PLUMBING FUNDAMENTALS
MODULE 9
DOMESTIC HOT WATER SUPPLY
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Why is there a need for Domestic Hot
Water Supply?



The supply is based on the need for Personal Hygiene
and Washing in order to remain healthy and safe.
Personal Hygiene – to maintain the bodies clean, a
regular supply of hot water is required to break down
and dissolve oil & dirt. Soap lathers much better in hot
water than cold. Hot water is more friendly to our skin
temperature since we are warm-blooded animals. Hot
water also helps to open skin pores, letting the soap get
down into the tissue to lift out the oil & dirt.
Washing – certain substances, such as fatty foods on a
plate, require a temperature of 60 degrees Centigrade to
lift them.
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Types of Fuel:

The methods of
heating water vary
but in the long run it
is a matter of
personal choice with
respect to cost and
availability of fuel.
The types of fuel are:
1. Electricity
2. Solid Fuel
3. Gas
4. Solar
5. Steam
6. Oil
7. Heat Pumps

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Types of Systems available:
Localized Water Heating
2. Centralized Hot Water Systems
3. Storage Water Heaters
4. Instantaneous Water Heaters
1.
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What is the operating principle of Hot
Water Supply & Distribution System?
The storage tank & heating device
of a hot water supply &
distribution system are so
assembled as to create a
circulation of water within them.
 The movement of the water is the
result of molecular activity. The
application of heat to a body of
water causes it to expand &
become less dense, which give it a
natural tendency to rise.
 The inequality of weights between
the hot & the cold water
contained in the tank results in
the circulation of the liquid.

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What are the factors to consider in Hot
Water Supply & Distribution System?

The operation and efficiency of
the hot water supply and
distribution system is dependent
upon the following:
1. Type of Heating System used
A. Direct System
a. Range Boilers
b. Gas Water Heater
c. Oil-Fired Water Heater
d. Electric Water Heater
e. Solar Water Heater
B. Indirect System
a. Primatic Cylinder
b. Calorifiers
c. Annular Cylinder
2. Type of Tank connection used
a. Vertical position
b. Horizontal position
c. Pipes, Valves & Fittings
3. Type of Installation used
a. Upfeed & Gravity Return
b. Overhead Feed & Gravity
Return
c. Pump Circuit System
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Direct Heating System: In this system the water that is
being heated by the boiler is actually used out of the hot water faucets.
Range Boiler - is a small cylindrical hot water tank that varies in size
from 300mm to 600mm in diameter & is not more than 1800mm long. It is
made of galvanized steel of Standard & Extra Heavy Gauge.
Range Boiler
Range Boiler & Furnace Coil – The
range boiler is usually mounted upright on
a stand. A drain is placed at the bottom
to remove sediment; a temperature &
pressure relief valve is placed at the top
for safety. The furnace coil is located in
the furnace box.
Range Boiler & Heater – The range
boiler is usually installed horizontally on a
stand. The heater may be fired by coal,
gas or oil.
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Gas Fired Water Heater:
The Installation
The Operating Principle
The Equipment
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Electric Water Heater:
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Solar Hot Water Installation:
Solar Panel and Collector
The Operating Principle
Installation
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What is Indirect Water Heating
System?
In this system the water that is
heated by the boiler is never used
out of the hot water faucets, but
circulates through a heat
exchanger. It takes the form of a
coil of pipe within the hot water
storage tank. The heated water
circulates through the system & in
turn heats the water held within
the storage tank, then returns to
the boiler to be reheated.
 The 3 types of Indirect System
currently used in buildings are:
1. Primatic Cylinder
2. Calorifiers
3. Annular Cylinder


The advantages of this system
are:
1. Since the water in the boiler
does not mix with the water in the
storage tank, the risk of rusty
water being drawn off through the
faucets is eliminated.
2. It keeps the carbonate
deposits to a minimum level
because once the temporary
hardness of the water has been
released it will not recur as the
same water is reheated over &
over again.
3. It can use steam as the
heating medium instead of water.
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to use
INDIRECT WATER HEATING SYSTEM
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3 Types of Indirect Water Heating
System:
1. Primatic Cylinder
Riser Diagram
2. Calorifier
3. Annular Cylinder
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Indirect Heating System: Heat Pump
Operating Principle
Equipment
Installation
Installation
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What are the available Types of Hot
Water Systems?
1. Localized Water Heating
(Single Appliance)
a. High Pressure
b. Low Pressure
2. Centralized Hot Water
System
a. High Pressure
b. Low Pressure
3. Storage Water Heaters
a. High Pressure
b. Low Pressure
4. Instantaneous Water
Heaters
a. High Pressure
b. Low Pressure
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Localized Water Heaters:
Above – Sink Electric Water Heater:
Designed to serve 1 fixture at a time.
Available from 7 to 34 liters storage &
normally have a 2000 watt element fitted.
It has a heat – up time of 12 minutes to 1
hour.
Undersink Electric Water Heater: Works
on the principle of displacement, hot water
only flowing when cold water enters the
cylinder & pushes the hot water out. This is
not suitable for use with dishwashers, unless
installed as low-pressure water heaters.
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What is Centralized Hot Water System?
In Centralized System, water is
heated & stored centrally and
distributed to the hot water
faucets via the hot water piping.
 For residences, an electric heating
element is directly immersed into
the water to be heated.
 For commercial & larger projects
an independent boiler or furnace
is used to heat the water
remotely.
 The hot water is stored in a Range
Boiler or Storage Tank that is
located as near the boiler as
possible to keep heat losses at a
minimum.


Parts of Centralized Hot
Water System:
1. Heating Element / Boiler
2. Thermostat
3. Range Boiler / Hot Water
Storage Tank
4. Hot Water Pipes
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Parts of the Centralized Hot Water System:

Range Boiler / Hot Water Storage Tank
– The hot water tank that serves the
domestic hot water system in a storage
capacity. The size of the tank depends on
the design of the building, the number of
occupants & the heating capacity of the
supply device. The Storage Tank is a
large cylindrical tank at 600 to 1200 mm in
diameter & not more than 4500 mm long.

Boiler / Heating Element – The size of
the heating element has a direct bearing on
the heating up time, which is also related to
the size of the storage cylinder. A general
guide for adequate supply is:
135 liters = 1500 watts at 60 degrees
centigrade in 5 hours & 15 minutes
180 liters = 2000 watts at 60 degrees
centigrade in 5 hours & 15 minutes

Thermostat – The key to a satisfactory &
economical water heater, automatically
switching off the power when the preset
temperature is reached & switching on again
when hot water is drawn off, or the
temperature drops through heat loss.
Recommended thermostat settings for average
family requirements are 65 to 70 degrees
centigrade.
Hot Water Pipes – Should be as short as
possible in order to avoid the use of “ Dead
Leg”. A “Dead Leg” is a long pipe run whereby
it takes a long time to push out the cold water
for the sake of a small amount of hot water.
The smallest pipe size that will provide a
satisfactory flow should be used.

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Storage Water Heater:
Single Boiling Type Water
Heater: Is filled with water to
the desired level before use. As
long as there is a reading on the
sight glass the heating element
will be covered. The cold water
supply may be from the cold tap
by means of a 3-way valve, which
supplies cold water to the cylinder
or delivers hot water from the
cylinder according to the position
of the knob. When water boils,
steam escapes through a whistle
connected into the top of the
vessel. The pressure from the
steam also turns off the electrical
energy to the element if a steam
switch is fitted. Boiling water is
drawn off through a faucet fitted
directly under the heater.
Single Boiling Type Water Heater
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Instantaneous Water Heater:

Instantaneous Water Heater instantly heats cold
water as it passes through the heater. This heater is
compact since storage is not required. Their 3 kinds
of model:
1. Shower Model – has a rated power consumption
of 6000 watts (6 kW) and provides a continuous
supply of hot water at a maximum rate of 3 LPM at a
showering temperature of 40 degrees Centigrade.
2. Lavatory Model – has a rated power consumption
of 3000 watts (3kW) & provides a continuous supply
of warm water for hand washing at a rate of about
1.4 LPM.
3. Multi – point Model – serves several fixtures
such as lavatory, sink, bidet & shower.
Shower Model of an
Instantaneous Water
Heater
Lavatory Model of
an Instantaneous
Water Heater
Operating Diagram
of an Instantaneous
Water Heater
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What are the Hot Water Storage Tank
Connections?
a.
b.
Cold Water Supply – Delivered into the tank via
a boiler tube that extends to within 150 mm of
the tank bottom. The purpose of this is to avoid
the possibility of cooling the hot water which
accumulates at the top of the tank. This cold
water line must have a small hole within from the
top of the tank. This hole serves as a vacuum
breaker & prevents siphonage.
Flow Connection – Connected to an opening on
the tank somewhere above its centerpoint. This
line is called flow connection because the heated
water flows from the heater into the tank.
c.
d.
e.
f.
Return Connection – Connected to a tapping on
the bottom of the tank. This line is called the
return connection because it returns the colder
water from the bottom of the tank to the heater.
Drain Valve – Located at the lowest point of the
storage tank.
Hot Water Distribution Pipe – Connected to a
tapping on the top of the tank at the point near the
flow inlet.
Blow – Off Valve – Installed to the storage tank
to control the temperature & pressure and to
prevent serious difficulties should the tank become
overheated.
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Types of Tanks used in Domestic Hot
Water System:
Expansion Tank
Operating Principle of Expansion Tank
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Multiple Installation of Storage Water
Heaters:


Where large volumes of hot water are
required over a short period at constant high
temperature to several outlets all being used
at one time, one can install 2, 3, 4 or more,
quick recovery mains pressure storage heaters
in parallel using the “equa flow” manifold. It
is designed to ensure that all heaters are
contributing.
The essential principle of “Equa – Flow” is that
the demand on each heater in the bank is the
same as any other.
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What are the Valves and Fittings used
in the Domestic Hot Water System?
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Valves and Fittings for Hot
Water Heating System:
Pressure
Relief Valve
– is designed
to open if the
pressure in
the system
reaches the
set point on
the valve.
Once the
valve opens,
the pressure
in the system
will be
relieved and,
when the
pressure
drops to an
acceptable
level, the
valve will
close again.
Air Vent – a
fitting used to
remove air,
either
manually or
automatically,
from the hot
water heating
system.
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Air Separator – removes
smaller air bubbles, called
microbubbles, from the
system.
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What are the Types of Installations of
Hot Water Distribution?

The installation for hot water distribution consists of the piping work
that conveys the heated water from the storage tank to the
plumbing fixtures.
1. Upfeed & Gravity Return (Recirculation) System – With this
system, as the hot water in the pipe cools, the cooled water, being heavier
than the hot water , slowly flows down the return pipes to the heaters while
the hot water replaces it in the system.
2. Overhead feed & Gravity Return (Recirculation) System – The
operating principle of the overhead system is based on the fact that in the
closed system of piping, water rises when heated. After it has reached the
high point of the system, natural forces of gravity return it to the storage
unit.
3. Pump Circuit System (Pumped Recirculation) – The circulation of
hot water to the plumbing fixtures by means of a mechanical device,
usually a centrifugal pump. This is used in buildings where the other
systems already mentioned are not suitable to produce a circulation of hot
water.
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Upfeed & Gravity Return System:
• Commonly used in residential installations.
• The purpose of this system is to permit
circulation of hot water within the piping
arrangement.
•The circulating return is economical since it
eliminates water waste.
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Overhead Feed & Gravity Return
System:
• The most efficient method of delivering hot water to
•It is dependent on the natural laws governing
expansion and gravity.
• It is generally used in multi-storey buildings
•Its advantage is that it allows continuous circulation
even if there is a mechanical defect in the system,
fixtures.
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Pump Circuit System:
• The circulation of hot water to the plumbing fixture by
means of a mechanical device, usually a centrifugal
pump. The rotary motion of the impeller of the
centrifugal pump creates an even movement of hot
water in the pipes which makes this pump practical to
use.
A Circulating Pump moves water through a piping
system. Low horsepower pumps are inexpensive
to operate.
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Available in:
1/25 hp
1/33 hp
1/40 hp
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Other Piping Layouts for Domestic Hot
Water Supply and Distribution:
Water Main Feed System
Overhead Tank Feed System
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Other Piping Layouts for Domestic Hot
Water Supply and Distribution:
Hot water supply system for a
three storey building
Hot water supply system for a
high-rise building
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Sizing Guide for Centralized Storage Water
Heaters (Vulcan brand): Approximately 5 gallons per outlet
OUTLETS
IDEAL
GALLONS
VULCAN
1 BATH or
3 OUTLETS
15
15
2 BATHS or
6 OUTLEST
30
24 or 36
3 BATHS or
9 OUTLETS
45
45
4 BATHS
OR 12
OUTLETS
60
71
5 BATHS or
15
OUTLETS
75
71 or 90
6 BATHS or
18
OUTLETS
90
90
7 BATHS or
21
OUTLETS
105
112
GALLONS
LITERS
kW RATING
At 220 volts
HEIGHT
DIAMETER
10
38
3.0 kW
46 cm
43 cm
24
90
3.0 kW
94 cm
44 cm
36
135
4.0 kW
134 cm
44 cm
45
170
4.0 kW
165 cm
44 cm
89
340
2 x 4.0 kW
168 cm
61 cm
112
425
2 x 4.0 kW
188 cm
65 cm
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CALCULATING DOMESTIC HOT WATER DEMAND
BY THE NUMBER OF FIXTURES:
Step 1. Determine the quantity of fixtures that
require hot water supply and multiply with the
corresponding factor according to type of
building served. Refer to Table 1.0
Step 2. Determine the capacity of the heater by
solving the probable maximum demand.
Step 3. Determine the storage tank capacity.
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Table 1.0 Hot water Demand per Fixture
( in gallons per minute )
FIXTURE
APARTMENT
CLUB
HOSPITAL
HOTEL
FACTORY
OFFICE
SCHOOL
Lavatory
(private)
2
2
2
2
2
2
2
Lavatory
(Public)
4
6
6
8
12
6
15
Bath tub
20
20
20
20
30
--
--
Dishwasher
15
50-150
50-150
50-200
20-100
--
20-100
Kitchen sink
10
20
20
20
20
--
10
Laundry tray
20
28
28
28
--
--
--
Pantry sinks
5
10
10
10
--
--
10
Showers
75
150
75
75
225
--
225
Slop sinks
20
20
20
30
20
15
20
DEMAND FACTOR
0.30
0.30
0.25
0.25
0.40
0.30
0.40
STORAGE FACTOR
1.25
0.90
0.60
0.80
1.00
2.00
1.00
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END OF PRESENTATION
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