Integrated optimization of adaptive CO2-based district heating and cooling networks into multi-energy systems

This paper presents an original procedure for the integrated optimization of the topology, design and operation of a CO2 District Heating and Cooling Network and associated Multi-Energy System. The goal is to understand the potential of CO2 networks to reduce the life-cycle cost and greenhouse gas emissions of the system, by determining, in one step, both the optimal size of the energy conversion and storage units, and the optimal layout and size of the network branches. The procedure (i) uses a multi-nodal approach for an adaptive selection of the users to be connected to the network, (ii) includes the CO2 temperature optimization to minimize energy consumption of the network, and (iii) allows different users’ comfort options. The optimization model, based on the DOMES method, is tested on an urban district with 18 nodes, considering different energy conversion and storage technologies, thermal networks and demand profiles. Results show that properly adapting the users’ connection to the CO2 network may reduce emissions by 26.6 ÷ 52.8% compared to the case without thermal network, while the impact on total costs is strongly influenced by the users’ thermal demand profiles and cooling comfort needs, ranging from a 7.0% reduction to a 23.1% increase.