II. Dimensioning of a Branched Distribution System Main Procedures 1. Determination of the design water flowrates 2. Determination of the pipe diameters 3. Determination of the tank elevation and the water head (pressure) at the crossroads “Design of Water Supply and Sewer Systems”

II. Dimensioning of a Branched Distribution System Topic II.1 Determination of the Design Water Flowrates General information 1. The distribution system is designed for the most unfavorable conditions: a fire could possibly burst out unfavorable conditions: a fire could possibly burst out during the hour of maximal consumption. during the hour of maximal consumption. 2. Only the main branches are dimensioned. The distribution branches are accepted to have a diameter of distribution branches are accepted to have a diameter of 80 mm for settlements with a number of population 80 mm for settlements with a number of population under under The distribution system is dimensioned section by section. A section is a part of a branch, between two section. A section is a part of a branch, between two crossroads, conveying a constant water quantity. crossroads, conveying a constant water quantity.

II. Dimensioning of a Branched Distribution System Topic II.1 Determination of the Design Water Flowrates Design water flowrates is the design water flowrate of a section, l/s is the maximal hourly flowrate, passing through the dimensioned section of the distribution system during normal operation, l/s is the design fire flowrate in the section, l/s for all sections of the main branches

II. Dimensioning of a Branched Distribution System Topic II.1 Determination of the Design Water Flowrates is the take off flowrate consumed within the limits of the designed section, l/s is the crossover flowrate of the section (equal to the sum of the take off flowrates of the sections, fed by the designed one), l/s is the crossover flowrate of the section (equal to the sum of the take off flowrates of the sections, fed by the designed one), l/s is the concentrated flowrate, consumed in the limits of the section and afterwards, l/s

II. Dimensioning of a Branched Distribution System Topic II.1 Determination of the Design Water Flowrates is the coefficient of equivalent distribution flowrate; =1 for branched distribution system dimensioning is the specific water quantity of the distribution system l/sm is the reduced length of the designed section, m is the maximal hourly demand of the settlement, l/s is the sum of the maximal hourly concentrated consumptions of the settlement (hospital, restaurant and factory), l/s is the reduced length of the whole distribution system, m

II. Dimensioning of a Branched Distribution System Topic II.1 Determination of the Design Water Flowrates is the real length of the section, m is reducing coefficient, =1 for bilateral take off along the length of the section, =0.5 for unilateral take off, =0 for no take off (transit flows) is the total take off flowrate of the designed section, l/s is the total reduced length of the section (it includes the proper reduced length and the reduced lengths of the sections fed by the designed one), m

II. Dimensioning of a Branched Distribution System Topic II.1 Determination of the Design Water Flowrates Water Flowrate Plan of the Distribution System (Drawing 2)

II. Dimensioning of a Branched Distribution System Topic II.1 Determination of the Design Water Flowrates Contents of the Water Flowrate Plan   Numeration of the quarters   Numeration of the crossroads   Numeration of the branches   Real, reduced and total reduced lengths of the sections, m   Total take off flowrate of the sections, l/s   Concentrated flowrate of the sections, l/s   Fire flowrate of the sections, l/s

II. Dimensioning of a Branched Distribution System Topic II.2 Determination of the Section Diameters Pressure flow Hydraulic parameters (6)   Flowrate – Q   Velocity – v   Diameter – D   Hydraulic gradient – I   Head loss – h   Roughness factor - n Available equations (3) Continuity equation Head loss equation Chezy - Maning equation Accepted parameters: Q, v, n = for steel pipes Calculated parameters: D, I, h

II. Dimensioning of a Branched Distribution System Topic II.2 Determination of the Section Diameters Velocity – accepted range of variation   Mean economical velocities (for metal pipes, normal operation) v = 0.90 – 1.40 m/s   Lower limit for velocities in the pipes v min = 0.3 m/s   Upper limit for velocities in the pipes v max = 2.00 m/s – for the network v max = 3.00 m/s – for the feeder

II. Dimensioning of a Branched Distribution System Topic II.2 Determination of the Section Diameters Additional conditions  Critical dynamic head H min H min = 14 m for normal operation conditions (average two-floor building construction of the settlement) H min = 14 m in case of fire H min = 14 m in case of fire  Minimal diameter of a main branch section D min = 100 mm  Equation of head loss balance (looping the system) is the sum of the head loss in the clockwise-water-movement is the sum of the head loss in the clockwise-water-movement sections of a system loop, m sections of a system loop, m is the sum of the head loss in the counter-clockwise-water- is the sum of the head loss in the counter-clockwise-water- movement sections of the same loop, m movement sections of the same loop, m misbalance of a loop, m misbalance of a loop, m Acceptable misbalance of a loop: for normal operation (maximal hourly demand) in case of fire (maximal hourly demand + fire quantity) The balance must be achieved for both loops at the same time. by changing diameters of some sections of the branches.

II. Dimensioning of a Branched Distribution System Topic II.2 Determination of the Section Diameters Dimensioning Table Note: Diameters are to be found for Q no, accepting the velocity in the range of the mean economical limits. Then v f and I f are found with the obtained diameter and Q d.

II. Dimensioning of a Branched Distribution System Topic II.3 Determination of the Water Tank Elevation and the Head (Pressure) at the Crossroads

II. Dimensioning of a Branched Distribution System Topic II.3 Determination of the Water Tank Elevation and the Head (Pressure) at the Crossroads - ground elevation of the water tank, m (coincides with the maximal water level elevation – sunken with the maximal water level elevation – sunken type service reservoir) type service reservoir) - ground elevation of the critical point, m - critical (minimal allowable) pressure, = 14 m - sum of the head loss from the critical point to - sum of the head loss from the critical point to the beginning of the distribution system, m the beginning of the distribution system, m - head loss in the feeder, m - usable depth of the tank, m = 4.5 – 5 m

II. Dimensioning of a Branched Distribution System Topic II.3 Determination of the Water Tank Elevation And the Head (Pressure) at the Crossroads Defining the Position of the Critical Point When the slope of the terrain is uniform, usually the critical point (crossroads) is the one of the highest elevation (case 1), or the most remote one from the Tank (case 2). Compare: Z i +Σh i-1 with Z 1 The maximal value defines the position of the critical point.

II. Dimensioning of a Branched Distribution System Topic II.3 Determination of the Water Tank Elevation And the Head (Pressure) at the Crossroads Defining the Feeder Head loss The head loss in the feeder is calculated by the following iterative procedure: procedure: 1.Assume the value of the head loss in the feeder h’ 1-T = m 2.Calculate the tank level as a first approximation Z 1,T and find the position of the tank on the map horizontals. 3.Trace the feeder from the tank to the settlement as a straight line (the shortest way). Measure the length of the feeder from the map L 1. 4.Calculate the head loss in the feeder as a second approximation h” 1-T. If it is lower than the accepted one (h’ 1-T ) the elevation of the tank is well defined. Otherwise, repeat the procedures from 2 to 4, increasing the tank elevation by the difference between the calculated and assumed values of the feeder head loss. Finally, find the elevations of the head line and the pressure at the crossroads:

II. Dimensioning of a Branched Distribution System Vocabulary of the Terms

II. Dimensioning of a Branched Distribution System Vocabulary of the Terms