Book - School of Science and Technology

Secondary outflow and return pipework 611Floor 4RisersX Y Z0.5kWOAFloor 30.5kWOBKitchenFloor 20.5kWOCFloor 10.5kWOFOG2kWOE2kWODFigure 21.7 Pipe sizing example: secondary returnsBy reference to Figure 21.8, an energy based chart for water flow in copper pipes,prepared on the same basis as Figure 9.2 (p. 235), the listings as columns 5, 6 and 7 ofTable 21.12 are produced, those in column 7 being the proportion of the availablepressure which is absorbed in the flow mains to each floor.Assuming circulation to be by gravity, the available pressure for floor 1, which is theworst case in this context, would be 5 50:25 ˆ 251 Pa and, by way of comparison, thatfor floors 2, 3 and 4 would be 402, 553 and 704 Pa respectively. From these pressures, theTable 21.11 Heat emissions from piping: worked exampleSectionPipesizeEmission(W/m)Length(m)Emission (W)SectionalTotalOA 28 9 3 27OB 35 10 3 30OC 42 12 3 36OD 42 12 2 24 117Riser X 117Riser Y 117OD 42 12 3 36OE 42 12 3 36OF 54 13 3 39OG 67 16 3 48 159510Returns as 2 ¤ 3 of flows 340Total (W) 850