Techno-economic analysis and multiobjective optimization of a novel proposal for addressing summer-supply challenges of district heating systems

A critical challenge of some district heating systems is too low summer demand, which results in a too low temperature at the consumption points. To prevent this large temperature drop along the path, the heat production plants have to oversupply hot water to the pipeline, which is itself problematic techno-economically. One more challenge of summer supply, if supplied by waste incineration plants, is that due to the low heating demand during the summer, there will be too much useless excess municipal solid waste at the disposal, causing further technical and economic issues. In the proposed concept of this study, an integrated district heating/cooling system is proposed to address both of these problems. For this, a solar-assisted chiller is utilized to not only take advantage of the excess waste of the power plant but also the excess hot water injected into the pipeline for cold supply. The research question is about the optimal sizing of the system. The sizing of the components of the system is carried out via a rigorous multiobjective genetic algorithm work package covering technical, economic, and environmental objectives, and then, the optimal design is techno-economic-environmentally analyzed. In summer, the velocity of hot water reaches the appropriate value of 0.8 m/s, and following the cold load supply, 67.8 kg/s extra mass flow rate of hot water with a temperature over 80 ℃ could feed the district heating system. Besides, at least 78 tonnes more waste will be burnt per day. It means challenges of the high amount of waste disposal, low velocity of hot water in district heating pipeline, and the high amount of waste heat will be solved, and the levelized cost of cooling production would decrease by 10%.