Multi-objective optimal renewal planning of energy supply systems for buildings from economic and environmental viewpoints

In this paper, based on the multi-objective optimization approach, a renewal planning method is proposed for the energy supply system to determine the optimal renewal one by selecting optimal renewal year and system's structure from both economic and environmental viewpoints simultaneously. In this method, one objective function is the annual total cost of the system, which is the summation of the annual capital, operational and maintenance costs based on the annualized cost method during the evaluation years. The other objective function is the average annual total amount of CO₂ emission during the evaluation years. The numerical optimal solution is derived for the system of an office building by the conventional mixed integer linear programming algorithm together with the ε-constraint method. As a result, the set of Pareto optimal solutions is derived, and the trade-off relationship between economy and environment is analyzed. Through the result of the set of Pareto optimal solutions, tolerating the increase of the system's annual total cost up to 1%, we can reduce the amount of CO₂ emission from the system up to 15%. One main result also obtained shows that it is necessary to introduce different types of electrically-driven equipment such as heat pumps to reduce CO₂ emission.