused the system was in a high flow and small temperature difference operation state.(3)The simulation results of the TRNSYS variable flow optimization simulation platform showed that the integrated-optimization scheme has achieved a better energy saving effect.Compared with the original system,the COP value of the chiller in the integrated-optimization system increased about 56.46%,and the average energy consumption of the air-conditioning water system has been reduced about 29.66%,among them,the average energy saving rate of the chiller,chiller water pump,cooling water pump,and cooling tower were 28.54%,34.68%,35.85%,26.33%;meanwhile,the average temperature differences of chilled water and cooling water increased approximately 19.95% and 6.95%,which indicated that the phenomenon of large flow rate and small temperature difference has been improved.(4)The hydraulic condition of the chilled water system was related to the setting position of the pressure difference control.Under partial load conditions,compared with the terminal constant pressure differential control of the most unfavourable loop method,the air conditioner's capital heads were higher when the system adopted the beginning-constant pressure differential control,and the rise of the capital head will cause the increasement of consumption pressure drop on the regulating valves and the decreasement of the valve authorities,which will further deteriorate the hydraulic conditions of the system.Therefore,it is more reasonable to adopt the terminal constant pressure differential control of the most unfavourable loop in the air-conditioning chilled water system. |
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