Design Optimization Investigation Of District Cooling And Heating Pipe Network System

With the rapid development of urbanization and building clusters in China,the district energy system becomes a novel way of building energy supply system because of its advantage in environment friendliness,energy conservation and so on.At the same time,there are an increasing demand for indoor thermal comfort and a huge market for the application of the district heating and cooling system in hot summer and cold winter area such as Yangtze valley,which is developed region in China.Therefore,for saving energy,reducing emission,protecting environmental,improving resident's life quality,et al.,it is practical to conduct research on the district heating and cooling system.The research of district heating and cooling system is an interdisciplinary field involved multiple disciplines.The major directions of this research includes: the system integration method and optimal operation strategy of energy station,the optimization design and operation control of energy transmission and distribution pipe network,the analysis of building cooling and heating load characteristics,et al..The pipe network of energy distribution,which is the bridge between energy station and energy users,is the key stability factor of district heating and cooling system.This dissertation focuses on two problems: pipe network layout optimization and pipe diameter optimization.The oretical foundations were provided for improving the economy of pipe network system to accelerate the application and development of district heating and cooling system.Based on graph theory,genetic algorithm and analytic hierarchy process,a new method about pipe network optimization of district heating and cooling system was proposed.Firstly,based on the graph theory and the classical fluid mechanics,the plane and space mathematical model of pipe network was established by simplifying and abstracting pipe network of district heating and cooling system.Secondly,in view of the advantages of genetic algorithm in solving combinatorial optimization problems,single parent binary genetic algorithm and integer genetic algorithm were adopted for the pipe network layout optimization and pipe diameter optimization,respectively.The genetic operators of the two algorithms were improved for layout optimization and diameter optimization.Thirdly,combined with the mathematical model of pipe network and the improved genetic algorithms,based on analytic hierarchy process,a new method of network optimization of district heating and cooling system was proposed.At first,some reasonable network layouts set were created through the layout optimization of pipe network by different objective functions;Then,through pipe diameter optimization,the optimal pipe diameter combination and annual equivalent cost for each layout in former set was calculated;Finally,by comparing the annual equivalent cost of these layouts,the optimal layout and optimal diameter of the district heating and cooling pipe network system were found aiming at the smallest annual equivalent cost.Based on hourly load of typical design day,the mathematical model of diameter optimization was established by means of the optimization objective function,which is the annual equivalent cost of pipe network.When calculating the annual operating cost of pipe network,the hourly cooling and heating load of typical design day in summer and winter were adopted;In addition,when calculating the annual heat loss cost of pipe network,the conversion of kinetic energy and heat energy of circulating water pump in pipe network was taken into consideration,and the influence of the energy conversion on the heat loss of the pipe network during cooling in summer and heating in winter was analyzed.Based on the above aspects,the calculation accuracy of diameter optimization mathematical model of district heating and cooling system was improved.Based on the above research,an optimization software of district heating and cooling pipe network was developed.Taking a district heating and cooling project in Changsha as an example,some parameters of the district heating and cooling pipe network were discussed for the influence of pipe diameter optimization,such as temperature difference between supply and return water,price of electricity,the d esign load and so on.The presented results can be applied to analyze and optimize the other pipe network of district heating and cooling projects.Therefore,the dissertation has significant theoretical value and practical significance.