Composite District Heating System Integrated With Geothermal Water Into Secondary Network By Absorption Heat Pump

With the increase of energy consumption and the decrease of fossil energy reserves,it is imperative to vigorously develop renewable energy heating.Integrating renewable energy into secondary network for district heating has enormous potential for energy saving.In this paper,the operation analysis and design optimization of composite district heating system,which integrates geothermal water into secondary network at the heating substation by means of absorption heat pump driven by primary hot water,are carried out.The system is referred to as the composite system integrated with geothermal water into secondary network.Firstly,this paper introduces the working principle of the composite system integrated with geothermal water into secondary network.After simplification of the system model,the physical model of the system is established.The mathematical models of the plate heat exchanger and the absorption heat pump are established and coupled.The simulation of the system is completed by Matlab.Secondly,a commercial center in Tianjin as the case study is conducted.The simulation results of the relationship between the heat produced by the heat pump and geothermal water inlet temperature,geothermal water flow rate,secondary circulating water inlet temperature,and driving heat water flow rate are given.The control curves of the temperature and flow rate of primary network and geothermal water under different control modes are given,which provides a basis for the control strategy of the system operation.Thirdly,with the objective function,which is the minimum annual cost of the composite system,this paper uses the orthogonal design to optimize the design of the system with four parameters including geothermal water flow rate,primary network water flow rate,heat produced by absorption heat pump and plate exchange area of geothermal water.The optimal solution is obtained and the performance of the system is analyzed.Finally,the comprehensive comparison between the composite system and the conventional district heating system is conducted.For each heating period,the energy conservation of the composite system is 1058.5 tons of standard coal,compared with the conventional district heating system.The annual cost of the composite system is 6605,000 yuan,and the dynamic recovery period is 2.57 years.The annual cost of the conventional district heating system is 7181,000 yuan,and the dynamic recovery period is 2.68 years.Therefore,the composite system integrated with geothermal water into secondary network is economical and has good energy saving and environmental protection benefits.