cold water supply and pipe sizing
TRANSCRIPT
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