12th International Symposium on District Heating and Cooling

The <strong>12th</strong> <strong>International</strong> <strong>Symposium</strong> on District Heating and Cooling,September 5 th to September 7 th , 2010, Tallinn, EstoniaCUTTING COSTS OF DISTRICT HEATING SYSTEMSBY USING OPTIMIZED LAYING TECHNIQUESAlexander Goebel 1 , Dr. Stefan Holler 11MVV Energie AG, Mannheim, GermanyABSTRACTThe soil covered plastic jacket pipe is the commonstate of the art laying technique in the district heatingsector: A preferable shallow trench is dug out andbackfilled with cable sand after the installation of thetwo pipes. Alternative possibilities concerning thedigging of the trench, the backfill and the piping itselfare evaluated in this paper. Results show, that anoptimized laying technique can save construction orrunning costs under the right boundary conditions:Backfill materials with insulation properties can reducethe heat losses by about 25 %. Using glass-reinforcedplastic pipes (GRP) instead of steel pipes leads topump energy savings of about 40 %.INTRODUCTIONIn the first place, excavation costs could be cut bydigging smaller and shallower trenches. However, thisis only possible if the location of the construction site isappropriate. In an urban area the situation is completelydifferent from a rural area concerning space andregulations. The paper describes the boundary conditionsand compares different methods from the technicalas well as the economical perspective using theexample of the district heating system in Mannheim,Germany.The second approach which will be presented in thepaper is the potential to reuse the excavated materialand to use self-compacting material when refilling thetrench. Furthermore, it is also possible to use newmaterials with better insulation properties in order to cutdown heat losses. In the paper the different propertiesof the new materials will be compared and evaluated.A third possibility to reduce costs is the use ofspecialized piping systems wherever possible.Nowadays a wide range of products is available on themarket. In many cases a specialized system fits someapplications better than a standard system does. Notonly insulation properties but also compensation,ductility and friction losses are important characteristicsof modern piping systems. In the paper it will be shown,how costs could be reduced by using less or nocompensation measures (cold laying, flexible pipes,fibre pipes), by avoiding welding measures (flexiblepipes for house connections, fibre pipes) or by reducingfriction losses (fibre pipes).MATERIALS AND METHODSThe cost saving potentials of the alternatives, concerningthe digging of the trench and the backfill, aremainly evaluated by outlining the results of researchreports. Calculations are used in order to estimate theinsulation properties of special backfill material. Alsothe cost saving potentials of pipes with low frictionlosses are evaluated with simple equations.RESULTSReuse of the excavated material [1], [4]Earlier research activities have proven, that plasticjacket pipes could be used with backfill materialshowing a greater grit size than cable sand. Specialprotection material is available not only for the mufflesbut also for the pipes. Field tests have shown, thatthere are promising money saving potentials becauseof the significant reduction of transport and disposalcosts. A consideration of reusing the excavated soil isalso reasonable from an environmental point of view.Following points are important, when it comes to anevaluation of this possibility at an individualconstruction site:the grading of the excavated materialsandy or cohesive groundcompacting propertiesthe friction between the ground and the jacket pipeprotection measures for muffles and the pipeunderground construction regulationsa place for the storage of the excavated material(beside the trench, container or any place near theconstruction site)formation of dust (especially in the summer)contaminationpH-valuean improvement of the excavated material withlime (especially with cohesive ground)a removal of the coarse materiala separation of the material, if the ground is split upin different layersThe use of self-compacting material [1], [4], [5]It is important to distinguish between the following twotypes of self-compacting material:stabilised sand mix297