Orthogonal Optimization Method In The Application Of The District Cooling System Pipe Network Optimization

The district cooling system?DCS?has the characteristics of large cooling capacity and long cooling distance,therefore,the water system of pipeline network as an important part of the DCS,which is an essential and weak link to decide whether the investment and energy consumption in the process of the whole system are reasonable or not.In recent practical engineering projects,the design of district cooling pipe network is basically in accordance with the design system of central heating pipe network.Parts of the targeted design methods are still only stay in the research stage,so they can't provide the design tools which facilitate the engineering technician to use.Aiming at the above problems,this paper researches the method of how to apply orthogonal optimization method on the pipe network optimization of the DCS.The main research work is as follows:Firstly,an optimization model is established by considering the full cost of the objective function composition and the constraints to meet the needs of users and their technical safety systems.The objective of the optimization model is the lowest annual equivalent cost.Constrained condition include cooling load needed by occupants,circuit pressure equilibrium and hydraulic stability,water velocity range,standard diameter range.Then it provides the basis for the optimization of the DCS pipe network.Secondly,taking diameter,water flow rate,pipe insulation layer thickness as optimization variables,actual pipe network optimization design model is based on the Shennong City cooling pipe network optimization model and the basic parameter.Combining with the engineering practice,the optimal solution is obtained by determining the level of the optimization variables,choosing suitable orthogonal table,reasonable arrangementing calculation scheme,calculating and analysing.The results show that that the orthogonal optimization method is a powerful tool for pipe network optimization of the DCS and it suitable to be used in general technicans.District cold pipe network design should focus on balancing the system initial investment and the resistance of the system and parameters combination of network design optimization is that:d_e=DN300,v_e=1.06m/s,?_te=0.035m.If other similar project lacks of investing and energy-saving requirements are not strictly,it can reference network design parameters: d_oe=DN250,v_oe=1.55m/s,?_ote=0.033 m.Thirdly,based on the thermal balance among the allowed temperature increase of the supply water and return water when the energy efficiency of the chiller degrades,the heat transfer of the pipeline and the heat from the friction of electric motors,deduces the computing model of the maximum length of the cooling pipeline in the DCS.The results show that the orthogonal optimization calculation results are reasonable.Under the condition of program one and program two,the maximum lengths of cooling pipes respectively are 1193¹796m and 887¹331m.