UTILIZATION OF ELECTRICAL ENERGY

1. Electrical heating

2. 
Learning Outcome 1:
Heat and temperature, heat capacity
and heat transfer.

Learning Outcome 2: Methods used to control heating in
various situations

Learning Outcome 3: The processes and techniques used
for water, space and industrial
process heating.

Learning Outcome 4: AS3000:2007 Wiring Rules
requirements.

Learning Outcome 5: Possible causes of malfunction in
electric heating equipment and the
tests required to diagnose faults
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3. Heat and temperature


What is the difference between Heat and Temperature?
Heat is a measure of the total kinetic energy of the molecules or atoms in a
body.
◦
The quantity of energy stored is measured in Joules
◦

Symbol – J
Temperature is a measure of the degree of movement of the random
oscillations of the molecules.

Alternatively, it can be defined as a measure of the hotness of a body.


No movement = No temperature. (ie. Absolute Zero)
If a body is not storing heat its temperature is absolute zero.
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4. Electrical Heating
Transfer of
Heat
Heat is transferred from a hotter region to
a colder region

5. Electrical Heating
Heat is Energy
Energy (W)in Joules (J)
Time in seconds (s)
Power in Watts (W)

6. Electrical Heating
Temperature Scales
The common
temperature
scale is CELSIUS
Water boils at 100oC
Ice melts at 0oC
Some countries use the
FAHRENHEIT scale
Water boils at 212oF
Ice melts at 32oF

7. Electrical Heating
Temperature Scales
The temperature
scale used in science and
engineering is the
absolute KELVIN scale
(K)
One Kelvin “degree”
is equal to
One Celsius “degree”
Zero Kelvin is “Absolute
Zero”
NO heat content;
NO molecular motion.
Water boils at 373K
Zero Kelvin (0K) is “Absolute
Zero”
and is equivalent to
-273oC
Ice melts at 273K
The “degree” symbol o is NOT used with the Kelvin scale

8. Electrical Heating
Temperature Scales
To convert Fahrenheit to Celsius:

9. Electrical Heating
Temperature Scales
To convert Celsius to Fahrenheit:

10. Electrical Heating
Temperature Scales
To convert Kelvin to Celsius:

11. Electrical Heating
Temperature Scales
To convert Celsius to Kelvin:

12. 
Kelvin
◦ 0K
absolute zero
◦ 273.15K
◦ 373.15K
steam point of water
◦ Note 100

ice point water
degrees between ice and steam
Celsius
◦ -273.15OC
absolute zero
◦ 0° C
ice point water
◦ 100° C
steam point of water
◦ Note 100
degrees between ice and steam
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13. 

The ability of a substance to store heat.
If equal masses absorb equal amounts of thermal
energy (heat), different substances show a
different temperature increase.
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14. Electrical Heating
Specific Heat Capacity
Specific Heat Capacity is the amount of heat energy
required to change the temperature of one kilogram of
a material through ONE KELVIN (or degree C)
Absolute Heat Energy (J)
Specific Heat Capacity(J/kg.K)
Mass (kg)
Temperature change (K or oC)

15. •
•
•
•
•
•
•
•
•
•
•
•
Solids ( J/kg°C )
Iron 450
Copper 390
Aluminium 900
Gold 130
Glass 840
NaCl 880
Ice 2090
Wood 1680
Sand 820
Diamond 500
Concrete 880
•
•
•
•
•
•
•
Liquids ( J/kg°C )
Water 4180
Methanol 2550
Ethanol 2480
Antifreeze 2380
Benzene 1720
Human body 3470
•
•
•
•
•
•
•
Gases ( J/kg°C )
Steam 1970
Oxygen 910
Nitrogen 1040
Dry air ~1000
Hydrogen 14300
Freon11 870
These are just examples only
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16. 
Q = m x c x (t 2-t 1)
◦
Where:
◦
Q = Quantity of heat
◦
m = mass in kg
◦
c = specific heat capacity (tables)
◦
t 2 – t 1 change in temperature
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17. 
Heat moves from high to low temperature levels.
The rate of heat transfer is partly dependant on
the difference between the two temperature
levels.

3 types of heat transfer
 Conduction
 Convection
 Radiation
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18. Electrical Heating
Heat Transfer - CONDUCTION

19. Electrical Heating
Heat Transfer - CONVECTION

20. Electrical Heating
Heat Transfer - RADIATION

21. 
Thermal conductivity is the material’s ability to transmit
heat by conduction.

Depends on four factors:
◦ Type of material
◦ Length of transfer path
◦ Cross-sectional area of path
◦ Temperature difference
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22. 
The frame of a motor is designed to conduct the
heat from the windings (centre of motor) to the
surface and then dissipate the heat to the
environment.

The frame of a Hot Water Service is designed to
ensure the heat is trapped in the centre of the
Service.
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23.  Two
basic types:
◦ Open Loop Control
◦ No actual control of the amount of heat
◦ Closed Loop Control
◦ Control over the amount of heat
(temperature)
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24. Examples:









On-Off control of a switch
Set the car throttle in one position for a trip…
Simmerstat on stoves to control the hotplates
O/H fan speed control
Fixed position of valve regardless of changes to flow
requirements
Garden sprinkler
Electric toaster
Microwave oven: Power setting. Time setting
Electric Blanket
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25. 
Three heat switching
◦ Example:
 Most old Urns
 Electric blankets (almost all)
 Some stoves in caravans
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26. Electrical Heating
Heat Control – 3-Heat Switch

27. Electrical Heating
Heat Control – 3-Heat Switch

28. Electrical Heating
Heat Control – Simmerstat
The SIMMERSTAT is an OPEN CYCLE temperature control
commonly used with stoves.
Active
Contacts
Compensating Bimetal
Pivot
Neutral
Operating Bimetal
Internal heater
element
Heating
Load

29. Heater element + bi-metal strip
Main Contacts
Magnet
(to give snap
action switch)
Adjustment
Aux. Switch
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31. Examples:
 Oven thermostat and element
 Toilet cistern water level control
 Car cruise control
 Almost all industrial processes
 HWS
 Electric Iron
 Electric frypan
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32. Electrical Heating
Heat Control – Open/Closed Cycle

33. Electrical Heating
Heat Control – Open/Closed Cycle

34. Electrical Heating
Heat Control – Open/Closed Cycle

35. Electrical Heating
Heat Control – Thermostats
A THERMOSTAT is a Closed-Cycle Control that:
•SENSES the output temperature
•COMPARES it with the pre-set value
•VARIES or SWITCHES the input energy

36. 
Four types are typically found in appliances.
The first three of these are totally mechanically
controlled:
◦ 1. Bimetal strip. When two metals with different
coefficients of thermal expansion are sandwiched
together, the strip will tend to bend as the temperature
changes.
In a thermostat, the bimetal strip operates a set of
contacts which make or break a circuit depending on
temperature. In some cases the strip's shape or an
additional mechanism adds 'hysteresis' to the
thermostat's characteristics
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38. 2. Bimetal disk. This is similar to (1) but the bimetal element is in the
shape of a concave disk (like the “clicker” play toy). These are not
common in adjustable thermostats with brad spans, but are the usual
element in an over-temperature switch.
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39. Electrical Heating
Heat Control – Thermostats
Bimetal Disc Thermostat
This thermostat has contacts operated by a cupped
bimetal disc.
At a pre-set temperature, the disc snaps the contacts
open.
When the disc cools to a preset value, disc returns and
the contacts snap closed.

40. Electric Iron Thermostat
Bimetal Strip
MIMS type element
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42. Thermal Cut-out
(with manual reset)
Thermostat
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43. Two Hot Water System Thermostats
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44. 3. Fluid operated bellows. These are not that common in small appliances
but often found in refrigerators, air conditioners, stoves, and so forth. An
expanding fluid (alcohol is common) operates a bellows which is coupled
to a set of movable contacts. As with (1) and (2), hysteresis may be
provided by a spring mechanism.
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45. Electrical Heating
Heat Control – Thermostats
Capillary Tube Thermostat
Bellows or
Diaphragm
Bellows Rod
moves to operate
contacts
Capillary Tube
Bulb with volatile
liquid

49. Electrical Heating
Heat Control – Thermostats
Bi-Metal Thermostat
Support Stem
Invar Rod
Brazed to Stem
Brazed to Rod
Mounting Flange & Screw
Thread
Helical Bi-Metal Strip

50. Bimetal Coil thermostat
Mercury Switch
Bimetal Coil
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51. Electrical Heating
Heat Control – Thermostats
Expanding Tube Thermostat
Retaining
Clips
Rod Free End
Moves to operate
contacts
Brass Tube
Tube
Expands/Contracts
Tube Brazed
to Support
Invar Rod
Tube
Brazed
to Rod

52. Expanding tube thermostat
Operating rod
Rod is welded
to the end of
the tube
The operating rod has a different
expansion rate than the tube
enclosing it.
Electrical
Contacts
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53. Bi-metal helix
Bulb type
Expanding rod type
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54. 4. Electronic thermostats. These typically use a temperature controlled
resistance (thermistor) driving some kind of amplifier or logic circuit which
then controls a thyristor or contactor.
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55. 
Note that these terms can only apply to a closed
loop system such as thermostats. If there is no
feedback, the system cannot have:
◦
◦
◦
◦
Hysteresis
Differential
Sensitivity
Accuracy
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56. 
Sensitivity

Is a measure of the change of output to a
change of input.

A more sensitive thermostat will have a smaller
differential.

It is a measure of how closely a unit can
maintain a given temperature.

It is better applied to temperature measuring
devices that give an analogue output. A more
sensitive device gives a greater change of
output to the change of input (temperature).
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57. Thermocouples
 Resistance Temperature Detectors (RTD’s)
 Diodes and semiconductor IC’s
 Gas expansion system
 Mercury expansion system
 Coiled bimetal strip (see P&N)
 Radiation Pyrometers

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58. Instantaneous
 Mains pressure - Storage
 Mains pressure - Heat exchanger
 Low pressure storage
 Solar
 Heat Pump HWS

L/O 3.1
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59. 
Instantaneous or tankless water heaters are small
cabinets that heat water on demand or instantly as it
passes through the heater.

They contain no significant water storage, possessing
only up to a 6 litre operating holding.

These water heaters only use energy when the hot water
outlet is turned on and shut down immediately when the
outlet is turned off.

61. 
Mains Pressure HWS: direct heated
◦
◦
◦
◦
Installed at ground level.
Requires a pressure relief system.
Requires an expansion control valve.
New houses require a tempering valve for warm water to
the bathroom.
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62. Mains Pressure HWS
-Direct heated
Insulation
Hot water Out
Note: The tank operates
at mains pressure.
Cold water In
Water Heater +
thermostat
L/O 3.1
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64. If both have the
same colour tags,
then this wont be
a problem
1400kPa
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65. Bottom Cold Water
Expansion Valve
must be
200kPa lower than
the top pressure
relief valve.
1200kPa
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66. Revision 01
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67. • Hot water (73°C max.) to
Pressure
laundry and kitchen.
Relief
• Warm water (50°C max.) to Valve
bathroom.
• If major renovations are
Tempering
carried out in the bathroom, Valve
then a tempering valve must
be added.
• The house owners can sign a
form saying they don’t want it
Cold Water
(as only adults will be using
Expansion
it), and the plumber will not
Valve
be responsible for any
consequences.
Hot Water
Outlet
(73°C max.)
Warm Water
Outlet
(50°C max.)
Cold Water
Inlet
Cold Water
Tap
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68. Heat exchange Storage HWS
Small Storage HWS designed
for under sink operation
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69. 
Must be mounted above taps.

Low pressure hot water only.

More to go wrong.
◦ If float valve sticks…
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70. Low Pressure HWS
Toilet cistern type
water level sensor
Element
and electrical
connection
Hot
Water
Out
Cold
Water
In
Gravity
Feed
Tank fills from
Bottom
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71. 
Faults:
◦ Element goes open circuit.
 Replace element.
◦ Thermostat either stays on, or stays off
 Replace thermostat
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72. • Solar
– Still requires booster
element
– 8-10 year pay back
period
– May require extra roof
support.
– Does the roof face the
required direction?
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73. 
In solar systems cold water travels through the roofmounted solar collector where the water absorbs heat
from the sun.

Water heating using solar energy occurs during the day
and the solar involvement varies significantly throughout
the year depending on the climatic conditions.

The apparatus of solar heaters includes the solar
collector, insulated storage tank and, if required, pump
and control valves.

74. 
Flat-plate collectors are the most common collector for
domestic water heating.

A typical flat-plate collector is an insulated rectangulartype metal box with a transparent cover (similar to a
greenhouse) and a black absorber plate.

76. 
The evacuated-tube collectors consist of rows of parallel
transparent double glass tubes, each containing an
electromagnetic energy absorber and covered with a
solar-sensitive coating.

Sunlight enters the tube, strikes the absorber and heats
the water flowing through the collector.

80. 
Calorifiers are cylinders with an internal coil which allows
the use of any type of boiler for hot water production.

The calorifier can be either mains-pressure or lowpressure hot water storage systems.

A significant amount of heat energy can be transferred to
the calorifier, allowing a large production of hot water
from a relatively small cylinder.

82. 
Heat pump HWS
◦
◦
◦
◦
More expensive than conventional HWS
Smaller than Solar HWS
Can operate with or without sunshine
Operates as a split system
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83. 
A heat pump water heater absorbs heat from the
surrounding environment and pumps the acquired heat
energy into a hot water storage tank.

The heat pump serves as a heater by absorbing heat
from the surrounding environment and pumping it into a
closed-system heat-exchanger water storage tank.

84. The compressor compresses cool refrigeration gas, causing it to become hot, highpressure refrigeration gas
This hot gas runs through a set of coils so it can dissipate its heat, and it condenses
into a liquid.
The refrigeration liquid runs through an expansion valve, and in the process it
evaporates to become cold, low- pressure refrigeration gas
This cold gas runs through a set of coils that allow the gas to absorb heat and cool
down the air inside the building
A solar heat pump works on the same principle only in reverse i.e the coils carrying
the hot gas are used to heat the water.
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86. 
If the water heater’s thermostat, which controls the
resistive heating element, malfunctions the pressurised
water in the tank could continue to heat and superheat
(beyond 100 °C).
This will cause two problems:

First, since water expands when heated, the water
pressure in the tank will increase as the water is
superheated.

If the pressure exceeds the vessels maximum pressure
threshold the tank could rupture or even explode.

87. 
Secondly, the release of superheated water (water
heated above 100 °C up to its critical temperature of 374
°C without boiling) causes the water to burst into steam
(1 litre of water can produce about 3 litres of steam),
causing a sudden increase in volume and release of
energy.

Lowering the pressure of water lowers the boiling point.
There is less pressure above the water to overcome.
The superheated vapour plume expands until its
pressure equals that of the surrounding atmosphere.

88. 
Types:
◦
◦
◦
◦
High Temperature radiators
Low temperature panels and convection units
Thermal storage systems
Heat pumps (reverse cycle air conditioners)
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89. Types:
◦ Low temperature panels and convection units
 Under-carpet / under concrete heaters (MIMS in concrete
slab)
 Can be operated using cheaper power at night
 Blower heaters
 Oil filled floor heaters
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90. 
Stoves (ranges):
◦ Four types of cooktops:




Coiled element
Solid element
“Ceramic” cooktop
Induction cooktop
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91. Revision 01
91

92. Coiled Element
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93. Solid element
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94. Ceramic cooktop
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95. Revision 01
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96. • Stoves:
– Wiring:
Half the elements
with their controls
Other half of the elements
with their controls
A
A
N
Revision 01
Connection Box
96

97. • Microwave ovens bombard food with
electromagnetic radiation at 2.45GHz
• Water absorbs the energy. The molecules vibrate
and get hot.
• The oven will dissipate the same energy in the
cavity no-matter what. (eg. 800W)
• Small quantities will cook faster. Large quantities
cook slower.
• Metal reflects the microwaves
• If a microwave oven is left empty, the microwaves
will reflect back into the magnetron and heat it up.
This destroys the magnetron.
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98. 
There are four (4) process heating methods
available for converting the electric energy to heat
energy.
1. Resistance
2. Infra-red
3. Induction
4. Dielectric
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99. Resistance process heating
All the heat generated by an element is transferred by either
convection or conduction
The elements used may be either wire, strip or solid rods.
Typical applications include; duct heaters, furnaces, refrigerators,
space heaters, greenhouse heating and trace heating.
In all cases their temperatures are controlled by thermostats
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100. 
Infra Red heating:
◦ Spray painting booths for cars

Induction Heating:
◦
◦
◦
◦
For directly heating small steel parts.
Similar to locking the rotor of a motor… it gets hot.
Usually the work piece has currents induced in it directly.
Frequencies between 50Hz and 5MHz used.
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101. 
Dielectric Heating:
◦ Used to heat non-conducting material.
◦ If an insulator is placed between two electrode plates,
and AC is applied to the plates, the molecules are
agitated and heat up.
◦ Used in plywood manufacture
◦ Used to dry breakfast cereal and dog biscuits

Electric Arc
◦ Used in the steel industry up to 150 tonnes
◦ Used in glass furnaces. eg. Bradford pink batts.
◦ Arc welders fall in this category.
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102. Demonstrate knowledge of the possible causes of
malfunction in electric heating equipment and
skills the testing and fault finding.
 5.1
List the possible causes of faults in a
malfunctioning electric heating
device/circuit.
 5.2
Conduct tests and locate a fault in a
malfunctioning electric heating
device/circuit.
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103. Open circuits
 -physical breaks in the element
 -breaks in wiring
Short circuits
 -resistance reduced to 0Ω
Partial open circuits
 -loose connections etc
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104. Revision 01
104

105. Element Testing
To test an element for continuity the appliance should first be
disconnected from power. After the appliance has been made safe to work
on, the element needs to be isolated from the rest of the electrical circuit
by removing at least one of the connecting wires. Once that is done, an
ohm meter or continuity tester's leads can be held against each terminal of
the element.
The exact resistance of an element is often not important as it will not
usually change over its life span except to become totally open (show
infinite resistance) when defective or becomes shorted to ground (see
below). In case you're curious, a large cooktop surface burner is usually in
the area of 27 ohms, a small 45 ohms. A griller element's resistance may
be in the area of 20 to 40 ohms depending on its wattage.
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106. Revision 01
106

107. Short to Earth
An element can also become partially shorted to ground.
While this may not be enough to create a dead short and
cause the element to fail outright, it can create a shock
hazard. To test an element for a short to ground, an
ohmmeter should be set on its highest ohm scale (1K or
10K) and tested from one of the element's terminals to the
element's metal sheath. It may be necessary to rub the
outer element surface with the meter probe to make a
good contact. If anything other than infinite resistance is
shown, replace the element.
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108. Revision 01
108

109. Heat damaged
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