Book - School of Science and Technology

Water systems ± applications 241Pipe section keyNet energyflow (kW)Pipe heat emission(W/m) Length (m) Total (kW)AB 260 188 30 5.64BC 180 178 20 3.56CD 100 148 20 2.96DE 20 92 10 0.92DF, CK, BO 80 135 10 1.35FG, KL, OP 60 125 10 1.25GH, LM, PR 40 112 10 1.12HJ, MN, RS 20 92 10 0.92. The apportionment of these heat emissions, section by section, must now be carried outsystematically on a `compound interest' basis. A first step would be to consider thethree identical main circuits on the right-hand side of the figure, taking the upperidentifications as follows:HeaterF G H JRated emission (kW) 20.00 20.00 20.00 20.00Heat from pipe HJ is allocated to J alone 0.9220.00 20.00 20.00 20.92Heat from pipe GH is allocated to H and J 0.55 0.5720.00 20.00 20.55 21.49Heat from pipe FG is allocated to G, H and J 0.40 0.41 0.4420.00 20.40 20.96 21.93Heat from pipe DF is allocated to all 0.32 0.33 0.34 0.35Final total 20.32 20.73 21.30 22.28. Proceeding similarly, the heat loss from pipe CD is allocated to heaters E, F, G, H andJ, that from pipe BC to heaters E, F, G, H, J, K, L, M and N, and lastly, that from pipeAB is allocated to all the heaters shown. This process produces the total loadings shownbelow and it will be seen that, although the average mains loss is just over 10%, that forheater J is 18.9% while that for heater O is only 3.5%.Heater Gross load (kW) Mains loss (%)O 20.71 3.5P 21.15 5.7R 21.74 8.7S 22.73 13.6K 21.09 5.4L 21.53 7.1M 22.12 10.6N 23.14 15.7E 22.35 11.7F 21.69 8.4