To Örebro University

Goal, Scope and Background: District heating, the utilization of centrally produced heat for space heating and domestic hot water generation, has the potential to contribute to the eco-efficient use of energy resources in the parts of the world where space heating is needed. In literature, environmental studies on district heating mainly consider the emissions from heat generation; the environmental impact from the distribution system is seldom discussed. This paper presents a life cycle assessment of the production of district heating pipes, based on a cradle-to-gate life cycle inventory commissioned by the Swedish District Heating Association. No external review has been performed but a reference group of district heating experts familiar with the practice was involved in the choice of cases as well as in reviewing parts of the study.

Methods: Manufacturing of district heating pipes at Powerpipe Systems AB, Goteborg, Sweden, was studied. Prefabricated polyurethane insulated district heating pipes were considered, with a steel tube and a protective casing made of high-density polyethylene. Production of pipes during the time period 1999-2000 was investigated. The functional unit used in the study is production of one district heating pipe unit. The studied pipes are: a twin pipe of the dimension DN25 (12m long) and single pipes of the dimensions DN25 (12m), DN100 (12m) and DN500 (16m).

Results and Discussion: A short description of the inventory, some inventory results and a life cycle impact assessment are presented. Characterizations according to GWP, AP, POCP and resource depletion are given as well as two weightings: Ecolndicator99 and Ecoscarcity. If the life cycle is grouped into 'Materials production', 'Transports', 'Manufacturing' and 'Waste management', the 'Materials production' gives rise to a dominating part of the environmental impact.

Recommendation and Perspective: To use materials in the pipes as efficiently as possible is the most important feature in order to reduce the environmental impact from production of district heating pipes. Twin pipes can be a more material efficient solution than single pipes. It is important to make sure that environmental improvements from changes in the pipe production phase are not offset by other effects in the total life cycle of the district heating pipe.