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, Estonia6. TOTAL SYSTEM HEAT LOSSTo calculate the total system heat loss, pipe lengths asshown in the pipe length histograms are to bemultiplied by the respective heat losses per pipe pair,as shown in the heat loss value histograms.Fig. 15 ―multiplied‖ by Fig. 6 leads to the total systemheat losses in Fig. 16.Heat Loss [kW]80.070.060.050.040.030.020.010.00.0ST.PUR.PE RefPB as measured std eng.PB increased insulation thicknessPB increased insulation thickness all SDR11system [-]Fig. 16, Total system heat loss, current insulation qualityThe graphs in Fig. 16 show the reference heat loss forsteel-PUR-PE in red and the currently measured heatloss for PB-PE-PE with non-optimized insulationthickness in orange. In green, total system heat loss isshown for current insulation quality but with optimizedinsulation thickness. The exclusive use of SDR11(blue) has a rather small effect.Improving insulation quality, as described in paragraph5 and shown in Fig. 7, leads to slightly lower totalsystem heat loss for freshly produced PB-PE-PE whencompared to the reference, see Fig. 17.Heat Loss [kW]60.050.040.030.020.010.00.0ST.PUR.PE RefPB impr. insulation thickness/qualitysystem [-]There is currently no experimental data on the rate ofageing of PB-PE-PE as a result of the exchange ofblowing agent with air. However, it is possible tocalculate a worst case situation (see fig. 18), using thepredicted values plotted in fig. 8.Heat Loss [kW]70.060.050.040.030.020.010.00.0ST.PUR.PE RefPB impr. insulation thickness/qualityPB impr. Insulation thickness/quality degassedsystem [-]Fig. 18, Total system heat loss, including worst caseIn practice and over time, the predicted total systemheat loss will slowly shift from the fresh value in purpleto the worst case value in blue. Average heat lossduring lifetime will be somewhere in-between.FUTURE RESEARCHHydraulic calculations in combination with insulationthickness form an interesting optimization problem:what diameter to select and which insulation thicknessto choose?Current design strategies for hydraulic networks,aiming at linear pressure drop with distance, seem tooadventitious to be optimal. In addition, heat losscalculations using standard casing dimensions showrapidly diminishing yields with each step up ininsulation thickness, suggesting the optimum issomewhere in-between.First attempts have been made to use Pipelab [6] in adouble optimization routine, trying to find optimalhydraulic performance in combination with optimalinsulation thickness distribution over the network.Given the specific hydraulic properties of PB (high fluidvelocities permitted) and the specific insulationproperties of PE foam (better at small size), this maylead to rather different design strategies whencompared to conventional rigid piping systems fordistrict heating and cooling.Fig. 17, Total system heat loss, reference and predictionfor improved insulation quality316