Book - School of Science and Technology

Secondary outflow and return pipework 603Table 21.4 Comparative demand unitsCategory of applicationFittingCongested Public PrivateBasin 10 5 3Bath 47 25 12Sink 43 22 1110 252105Litre/s21.0520.110 2 5 10 2 2 5 10 3 2 5 10 4 2Figure 21.4 Demand units and flow probabilityDemand unitsUsing a simple diagram of the outflow system, the individual and the cumulative`demand unit' totals may be marked up against each section of the pipework andthen, using Figure 21.4 which is based upon probability of simultaneous use, thesemay be converted to flow rates in litre/s. For showers and basin spray taps, thewhole flow rate, as given in Table 21.3, must be added to the individual andcumulative totals.