ASSESSMENT OF FEASIBLE OPERATING TEMPERATURE REDUCTION IN TURIN’S DISTRICT HEATING NETWORK

The purpose of this work is to present a feasibility study on lowering the operating temperature of the district heating network of Turin, managed by IREN SpA. Reducing the network’s operating temperature is necessary to achieve the European decarbonization targets for the energy sector by 2050. Indeed, this would allow the replacement of current fossil-fuel-based technologies with innovative solutions that exploit waste heat and heat pumps. Lowering the temperature difference between the supply and return lines of the network implies an increase in water mass flow rates to maintain constant thermal power. Therefore, a model was created to first simulate the current operation of the network: by verifying the mass conservation and momentum conservation equations at each node and branch, the pressure, flow rate, and velocity profiles in the network were obtained, ensuring the fulfilment of the loads at all major network hubs. This model was then “evolved” into an optimization model, in which the maximum possible increase in flow rates was evaluated while respecting the physical and operational limits of the current network, imposed as maximum and minimum pressure and velocity values. Three different optimization models were created: one with a single multiplicative coefficient for all loads and sources, one with separate multiplicative coefficients for loads and sources, and finally one with a multiplicative coefficient for the loads and an unknown vector of additional flows from the sources. Finally, a model was developed to determine the optimal positions and simulate the addition of heat pumps at selected hubs of the network. This model was designed to observe the effect of new low-temperature technologies and to partially simulate the role of future prosumers. It was implemented by introducing an unknown vector of flows at the hubs, limited by a maximum flow and a maximum number of units installed. All models were applied under six different initial load conditions, corresponding to six typical operational scenarios of the network: from the heavily loaded winter case to the lightly loaded summer case, including scenarios requiring higher loads at the Turin Nord or Moncalieri plants. The results obtained were truly remarkable from two perspectives: on one hand, the possible increase coefficients for flows to the loads were high, even under the most heavily loaded conditions; on the other hand, it was observed that a large part of the increased flows to the loads could be supplied by the current capacity of existing plants, although this would involve the use of storage tanks or boilers, which would also require economic, environmental, and operational considerations regarding their activation. In the case of installing heat pumps at selected hubs of the network, even higher multiplicative coefficients were achieved, highlighting the importance of both the role and the location of the plants, even small-scale ones, when strategically installed within the network. This study therefore demonstrates the current and future potential of the Turin district heating network, providing data on the network’s capacity under typical operating conditions and analysing certain prospective technological solutions. The results obtained can be used for further studies and feasibility assessments of new strategies, aimed at achieving the network’s decarbonization goals.