COLD WATER SUPPLY SYSTEM

Introduction

Building water supply system is a system inplumbing which provides and distributes water tothe different parts of the building or structure, forpurposes such as drinking, cleaning, washing,culinary use, etc.; it includes the waterdistributing pipes, control devices, equipment,and other appurtenances.

Introduction

Cold water system provides water for the

following purposes;

1. Drinking purpose.

2. Cooking purpose.

3. Sanitary purpose.

4. Washing purpose.

5. Gardening

Definitions

1. Cistern – a container for water having a free water surface at atmospheric pressure

2. Feed cistern – any storage cistern used forsupplying cold water to a hot water apparatus

3. Storage cistern – any cistern other than aflushing cistern, having a free water surfaceunder atmospheric pressure, but not including adrinking trough or drinking bowl for animals.

Definitions cont……..

3. Capacity of a cistern - the capacity up to the water line

4. Water line – a line marked inside the cistern to indicate the water level at which the ball valve should be adjusted to shut off.

5. Overflowing level – the lowest level at which water can flow into that pipe from a cistern.

Definitions cont……6. Warning pipe – an overflow pipe so fixed that its

outlet end is in an exposed and conspicuous position and where the discharge of any water from the pipe may be readily seen and, where practicable, outside the building.

7. Communication pipe – any service pipe from the water main to the stop valve fitted on the pipe.

8. Service pipe – any pipe for supplying water from a main to any premises as is subject to water pressure from that main, or would be so subject but for the closing of some stop valve.

Definitions cont….

9 Distributing pipe – any pipe for conveying water from a cistern, and under pressure from that cistern.

10 Supply pipe – so much of any service pipe which is not a communicating pipe.

11 Main – a pipe for general conveyance of water as distinct from the conveyance to individual premises.

Definitions cont………..12 Hot water cylinder or tank – a closed container

for hot water under more than atmospheric pressure. Note: a cylinder is deemed to include a tank.

13 Potable – water suitable for drinking.

14 Fitting – anything fitted or fixed in connection with the supply, measurement, control, distribution, utilization or disposal of water.

Fig1.1 Connection to water main

water mainWater authorities

stop valve

service pipe

Installed and maintained by

water authority

Installed and maintained by

building owner

Stop valve

chamber

760mm

(minimum)Communication pipe

Distribution systems

There are two types of water supply systems;

1. non storage or direct and

2. storage or indirect systems

Non storage or Direct Systems

• It is a system whereby all the sanitary fittings are supplied with cold water direct from the main. In this system, a cold water feed cistern is usually required to feed the hot water supply system

Fig 1.2 Direct cold water supply system

Storage or Indirect Systems

• It is a system whereby all the drinking waterused in the building is supplied from the mainand water used for all other purposes issupplied indirectly from a cold water storagecistern.

• The cistern also supplies water to the hotwater cylinder therefore its capacity willalmost double the capacity required for thedirect system

Fig 1.3 Indirect cold water supply system

Table 1.1 Advantages of Direct and Indirect cold water systems

S/No Direct or non storage S/No Indirect or storage

1 Less pipework and smaller

or no cistern, making it

easier and cheaper to

install.

1 Large capacity cistern provides a

reserve of water during

interruption of supply.

2 Drinking water is available

at all draw-off points.

2 Water pressure on the taps

supplied from the cistern is

reduced, which minimizes wear

on taps and noise.

3 Smaller cisterns which may

be sited below the ceiling.

3 Fittings supplied with water from

the cistern are prevented from

causing pollution of the drinking

water by back siphon age

4 In systems without cistern

there is no risk of polluting

the water from this source

4 Lower demand on the water main

Prevention of Back Siphonage

• Back siphonage is the back flow of water, which may be contaminated, into the drinking water supply.

• The condition for back siphonage to happen is the creation of negative pressure or partial vacuum in the pipe connected to an appliance having its outlet submersed in water, which may be contaminated.

Prevention of Back Siphonage cont…

• Back pressure is the result of water pressure in the system being greater than that in the supply. Higher system pressures can be caused by the expansion of water in unvented domestic hot water supplies, or in systems where a pump is used.

• Negative pressures in the supply main may be caused by a major leak in the main or the fire services drawing off vast amounts of water.

The points which must be observed for prevention of risk of back siphonage

1. The ball valves in the cisterns must be above the overflow pipe and if the silencer pipe is fitted must discharge water above the ball valve through a spray.

2. The outlets of taps connected to sanitary appliances must be well above the flooding level of the appliance.

The points which must be observed for prevention of risk of back siphonage cont…..

3. Flushing valves for WCs must be supplied from a cold water storage cistern.

4. Appliances having low-level water inlets, for example bidets and certain types of hospital appliance, must be supplied from a cold water storage cistern and never direct from the main

Water Storage

Purposes of water storage

Provide for an interruption of supply

Accommodate peak demand

Provide a pressure (head) for gravity supplies

Design factors

Type and number of fittings

Frequency and pattern of use

Likelihood and frequency of breakdown of

supply (often design for 12- or 24-hour reserve

capacity)

According to regulations, the installed cistern must be;

1. Watertight, adequate strength, and manufactured from plastic, galvanized steel, asbestos cement or copper.

2. Sited at a height that will provide sufficient head and discharge of water to the fittings supplied.

3. placed in a position where it can be readily inspected and cleansed

According to regulations, the installed cistern must be;

4. Provided with dust proof but not air tight cover and protected from damage by frost.

5. Fitted with an efficient overflow pipe which should have a fall as great as practicable not less than 1 in 10.

Fig 1.4 Method of installing cold water storage or feed cistern

40mm40mm

25mm

50mm

50mm

Timber bearersRising main

Distributing pipe

to sanitary

appliances

Full-way

gate valve

Ceiling joists

Stop valve

Warning or

overflow pipe

Vent pipe from

hot-water cylinder

Inlet silencer

Fig 1.6 Method of duplicating cold water storage cisterns

Man

ifold

Cold-water

Feed pipes

Dra

in

pipeO

verflo

w a

nd

war

ning p

ipe

Isola

ting

valv

es

Ris

ing

ma

in

Wat

er

leve

l

Bal

l

valv

e

Table 1.2 Provision of cold water storage to cover 24 Hours interruption of supply

Type of building Storage (L)

Dwelling houses and flats per resident 90

Hostels per resident 90

Hotels per resident 140

Offices without canteens per head 40

Offices with canteens per head 45

Restaurants per head/per

meal

10

Day schools per head 30

Boarding schools per head 90

Nurses homes and medical quarters per resident 115

Table 1.3 Recommended minimum storage of cold and hot water systems

(Source: Garrett, R. H., 2008. Hot and Cold Water Supply)

Type of building

Minimum cold water

storage (litres)

Minimum hot water

storage (litres)

Hostel 90 per bed space 32 per bed space

Hotel 200 per bed space 45 per bed space

Office premises:

- with canteen facilities

- without canteen facilities

45 per employee

40 per employee

4.5 per employee

4.0 per employee

Restaurant 7 per meal 3.5 per meal

Day school:

- nursery or primary

- secondary or technical

15 per pupil

20 per pupil

4.5 per pupil

5.0 per pupil

Boarding school 90 per pupil 23 per pupil

Children’s home or

residential nursery 135 per bed space 25 per bed space

Nurses’ home 120 per bed space 45 per bed space

Nursing or convalescent

home 135 per bed space 45 per bed space

Note: Minimum cold water storage shown includes that used to supply hot water outlets

Table 1.4 Estimation of cold water storage per occupant

Type of buildingStorage per

occupant (litres)

Hospitals, per staff on duty 45

Hostels 90

Hotels 135

Houses and flats 135

Offices with canteens 45

Offices without canteens 35

Restaurant (* per meal) 7

Schools, boarding 90

Schools, day 30

Table 1.5 Provision of cold water storage to cover 24Hours interruption of supply. Based on sanitaryappliances

Sanitary appliance Storage (L)

Water closet (WC) 180

Sink 135 - 225

Water basin 90 - 250

Shower 135 - 225

Urinal 135 - 250

Table 1.6 Access to storage cistern

Table 1.7 Water storage plant room area

Design principles

I. Cold water system

A: Potable water• Drinking purpose.• Cooking purpose.

B: Non-potable water Flushing water(fresh

or salt water) Cleansing water Fire service

Swimming-poolfiltration

Irrigation(e.g. forlandscape)

Fountain circulation Air-conditioning

water, etc.

II. Hot water system (e.g.in hotels & hospitals

Design principles cont….

Major tasks of water systems design:

1. Assessment & estimation of demands

2. Supply scheme & schematic

3. Water storage requirements

4. Piping layout

5. Pipe sizing

6. Pump system design

Water demand Water demand depends on:

Type of building & its function

Number of occupants, permanent or transitional

Requirement for fire protection systems

Landscape & water features

Typical appliances using the cold water

WC cistern, wash basin, bath, shower, sink

Washing machine, dishwasher

Urinal flushing cistern

Water demand cont…… Simultaneous demand

Most fittings are used only at irregular intervalsIt is unlikely that all the appliances will be used

simultaneously . Therefore there is no need to sizepipe work on continuous maximum

Key factors to consider:

Capacity of appliance (L)Draw-off flow rate (L/s)Draw-off period, or time taken to fill appliance (sec)Frequency of use, time between each use (sec)

Water demand cont……

Loading Unit (L.U) : A factor given to an appliance

relating the flow rate at its terminal fitting to

Length of time in use

Frequency of use for a particular type

Use of building

NOTE

Evaluate the ‘probable maximum’

Relates the flow rate to the probable usage

Consider design & minimum flow rates

Table 1.8 Design flow rates and loading units

How about urinals? 0.004L/s/urinal continuous

Required design flow (from graph) = 0.7 L/s + 0.008L/s = 0.71 L/s

Figu

re 1

.7 C

on

vers

ion

ch

art

–lo

adin

g u

nit

s to

flo

w r

ate

12 wash basins × 1.5 = 1810 WCs × 2 = 202 urinal bowls × — = —2 cleaners’ sinks × 3 = 6Total loading units = 44

Exam

ple

of

use

of

load

ing

un

its

Design flow considerations

A small increase in demand over design level will

cause a slight reduction in pressure/flow (unlikely

to be noticed by users)

Exceptional cases:

Cleaners’ sinks (depends on one’s behavior)

Urinal flushing cisterns (continuous small flow)

Team changing rooms at sport clubs (high

demand)

Special events (ad hoc demand)

Pipe sizing-Introduction

Correct pipe sizes will ensure adequate flow rates atappliances and avoid problem caused by over sizing andunder sizing;

Over sizing will mean:– additional and unnecessary installation costs;– delays in obtaining hot water at outlets;– increased heat losses from hot water distributing pipes.

Under sizing may lead to:– inadequate delivery from outlets and possibly no

delivery at some outlets during simultaneous use;– some variation in temperature and pressure at outlets,

especially showers and other mixers;– some increase in noise levels.

Fig 1.8 Pipe sizing-Introduction

Sizing procedure for supply pipes

• The procedure below is followed by an explanation of eachstep with appropriate examples.

(1) Assume a pipe diameter.

(2) Determine the flow rate:

(a) by using loading units;

(b) for continuous flows;

(c) obtain the design flow rate by adding (a) and (b).

(3) Determine the effective pipe length:

(d) work out the measured pipe length;

(e) work out the equivalent pipe length for fittings;

(f) work out the equivalent pipe length for draw-offs;

(g) obtain the effective pipe length by adding (d), (e) and (f).

Sizing procedure for supply pipes cont…

(4) Calculate the permissible loss of head:

(h) determine the available head:

(i) determine the head loss per metre run throughpipes;

(j) determine the head loss through fittings;

(k) calculate the permissible head loss.

(5) Determine the pipe diameter:

(l) decide whether the assumed pipe size will give

Equivalent pipe length

• Equivalent pipe length Is the expression of frictionresistances to flow through valves and fittings interms of pipe lengths having the same resistance toflow as the valve or fitting.

• For example, a 20 mm elbow offers the sameresistance to flow as a 20 mm pipe 0.8 m long.

• Effective pipe length. The effective pipe length is thesum of the measured pipe length and the equivalentpipe lengths for fittings (e) and draw-offs (f).

Fig 1.9 Equivalent pipe length cont…(s

ee

tab

les

1.9

& 1

.10

)

Table 1.9 Equivalent pipe lengths (copper, stainless steel and plastics)

(Source: Garrett, R. H., 2008. Hot and Cold Water Supply)

Equivalent pipe lengths (copper, stainless steel and plastics) cont…

Notes:

1. For tees consider change of direction only. For gate valves losses are insignificant.

2. For fittings not shown, consult manufacturers if significant head losses are expected.

3. For galvanized steel pipes in a small installation, pipe sizing calculations may be based on the data in this table for equivalent nominal sizes of smooth bore pipes. For larger installations, data relating specifically to galvanized steel should be used. BS 6700 refers to suitable data in the Plumbing Engineering Services Design Guide published by the Institute of Plumbing.

Table 1.10 Typical head losses and equivalent pipe lengths for taps

(Source: Garrett, R. H., 2008. Hot and Cold Water Supply)

Fig 1.10 Example of measured and effective pipe length

Note: There is no need to consider both branch pipes to taps.

Measured pipe length = 4.75 m Equivalent pipe lengths:

elbows 2 x 0.8 = 1.6 m tee 1 x 1.0 = 1.0 m Stop valve 1 x 7.0 = 7.0 m taps 2 x 3.7 = 7.4 m check valves 2 x 4.3 = 8.6 m Effective pipe length = 30.35 m

Figure 1.11 Example of permissible head loss

This formula is used to determine whether the frictional resistancein a pipe will permit the required flow rate without too much lossof head or pressure. Figure 1.10 illustrates the permissible headloss for the example in figure 1.9.

Pre

ssu

re a

t ta

ps

45

m h

ead

Figu

re 1

:12

He

ad lo

ss t

hro

ugh

sto

p v

alve

s

No

te G

ate

valv

es a

nd

sp

her

ical

plu

g va

lves

off

er

littl

e o

r n

o r

esis

tan

ce t

o f

low

pro

vid

ed t

hey

are

fu

lly o

pen

.

Figu

re 1

.13

He

ad lo

ss t

hro

ugh

flo

at-o

pe

rate

d v

alve

s

Figu

re 1

.14

Det

erm

inat

ion

of

pip

e d

iam

ete

r

No

tes

Figu

res

sho

wn

are

fo

r co

ld w

ater

at

12

°C.

Ho

t w

ater

will

sh

ow

slig

htl

y m

ore

fav

ora

ble

hea

d lo

ss r

esu

lts.

BS

67

00

giv

es h

ead

loss

in k

Pa.

1 m

hea

d =

9.8

1 k

Pa.

Table 1:11 Maximum recommended flow velocities

Water

temperature

(°C )

Flow velocity

Pipes readily

accessible

(m/s)

Pipes not readily

accessible (m/s)

10 3.0 2.0

50 3.0 1.5

70 2.5 1.3

90 2.0 1.0

Wo

rk t

hro

ug

h t

he c

alc

ula

tio

n s

heet

Se

e fig

ure

1.1

5, u

sin

g th

e d

ata

sh

ow

n in

fig

ure

5.1

0

an

d Ta

ble

1.1

3.

Figu

re 1

.15

Pip

e s

izin

g d

iagr

am

Bib

tap

at

0.3

l/s

in f

req

ue

nt

use

.

1-T

ee

2-c

he

ck v

alv

es

3-e

lbo

ws

1-T

ee

2-C

he

ck v

alv

es

1-E

lbow

1-Elbow; 1-DN20, 0.3l/s Tap 1-T

ee

2-c

he

ck v

alv

es

3-e

lbow

s

(1)

Pip

e

refe

ren

ce

(2)

Lo

adin

g

Un

its

(3)

Flo

w r

ate

(L/s

)

(4)

Pip

e si

ze

(mm

dia

met

er)

(5)

Lo

ss o

f h

ead

(m/m

ru

n)

(6)

Flo

w v

elo

city

(m/s

)

(7)

Mea

sure

d

pip

e ru

n (

m)

(8)

Eq

uiv

alen

t

pip

e le

ng

th (

m)

(9)E

ffec

tive

pip

e

len

gth

(m

)

(10)

Hea

d

con

sum

ed (

m)

(11)

Pro

gre

ssiv

e

hea

d (

m)

(12)

Ava

ilab

le

hea

d (

m)

(13)

Fin

al P

ipe

size

(m

m)

(14)

Rem

arks

En

ter

pip

e re

fere

nce

on

cal

cula

tio

n s

hee

t

Det

erm

ine

load

ing

Un

its

(Tab

le 1

.8)

Co

nve

rt lo

adin

g u

nit

s to

flo

w r

ates

(F

ig. 1

.7)

Mak

e as

sum

pti

on

as

to p

ipe

size

(In

sid

e

dia

met

er)

Wo

rk o

ut

fric

tio

nal

res

ista

nce

per

met

re

(Fig

. 1.1

4)

Det

erm

ine

velo

city

of

flo

w (

Fig

1.1

4)

Mea

sure

len

gth

of

pip

e u

nd

er c

on

sid

erat

ion

Co

nsi

der

fri

ctio

nal

res

ista

nce

s in

fit

tin

gs

(Tab

le 1

.9 a

nd

Fig

ure

s 1.

12 &

1.1

3)

Ad

d t

ota

ls in

co

lum

ns

7 &

8

Hea

d c

on

sum

ed:

Mu

ltip

ly c

olu

mn

5 b

y

colu

mn

9

Ad

d h

ead

co

nsu

med

in

co

lum

n 1

0 to

pro

gre

ssiv

e h

ead

in p

revi

ou

s ro

w o

f co

lum

n

11 Rec

ord

ava

ilab

le h

ead

at

po

int

of

del

iver

y

Co

mp

are

pro

gre

ssiv

e h

ead

wit

h a

vaila

ble

hea

d t

o c

on

firm

pip

e d

iam

eter

or

no

t

No

tes

Table 1.12 Example of a suitable calculation sheet with explanatory notes

Table 1.13 Calculation sheet

Pipe sizing cont…

Pipe sizing for hot water systems is the same as cold water,

except cold feed pipe must also be considered

Useful formulae for pipes:

1. Thomas Box formula

d = pipe diameter (mm)

q = flow rate (l/s)

H = head or pressure (m)

L = effective length of pipe (actual length + allowance for bends, tees, etc.)

Where;

Example: Determine the pipe size using Thomas Box formula.

Hence, the nearest commercial size is 32 mm bore steel or 35 mm outside diameter copper.

Answer: Using Thomas Box formula,

= 27.83 mm

2. Relative discharge of pipes

Example:

(a) Compute the number of 32 mm short branches that can be served from 150 mm main.

(b) Determine the size of water main required to supply 15 nos. 20 mm short branch pipes.

Answer:

Answer:

Hence, the nearest commercial size is 65 mm.

Fig

1.1

6 T

ypic

al L

ayo

ut

Pla

n (

Two

flo

ors

)

Ø15

Ø15

Ø20

Ø15

Ø15

Ø15

Ø15

Ø15

Ø15

HOSE REEL-1

WET ZO

NE - A