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, EstoniaThe installation of a supply and return closely togetherin the ground has a small, but positive effect on theheat loss of the pair, as is shown in Fig. 3.PB std insulation thicknessPB closeFig. 1a, Supply and return pipeFor flexible systems, there is no space requirementbetween the pipes for installation purposes, and pipesare best installed right next to each other, see Fig. 1b.Heat Loss [W/m]5045403530252015105016 20 25 32 40 50 63 75 90 110Nominal diameter [mm]Fig. 3, Heat loss per pair, standard and close togetherFor the rest of this paper, flexible pipes are supposedto be installed closely together.3. PIPE PER PIPE COMPARISONFig. 1b, Supply and return closely togetherWhen supply and return are installed closely togetherthe temperature profile in the ground is altered inbenefit of the in-ground heat loss.Even though internal diameters and friction coefficientsare different between Steel-PUR-PE and PB-PE-PEand therefore will lead to a different selection ofdiameters in the engineering process, an approximatecomparison can be made, see Fig. 4.Dependant on the refill, it may be difficult to achievedefined compaction when supply and return areinstalled too closely together. However, similartemperature effects can be reached by installinglikewise in vertical orientation.As mentioned before, the in-ground heat losses arecalculated using the multipole method by JohanCleasson and Camilla Persson in 2005 [5].See Fig. 2 for a calculated temperature profile.Heat Loss [W/m]50454035302520151050St std PB close16 20 25 32 40 50 63 75 90 110Nominal diameter [mm]Fig. 2, Temperature profile supply and return closelytogether in the ground311Fig. 4, Heat loss per pair, flexible PB versus SteelOn the left of the graph, two diameters are included forwhich no steel counterpart has been incorporated. Thereason for this is that PB allows for higher fluidvelocities. However, in the current range, using thesmaller diameters does not create a heat lossreduction.