Water Supply Systems Lecture 2

Water Supply Systems Lecture notes 2

dr Patryk Wójtowicz

Monday 1 December 14

Contents • Design considerations - key parameters • Water demand calculations: • estimation of base water demand • water demand forecasting • peaking factors • leakage and unaccounted-for water • water for fire protection Monday 1 December 14

Design considerations •

The design considerations of water supply systems involve topographic features of terrain and economical parameters (restrictions)

•

Some essential parameters for network sizing are:

•

the projection of residential, commercial and industrial water demand

• • • • • •

per capita water consumption peak flow factors minimum and maximum pipe sizes pipe material system safety and reliability requirements selection of optimal design period of a water distribution system in a pre-decided time horizon

Monday 1 December 14

Water demand •

The estimation of water demand for the sizing of any water supply system or its components is the most important part of the design methodology

•

Water demands (water duties) are generated from:

• • • • • • •

residential industrial and commercial developments community facilities and services

Customer demand

firefighting demand account for system losses (unaccounted-for water or UFW) periodical flushing treatment facility water demand

Monday 1 December 14

Water demand •

• •

Water demand is not constant, and is affected by a number of factors:

• • • • • • • •

climate economic and social factors water pricing, completeness of meterage, system management land use resort to private supplies population and type of a city standard of living, extent of sewage system industrialization of the area (size and type)...

A comprehensive study should estimate water demand considering all the site-specific factors Variations of water demand are observed in different time horizons (i.e. year, month, day, hour)

Monday 1 December 14

Historical water consumption in Poland 1965-2005

Monday 1 December 14

Historical water consumption in households in Poland 1953-2005

Monday 1 December 14

Monthly water consumption variations (for a selected Polish city)

Monday 1 December 14

Example of average daily water consumption variations throughout a year (for a selected Polish city)

Monday 1 December 14

Diurnal water variation in water demand (for a selected Polish city)

Monday 1 December 14

Table 4.3 Calculation of nodal demands using pattern multipliers Time

Pattern Multiplier

Demand

1:00

1.1

200 gpm × 1.1 = 220 gpm

2:00

1.8

200 gpm × 1.8 = 360 gpm

As one can imagine, usage patterns are as diverse as the customers themselves. Figure 4.11 illustrates just how different diurnal demand curves for various classifications can be. A broad zoning classification, such as commercial, may contain differences significant enough to warrant the further definition of subcategories for the different types of businesses being served. For instance, a hotel may have a demand pattern that resembles that of a residential customer. A dinner restaurant may have its peak usage during the late afternoon and evening. A clothing store may use very little water, regardless of the time of day. Water usage in an office setting may coincide with coffee breaks and lunch hours. Figure 4.11 Demand Multiplier

system-wide diurnal curve can be constructed using the same mass balance techques discussed earlier in this chapter. The only elaboration is that the mass balance performed as a series of calculations, one for each hydraulic step of an EPS simulaon.

Time

Time

Factory

Restaurant

Demand Multiplier

ime Increments. The amount of time between measurements has a direct corretion to the resolution and precision of the constructed diurnal curve. If measureents are only available once per day, then only a daily average can be calculated. ikewise, if measurements are available in hourly increments, then hourly averages an be used to define the pattern over the entire day.

the modeler tries to use a time step that is too small, small errors in tank water level an lead to large errors in water-use calculations. This type of error is explained furer in Walski, Lowry, and Rhee (2000). Modeling of hydraulic time steps smaller an one hour is usually only justified in situations in which tank water levels change pidly. Even if facility operations (such as pump cycling) occur frequently, it may 1 December illMonday be acceptable for14 the demand pattern time interval to be longer than the hydraulic

Single Family

Demand Multiplier

Developing System-Wide Diurnal Curves

Businesses Demand Multiplier

Diurnal curve for different user categories

Time

Time

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Monday 1 December 14

Monday 1 December 14

Monday 1 December 14

Water demand forecasting • Forecasting is made for different time horizons: • current (actual) water demand - prepared for 164

Water Consumption

Chapter 4

existing water networks, based on trends in historical data Figure 4.13

Several methods for projecting future demands

5.0

4.5

4.0 Peak Day Demand, MGD

• average-term forecast • long-term forecast

Constant Percent Growth

Growth to Buildout

3.5

Linear Growth

3.0

Economic Downturn

2.5 Annual Demand Data 2.0

1.5 1960

1970

1980

1990

2000

2010

2020

2030

2040

Time, year

•

Different methods for projecting future demands

Average- and long-term forecasts are mainly based on unit water demands (index method) Disaggregated Projections

Rather than basing projections on extrapolation of flow rate data, it is somewhat more rational to examine the causes of demand changes and then project that data into the future. This technique is called disaggregated projection. Instead of predicting demands, the user predicts such things as industrial production, number of hotel rooms, and cost of water, and then uses a forecasting model to predict demand. The simplest type of disaggregated demand projection involves projecting population and per capita demand separately. In this way, the modeler can, for example, separate the effects of population growth from the effects of a decrease in per capita consumption due to low-volume fixtures and other water conservation measures.

Monday 1 December 14

These types of approaches attempt to account for many variables that influence future demands, including population projections, water pricing, land use, industrial growth, and the effects of water conservation (Vickers, 1991; and Macy, 1991). The IWR-

Population projection formulas • Arithmetic (recommended for cities up to 20 000): ⎛ i + t⎞ Pf = Pc ⎜ 1+ ⎟ ⎝ 100 ⎠

• Geometric (recommended for cities up to 20 000): i ⎞ ⎛ Pf = Pc ⎜ 1+ ⎝ 100 ⎟⎠

t

• Exponential (recommeded for cities from 20 000): Pf - future population Pc - current population i - growth rate in % t - time in years Monday 1 December 14

Pf = Pc + e

⎛ i+t ⎞ ⎜⎝ ⎟ 100 ⎠

Water demand forecasting To capture variability of water demand there are several characteristic parameters describing water consumption and usage

•

Average day water demand Qavd expressed in m3/d: Q avd

•

Q year 3 = , m /d 365

Maximum day water demand Qmaxd (m3/d) Q maxd = Q avd ⋅ N d where: Nd - daily peaking factor

Monday 1 December 14

Daily and hourly peaking factors (Polish regulations)

Monday 1 December 14

Calculation of water demand (cont.)

• Peak hour water demand Q (typically expressed in Q maxh

3 dm /s

Q maxd = Nh ⋅ 24

where: Nh - hourly peaking factor

Monday 1 December 14

or

maxh 3 m /h):

Water demand • The residential forecast of future demand

is usually based on house count, census records and population projections

• The industrial and commercial facilities have a wide range of water demand

• This demand can be estimated based on historical data from the same or comparable other system

• Planning guidelines provided by engineering

bodies, governmental and regulatory agencies should also be considered

Monday 1 December 14

Water demand •

The firefighting demand can be estimated using equations (Kuichling or Freeman formula) or according to local guidelines or design codes in national firefighting regulations

•

Estimation of water losses is not straightforward and depends on a number of factors:

• • • • • •

age of system minimum prescribed pressure maximum pressure in the system pipeline material quality of pipeline materials and maintenance works specific local conditions (mine damages, earthquakes) ...

Monday 1 December 14

Calculation of residential water demand (Polish regulations)

Monday 1 December 14

Typical water duties in USA TABLE 3.2

Typical Water Duties

Land Use

Water Duty, (gal/day/acre) Low High Average

Low-density residential

400

3300

1670

Medium-density residential

900

3800

2610

High-density residential

2300

12000

4160

Single-family residential

1300

2900

2300

Multifamily residential

2600

6600

4160

Office commercial

1100

5100

2030

Retail commercial

1100

5100

2040

Light industrial

200

4700

1620

Heavy industrial

200

4800

2270

Parks

400

3100

2020

Schools

400

2500

1700

Source: Adapted from Montgomery Watson study of data of 28 western U.S. cities. Note: gal X 3.7854 = L.

Monday 1 December 14

TABLE 3.3

Typical Rates of Water Use for Various Establishments

seats in a restaurant) and multiply by the typical unit flow to determine the average daily flow from that establishment.

Typical of water wateruse use various Typical rates rates of forfor various establishments establishments in (USA) USA Table 4.1 provides typical unit loads for a number of different types of users. Ranges are given because there is considerable variation between establishments within a given category. Table 4.1 Typical rates of water use for various establishments Range of Flow User

(l/person or unit/day)

(gal/person or unit/day)

Airport, per passenger

10–20

3–5

Assembly hall, per seat

6–10

2–3

Bowling alley, per alley

60–100

16–26

Pioneer type

80–120

21–32

Children’s, central toilet and bath

160–200

42–53

Day, no meals

40–70

11–18

Luxury, private bath

300–400

79–106

Labor

140–200

37–53

Trailer with private toilet and bath, per unit (2 1/2 persons)

500–600

132–159

Resident type

300–600

79–159

Transient type serving meals

60–100

16–26

Apartment house on individual well

300–400

79–106

Apartment house on public water supply, unmetered

300–500

79–132

Boardinghouse

150–220

40–58

Hotel

200–400

53–106

120–200

32–53

Motel

400–600

106–159

Private dwelling on individual well or metered supply

200–600

53–159

Private dwelling on public water supply, unmetered

400–800

106–211

40–100

11–26

Camp

Country clubs

Dwelling unit, residential

Lodging house and tourist home

Factory, sanitary wastes, per shift

Table extracted from Ysuni, 2000 based on Metcalf and Eddy, 1979

Monday 1 December 14

Typical rates of water use for various establishments in USA (cont.) 148

Water Consumption

Chapter 4

Table 4.1 (cont.) Typical rates of water use for various establishments Range of Flow User

(l/person or unit/day)

(gal/person or unit/day)

Fairground (based on daily attendance)

2–6

1–2

Average type

400–600

106–159

Hospital

700–1200

185–317

Office

40–60

11–16

Picnic park, with flush toilets

20–40

5–11

Average

25–40

7–11

Kitchen wastes only

10–20

3–5

Short order

10–20

3–5

Short order, paper service

4–8

1–2

Bar and cocktail lounge

8–12

2–3

Average type, per seat

120–180

32–48

Average type, 24 h, per seat

160–220

42–58

Tavern, per seat

60–100

16–26

Service area, per counter seat (toll road)

1000–1600

264–423

Service area, per table seat (toll road)

600–800

159–211

Day, with cafeteria or lunchroom

40–60

11–16

Day, with cafeteria and showers

60–80

16–21

Boarding

200–400

53–106

1000–3000

264–793

First 7.5 m (25 ft) of frontage

1600–2000

423–528

Each additional 7.5 m of frontage

1400–1600

370–423

40–60

11–16

Indoor, per seat, two showings per day

10–20

3–5

Outdoor, including food stand, per car (3 1/3 persons)

10–20

3–5

Institution

Restaurant (including toilet)

School

Self-service laundry, per machine Store

Swimming pool and beach, toilet and shower Theater

Table extracted from Ysuni, 2000 based on Metcalf and Eddy, 1979

Monday 1 December 14

Other investigators have linked water use in nonresidential facilities to the Standard Industrial Classification (SIC) codes for each industry as shown in Table 4.2. To use this table, the modeler determines the number of employees in an industry and multi-

Unit (average) water demand for industrial facilities according to the population (Poland)

Monday 1 December 14

Average rates of nonresidential water use from establishment-level data in USA (according to SIC code) Section 4.1

Baseline Demands

Table 4.2 Average rates of nonresidential water use from establishment-level data Category

SIC Code

Construction General building contractors

15

31

246

118

66

Heavy construction

16

20

30

17

25

150

164

2790

Food and kindred products

20

469

252

Textile mill products

22

784

20

Apparel and other textile products

23

26

91

Lumber and wood products

24

49

62

Furniture and fixtures

25

36

83

Paper and allied products

26

2614

93

Printing and publishing

27

37

174

Chemicals and allied products

28

267

211

Petroleum and coal products

29

1045

23

Rubber and miscellaneous plastics products

30

119

116

Leather and leather products

31

148

10

Stone, clay, and glass products

32

202

83

Primary metal industries

33

178

80

Fabricated metal products

34

194

395

Industrial machinery and equipment

35

68

304

Electronic and other electrical equipment

36

95

409

Transportation equipment

37

84

182

Instruments and related products

38

66

147

Miscellaneous manufacturing industries

39

36

55

50

226

68

3

Transportation and public utilities Railroad transportation

40

Local and interurban passenger transit

41

26

32

Trucking and warehousing

42

85

100

U.S. Postal Service

43

5

1

Water transportation

44

353

10

Transportation by air

45

171

17

Transportation services

47

40

13

Communications

48

55

31

Electric, gas, and sanitary services

49

51

19

53

751 518

Wholesale trade

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Sample Size

Special trade contractors Manufacturing

(SIC) Standard Industrial Classification

Use Rate (gal/employee/day)

Wholesale trade–durable goods

50

46

Wholesale trade–nondurable goods

51

87

233 Table from Dziegielweski, Opitz, and Maidment, 1996

149

Average rates of nonresidential water use from establishment-level data (cont.) 150

Water Consumption

Chapter 4

Table 4.2 (cont.) Average rates of nonresidential water use from establishment-level data Category

SIC Code

Use Rate (gal/employee/day) 93

1044

52

35

56

Retail trade Building materials and garden supplies

Sample Size

General merchandise stores

53

45

50

Food stores

54

100

90

Automotive dealers and service stations

55

49

498

Apparel and accessory stores

56

68

48

Furniture and home furnishings stores

57

42

100

Eating and drinking places

58

156

341

Miscellaneous retail

59

132

161

192

238

Finance, insurance, and real estate Depository institutions

60

62

77

Nondepository institutions

61

361

36

Security and commodity brokers

62

1240

2

Insurance carriers

63

136

9

Insurance agents, brokers, and service

64

89

24

Real estate

65

609

84

Holding and other investment offices

67

290

5

137

1878

Services Hotels and other lodging places

70

230

197

Personal services

72

462

300

Business services

73

73

243

Auto repair, services, and parking

75

217

108

Miscellaneous repair services

76

69

42

Motion pictures

78

110

40

Amusement and recreation services

79

429

105

Health services

80

91

353

Legal services

81

821

15

Educational services

82

110

300

Social service

83

106

55

Museums, botanical, zoological gardens

84

208

9

Membership Section 4.1 organizations

86

212

45

Engineering and management services

87

58

5

Services, NEC

89

73

60

106

25

Public administration

Baseline Demands

Executive, legislative, and general 91 155from establishment-level 2 Table 4.2 (cont.) Average rates of nonresidential water use data Justice, public order, and safety Category Administration of human resources

Environmental quality and housing

92 SIC Code 94

18 Use Rate (gal/employee/day) 87

4Sample 6Size

95

101Table from Dziegielweski, Opitz, and 6 Maidment, 1996

Administration of economic programs

96

274

5

National security and international affairs

97

445

2

Table from Dziegielweski, Opitz, and Maidment, 1996

Monday 1 December 14

Unaccounted-For Water Ideally, if individual meter readings are taken for every customer, they should exactly

151

Average water demand for selected commercial facilities (Poland)

Monday 1 December 14

Unaccounted-For Water (UFW) •

Ideally, if individual meter readings are taken for every customer, they should exactly equal the amount of water that is measured leaving the treatment facility

•

In practice not all of the outflows are metered. These lost flows are referred to as unaccounted-for water (UFW)

•

The most common reasons for discrepancies are:

• • • •

leakage overflows at tanks errors in flow measurement (under-register at low flow rates) unmetered water usage (illegal connections, usage of fire hydrants, blow-offs and other maintenance appurtenances)

Monday 1 December 14

Leakage •

•

Leakage is commonly the largest component of UFW and includes:

• • • •

distribution losses from supply pipes distribution and trunk mains services up to the meter connections to tanks

The amount of leakage varies from system to system, but there is a general correlation between the age of a system and the amount of UFW. Projections of leakage must include special areas (mine damages, earthquakes etc.)

•

New and well maintained systems may have as little as 5% leakage, while older systems may have 40% leakage or even higher

•

Other factors affecting leakage include:

• • •

system pressure (the higher the pressure, the more leakage) burst frequencies of mains and service pipes leakage detection and control policies

Monday 1 December 14

Estimating water leakage • For existing networks made of traditional materials

(cast iron) properly maintained leakage index may be estimated from 0.5 m3/h km to 0.3 m3/h km

• For new networks (after renovation), properly built and maintained leakage index should not be higher than 0.3 - 0.2 m3/h km

• For water demand forecasting leakage should be

between 5% to 10% of average daily water demand

Monday 1 December 14

Estimating water leakage

Monday 1 December 14

Leak Losses for Circular Holes Under Different Pressures* Leak Losses, gpm Diameter of Hole, in.

Area of Hole, in.2

20

40

60

80

100

0.1

0.007

1.067

1.510

1.850

2.136

2.388

2.616

2.825

0.2 0.3 0.4 0.5 0.6

0.031 0.070 0.125 0.196 0.282

4.271 9.611 17.087 26.699 38.477

6.041 13.593 24.165 37.758 54.372

7.399 16.648 29.597 46.245 66.593

8.544 19.224 34.175 53.399 76.894

9.522 21.493 38.209 59.702 85.971

10.464 23.544 41.856 65.400 94.176

11.302 25.430 45.209 70.640 101.721

0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0

0.384 0.502 0.636 0.785 0.950 1.131 1.327 1.539 1.767 2.011 2.270 2.545 2.836 3.142

52.331 68.350 86.506 106.798 129.225 153.789 180.488 209.324 240.295 273.402 308.646 346.025 385.540 427.191

74.007 96.662 122.338 151.035 182.752 217.490 255.249 296.028 339.829 386.649 436.491 489.353 545.237 604.140

90.640 118.387 149.833 184.979 223.825 266.370 312.615 362.559 416.203 473.547 534.590 599.333 667.776 739.918

104.662 136.701 173.012 213.596 258.451 307.578 360.977 418.648 480.590 546.805 617.292 692.050 771.081 854.383

117.010 152.840 193.434 238.807 288.957 343.882 403.584 468.062 537.317 611.347 690.153 773.736 862.095 955.230

128.184 167.424 211.896 261.600 316.536 376.704 442.104 512.737 588.601 669.697 756.025 847.585 944.378 1,046.400

138.454 180.839 228.874 282.561 341.898 406.887 477.527 553.819 635.762 723.355 816.600 915.496 1,020.040 1,130.240

Leak Losses for Joints and Cracks*

Water Pressure, psi 120

140

160

180

Area3.021 of Joint 12.083 or Crack

3.204

12.816 27.186 28.835 48.331 Length, Width, 51.263 75.518 80.098 in.108.745 in. 115.34120

200 3.337 13.509 30.395 54.036 84.431 121.581 40

Leak Losses, gpm Water Pressure, psi 60

80

100 120 140 160 180

148.014

156.993 165.485 3.2 4.5 5.5 6.4 7.1 7.8 8.4 9.0 9.6 205.052 216.144 244.676 1⁄16 259.5196.4 273.557 1.0 9.0 11.0 12.7 14.2 15.6 16.9 18.0 19.1 302.070 320.394 337.725 1 1.0 12.7 18.0 38.2 365.505 ⁄8 387.676 408.647 22.1 25.5 28.5 31.2 33.7 36.0 434.981 1 461.367 486.323 1.0 25.5 36.0 44.1 51.0 57.0 62.4 67.4 72.1 76.5 ⁄ 4 510.498 541.465 570.755 592.057 627.972 661.941 * For leaks emitted from joints and cracked service pipes, an orifice coefficient of 0.60 679.658 720.886 759.880 in the following equation: 773.299 820.208 864.575 Q = (22.796)(A)( P ) 872.983 925.938 976.024 Where: flow, in gpm;1,094.220 A = area, in in.2; P = pressure, in psi 978.707 Q = 1,038.070 1,090.470 1,156.620 1,219.180 1,208.280 1,281.570 1,350.890

1 1.0 193.325 ⁄32

* Calculated using Greeley’s formula (see equation on following page).

For losses from such items as pipes or broken taps, assum Greeley’s formulaof(used for leakages from pipes or orifice coefficient Leak Losses for Joints and Copyright Cracks*(C) 2012 American Water Works Association All Rights Reserved Distribution0.80 and calculate flow in gallons per mi broken taps, assuming from Greeley’s formula: an orifice coefficient of 0.80) Area of Joint or Crack

Leak Losses, gpm

Length, Width,

Water Pressure, psi

Q

in.

in.

20

40

60

80

100 120 140 160 180 200

1.0

1⁄32

3.2

4.5

5.5

6.4

7.1

7.8

8.4

9.0

1.0

1⁄16

6.4

9.0

11.0

12.7

14.2

15.6

16.9

18.0

19.1 20.1

1.0

1⁄8

12.7

18.0

22.1

25.5

28.5

31.2

33.7

36.0

38.2 40.3

1.0

1⁄4

25.5

36.0

44.1

51.0

57.0

62.4

67.4

72.1

76.5 80.6

9.6

10.1

* For leaks emitted from joints and cracked service pipes, an orifice coefficient of 0.60 is used in the following equation: Q = (22.796)(A)( P ) Where: Q = flow, in gpm; A = area, in in.2; P = pressure, in psi Monday 1 December 14

43, 767 1, 440

#

A# P

Where: Q = flow, in gpm A = the cross-sectional area of the leak, in in.2 P = pressure, in psi

No pipe installation will be accepted if the amount of mak water is greater than that determined by the following formula

Fire protection

AWWA M31 Distribution System Requirements for Fire Protection

•

Fire storage is the amount of stored water required to provide a specified fire flow for a specified duration

•

The rate of flow to be provided for fire flow is typically dependent on the land use and varies by community

•

The fire flow criteria are usually given in national or local regulations (e.g. fire marshall)

Monday 1 December 14

includes determining fire flow demands according to the ISO approach. Although the actual water needed to fight a fire depends on the structure and the fire itself, the ISO method yields a Needed Fire Flow (NFF) that can be used for design and evaluation of the system. Different calculation methods are used for different building types, such as residential, commercial, or industrial.

Fire protection water demands (USA and Poland)

For one- and two-family residences, the needed fire flow is determined based on the as shown in Table distance between Typicalstructures, fire flow requirements (USA)4.5. Table 4.5 Needed fire flow for residences two stories and less Distance Between Buildings (ft)

Fire Flow (gpm)

More than 100

500

31-100

750

11-30

1,000

Less than 11

1,500

For commercial and industrial structures, the needed fire flow is based on building area, construction is, frame or masonry construction), occupancy (such as TABLE 3.4 Typical Fireclass Flow (that Requirements a department store or chemical manufacturing plant), exposure (distance to and type Land Use Fire Flow Requirements, gal/m* of nearest building), and communication (types and locations of doors and walls). The Single-family 500-2000 formula canresidential be summarized as: Multifamily residential Commercial Industrial Central business district

where

1500-3000 2500-5000 0.5

NFF = 18FA

O(X + P )

3500-10,000

(4.12)

2500-15,000

NFF = needed fire flow (gpm) Note: gal X 3.7854F= = L. class of construction coefficient A = effective area (ft2) Monday 1 December 14 O = occupancy factor

Polish fire flow requirements for communities

Supplementary reading • CH3 Introduction to Water Sources. Alaska Department of Environmetal Conservation.

Monday 1 December 14