engleski

Impact of a waste heat integration on district heating systems’ multi-objective optimization results

Fourth generation district heating systems are complex due to the large number of possible technologies and energy sources which could be used in order to supply thermal energy to final customers. In addition, these systems are often connected with power sector, natural gas grids and sometimes, even with transport sector through vehicle-to-grid interconnection. In such smart energy systems, waste heat has a crucial role but sometimes its integration could represent challenging task due to seasonality, i.e. mismatch with existing heating demand. Also, temperature difference between heat source and heat sink, i.e. supply temperature of the district heating grid, could be such that booster heat pumps are needed. This paper answers the question: is there a saturation of total cost and total carbon dioxide emissions decrease of the district heating system, with increase of a potentially available waste heat? Such detailed modelling of integration of intermittent renewable energy sources in power sector has already been performed. In order to carry out this analysis, multi-objective optimization was used. Hourly model of district heating system for a whole year horizon was developed as linear programming (LP), i.e. mixed-integer linear programming (MILP). Two objective functions were defined as a total discounted cost, in terms of discounted investment and operational costs which include operational and fuel cost, and total carbon dioxide emissions. In order to handle multi-objective optimization problem, weighted sum approach, in combination with epsilon constraint method has been used. The model is capable of defining supply capacities, including thermal storage size, and hourly system operation for a whole year horizon. The code was written in Julia programming language, while Cbc solver has been used. Available waste heat has been treated as exogenous variable since it is often treated like this in real-life scenarios. Different waste heat hourly distributions with various seasonality characteristics have been analysed. The obtained results show that there is saturation of objective functions once certain share of available waste heat is approached.

district heating ; multi-objective optimization ; energy planning ; waste heat ; thermal storage

nije evidentirano