Life Cycle Assessment of the District Heat Distribution System - Part 2: Network Construction (11 pp)

Part 1: Pipe Production [Int J LCA 9 (2) 130-136 (2004)] Part 2: Network Construction [Int J LCA 10 (6) 425-435 (2005)] Part 3: Use Phase and Overall Discussion [DOI: http://dx.doi.org/10.1065/lca2005.08.225] Preamble. This series of three papers is based on research performed for the Swedish District Heating Association with the purpose of mapping the environmental life cycle impacts from the different phases involved in district heat distribution. Part 1 concerns production of district heating pipes while Part 2 describes construction of the district heating pipe network. In Part 3, the use phase is evaluated based on heat losses from the network during heat distribution. Part 3 also includes a discussion in which the three evaluated life cycle phases are compared. In a district heating network, hot water is transported from a central heat generation plant to buildings where the heat is utilised for space heating and domestic hot water generation. This paper presents a life cycle assessment of the construction of district heating pipe networks, based on a gate-to-gate life cycle inventory commissioned by the Swedish District Heating Association. In the literature, environmental studies on district heating mainly consider emissions from heat generation; environmental impacts from construction of the distribution system are seldom discussed. The purpose of the study is to identify environmentally significant parts in the construction of district heat distribution networks and to provide information for a larger study including more parts of the life cycle of such district heat distribution. No external review has been performed, but a reference group of district heating experts familiar with the practice was involved in the choice of systems to be studied as well as in reviewing parts of the study. The study covers construction of the main pipe system according to the guidelines from the Swedish District Heating Association. Construction of the pipe system was assumed to take place in Sweden by Swedish entrepreneurs during the time period 1999-2000. Transport of the district heating pipes from the factory to the excavation site is included in this study, but not the production of the pipes. The functional unit used in the study is 100 metres of pipe system (flow and return pipe). The studied systems are: twin pipe of the dimension DN25 and single pipes of the dimensions DN25, DN100 and DN500. Two different surroundings were studied: urban environment, char