| As a relatively new system and highly centralized form of air conditioning cooling source,DCS(district cooling system)has been rapidly promoted in China.There is a big difference between the actual operation results and expectation from existing systems.At present,China is experiencing a rapid urbanization and nation-wide energy saving.As a relatively new system and highly centralized form of air conditioning cooling source,wether DCS can be adapted to China's specific national conditions is an urgent question to answer.There are seldom comprehensive researches on operation effect of existing projects in the current studys.Comprehensive research on existing systems could help to master the operation of DCS and give the important feedback about theexperience and drawbacks to theoretical and modeling research.At the same time,it has great significance for planning,designing and reconstruction of DCS.This paper firstly conduct operation monitoring on two DCSs in Jiangsu province and establish a Web monitor platform for one of them.On basis of operational monitoring,the real characteristics of the cooling load is analyzed and the cooling load difference based on the different building-mix is compared based on the data of cooling capacity,chiller operation strategies and energy comsumption and et al.The chiller operation strategies are analyzed and load ratio and COP of chillers,EER and cooling loss of the systems are calculated.Besides,through the comparsion of relevant index belong to above systems,the role chilled water storage system play in DCS is emphatically analyzed.The results show that the DCSs have obviously fluctuate load in actual use,and the medium and low load occupies a considerable proportion in cooling season.DCS equipped with chilled water storage system has the advantages of keeping the chillers and system running in high efficiency comparied with conventional DCS.The cooling loss of DCS is about 10%,which is affected by load and operation strategy.According to the result of operation analysis,it is proposed that if reasonable building-mix in pre-planning could help to optimize the load characteristic of DCS.In this part,firstly typical building models of residential,office and shopping building are built in reference of some relevant energy-saving design standards,hourly cooling load of the models above is calculated through EnergyPlus,load characteristics of three typical buildings are analyzed.Secondly,building combination model of DCS is constructed based on the system load fluctuation index as the objective function,the load fluctuation coefficient of different building combinations is obtained.On this basis,the influence of three kinds of buildings above have on the system load is analyzed according to the change of load fluctuation coefficience and some reasonable forms of building combinations are given.The study shows that residential building has a greater load fluctuation than office and shopping mall building.The combinations with small proportion of residential buildings should be avoided if there are above three kinds of buildings in the system.The DCS will hava a obviously fluctuate load if the residential building area ratio is less than 0.5,and the stability of system is inferior to the DCS which is cooling for single type of above buildings.However,in practice,it is difficult to achieve the optimization building combination as it is awalys limited by a lot of factors.Part of building combinations propably contribute to seriously fluctuant load to have a negative impact on the running of chillers and system,appropriate techbologies such as chilled water storage system should be introduced into DCS at this moment.Subsequently this paper proposes a simple method for the analysis and selection for suitable DCS form:choose the traditional method of reasonal capacity of chillers or other suitable techonlogies such as chilled water storage system to improve the operation.The simple DCS with ideal chillers configuration and operation strategies is run under the load of the building combination,time ratio of different range of part load ratio of chillers is analyzed,and then suitable system form is chosen or suitable technologies is introduced.All the analysis and discussions are based on the assumption that there is a positive correlation between the part load ratio and COP value of chillers,it is believd that the higher load rate of chillers lead to higher efficiency of chillers and system.The results of this study could be used as a reference for the planning,design and modification of DCS.The study shows that extra suitable technologies should be introduced into the DCS which is cooling for above three kinds of buildings when then load fluctuation coefficient is over than 0.655. |
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