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 modified calculation procedure is made up of thefollowing equations:RRR1 ,steeliD i12 steel1 D ln2 i D Doln Diinsulationo(1)(2)(3)RUUhflow14 returnR RsR Rsembedmenti,flowi,return 2(Z R sln1 DC sembedment R Rh R Rh1 R,steel1 R,steel0) R R2 ,jacket,jacket R R(7),embedment(8),embedment(9)R,jacket12 C D ln DCinsulation(4) i i , 50C0 ,0001T i , average 50K(10)RR,embedments12 embedment DlnC 2sD1 4 ( Z R0 s) ln2 s DC 2 sembedmentembedmentC(5)(6)TflowTreturnf r Uflow UreturnTsoil (11) 2 Ti, average Tfluid QRi R R,steel R,jacket(12)heat losses of the district heating line[W/m]18016014012010080604020without insulation materialwith insulation materialreduction in %30%25%20%15%heat loss reduction010%0 200 400 600 800 1000nominal diameter [DN]Fig. 3 Reduction of the heat losses for DN 15 to DN 1000The average temperature of the insulation wascalculated with following equation and put back into(10). A VBA script was used to iterate five times.Fig. 3 shows the results of the calculation. Theinsulation material was taken into account with a valueof 0,33 W/m*K (λ embedment ). Around and in between theflow and the return pipe a space of 0,2 m for each pipesize was chosen (s embedment ). The depth of cover had avalue of 1 m (Z). Like in the previous example, the flowtemperature was at 120 °C and the return temperaturewas at 50 °C.Fig. 3 shows, that savings are significant lower withsmall diameters. Also the specific thickness of the PURinsulation, which differs because of standardised jacketpipe diameters, has an impact.The heat losses of a DN 250 pipe are reduced from 67to 51 W/m (24%). This means, that the heat lossreduction is 6% less compared to Fig.1.299