Study On Optimal Design Of District Cooling System Pipe Network In Shanghai EXPO

With the development of economy and the improvement of life levels, district cooling system(DCS) is more important and even will be one of the most outstanding marks in developed countries or districts in future. Recently, there is a obvious trend to use district cooling system in China. For example, district cooling projects have been adopted and operated in Gangzhou universities' campus and Zhongguancun west district in Beijing. As an basic and important component of district cooling system, DCS has caused great attention to its investment analysis due to its large scale, complicated structure and enormous investment.In China, researches on district cooling system are in the initial stage and few studies have been made. The traditional design only satisfied the needs of technology but dissatisfied the needs of economy, it not only wastes a mass of money, but also brings problems to circulation, maintenance and management, the more serious situation, it will need to reconstruction or repeated construction, consequently, it caused unnecessary repeated construction and loss.This research is part of the National Key Technology Project, "Study and demonstration on technologies of utilization urban clean and efficient energy", supported by the Ministry of Science and Technology of the People's Republic of China and also based on Expo Science technology Project, " Distribution energy supplying system and District Heating & Cooling system in Shanghai EXPO", supported by Shanghai Science and Technology Bureau. A study on the whole optimal design of complicated Cooling -supply network was made, including optimal pipe network layout and pipe diameter election. This thesis involved of mathematic model, optimal algorithm, parametric definition and zero restriction of constrained condition, and etc. The main studies and conclusions are as following:Firstly, a mathematic model is established about the whole optimal design of DCS system pipe network, including the arrangement of pipe network and the selection of pipe diameter. The objective function of the mathematic model is annual equivalent cost, involving of the initial investment, operation cost, energy loss, management cost. Constrained conditions include diversified pipe diameter, flow velocity, flow rate needed by occupants, flow equilibrium of pipe network, circuit pressure equilibrium and hydraulic stability. Practical engineering project was used to evaluate mathematic model in designing district cooling pipe network.Secondly, since optimal design of district DCS pipe network was a typical problem of combinatorial optimization, genetic algorithm was selected in this problem. Operation mechanism was analyzed and the methods was proposed referring to integer coding, the most optimal individuals reserving, crossover and mutation probabilities adapting automatically in genetic algorithm design and operation. Analytical results of practical engineering project show that genetic algorithm could be used in optimal design of DCS pipe network, especially, in the whole optimal design of complicated district multi-cooling resources network. The developed genetic algorithm is better than traditional design method.Thirdly, based on the graph theory and genetic algorithm, single-parent genetic algorithm was adopted in the optimal arrangement of branch pipe network. Fitness functions, single-parent exchange operator and inversion operator were designed. Comparison with Dijkstra algorithm, several layout schemes of lower annual cost were obtained from single-parent genetic algorithm regarding least annual cost as objective. Thus, its calculate efficiency, convergent speed and the quality of result are all better than Dijkstra algorithm.Fourthly, single-parent genetic algorithm was adopted in optimal layout of district cooling water system of the first energy station in Shanghai EXPO. A several of layout schemes of lower investment and circulation cost were obtained. The results provide theoretical basis for schemes evaluation and decision making.Fifthly, heating and cooling supplying scheme was designed in Living District B of Shanghai EXPO. By the optimal design of the cooling water pipe network with genetic algorithm, the design scheme of the lowest annual cost was obtained. Meanwhile, the influence of hydraulic stability factor and adjust method on system economics and optimal results is especially analyzed. The analytical results demonstrate that the optimal design can reduce investment and running-cost by comparison with common methods.Sixthly, taking cooling water pipe network in District 1 in Shanghai EXPO as an example, the influence of flow velocity, the designed load, electricity price and the conveying distance on the economy of pipe network in district cooling system were discussed. Main factors for optimal velocity were also analyzed. It is concluded that annual cost increases with the increase of the designed load and the electricity price and the conveying distance. It is also concluded that there is a optimal velocity in the optimal design of the district cooling system, annual cost will be raised with the design velocity which deviates from the optimal velocity, and the optimal velocity increases with the amount of the designed load growing. whereas, it decreases with the growth of electricity price and temperature difference between the feed water and the return water. The conveying distance of the cooling water has no influence on the optimal velocity.Lastly, the of optimal design of computer simulation analysis of hydraulic cases for district cooling & air-conditioning water system is developed by Visual BASIC 6.0 in Windows XP. The program functions are calculation of optimal design, computer simulation analysis of hydraulic cases with friendly interface, data input and output.