Multi-objective design optimization of a cryo-polygeneration system in tropical climates - a techno-economic case study for a large-scale utility customer

Abstract

Small-medium scale decentralized polygeneration systems can provide multiple energy services for urban districts like universities and hospitals, with several energetic, economic and environmental benefits. Indeed, their impact on both energy efficiency, cost and emissions reduction might be disruptive especially in urban districts located in a tropical region, where the cooling demand is approximately stationary throughout the whole year. In this paper a multi-objective optimization model for distributed energy system in tropical climate is presented. The superstructure of the system comprehends a district cooling network that connects the users to medium-scale gas turbine system, solar PV plant, thermal and electrical chiller and a thermal storage. The optimization aims to determine the optimal design structure of the system, the size of each component inside the optimal solution and the optimal operation strategy. The multi-objective optimization is based on a three-level structure: 1) the simulation level developed in TRNSYS; 2) the optimization level based on a paretosearch algorithm developed in Matlab; 3) the Matlab-TRNSYS interface level. In this way the Pareto Front is identified and the possible improvements in both economic and environmental terms can be highlighted. The model has been applied to a specific real case study, namely a polygeneration system to be installed in the NTU campus located in Singapore, and it has been optimized for two different superstructure configurations. The results contribute significantly to developing an efficient and cost-effective energy storage polygeneration system and revealed that the optimized operation of the decentralized energy systems reduces energy costs and CO2 emissions, as compared with a scenario without integration of renewables and electric energy storage system as well as conventional energy supply systems. Indeed, numerical results show that the Pareto frontier provides good balancing solutions for planners based on economic and sustainability priorities.