District heating networks: an inter-comparison of environmental indicators.

The installation of district heating (DH) systems constitutes an advantage from the energetic, climate, and air quality aspects. However, the configuration and operational features of a DH system affect significantly its environmental performance. The objective of the present study is the energetic and environmental assessment of DH networks that present differences in size and operating configurations, to define relevant environmental performance indicators. Three case studies in Italy are analyzed, following a methodology based on the impact pathway approach that was presented by the authors in previous studies. Case studies are evaluated in terms of total emission, pollutant concentration (NO, CO, PM), and health damage external costs. Results show that lower pollutant emissions are associated with the installation of a DH system compared to autonomous residential boilers. Air quality is also improved and health externalities are reduced. The results of CO savings are differentiated depending on the efficiency and emission factors of the systems. An inter-comparison of different cases is then presented, based on the elaboration of specific indicators of environmental and health impacts. This section shows that, besides the size of the DH system, other factors, such as population density and geographical distribution of pollutants concentration, are important. Among the indicators considered, those based on health externalities provide more complete and comparable information on the final impact of the alternative solutions on the exposed population. Their application seems thus promising for the evaluation of alternative planning strategies for DH systems.