A tool for the optimal design of climate resilient thermal energy networks. Part 2: District heating and cooling network model

The 5th generation District Heating and Cooling Systems, comprising a low temperature network and substations equipped with heat pumps to upgrade heat, are the most suitable networks for exploiting low temperature sources and geothermal energy at the urban scale. However, comprehensive modelling tools are lacking. To fill this gap, in the framework of the PNRR project NEST, task 8.5.3, an open-source unique tool to analyze the community energy demand and design the district geothermal system is provided. The tool will address the climatic resilience issue of the network, by considering future energy needs and ground source temperature evolution. This paper deals with the incompressible network that connects the central heat pump to substations. Time dependent loads, bidirectional flows, and decentralized pumping system are the main challenges to tackle with the hydraulic network solver. The Todini’s gradient algorithm is implemented providing a linearization of equations within an iterative procedure. Then, temperatures are calculated imposing the energy balance to the network’s components. A case study is analyzed showing the implemented strategies to overcome the numerical challenges and the useful results provided by the tool for the design process and energy evaluation of the network.