On the performance of district heating systems in urban environment: an emergy approach

Abstract District heating networks are commonly assumed in the literature as an environmentally friendly solution for providing heating services for the built environment, due to the centralized heat production located outside urban centers and potential utilization of renewable heat sources (solar, geothermal etc.). However, the impacts associated with both construction and operation phases are frequently overlooked. The main scope of this paper is to make use of the emergy approach to infer environmental performance of the heat provided by district heating networks, considering two types of district heating systems: ESPEX (four-pipe network) and traditional two-pipe district heating network. For centralized heat production, three options were considered: central boiler fueled by fossil fuel mix, natural gas, and solar plant. Additionally, a natural gas distribution network with individual gas boiler in each dwelling was considered. An emergy evaluation was performed to enable the comparison of these systems on the same basis. All systems were applied to the district of Vraen, located in Varnamo, Sweden. The overall results showed that four-pipe ESPEX district heating network with central solar plant is the most suitable solution from the emergy point of view. The second most suitable solution was the two-pipe district heating network with solar plant as the heat production unit. On the other hand, networks with central boiler that used the fuel mixture (bioethanol and fossil fuels) and natural gas had lower environmental performance than the natural gas distribution network with individual boiler in each dwelling.

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