Water Demand And Distribution.ppt

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Distribution of per capita water demandWater Demand and WaterDistribution System DesignRobert PittUniversity of Alabama(Chin 2000 Table 3.5)System DesignFuture Per Capita Estimates of Water UseProjected Consumption of Water for Various Purposes in theYear 2000From: Water Supply and Sewerage, Sixth Edition. Terence J. McGhee. McGraw-HillPublishing Company. 1991.UseDomesticIndustrialCommercialPublicLoss and WasteTOTALGallons PerCapita/Day79.242.2426.415.8413.2176.88 Can do estimates based on number and/or types of structuresin design area and using existing data. Residential:Residentiales de t a WaterWate ConsumptionCo su pt oFrom: On-Site Wastewater Treatment: Educational Materials Handbook. NationalSmall Flows Clearinghouse. West Virginia University, 1987.Percentage of TotalHome y/DishesDrinking/CookingTOTALDaily Water Use Per PersonGallonsPercent32452130143702051001

From: Water Resources Engineering, 1st Edition. Larry W. Mays, John Wiley& Sons, Inc. 2001. (Table 11.1.4 page 346)UnitsAverage UsePeak UseHotelsL/day/m210.417.6MotelsL/day/m2919.163 163.1Barber shopsL/day/barberchair207Beauty tsAverage UsePeak UseL/day/m288.4265Retail y/student20.41864050High schoolsL/day/student25.1458Bus-rail lsL/day/bed13103450Nursing homesL/day/bed5031600Medical officesL/day/m225.2202LaundryL/day/m210.363.9Night clubsFrom: Water Resources Engineering, 1st Edition. Larry W. Mays, John Wiley& Sons, Inc. 2001. (Table 11.1.4 page 346)5From: Water Resources Engineering, 1st Edition. Larry W. Mays, John Wiley& Sons, Inc. 2001. (Table 11.1.4 page 346)Laundromatsm2Car 17.8Golf-swim clubsL/day/member11784Bowling udent401946From: Water Resources Engineering, 1st Edition. Larry W. Mays, John Wiley & Sons,Inc. 2001. (Table 11.1.5 Page 347)UnitsAverage UseWashing machineL/load130 – 27010 – 30UnitsAverage UsePeak UseNew officebuildingsL/day/m23.821.2St d d toiletStandardt il tL/fl hL/flushUltra volume toiletL/flush 6Old officebuildingsL/day/m25.814.4Silent leakL/day 150TheatersL/day/seat12.612.6Nonstop running toiletL/minute 20L/day/inside m210.21280Service stationsDishwasherL/load50 –120L/load40 –100100L/minute 20L20 – 40Running garbage disposalL/minute10 – 20Bathroom faucetL/minute 20ApartmentsL/day/occupied unit8211640Water saver dishwasherWater-saverFast foodrestaurantsL/day/establishment678020300Washing dishes with tap runningWashing dishes in filled sink2

From: Water Resources Engineering, 1st Edition. Larry W. Mays, John Wiley & Sons,Inc. 2001. (Table 11.1.5 Page 347)UnitsAverage UseL8Shower headL/minute20 – 30Low-flow shower headL/minute6 – 11L100 – 300Brushing teethFilling bathtub750-m2L/month7600 – 16000Standard sprinklerL/hour110 – 910One drip-irrigation emitterL/hour1 – 10½-Inch diameter hoseL/hour1100Wateringlawn5/8-Inch diameter hoseL/hour1900¾-Inch diameter hoseL/hour2300From: Water Resources Engineering, 1st Edition. Larry W. Mays, John Wiley & Sons,Inc. 2001. (Table 11.1.5 Page 347)UnitsAverage UseWashing car with running waterL/20 minutes400 – 800Washing car with pistol-gripfaucetL/20 minutes 60Uncovered poolL lost/month3000 – 11000 Covered ppoolL lost/month300 – 1200Diurnal curves for different user categoriesGiven average annual consumption rates, stillneed to estimate peak demand because Water use varies during the day Water use varies from day to day Water use varies weekly and seasonally(Walski, et al. 2001 figure 4.8)3

Typical daily cycles in water demandPeak Water Use Estimation: Estimation ofAverage Daily Rate Based on a Maximum Time PeriodGoodrich Formula: Estimates maximum demand ((expressedpas dailyy water demand basedon time period for which maximum water demand is desired) forcommunity when given annual average per capita daily water use rate:p 180 t 0.10wherep percentage of average annual rate (volume/day) used in period oftime of interestt length of period for which peak demand is required (days) (validtime periods – 2 hours to 360 days) **Daily rate based upon a maximum hour is approximatelyequal to 150 percent of average annual daily rate.(Chin 2000 Figure 3.23)Peak Water Use Estimation Consumption rate for max day 180% of the annual averagedailyy consumptionpTypical demand factors Consumption rate for max week 148% of the annual averagedaily consumption Consumption rate for max month 128% of the annualaverage daily consumption Consumption rate for max hour 150% of the max day,or 270% of the annual average daily consumption(Chin 2000 Table 3.6)4

Fire DemandIn metric units (AWWA 1992):NFFi Ci Oi X P iConstruction coefficient, FC is the construction factor based on the size of the building andits construction,O is the occupancy factor reflecting the kinds of materials stored inthe building (ranging from 0.75 to 1.25), and(X P) is the sum of the exposure factor and the communicationfactor that reflect the proximity and exposure of the other buildings.C i 220 F AiC (L/min),A (m2) is the effective floor area, typically equal to the area of thelargest floor plus 50% of all other floors,F is a coefficient based on the class of construction(Chin 2000 Table 3.7)Needed fire flow for one- and two-family dwellingsOccupancy factors, Oi(Chin 2000 Table 3.8)(Chin 2000 Table 3.9)5

Required fire flow durations(Walski, et al. 2001)(Chin 2000 Table 3.10)Design periods and capacities in water-supply systemsExample 3.16 from Chin 2000Estimate the flowrate and volume required to provide adequateprotection to a 10-story noncombustible building with and effective floorarea of 8,000 m2.NFFi C i Oi X P iCi 220 F AiThe construction factor is calculated as (F 0.8 for class 3noncombustible construction and the floor area is 8,000 m2):Ci 220 0.8 8000m2 16,000L / minThe occupancy factor C is 0.75 (C-1 noncombustible) and the (X P) isestimated using the median value of 1.4. Therefore, the required fireflow is:NFFi 16,000L / min 0.75 1.4 17,000 L / minThe flow must be maintained for a duration of 4 hours, and therequired volume is therefore:V 17,000 L / min 4 hours 60 min/ hr 4.08 x10 6 L 4,080m 3(Chin 2000 Table 3.11)6

Methods of Water Distribution Pumping with Storage––––M t commonMostWater supplied at approximately uniform rateFlow in excess of consumption stored in elevated tanksTank water provides flow and pressure when use is high Fire-fighting High-use hours Flow during power failureWater Distribution System Components Pumping Stations Distribution Storage Distribution System PipingOther water system components include watersource and water treatment– Storage volume throughout system and for individualservice areas should be approximately 15 – 30% ofmaximum daily rate.Looped and branched networks after network failureThe Pipe System Primary Mains (Arterial Mains)– Form the basic structure of the system and carryflow from the pumping station to elevated storagetanks and from elevated storage tanks to thevarious districts of the city Laid out in interlocking loopsM i nott more thanMainsth 1 kmk (3000 ft) aparttValved at intervals of not more than 1.5 km (1 mile)Smaller lines connecting to them are valved(Walski, et al. 2001 figure 1.2)7

The Pipe System, Cont. Secondary LinesThe Pipe System, Cont. Small distribution lines– Form smaller loops within the primary mainsystem– Run from one primary line to another– Spacings of 2 to 4 blocksg amounts of water for fire fightinggg– Provide largewith out excessive pressure loss– Form a grid over the entire service area– Supply water to every user and fire hydrants– Connected to primary, secondary, or other smallmains at both endsycan be shut down for repairsp– Valved so the system– Size may be dictated by fire flow except inresidential areas with very large lotsPipe sizes in Municipal Distribution SystemsVelocity in Municipal Distribution Systems Small distribution lines providing only domestic flowmay be as small as 4 inches, but:– 1300 ft in length if dead ended,ended or– 2000 ft if connected to system at both ends. Otherwise, small distribution mains 6 in High value districts – minimum size 8 in Major streets – minimum size 12 in Fire-fighting requirements 150 mm (6 in.) National Board of Fire Underwriters 200 mm (8 in.)(McGhee, Water Supply and Sewerage, 6th Edition) Normal use 1m/s, (3 ft/s) Upper limit 2 m/s (6 ft/s) (may occur invicinity of large fires)(Viessman and Hammer, Water Supply and PollutionControl, 6th Edition)1 V 1.7 m/s (3 V 5 ft/s)8

Pressure in Municipal Distribution Systems(American Water Works Association)AWWA recommends normal static pressure of 400-500kPa, 6075lb/in2- supplies ordinary uses in building up to 10 stories- will supply sprinkler system in buildings up to 5stories- will provide useful fire flow without pumper trucks- will provide a relatively large margin of safety tooffset sudden high demand or closure of partof the system.Pressure in Municipal Distribution Systems(McGee) Pressure in the range of 150 – 400kPa (20 to40 lb/in2) are adequate for normal use and maybe used for fire supply in small towns wherebuilding heights do not exceed 4 stories.Typical elevated storage tankMinimum acceptable pressures indistribution systems(Chin 2000 Table 3.12)(Chin 2000 Figure 3.24)9

Hardy Cross MethodFor Hardy-Cross Analysis: Used in design and analysis of waterdi t ib ti systemsdistributiontforf many years. Based on the hydraulic formulas we reviewedearlier in the term. Water is actually removed from the distribution system of acity at a very large number of points. Its is not reasonable to attempt to analyze a system with thisdegree of detail Rather, individual flows are concentrated at a smaller numberof points, commonly at the intersection of streets. The distribution system can then be considered to consist of anetwork of nodes (corresponding to points of concentratedflow withdrawal) and links (pipes connecting the nodes). The estimated water consumption of the areas containedwithin the links is distributed to the appropriate nodesNetwork model overlaid on aerial photographSkeletonization - An all-link network(Walski, et al. 2004 figure 3.4)(Walski, et al. 2004 figure 3.32)10

Minimal skeletonization(Walski, et al. 2004 figure 3.33)Maximum skeletonization(Walski, et al. 2004 figure 3.35)Moderate skeletonization(Walski, et al. 2004 figure 3.34)Customers must be served from separate pressure zones(Walski, et al. 2001 figure 7.17)11

Profile of pressure zonesImportant tankelevations(Walski, et al. 2001 figure 7.20)Hardy-Cross Method of Water DistributionDesign Definitions– Pipe sections or links are the most abundant elements in thenetwork.(Walski, et al. 2001 figure 3.10)Steps for Setting Up and Solving a Water DistributionSystem using the Hardy-Cross Method1.Set up grid network to resemble planned flowdistribution patternpattern. These sections are constant in diameter and may contain fittings andother appurtenances. Pipes are the largest capital investment in the distribution system.– Node refers to either end of a pipe. Two categories of nodes are junction nodes and fixed-grade nodes. NodesN d whereh theh iinflowfl or outflowfl isi knownkare referredfd to asjunction nodes. These nodes have lumped demand, which may varywith time. Nodes to which a reservoir is attached are referred to as fixed-gradenodes. These nodes can take the form of tanks or large constantpressure mains.12

Steps for the Hardy-Cross Method2.Steps for the Hardy-Cross MethodCalculate water use on each street (including fire demandon the street where it should be located).StreetN bNumberBuildingDDescriptioni tiWithout Fire DemandMGDft3/secMGDft3/sec1**5 A, 1 S0.0590.0922.003.100.0303.With Fire Demand (worstb ildi )building)23A0.0190.0300.019318 A0.120.180.120.1843 A, 1 O, 1 450.0700.0450.070710 450.0700.0450.070108A0.0520.0800.0520.08011No buildings0.00.00.00.0Total without Fire Demand 0.75 cfsInfluent 2.5 MGD 3.87 cfsL ft OverLeftOtot OtherOth NeighborhoodsN i hb h d 3.123 12 cfsfDistribute 50/50 to two outflow nodes 1.56 cfs(arbitrary for this problem – would be based on known“downstream” requirements).Steps for the Hardy-Cross MethodSteps for the Hardy-Cross Method5.4.Assume internallyy consistent distribution of flow,i.e., at any given node and for the overall waterdistribution system: flow entering node flow leaving nodeAdd up the flow used in the neighborhood without firedemand and distribute it out the nodes where knownoutflow is required. Repeat for fire demand.For the inflow node,split the flow among thepipes leaving that node(there will be noadditional outflow sinceno water has been usedby the neighborhood asyet).Inflow Outflows13

Steps for the Hardy-Cross Method6.For each of the pipesleaving the inflownode, put the waterdemand for thatstreet at the node atthe end of the pipe.Steps for the Hardy-Cross Method9a. Check each node to see if inflow equals outflow.Steps for the Hardy-Cross Method7.For the above node and the next pipes in the distributionsystem, subtract the water used on the street (andaggregated at the node) from the water flowing down thepipe. Pass the remaining water along to one or more ofthe pipes connected to that node.8.Repeat Steps 6 and 7 for each pipe and node in thedistribution system. The calculation can be checked byseeing if the total waterater ooutflowtflo from the systems stem equalseq alsthe total inflow to the system, as well as checking eachnode to see if inflow equals outflow.Steps for the Hardy-Cross Method9b. Check each node to see if inflow equals outflow.14

Steps for the Hardy-Cross Method10.Select initial pipe sizes (assume a velocity of 3 ft/sec for normal flow with no firedemand). With a known/assumed flow and an assumed velocity, use thecontinuity equation (Q VA) to calculate the cross-sectional area of flow. (whenconducting computer design, set diameters to minimum allowable diameters foreach type of neighborhood according to local regulations)Flo (ft3/sec)FlowVelocitVelocity(ft/sec)Area (ft2)Diameter(ft)Diameter(in)Act al .0003.00.330.657.8860 9220.922303.00 310.310 0.5623.00.190.495.96PipeNumberSteps for the Hardy-Cross Method11.Steps for the Hardy-Cross Method12.Paying attention to sign ( /-), compute the head loss in eachelement/pipe of the system (such as by using DarcyWeisbach or Hazen-Williams).Determine the convention for flow. Generally, clockwiseflows are positive and counter-clockwise flows are negative.Steps for the Hardy-Cross Method13.Compute the sum of the head losses around eachloopp ((carryingy g the appropriatepp psigng throughoutgthecalculation).14.Compute the quantity, head loss/flow (hL/Q), foreach element/pipe (note that the signs cancel out,leaving a positive number).15.Compute the sum of the (hL/Q)s for each loop.Hazen Williams1.85Q hL L 2.63 0.432CD Darcy WeisbachhL fL V 2 D 2 g 15

Steps for the Hardy-Cross Method16.Compute the correction for each loop.Steps for the Hardy-Cross Method17.Apply the correction for each pipe in the loop that isnot shared with another loop.pQ1 Q0 Q18.For those pipes that are shared, apply the followingcorrectionti equationti (continuing( ti i tot carry allll thethappropriate signs on the flow):Q1 Q0 Qloop in – Qshared loop hL Q loophLloop Qn wheren 1.85Steps for the Hardy-Cross Method19.Reiterate until corrections are sufficiently small (10 – 15% orless of smallest flow in system), or until oscillation occurs.20.Calculate velocities in each pipe and compare to standards toensure that sufficient velocity (and pressure) are available ineach pipe. Adjust pipe sizes to reduce or increase velocitiesas needed.21.Repeat all the above steps until a satisfactory solution isobtained.22.Apply fire flow and other conditions that may be critical andreevaluate.Example for the Hardy-Cross Method(From McGhee, Water Supply and Sewerage, Sixth Edition)16

Example for the Hardy-Cross MethodExample for the Hardy-Cross MethodConvert units to U.S. Customary units: Insert data into spreadsheet for Hardy-Cross (solve usingHazen Williams).Hazen-Williams).ASSUME: Pipes are 20-year old cast iron, so C 100. Pipe Length (ft)Pipe Diameter(in)Flow0 (ft3/sec)BC4921186 236.23CD328116-5.54DA360912-2.6AB2625103.29Pipe SectionSteps for the Hardy-Cross Method Paying attention to sign ( /-), compute the head loss in eachelement/pipe of the system by using Hazen-Williams (checkth t thethatth signi forf theth headh d losslisi theth same as theth signi forf thethflow).Hazen Williams1.85Q hL L 2.63 0.432CD Example for the Hardy-Cross Method Calculate head loss using Hazen-Williams.PipeSectionFlow0 (ft3/sec)Pipe Length(ft)Pipe Diameter(in)hL .626-19.9319 93AB2625103.2954.3917

Example for the Hardy-Cross Method Example for the Hardy-Cross MethodCalculate hL/Q for each pipe (all of these ratios havepositive signs, as the negative values for hL and Qcancel out).Flow0 (ft3/sec)hL (ft)hL/Q .937.66AB3.2954.3916.53Pipe Section Calculate head loss using Hazen-Williams and column totals:Pipe SectionhL (ft)hL/Q (sec/ft2)BC19.033.05CD-18.113.27DA-19.9319 937 667.66AB54.3916.53 hL 35.38 (hL/Q) 30.51Example for the Hardy-Cross Method Calculate the correction factor for each pipe in the loop.Example for the Hardy-Cross Method Calculate the new flows for each pipe using the followingequation: hL Q lloophLloop Qn Q1 Q0 Qwhere n 1.85Flow0 (ft3/sec) Q (ft3/sec)Flow1 0.627-3.23AB3.29-0.6272.66Pipe Section -(35.38)/1.85(30.51) -0.62718

Final Flows for the Hardy-Cross ExampleExample for the Hardy-Cross MethodHARDY CROSS METHOD FOR WATER SUPPLY DISTRIBUTIONTrial IPipe SectionBCPipe Length Pipe Diameter(f t)(in)492118Flow 0(ft3/sec)6.2HL (f t)19.03HL/Q(sec/f 625103.354.3916.533.27n (HL/Q)(sec/ft2)56.46 (HL) (f t)35.38-0.627Flow 1(ft3/sec)5.60-0.627-6.17 Q (f t3/sec)-0.627-3.23-0.6272.66 Q (f t3/sec)-0.012Flow 2(ft3/sec)5.59-0.012-6.18Trial 2Pipe SectionBCCDPipe Length Pipe Diameter(f t)(in)4921183281Flow 1(ft3/sec)5.60HL (f t)15.64HL/Q(sec/f 02.6636.7913.813.58n (HL/Q)(sec/ft2)54.38 (HL) (f t)0.64-0.012-3.24-0.0122.65 Q (f t3/sec)0.000Flow 3(ft3/sec)5.590.000-6.180.000-3.240.0002.65Trial 3Pipe SectionBCPipe Length Pipe Diameter(f t)(in)492118Flow 2(ft3/sec)5.5915.58HL/Q(sec/f t2)2.79HL (f 2625102.6536.4913.76n (HL/Q)(sec/ft2)54.34 (HL) (f t)0.00Pressure Water Distribution SystemExtended period simulation (EPS) runs showing lowpressure due to elevation or system capacity problemThe pressure at any node can be calculated by starting witha known pressure at one node and subtracting the absolutevalues of the head losses along the links in the direction offlow.In this example, assume that the pressure head at node Cis 100 ft. and the pressure head at node A is desired.There are two paths between the known and unknownnodes for this example and both should be examined: CBand BA or CD and DA.In the first case: 100 ft. – 15.58 ft. – 36.49 ft. 47.93 ft.And in the second: 100 ft. – 22.16 ft. – 29.91 ft. 47.93 ft.(Walski, et al. 2001 figure 7.3)19

Pressure comparison for 6-, 8-, 12-, and 16- inch pipes(Walski, et al. 2001 figure 7.4)Head loss comparison for 6-, 8-, 12-, and 16- inch pipes(Walski, et al. 2001 figure 7.5)EPANet Water Distribution Model20

Retail spaceRetail space L/day/sales mL/day/sales m2 434.3 11 Elementary schools L/day/student 20.4 186 High schools L/day/student 25.1 458 Bus-rail depot L/day/m 2 136 1020 Car washes L/day/inside m2 194.7 1280 Churches L/day/member 0.5 17.8 Golf-swim clubs L/day/member 117 84 Bowling alleys L/day/alley 503 503 Residential colleges L/day .

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