Overcoming bottlenecks due to supply temperature reductions in existing district heating

In the past decades, across the world and the Europe, several district heating networks have been built in the urban areas using the design criteria of that time. The criteria include the adoption of high design supply temperature (often larger than 100 °C) in order to reduce the size of the pipelines installed. This is the criteria that has been also used for the networks installed in major cities, which are characterized by several thousands of pipelines and a multitude of substations. These networks are often still operated using their design supply temperature, despite this is no more suitable to the smart exploitation of the energy resources (e.g. renewable, waste heat and in general low exergy heat). The work aims at the analysis of actions that allow to quantify which supply temperature reduction can be achieve by overcoming the issues due to the water congestion in the district heating pipelines. In fact, reduction of the supply temperature leads to the problem of the increase of the mass-flow rates circulating in the pipelines; this could set significant limitations on temperature reduction in fully-loaded infrastructures. This issue is analyzed by using a fluid-dynamic model of the thermal network. The work is applied to a real case, i.e. a district heating network still fed with overheated water.