CVS 467.Chapter 2.Water Supply and Drainage.pdf

CVS 467:Building Physics & Services
Chapter 2: DomesticWater Supply and Drainage
L. O. Muku
Department of Civil& Structural Engineering
19-Sep-22
DCSE, MOI UNIVERSITY

Domestic ColdWater Supply System
Introduction
 Building water supply system is a system in plumbing which
provides and distributes water to the different parts of the
building, for purposes such as drinking, cleaning, washing,
culinary use, sanitary use, gardening etc.
 It includes the water distributing pipes, control devices,
equipment, and other appurtenances.
19-Sep-22

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. Capacity of a cistern - the capacity up to the water line.
5. Water line – a line marked inside the cistern to indicate the water
level at which the ball valve should be adjusted to shut off.
19-Sep-22

Definitions…
6. Overflowing level – the lowest level at which water can flow into
warning/overflow pipe from a cistern.
7. 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.
8. Communication pipe (CP) – any service pipe from the water main to
the stop valve fitted on the pipe.
9. Service pipe (SP) – 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.
19-Sep-22

Definitions…
10. Distributing pipe – any pipe for conveying water from a cistern, and
under pressure from that cistern.
11. Supply pipe – so much of any service pipe which is not a
communicating pipe.
12. Main – a pipe for general conveyance of water as distinct from the
conveyance to individual premises.
13. 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.
14. Fitting – anything fitted or fixed in connection with the supply,
measurement, control, distribution, utilization of water.
19-Sep-22

Fig 2.1: Connection to water main
19-Sep-22
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

Distribution systems
There are two types of water supply systems;
1. Direct or non-storage and
2. Indirect or storage systems
19-Sep-22

Direct/Non-Storage Systems
 It is a system whereby all the sanitary fittings are supplied with cold
water direct from the main or service line and are subject to the pressure
from the mains.
 Cold water feed cistern is usually required to feed the hot water supply
system only and is usually small.
 Less pipe work and smaller storage cistern make it cheaper to install.
 Drinking water is usually available at wash hand basins.
(Fig. 2.2 next slide)
19-Sep-22

Direct/Non-Storage System..Figure
19-Sep-22

Indirect/Storage System
 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.
 Storage cistern is large since it supplies all sanitary fittings and the hot
water cylinder (approx. double that one for direct system.
 Large space is required in the roof to accommodate the cold-water
storage cistern.
 Large storage provides a reserve of water during the failure of the mains
supply.
 Reduced water pressure on the taps minimizes noise and wear/tear.
19-Sep-22

Fig 2.3: Indirect cold water supply system
19-Sep-22

Advantages & Disadvantages of Direct ColdWater System
19-Sep-22
S/No Advantages Disadvantages
1. Less pipework and smaller or no
cistern, making it easier and cheaper
to install.
There is no cold water storage if the cold water main is under
repair
2. Little or no structural support is
required for cisterns in the roof space
Can be noisy due to the high flow rates and pressures of the
water supply
3. Drinking water is available at all
draw-off points.
Greater risk of contamination to the cold water main due to
the fact that all connections, taps, outlets and appliances are
connected direct to the mains supply
4. Smaller cisterns which may be sited
below the ceiling.
Can cause a lot of water damage due to the high pressure
and flow rate, should there be a leak
5. In systems without cistern there is no
risk of polluting the water from its
source
Water hammer can be a problem where poor installation
practice has been used or where taps and valves are worn or
faulty

Air Chambers
19-Sep-22
1. Less pipework and smaller or no
cistern, making it easier and cheaper
to install.
There is no cold water storage if the cold water main is under
repair
2. Little or no structural support is
required for cisterns in the roof space
Can be noisy due to the high flow rates and pressures of the
water supply
3. Drinking water is available at all
draw-off points.
Greater risk of contamination to the cold water main due to
the fact that all connections, taps, outlets and appliances are
connected direct to the mains supply
4. Smaller cisterns which may be sited
below the ceiling.
Can cause a lot of water damage due to the high pressure
and flow rate, should there be a leak
5. In systems without cistern there is no
risk of polluting the water from its
source
Water hammer can be a problem where poor installation
practice has been used or where taps and valves are worn or
faulty

Indirect ColdWater Installations
19-Sep-22
1. Large capacity cistern provides a
reserve of water during interruption
of supply.
The rising main must be protected against backflow from
the cistern
2. Water pressure on the taps supplied
from the cistern is reduced, which
minimizes wear on taps and
noise/reverberation.
Drinking water is not available at other appliances except at
the kitchen sink.
3. Fittings supplied with water from the
cistern are prevented from causing
pollution of the drinking water by
back siphonage
Storage tank requires more space in the roof area and
more support.
4. Reduces the demand on the cold
water main at times of peak
demand
More structural support required to carry the weight of the
cisterns when full of water
5. Reserve water in the cistern should
the cold water mains fail
Greater cost of installation
6. Reduced pressure at outlets and taps

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.
 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.
19-Sep-22

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.
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 appliances, must be supplied from a cold
water storage cistern and never direct from the main 19-Sep-22

Water Storage
Purposes of water storage
oProvide for an interruption of supply
oAccommodate peak demand
oProvide a pressure (head) for gravity supplies
Design factors
oType and number of fittings
oFrequency and pattern of use
oLikelihood and frequency of breakdown of supply (often design for
12- or 24-hour reserve capacity)
19-Sep-22

Considerations/Guidelines for installation of
cistern
1. Watertight, adequate strength, and manufactured from plastic,
galvanized steel, 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.
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.
19-Sep-22

Cold water Storage or feed cistern installation (Illustrations)
19-Sep-22
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

Duplicating cold water storage cisterns(Illustrations)
19-Sep-22
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Cold-water
Feed pipes
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Rising
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HotWater Systems
Types of HotWater Systems
19-Sep-22

Localized HotWater Systems
 A system in which water is heated locally to its needs.
Instantaneous water heaters
heats flowing water
 water flows through a heating element
controlled by a flow switch
 0.05 litres output flow
Storage tank water heaters
stores heated water in a tank
water flows through electric immersion heater
controlled by thermostat
temperature and pressure
relief valves
19-Sep-22

Centralized HotWater Systems
 A system in which water is heated and stored centrally within the
building, supplying water through a system of pipework.
 Centralized systems consists of:
-Water heaters
- Hot water storage cylinders
- Cold water storage cistern
- Expansion vessel
- Water heating system + Pipe work system
Centralized systems can be separated into:
o Vented systems
o Unvented systems
19-Sep-22

Centralized HotWater Systems…
 A system in which water is heated and stored centrally within
the building, supplying water through a system of pipework.
 Centralized systems consists of:
- Water heaters
- Hot water storage cylinders
- Cold water storage cistern/Expansion vessel
 Water heating system + Pipework system
Centralized systems can be separated into:
o Vented systems
o Unvented systems
19-Sep-22

Centralized HotWater Systems…
 As water expands when heated, some sort of device must incorporated
to accommodate expansion of the hot water storage cylinder.
 Expansion vessels are installed to provide an outlet to allow air to
escape.
Read more about the Vented & Unvented centralized hot water
systems
19-Sep-22

Centralized system vs localized system
19-Sep-22

Installation of HotWater Supply Systems
 The main considerations that need to be taken in the design of a hot
water supply system includes:
1.Type of hot water supply system
 Localized or Centralized?
 Direct or Indirect?
2. Supply pipes and water circulation design
 Location of water heaters
 Piping configurations
 Circulation design
 Zoning
3. HotWater Heaters
 Electric or Gas?
 Instantaneous or Storage? 19-Sep-22

Installation of HotWater Supply Systems…
4. Hot water demand requirements
o Water temperature requirements
o Peak periods (Mornings & Evenings)
5. Cost and efficiency of the system
o Standby loss
o Tank insulation
o Heat traps
19-Sep-22

Exercises
1. Two cold water storage tanks, each containing 4500 litres, are sited in a
water storage room on the roof of a building that houses a very busy hotel
and hence the tanks require to be refilled every two hours. The vertical
height from the water mains and the ball valves is 26 m and the horizontal
length from the water mains is 8.5 m. the horizontal length from the rising
main to the face of the tanks is 0.5 m. If the pressure on the mains supplying
the cold-water storage tank is 300 kPa during the peak demand periods,
determine the diameter of the rising main assuming that the frictional losses
in the pipe and fittings to be 30 % of the net length of the pipe. Sketch and
label the installation.All groups
2. A cold-water storage tank in a house with five occupants is to have a capacity
of 100 litres/person and be fed from a water main able to pass 0.25 l/s.
How long will it take to fill the tank? G7 & 8
3. Sketch and describe a suitable cold-water services installation for a 20-storey
hotel where the mains water pressure is only sufficient to reach the fifth
floor.All groups 19-Sep-22

Surface-Water Drainage
Introduction
 Design calculations for roofs, gutters and ground drainage are presented
along with practical exercises in suitable arrangements.
 It is important for the designer to maintain the closest contact with the
architect during this process because of the required integration.
Flow load
 Normally ground surface-water systems are designed on the basis of a
rainfall intensity of 50 & 75 mm/h for roofs.
 The drain flow load is represented by the impermeability factor, and
typical figures are shown inTable in the next slide.
19-Sep-22

Surface-water drainage…
Table : Ground impermeability factors.
The drain water flow rate Q is given by:
Example 2.1: Roadways and gardens on a commercial estate cover an area of 75
000 sq. m, of which 20% is garden and grassed areas. Estimate the surface-
water drain flow load in l/s. How many 15 l/s surface-water drain gulleys are
needed? (Rainfall intensity be 50 mm/h)
Solution.
 FromTable above, impermeability factors are 0.9 for the roads and 0.25 for
gardens and grass.
 Therefore:
19-Sep-22

Solution.
Roof Drainage
 A rainfall intensity of 75 mm/h is commonly used in computing for flow load.
 The flow load Q for a roof is calculated from:
19-Sep-22

Roof Drainage..
 The flow load Q for a roof is calculated from:
 where Ar is the surface area of a sloping roof of pitch up to 50◦ and no
evaporation takes place.
 For a roof pitch of greater than 50◦:
where θ is the roof pitch in degrees.
 The flow capacity of a level half-round gutter is given by:
whereAg is the cross-sectional area of the gutter in mm².
19-Sep-22

Roof Drainage..
 For level gutters other than half-round the flow capacity can be found from:
where Ao is the area of flow at the outlet, mm², and W is the width of the
water surface, mm.
 A fall of 1 in 600 increases flow capacity by 40%.The frictional resistance of a
sloping gutter may reduce water flow by 10%, and each bend can reduce this
further by 25%.
 W will normally be the width across the top of the gutter.
 In rectangular gutter sizes,Ao, can be found from:
where D is the gutter depth (mm).
19-Sep-22

Roof Drainage..
Table 2.3:Typical flow capacities for a PVC half-round gutter at a 1 in 600 fall.
19-Sep-22

Example 2.2
A sports centre roof of dimensions 15 m×8 m is laid to fall to a PVC half-round
gutter along each long side. Find an appropriate gutter size when the gutter is
to slope at 1 in 600. Each gutter can have a centre or end outlet.
Solution
The flow load is:
 Each gutter will carry half of Q, that is, 1.26 l/s. For one gutter, the fall will
increase the carrying capacity by 40% and friction will reduce it by 10%. The
required gutter area can then be found from:
19-Sep-22

Hence, Therefore,
For a half-round gutter: and hence,
 Thus a 125 mm half-round gutter with an end outlet would be used along each
side.
 This can be checked with the data in Table 2.3. A smaller 100 mm gutter
would be possible if a centre outlet was appropriate to the appearance of the
building and the underground drain layout.
19-Sep-22

Disposal of surface-water
 Surface-water can be removed from a site by one or more of the following
methods:
1. Sewer: Where the local authority agrees that there is adequate capacity,
surface-water is drained into either a combined sewer or a separate surface-
water sewer.
2. Soakaway:
3. Storage: An artificial pond or lake, or even an underground storage tank, will
be necessary if the expected run-off from a curtilage is at a greater rate than
could be accommodated by a sewer or watercourse.
4. Watercourse: The relevant local authorities may allow the disposal of surface-
water into watercourses. Expected flow rates at both normal and flood water
levels must be established.
19-Sep-22

Exercises
1. A roof sloping at 42◦ has a level box gutter 125 mm wide and 50 mm deep.
The roof is 15 m long and 5 m up the slope. Calculate whether the gutter
will adequately convey rainwater when the rainfall intensity is 75 mm/h.
Recommend the outlet location.All Groups
2. Storage soakaway pits 2.25 m deep are to be employed for a tarmac-covered
car park of dimensions 100 m×30 m. Determine the number and size of the
pits needed. Draw a suitable drainage layout for the car park. Group 2 & 3
3. A housing estate has footpaths and roads covering an area of 4000 m2.
Calculate the rainwater flow load and the number of drain gullies required.
Group 4 & 5
4. A PVC half-round gutter 150 mm wide slopes at 1 in 600 and has an end
outlet to a rainwater pipe. The water depth at the outlet is half the gutter
depth. Assume that Ao is half the gutter cross-sectional area. Take W as the
gutter width. Calculate the gutter flow capacity. Group 1 & 6
19-Sep-22

Exercises..
5. The flat roof of a school is to be of dimensions 30 m×20 m with a
rectangular gutter on each long side and sloping at 1 in 600 to an outlet at
each end. Calculate suitable dimensions for the gutter. Group 7
5. A pitched roof of dimensions 20 m× 5 m drains into a level box gutter 120
mm wide and 80 mm deep on one long side. The gutter has one end outlet.
Calculate whether this is a satisfactory arrangement. Group 4
19-Sep-22

Below-ground drainage
Introduction
 Below-ground drainage systems are designed to operate without the input of
energy, wherever possible, to be reliable and to require little, if any,
maintenance.
 Their layout has to be such that drains are not subject to undue stress from
foundations or traffic and are fully accessible for occasional clearance.
 Design calculations can be made on the basis of flow rates, utilizing discharge
units, gradients, pipe material and pipe diameter.
Design principles
1. Sanitary discharge services operate by gravity flow and require no energy
input.
2. Drains are laid to fall at an even gradient, which produces a self-cleaning
water velocity so that potential deposits are accelerated and floated
downstream.
19-Sep-22

Design principles..
3. Large drops in drain level are accommodated in a back-drop manhole, rather
than a lengthy steep slope, in order to minimize excavation.
4. Pipes are laid in a series of straight lines between access points used for
inspection, testing and cleaning.
5. Selected trench bedding and backfill material is used to provide continuous
pipe support, to spread imposed ground loads due to the weight of soil and
passing traffic, to protect drains from sharp objects and other services
19-Sep-22

Access provision
 Blockages may happen, as drain systems are likely to be in place for a hundred
years or more and demands upon them continue to increase.
 Cleanability is an essential feature of good design.
 Access points are provided for removing compacted material and for using
rigid rods to clear blockages in the direction of flow, even though flexible
water-jetting techniques are currently available and it is possible to clear
obstructions from either direction.
5 Common types of access to below-ground drainage systems are:
1. Shallow access chamber:
 a removable threaded cap on a branch fitting to allow access in either direction
located such that the distance from ground level to drain invert is less than 600
mm to facilitate reaching into the drain.
19-Sep-22

Access provision..
2. Inspection chamber:
 600 mm deep, 500 mm diameter chamber for access to screwed
caps on drain junctions – usually referred to as sealed inspection chamber
or,
 Open-channel inspection chamber: a 600 mm deep, 500 mm diameter access
chamber with benched smooth surfaces for drain junctions.
3. Manhole:
 main access point for an operative wearing breathing apparatus to climb down
steps to any depth;
✓ a 1 m deep manhole is 450 mm2.
✓ a 1.5 m deep manhole has dimensions of 1200 mm×750 mm or 1050
mm in diameter and a cover 600 mm2.
19-Sep-22

Access provision..
4. Rodding eye:
 a 100 mm diameter drain pipe extended from any depth to ground level to
allow rodding in the downstream direction.
5. Gulley:
 ground-level connection point for various waste pipes and the below-ground
100 mm diameter drain providing a water trap against sewer gas and allowing
debris removal and rodding access.
 it may have a sealed lid or open grating.
 first access point close to the building just after the base of the internal
drainage stack.
19-Sep-22

Illustrations of Access to below-ground drainage
19-Sep-22

Typical site layout showing access
19-Sep-22

Exercises
1. The flow from a 100 mm stack is equivalent to 750 discharge units and is to
run underground for 30 m before entering the foul sewer at a depth 375 mm
lower than at the building end. Find a suitable diameter for a spun precast
concrete drain so that it will not be more than two-thirds full at maximum
flow rate.All Groups
(Check Example 9.1 in Chadderton).
19-Sep-22

CVS 467.Chapter 2.Water Supply and Drainage.pdf

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