Cost effective District Heating networks
Description of the Project
This project consisted of three tasks:
1. Cold Installation of Rigid District Heating Pipes (1999: T3.1)
Of all possible options cold pipe installation is the simplest kind of laying technology, which opens new and effective possibilities of construction-site organization. With appropriate preparation the activities can be performed in a single-day-construction manner. The static stresses caused by cold pipe installation exceed the stresses resulting from the 0.2% yield strain. The design is governed by a fatigue analysis based on the appropriate number of load cycles for district heating. Hence, the material's mechanical stress resistance is used to an extensively high degree.
With cold pipe installation resulting stresses can reach the stresses of the actual yield strain. As a consequence, the pipe endings, which are generally located in the expansion zone, undergo considerable displacements. Solutions have been worked out to control the high stresses and strains. These are described in the later sections of this report. In general, operating the system at moderate temperatures, cuts back some of the disadvantages and restrictions of the cold pipe installation method.
2. New Ways of Installing District Heating Pipes (1999: T3.2)
The investments into new district heating networks in Central and Northern Europe is estimated to be about half a Billion US$ per year. With new laying technologies it seems to be possible to reduce the overall costs by 10 to 15%. The savings expected to be 50 to 75 Mill. US$ explain the utilities' interest in these develop-ments.
Two ways of construction have been established which primarily reduce the volume of earthworks for the pipelines and also influence their installation. One of these techniques arranges the pipes not horizontally (Side-by-Side) but vertically on top of each other (Piggy-Back laying), whereas the other combines two medium pipes in one jacket pipe (Twin-Pipe). Piggy-Back Laying has been practiced for 7 years while Twin-Pipes are in use for 15 years. Both techniques allow smaller trenches and thus lower the required efforts for civil-work. In this report the technical specialties of the two techniques are described and possible savings are demonstrated.
3. Reuse of Excavated Materials (1999: T3.3)
On grounds of environmentally friendly construction the utilities are trying to use recycled material or industrial leftover instead of raw material as trench backfill. Environmental protection has been proven to not always increase construction costs, but also lower costs in certain cases. Priorities in the case of trench-backfilling are with the use of excavated materials because they are the least-cost alternative available.
The calls for cost-efficiency and ecology don't necessarily exclude but may rather complement each other in the case of pipeline construction. The elevated prices for new material and the frequently rising prices for the deposit of overburden both point in the same direction as does the call to protect the environment, i.e. to reuse existing material. Despite the fact that the cost relations and boundary conditions are varying within regions and even more on a national level since the access to resources underlies strong regional differences, the protection-constraints apply in general. Facing these constraints the utilities are trying to use advanced technologies since they are exposed to specifically high attention by the public, if compared to private companies.
For the reuse of material for pipeline construction several interesting solutions exist at different places. In this report only construction methods will be described that may be transposed onto other places and their construction sites. The report will cover construction techniques, which use mainly recyclable materials or recycled industrial waste.
Cold Installation of Rigid District Heating Pipes
[Summary Report - PDF - 3-pages, 26Kb]
New Ways of Installing District Heating Pipes
[Summary Report - PDF - 2-pages, 14Kb]
Cost effective DH&C networks
[Summary Report - PDF - 3-pages, 17Kb]
Mannheimer Versorgungs- und Verkehrgesellschaft (MVV), Mannheim, Germany
Chalmers University, Goteburg, Sweden