Ottimizzazione e progettazione di district anergy networks utilizzanti CO2

One of the main global goals in the context of the rapid climate change is the reduction of the energy consumption. Among the most interesting sectors, with an important margin of improvement, it is possible to find the urban areas. Urban areas are mainly composed of residential buildings, where is well established the district energy network as the best way for heat distribution. The district network is a grid of pipes driving a working fluid and connecting the buildings among each other, in order to share thermal energy. The evolution of this system relies on two aspects, reducing the temperature of the working fluid and lately moving from water to refrigerants, in order to reach a more efficient system. In the past two decades the CO2 has faced a growing popularity as a refrigerant, joining the hydrocarbon and HFO as the present and next generation of working fluids. The present work investigates the CO2 network, which exploits the latent heat of the carbon dioxide near the saturation state in a vapour and liquid pipes to transfer heat to the users. The CO2 has been chosen for the fact that it is the only non-flammable, non-toxic, natural refrigerant available with the most appropriate range of temperatures. This work presents a method meant for decision makers to implement a district energy network based on CO2 in a neighborhood, in this way the best design alternatives are evaluated before making a decision. The method is characterized by two branches, in order to achieve the network topology design first and secondly to cross the results with the optimization of the energetic model. The network design relies on a MILP problem, in order to develop a tree graph, which connects the buildings to the available pathway of the neighborhood. The problem consists of a system of equations which is fed by the most severe energy demand of each building, the starting point of the graph and the streets of the district are taken as the available path to place the network. Moreover a bunch of options are approached in order to develop a set of configurations, among which there are the variation of the starting point of the graph and the adoption of a discrete variable as the power assigned to the centralized feeding technology of the network. The results of the network design are merged with the optimization of a set of conversion technologies, where it is simulated the whole neighborhood by splitting the buildings connected to the network with the heat pumps to the ones disconnected and with standalone technology. The set of conversion technologies includes the PV panels, the network based heat pumps, the central plant, the electrical heater, the ground source heat pump (GSHP), the decentralize refrigeration, the power-to-gas and the storages composed by batteries and CO2 tanks. Furthermore, to fully exploit the potential of the district network based on a refrigerant is integrated in order to achieve the waste heat recovery of a data center. The validation of the method is carried out by the case study about the district of Ronquoz in Sion (Switzerland), which is going to face a complete requalification in the following years. The implementation of the method results in a minimum of the cost for a district network that covers 80% of the neighborhood. The connection of the data center voids the investment cost of the dedicated refrigeration system, while the total operating cost increases by the 95%.