water distribution system

Water System Design For Brgy. Aurelio Freires Sr., Lebak, Sultan Kudarat 1 | P a g e

INTRODUCTION

Water is considered as one of the most important elements of life, with air and food. It

is also considered by most philosophers as the basic element typifying all liquid substances. In

fact, water covers almost 75% of the Earth’s surface. Water is the major constituent of living

matter. From 50 to 90 per cent of the weight of living organisms is water. In atmospheric

temperature and pressure, water exists in liquid state.

According to World Health Organization (WHO), there are currently more than 100

million people in the world that lacks access to safe potable water, such as a connection to

water mains or a protected well. Instead, water is limited or available through unprotected

sources. To address the issue of water supply, the design of water supply system aims to supply

and distribute sufficient quantity and potable quality of water at acceptable residual pressures

to all points of demand or households.

Earth has adequate amount of water for human and other uses but on how to acquire it

lies the problem. Other problem is if it is accessible would it be safe for human consumption or

if it is safe to be use in the intended purpose. Luckily, there are many ways to counteract these

problems.

One of the solutions is the use of a submersible pump. A well is first bore and then

putting the pump to draw the water up a storage tank. From the storage tank the water will be

delivered to their respective destination to be use.

This design aims to supply potable water to an urban barangay in Lebak, Sultan Kudarat,

named Brgy. Aurelio Freires Sr. As one the trade centers of the municipality, the latter barangay

needs a supply of safe drinking water to its residential and business establishments, schools,

churches, hospitals and the likes. The designer decides to include supplying water for the fire

hydrants on the said area.




Summarized Breakdown of Demands

Below is the summary of the consumptions in the circuit. For complete calculations, please refer to the appendices.

CONSUMERS

NUMBER

CONSUMPTION

Residential Establishments

280

121,043.64 Gallons per Day

Shopping Stores and Marts

26


Clinic and Hospitals

4


Food Chains, Cafes and Restaurants

6


Churches

5


Schools

2


Offices

7

924.00 Gallons per Day

Total Consumption 170,473.64 Gallons per Day

Total Number of Fire Hydrants: 47

Fire Hydrants Water Requirements: 1,575 Gallons per Hour per Fire Hydrant

Spacing Between Fire Hydrants: 450 Feet


Water Storage Tank Design

Please refer to the figure and appendices for the realistic view and calculations of the water storage tank design.

Here is the summary,

Height: 28 Feet

Diameter: 17 Feet

H/D: 1.65

Thickness: 0.375 Inches (Semi-Spherical Bottom)

0.25 Inches (Cylindrical Body and Cone Top)

Capacity: 5,712 Cubic Feet

Material: Mild Steel

Elevation: 73.5 Feet




Pump Selection

The ground water is 216.48 feet from the ground.

Calculations for the appropriate pump to be used are shown in the appendices. Below is the summary.

Total Static Head 318 Feet

Total Dynamic Head 323.37 Feet

Fluid Horsepower 19.38 Horsepower

Brake Horsepower 25.85 Horsepower

The pump chosen has the following specifications:

Model SP 46

Pump Type SP 46-15

Motor MS 6000

Efficiency 81% - 86%

Frequency 60 Hz

Power Rating 30 Hp

Weight 235 Lbs


Grundfos A/S Submersible Pump Model SP 46-15



Piping Network

For the Consumers column, the designer uses abbreviations (ie, R for Residential Establishments). Please refer to the schematic drawing of the area. Below is the summary of the piping network of the system. The number and types of fittings and valves used are also included after the table.

Line Diameter (Inch)

Length (Feet) Consumers Consumption

(Gallons per Day) Water Velocity

(Feet per Second)

Main 4 7,615.17 Whole System 170,473.64 3.02248

1 3 1,848.02 29R, 12S, 2O, 1A, 1F, 1H 17,732.25 0.55892

2 3 1,150.02 21R, 4S, 1A, 1F, 1H 14,717.25 0.46388

3 3 2,159.69 34R, 4O, 1S, 1C 8,991.75 0.28342

4 3 1,380.10 23R 5,462.50 0.17218

5 3 1,380.10 21R 4,987.50 0.15721

6 3 311.50 9R, 2S 2,415 0.07612

7 2 410.21 13R, 1C 3,100 0.21985

8 2 2,102.71 15R, 1H 5,807.50 0.41187

9 2 779.58 15R, 1S 3,701.25 0.26249

10 2 544.58 3R 712.50 0.05053

11 2 597.71 9R, 2F 2,807 0.19907

12 2 430.37 9R 2,137.50 0.15159

13 2 1,313.69 35R 8,312.50 0.58952

As observed from the table above, the total consumption in the distribution lines does not equal the total flow in the main line. This is because there are consumers directly connected to the main line.


Valves And Fittings

Main Line 3 90o elbows, 10 tees, 1 cross-tee and 27 gate valves

Line 1 1 90o elbow, 2 tees, 3 cross-tees and 14 gate valves

Line 2 6 tees, 1 cross-tee and 12 gate valves

Line 3 6 gate valves

Line 4 2 gate valves

Line 5 1 tee and 4 gate valves

Line 6 1 90o elbow and 2 gate valves

Line 7 1 dead-end cap and 1 gate valve

Line 8 2 90o elbows and 4 gate valves

Line 9 1 dead-end cap and 3 gate valves


Line 11 1 90o elbow, 1 dead-end cap and 4 gate valves


Line 13 3 dead-end caps and 6 gate valves

The designer utilizes the use of gate valves in the system so that repairs will be somehow easier in case necessary.



Miscellaneous Accessories

Water Meter

A water meter will be connected between the mainline and the tank. This is to monitor the total volume consumption in the entire system.

Float Switch

Float switch will turn the pump on and off automatically. A certain water level in the tank will be set for the switch to operate.

Check Valve

Check valve will be connected to avoid the back flow of the water. Once the water passes the valve, it won’t be able to pass the valve the other way around.

Pressure Gage

This will be installed to monitor the pressure of the water. With this, the maintenance crews can easily turn off the system to avoid further damages in case of irregularities.


Project Bill and Costing

ITEMS

UNIT PRICE

QUANTITY COST

Water Storage Tank

3/8" Thk 4'x8' MS Plain Sheet P 11,520.00 per sht

10 shts P 115,200.00

1/4" Thk 4'x8' MS Plain Sheet

8,800.00 per sht

60 shts

528,000.00

150mm OD x 20ft L Steel Bar

7,850.00 per pc

20 pcs

157,000.00


2,500.00 per pc

50 pcs

125,000.00


600.00 per pc

5 pcs

3,000.00


780.00 per pc

15 pcs

11,700.00


330.00 per pc

10 pcs

3,300.00

Quick Drying Enamel Paint

500.00 per gal

20 gals 10,000.00

P 953,200.00

Piping

4" OD x 20ft L G.I. Pipes P 4,450.00 per pc

400 pcs P 1,780,000.00

3" OD x 20ft L G.I. Pipes

3,010.00 per pc

415 pcs

1,249,150.00

2" OD x 20ft L G.I. Pipes

1,650.00 per pc

315 pcs 519,750.00

P 3,548,900.00

Valves And Fittings

4" OD 90 G.I. Deg Elbow P 250.00 per pc

6 pcs P 1,500.00

3" OD 90 G.I. Deg Elbow

180.00 per pc

4 pcs

720.00

2" OD 90 G.I. Deg Elbow

120.00 per pc

7 pcs

840.00

4" OD G.I. Gate Valve

2,900.00 per pc

35 pcs

101,500.00


2,050.00 per pc

40 pcs

82,000.00


1,350.00 per pc

15 pcs

20,250.00

4" OD G.I. Thrdd Tee

580.00 per pc

16 pcs

9,280.00

3" OD G.I. Thrdd Tee

430.00 per pc

10 pcs

4,300.00

4" OD G.I. Thrdd Cross-Tee

910.00 per pc

2 pcs

1,820.00

3" OD G.I. Thrdd Cross-Tee

640.00 per pc

5 pcs

3,200.00

4"-3" OD G.I. Reducer

600.00 per pc

18 pcs

10,800.00

3"-2" OD G.I. Reducer

450.00 per pc

16 pcs 7,200.00

P 243,410.00

Pump

Grundfos A/S SP 46-15 P 250,000.00 per set

1 set P 250,000.00

Accessories

P 150,000.00

Indirect Cost

P 1,800,928.50

TOTAL PROJECT COST

P 6,946,438.50


References

1. Microsoft ® Encarta ® Encyclopedia 2005 © 1993-2004 Microsoft Corporation.

2. Handbook of Mechanical Engineering Calculations, Section 14.12, Water Supply and

Storm-Water System Design

3. Twort's Water Supply, 6th Edition, 2009

4. National Statistics Office (NSO) Record for Sultan Kudarat Province, 2007

5. Pumps and Blowers by Church, 1972

6. http://www.epcor.ca

7. Piping Systems Manual by Brian Silowash, 2010

8. Water In A Changing World: The UN World Water Development Report 3

9. Hydraulics and Pneumatics by Andrew A. Parr

10. Pump Handbook by Igor J. Karassik, Joseph P. Messina, Paul Cooper & Charles C. Heald

11. http://www.wikipedia.org

12. US Technical Manual

13. Grundfos A/S Submersible Pumps Brochure

14. Grundfos A/S Data Sheet Brochure for SP 46

15. http://www.coa.gov.ph


APPENDICES


Breakdown of Demands

There are approximately 280 residential buildings, 26 shopping marts and stores, 5 churches, 7 offices and firms, 6 food chains and restaurants, 4 hospitals and medical clinics, and 2 schools in the system. Below is the summary of the total consumption. US Gallon unit system is used.

Residential Buildings

Average Consumption per Person: 50 Gallons per Day

Average Number of Members per Family: 4.75 Persons

Total Consumption: 280 x 50 x 4.75 = 66,500 Gallons per Day

Considering a 10-year operation of the system, the demand for residential establishments increases proportionally with population hike. Considering a 2.5% average annual increase in population, the projected demand after 10 years is

Total Consumption (10 years) = 66,500 x 1.02510 = 85,125 Gallons per Day

Marts and Stores

Average Consumption per Employee: 27.75 Gallons per Day

Average Number of Employees per Store: 5 Persons

Total Consumption: 26 x 27.75 x 5 = 3,607.5 Gallons per Day

Churches

Average Consumption per Person: 50 Gallons per Day

Average Number of Occupants: 5 Persons

Total Consumption: 5 x 50 x 5 = 1,250 Gallons per Day

Offices

Average Consumption per Employee: 16.5 Gallons per Day

Average Number of Employees per Office: 8 Persons

Total Consumption: 7 x 16.5 x 8 = 924 Gallons per Day


Restaurants

Average Consumption per Table: 25.75 Gallons per Day

Average Number of Tables per Chain: 13 Tables

Total Consumption: 6 x 25.75 x 13 = 2008.5 Gallons per Day

Schools

Average Consumption per Student/Staff: 13.2 Gallons per Day

Average Number of Students per School: 500 Students

Average Number of Staffs: 15 Persons

Total Consumption: 2 x (15 + 500) x 13.2 = 13,596 Gallons per Day

Hospitals

Average Consumption per Bed: 112.25 Gallons per Day

Total Number of Beds: 60 Beds

Total Consumption: 60 x 112.25 = 6,735 Gallons per Day

According to Tworts, areas with equable climates have peak demand factors of 1.25 to 1.35. 1.3 is to be used and to compensate peak demands, this factor is to be multiplied to the total consumptions of residential establishments, churches and hospitals.

ConsumptionRCH = 1.3 x (85,125 + 1,250 + 6,735) = 121,043 Gallons per Day

Leaks in the system can never be avoided. 5% of the actual demands are added to the total demand. Another 15% is added as a factor of safety in case of any sudden increase in overall demands.

TOTAL CONSUMPTION OF THE SYSTEM

TCS = (121,043 + 13,596 + 2,008.5 + 924 + 3,607.5) x 1.05 x 1.15 = 170,473.64 Gallons per Day

= 22,790 ft3/day


FIRE HYDRANT REQUIREMENTS

The system is to be designed to provide water in case of fire accidents. Standard spacing between fire hydrants according to Twort’s is 100m to 150m (328ft to 492ft), thus 450ft spacing will be used by the designer.

The approximated number of fire hydrants in the site is the length of all pipes combined divided by the spacing. That is,

NFH = LT/450 = 21,198/450 = 47 fire hydrants

An empirical formula from Handbook of Engineering Calculations can be used to identify the required demand of all fire hydrants. Note that population after 10 years is being considered.

QFHT = 1020 x P0.5 x (1 – 0.01P0.5) GPM; where P is the population in thousands.

QFHT = 1020 x (0.28 x 4.75 x 1.02510)0.5 x [1 – 0.05(.28 x 4.75 x 1.02510)0.5] GPM

QFHT = 1,233 GPM = 73,980 Gallons per Hour = 9,890 Cubic Feet per Hour

QFH = QFHT/ NFH = 9,890/47 = 210 Cubic Feet per Hour per Hydrant.


Water Storage Tank Design

STORAGE CAPACITY AND TANK DIMENSIONS

There are 2 conditions to be considered in selecting the appropriate water storage tank capacity.

A. 25% Of The Total Consumption in 1 day

In this condition, say the system operates four times in a day.

QA = 0.25 x TCS = 0.25 x 22,790 ft3/day x 1day

QA = 5,700 ft3

B. 100% Of The Total Consumption + Required Demand For Fire Hydrants

In this condition, let the water storage tank supply the system for 2 hours and let it be assumed that there are 4 fire hydrants being used.

QB = 2 x (TCS + 4QFH) = 2 x [1 x (22,790/24) + 4 x 210]

QB = 3,580 ft3

Between the two, QA will be selected because it is larger and can also compensate the second condition. The tank will be designed to be 28ft high, and having a cylindrical body and semi-spherical bottom. The top will be of cone, but will be neglected in calculating the radius of the tank.

Q’Tank = (28 – r) x πr2 + 2πr3/3 = QA = 5,700 ft3

r = 8.49ft or say, r = 8.5ft.

(h/d)tank = 28/(2x8.5) = 1.65

QTank = (28 – 8.5) x π(8.5)2 + 2π(8.5)3/3 = 5,712 ft3

HEAD LOSSES

From the figure of the piping system, the largest possible head loss may occur in joint J, which is also the farthest joint from the tank. Since the pipe is the main distribution line, they supply the total demand in the system. Considering the maximum total consumption, the maximum head loss will be calculated.


Head Loss Through Straight Pipes

This can be calculated by either the Darcy-Weisbach Formula or the Hazen-Williams Equation. In this design, the latter will be used.

hf = 0.42262 x L x (V/C)1.85 x (1/D)1.7

where hf is the head loss in feet

L is the total equivalent length in feet

C is equal to 100, for Galvanized Steel Pipes

V is the water velocity in feet per second

D is the pipe’s diameter in feet

Head Loss Through Valves and Fittings

Equivalent length for valves and fittings can be solved using the formula below. This is to be added to the length of the pipe, and the Hazen-William Equation will give the head loss with valves and fittings being considered.

LEquivalent = kD/f

where L is the valves or fittings’ equivalent length in feet

k is the head loss coefficient of the fitting or valve

D is the pipe’s internal diameter

f is the friction factor from the Moody Diagram (0.032).

A. Considering Pipeline ABCDEFGHIJ

There are 6 Tees (line flow, threaded), 14 Gate Valves (fully open) and 1 900 Elbow (threaded).

LEquivalent = [(6x0.9) + (14x0.15) + (1x1.5)] x (4/12)/0.032

LEquivalent = 93.75 ft

Total Pipe Length = 4,801.71 ft

Total Equivalent Length L = 4,801.71 + 93.75 = 4895.46 ft


Velocity V = 3.0226 fps

D = 1/3 ft.

hf = 0.42262 x 4,895.46 x (3.0226/100)1.85 x (3)1.7 = 20.68 ft.

B. Considering Pipeline ARQPONMLKJ

There are 7 Tees (6 line flow and 1 branch flow, threaded) and 14 Gate Valves (fully open).

LEquivalent = [(6x0.9) + (14x0.15) + (1x2)] x (4/12)/0.032

LEquivalent = 98.96 ft

Total Length L = 3,626.46 ft

Velocity V = 3.0226 fps

D = 1/3 ft.

hf = 0.42262 x 3,626.46 x (3.0226/100)1.85 x (3)1.7 = 15.32 ft.

WATER STORAGE TANK ELEVATION

The sufficient elevation of the tank that can surpass the maximum head loss in the design circuit can be calculated by simply using the Bernoulli’s Theorem. This is done by summing up head from the bottom of the tank where the discharge of the tank is located to the point in the pipeline where the largest head loss is. That is,

푃훾 +

푣2푔 + 푍 =

푃훾 +

푣2푔 + ℎ

where is the pressure head at the free surface of water in the storage tank

is the velocity head at the free surface of water in the storage tank

푍 is the elevation head of the tank relative to the ground

is the average pressure head needed in the distribution lines

is the velocity head needed to maintain flow


ℎ is the largest head loss in the design circuit

PA is equal to zero since the pressure on the water surface in the tank is atmospheric. VA is also assumed to be zero for large tanks.

The average pressure demand in residential and other establishments for their faucets, showers and toilets is 20 psi or 2,880 lbf/ft2. Additionally, US Technical Manual says that it should not exceed 75 psi or 10,800 lbf/ft2 in which the plumbing lines will fail. For this design, 30 psi or 4,320 lbf/ft2 will be used.

US Technical Manual says that VB must not exceed 10 fps. For this design, 5 fps is reasonable since the average velocity in the main lines is 3.0226 fps, and the velocity in the distribution lines is expected to be in the neighborhood of the latter since the diameter and the volume flow both decrease.

0훾 +

02푔 + 푍” =

4,32062.34 +

52(32.2) + 20.68

Z”A = 90.36 ft

This value of Z”A will be subject to 2 corrections. The (1) minimum height of water in the tank where the pump will start to operate again and (2) the head loss in the vertical pipe must be considered.

HTW = ½ x (h – r) + r = ½ x (28 – 8.5) + 8.5 = 18.25 ft

Z’A = 90.36 ft – 19.125 ft = 72.11 ft

The discharge pipe of the tank is located directly at the bottom of the tank. Therefore, Z’A also indicates the total length of the discharge vertical pipe connected to the main line. Using the Hazen-Williams Equation, the head loss can be calculated. That is,

hf = 0.42262 x 115.30 x (5/100)1.85 x (12/4)1.7 = 1.20 ft

Therefore, ZA = 72.11 + 1.20 = 73.5 ft.

BURSTING PRESSURE

The material to be used for the water storage tank is Mild Steel as suggested by wikipedia.org, and as one of the most commonly used material. Mild Steel has less than 0.15% carbon content and is readily available in the market.


Material Mild Steel

Unit Weight 0.282 lb/in3

Yield Stress 27,000 psi

Maximum Allowable Stress

δd = yield stress/ factor of safety

Usual factor of safety is 4

δd = 27,000 psi/4 = 6,750 psi

Actual Maximum Stress (Cylindrical Body)

The stress developed by the hydrostatic force is radial. The designer chooses the cylindrical body to be ¼-in. thick.

δA = PwD/2t

Where Pw = the maximum pressure inside the tank = γw(h)/144

D = tank diameter

t = cylindrical body thickness

Pw = 62.34(28)/144 = 12.12 psi

δA = PwD/2t

δA = 12.99(2x8.5)/2(0.25/12)

δA = 4,945 psi

Since the maximum allowable stress is greater than the actual maximum stress, the dimensions and material of the cylindrical body are appropriate. Thus, the tank is safe from bursting pressure.

Semi-spherical Bottom Thickness The pressure or stress at the bottom of the tank is expected to be greater than that on the cylindrical body, it is reasonable to make the semi-spherical bottom thicker than the body. Thus, a 3/8-in. metal sheet is to be used.


Pump Selection

TOTAL STATIC HEAD:

hz = hs + za + htank

Where hz is the total static head, feet

hs is the total suction lift, feet

za is the water tank elevation relative to the design circuit, feet

hww is the head of the weight of the water, feet

From my interview with Mr. Rommel A. Malimban, a resident of the barangay, via SMS, he said that he used 11 6-m pipes in his pitcher pump that provides potable water. Using the same assumption as he did,

hs = 11 pipes x 6 m/pipe x 3.28 ft/m = 216.5 ft

hz = hs + za + hww

hz = 216.5 + 73.5 + 28 = 318 ft

TOTAL DYNAMIC HEAD

The water storage tank is designed to be sufficiently filled up with water in 3 hours prior to the time the pump starts operating. Therefore, the pump will only deliver enough volume of water per unit time to meet the requirement. Thus,

QPump = QTank / 3 hrs

QPump = 5,712 ft3 / 3 hrs = 1,904 cfh = 0.5289 cfs

Pipes to be used are of 4 inches diameter. So the total cross-sectional area is π/36 ft2. Then for the pump,

Vsuction = Vdischarge = 1,904 / π/36 = 21,818.23 fph = 6.061 fps

The head loss of the pipe circuit from the pump to the water storage tank must be considered. The total length of the pipes is 290 ft. There are 2 90O-Elbow, and 1 Gate Valve along. That is,


LFittings = kD/f = [(2 x 1.5) + (1 x 0.15)] / (3 x 0.032) = 32.8125 ft.

LTotal = 32.8125 + 318 = 350.8125 ft.

hPipes = 0.42262 x LTOTAL x (V/C)1.85 x (1/D)1.7

= 0.42262 x 322.8125 x (6.061/100)1.85 x (3)1.7 = 5.37 ft.

Therefore, the total dynamic head, hd can be solved. That is,

hd = hz + hpipes = 318 + 5.37 = 323.531 ft

FLUID HORSEPOWER

From Pumps and Blowers by Church, the formula for the fluid horsepower is

HPFluid = w x hd / 550

Where HPFluid is the fluid horsepower, hp

hd the total dynamic head or discharge head, feet

w is the delivered weight, lbps

w = QPump x 62.34 = 32.97 lbs per second

HPFluid = 32.97 x 323.531 / 550 = 19.38 hp

BRAKE HORSEPOWER

From Pumps and Blowers by Church, the formula for the brake horsepower is

HPBrake = HPFluid / ηPump

Where HPBrake is the brake horsepower, hp

HPFluid is the fluid horsepower, hp

ηPump is the overall pump efficiency


The usual overall pump efficiency ranges from 60% to 80%. Thus in this design, an average of 75% will be used. That is,

HPBrake = 19.38 / 0.75 = 25.85 hp

The graph or diagram above is from the Submersible Pumps Brochure of Grundfos A/S. Using the total dynamic head 318 ft (96.92 m) and the total pump volume discharge capacity 1,904 cfh (53.92 cmh), the intersection lies on the area of Model SP 46. Thus, the latter is the pump to be selected.

From the Grundfos Data Sheet Brochure for SP 46, there are various types of the model that suits several brake horsepowers required. All pump types are driven by the same motor, MS 6000. For a 25.85-hp brake horsepower, Model SP 46-15 is chosen. Below are the specifications of the latter.

Model: SP 46 Pump Type: SP 46-15 Motor: MS 6000 Efficiency: 81% - 86% Frequency: 60 Hz Power Rating: 30 Hp Weight: 235 LBS

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