Cold water supply and pipe sizing from MBEYA UNIVERSITY OF SCIENCE AND TECHNOLOGY(for diploma students)

1. COLD WATER SUPPLY SYSTEM
Introduction
Building water supply system is a system in
plumbing which provides and distributes water to
the different parts of the building or structure, for
purposes such as drinking, cleaning, washing,
culinary use, etc.; it includes the water
distributing pipes, control devices, equipment,
and other appurtenances.

2. Introduction
Cold water system provides water for the
following purposes;
1. Drinking purpose.
2. Cooking purpose.
3. Sanitary purpose.
4. Washing purpose.
5. Gardening

3. Definitions
1. Cistern – a container for water having a free
water surface at atmospheric pressure
2. Feed cistern – any storage cistern used for
supplying cold water to a hot water apparatus
3. Storage cistern – any cistern other than a
flushing cistern, having a free water surface
under atmospheric pressure, but not including a
drinking trough or drinking bowl for animals.

4. 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.

5. 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.

6. 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.

7. 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.

8. Fig1.1 Connection to water main
water main
Water authorities
stop valve
service pipe
Installed and maintained by
water authority
Installed and maintained by
building owner
Stop valve
chamber
760mm
(minimum)
Communication pipe

9. Distribution systems
There are two types of water supply systems;
1. non storage or direct and
2. storage or indirect systems

10. 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

11. Fig 1.2 Direct cold water supply system

12. Storage or Indirect Systems
• It is a system whereby all the drinking water
used in the building is supplied from the main
and water used for all other purposes is
supplied indirectly from a cold water storage
cistern.
• The cistern also supplies water to the hot
water cylinder therefore its capacity will
almost double the capacity required for the
direct system

13. Fig 1.3 Indirect cold water supply system

14. 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

15. 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.

16. 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.

17. 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.

18. 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

19. 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)

20. 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

21. 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.

22. Fig 1.4 Method of installing cold water storage or feed cistern
40mm
40mm
25mm
50mm
50mm
Timber bearers
Rising 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

23. Fig 1.6 Method of duplicating cold water storage cisterns
M
anifold
Cold-water
Feed pipes
D
rain
pipe
O
verflow
and
w
arning
pipe
Isolating
valves
Risingmain
W
ater
level
B
allvalve

24. 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

25. 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

26. Table 1.4 Estimation of cold water storage per occupant
Type of building
Storage 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

27. Table 1.5 Provision of cold water storage to cover 24
Hours interruption of supply. Based on sanitary
appliances
Sanitary appliance Storage (L)
Water closet (WC) 180
Sink 135 - 225
Water basin 90 - 250
Shower 135 - 225
Urinal 135 - 250

28. Table 1.6 Access to storage cistern

29. Table 1.7 Water storage plant room area

30. 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-pool
filtration
 Irrigation(e.g. for
landscape)
 Fountain circulation
 Air-conditioning
water, etc.
II. Hot water system (e.g.
in hotels & hospitals

31. 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

32. 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

33. Water demand cont……
Simultaneous demand
Most fittings are used only at irregular intervals
It is unlikely that all the appliances will be used
simultaneously . Therefore there is no need to size
pipe 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)

34. 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

35. Table 1.8 Design flow rates and loading units

36. How about urinals?
0.004L/s/urinal continuous
Required design flow (from graph)
= 0.7 L/s + 0.008L/s = 0.71 L/s
Figure1.7Conversionchart–loadingunitstoflowrate
12 wash basins × 1.5 = 18
10 WCs × 2 = 20
2 urinal bowls × — = —
2 cleaners’ sinks × 3 = 6
Total loading units = 44
Exampleofuseofloadingunits

37. 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)

38. Pipe sizing-Introduction
Correct pipe sizes will ensure adequate flow rates at
appliances and avoid problem caused by over sizing and
under 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.

39. Fig 1.8 Pipe sizing-Introduction

40. Sizing procedure for supply pipes
• The procedure below is followed by an explanation of each
step 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).

41. 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 through
pipes;
(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

42. Equivalent pipe length
• Equivalent pipe length Is the expression of friction
resistances to flow through valves and fittings in
terms of pipe lengths having the same resistance to
flow as the valve or fitting.
• For example, a 20 mm elbow offers the same
resistance to flow as a 20 mm pipe 0.8 m long.
• Effective pipe length. The effective pipe length is the
sum of the measured pipe length and the equivalent
pipe lengths for fittings (e) and draw-offs (f).

43. Fig 1.9 Equivalent pipe length cont…(seetables1.9&1.10)

44. Table 1.9 Equivalent pipe lengths (copper, stainless steel and plastics)
(Source: Garrett, R. H., 2008. Hot and Cold Water Supply)

45. 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.

46. Table 1.10 Typical head losses and equivalent
pipe lengths for taps
(Source: Garrett, R. H., 2008. Hot and Cold Water Supply)

47. 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

48. Figure 1.11 Example of permissible head loss
This formula is used to determine whether the frictional resistance
in a pipe will permit the required flow rate without too much loss
of head or pressure. Figure 1.10 illustrates the permissible head
loss for the example in figure 1.9.
Pressureattaps45mhead

49. Figure1:12Headlossthroughstopvalves
NoteGatevalvesandsphericalplugvalvesoffer
littleornoresistancetoflowprovidedtheyare
fullyopen.

50. Figure1.13Headlossthroughfloat-operatedvalves

51. Figure1.14Determinationofpipediameter
NotesFiguresshownareforcoldwaterat12°C.
Hotwaterwillshowslightlymorefavorableheadlossresults.
BS6700givesheadlossinkPa.
1mhead=9.81kPa.

52. 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

53. Workthroughthecalculationsheet
Seefigure1.15,usingthedatashowninfigure5.10
andTable1.13.
Figure1.15Pipesizingdiagram
Bibtapat0.3l/s
infrequentuse.
1-Tee
2-checkvalves
3-elbows
1-Tee
2-Checkvalves
1-Elbow
1-Elbow; 1-DN20, 0.3l/s Tap
1-Tee
2-checkvalves
3-elbows

54. (1)Pipe
reference
(2)Loading
Units
(3)Flowrate
(L/s)
(4)Pipesize
(mmdiameter)
(5)Lossofhead
(m/mrun)
(6)Flowvelocity
(m/s)
(7)Measured
piperun(m)
(8)Equivalent
pipelength(m)
(9)Effectivepipe
length(m)
(10)Head
consumed(m)
(11)Progressive
head(m)
(12)Available
head(m)
(13)FinalPipe
size(mm)
(14)Remarks
Enterpipereferenceoncalculationsheet
DetermineloadingUnits(Table1.8)
Convertloadingunitstoflowrates(Fig.1.7)
Makeassumptionastopipesize(Inside
diameter)
Workoutfrictionalresistancepermetre
(Fig.1.14)
Determinevelocityofflow(Fig1.14)
Measurelengthofpipeunderconsideration
Considerfrictionalresistancesinfittings
(Table1.9andFigures1.12&1.13)
Addtotalsincolumns7&8
Headconsumed:Multiplycolumn5by
column9
Addheadconsumedincolumn10to
progressiveheadinpreviousrowofcolumn
11
Recordavailableheadatpointofdelivery
Compareprogressiveheadwithavailable
headtoconfirmpipediameterornot
Notes
Table 1.12 Example of a suitable calculation sheet with explanatory notes

55. Table 1.13 Calculation sheet

56. 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;

57. 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

58. 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.

59. Fig1.16TypicalLayoutPlan(Twofloors)
Ø15
Ø15
Ø20
Ø15
Ø15
Ø15
Ø15
Ø15
Ø
15
HOSE
REEL-1
W
ET
ZONE
- A