UNIT-III

Power plants:
❖ working principle of Steam power plants
❖ working principle of Diesel power plants
❖ working principle of Hydro power plants
❖ working principle of nuclear power plants

Thermal Engineering
❖ working principle of Boilers (Cochran boiler,
Babcock and Wilcox boiler, La Mont boiler)
❖ Refrigeration cycle (Ideal Vapour Compression
refrigeration cycle) and air-conditioning system
(Summer air-conditioning system)
❖ IC engines, Otto cycle, Diesel cycle, 2-Stroke and 4-
Stroke engines, SI/CI Engines,
❖ Components of Electric and Hybrid Vehicles
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Definition of Power plants

A power plant may be defined as a machine or assembly of
equipment that generates and delivers a flow of mechanical or
electrical energy.
The main equipment for the generation of electric power is generator. When
coupling it to a prime mover runs the generator, the electricity is generated.
The type of prime move determines, the type of power plants.

The major power plants are:

1. Steam power plant The Steam Power Plant, Diesel

2. Diesel power plant Power Plant, Gas Turbine
Power Plant and Nuclear
3. Gas turbine power plant Power Plants are called
THERMAL POWER PLANT,
4. Nuclear power plant because these convert heat
5. Hydro electric power plant into electric energy.
1.Steam power plants

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 Working Principle of Steam Power Plant
❑ Coal received in coal storage yard of power station is transferred in the furnace by
coal handling unit.

❑ Heat produced due to burning of coal is utilized in converting water contained in

boiler drum into steam at suitable pressure and temperature.

❑ The steam generated is passed through the superheater. Superheated steam then
flows through the turbine.

❑ After doing work in the turbine die pressure of steam is reduced. Steam leaving the
turbine passes through the condenser which maintain the low pressure of steam at
the exhaust of turbine.

❑ Steam pressure in the condenser depends upon flow rate and temperature of
cooling water and on effectiveness of air removal equipment.

❑ Water circulating through the condenser may be taken from the various sources
such as river, lake or sea. If sufficient quantity of water is not available the hot water
coming out of the condenser may be cooled in cooling towers and circulated again
through the condenser.

❑ Bled steam taken from the turbine at suitable extraction points is sent to low
pressure and high pressure water heaters.

Working Principle of Steam Power Plant

❑ Air taken from the atmosphere is first passed through the air pre-heater, where it is
heated by flue gases. The hot air then passes through the furnace.

❑ The flue gases after passing over boiler and superheater tubes, flow through the
dust collector and then through economiser, air pre-heater and finally they are
exhausted to the atmosphere through the chimney.
The key components and their functions within a steam power plant:
1. Boiler: The boiler is responsible for heating water to generate steam. This is
typically achieved by burning fossil fuels (such as coal, oil, or natural gas) or
by using nuclear energy. The generated steam is at high pressure and
temperature.
2. Turbine: The high-pressure steam from the boilers is directed into a turbine.
The turbine is designed with blades that are turned by the force of the
steam’s high-speed flow. As the steam flows through the turbine, its high-
pressure energy is converted into rotational mechanical energy.
3. Generator: The turbine is connected to a generator, which consists of coils
of wire within a magnetic field. As the turbine spins, it turns the rotor of the
generator, creating a moving magnetic field. This movement induces an
electric current in the wire coils, ultimately producing electrical energy.
4. Condenser: After passing through the turbine, the steam is directed to the
condenser. Here, the steam is cooled and condensed back into water,
releasing its latent heat. This process allows for the efficient reuse of the
water in the boiler, reducing water consumption and increasing overall
efficiency.
5. Cooling System: Steam power plants require a cooling system to dissipate
excess heat from the condenser. This can involve cooling water from nearby
water bodies, cooling towers, or other heat exchange methods.
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Advantages

❖ As compared with the power generating plant, it has a low initial cost
and hence economical.
❖ Less land area is required as compared with the hydro power plant.
❖ Coal is used as fuel and the cost of coal is cheaper than petrol and
diesel fuel. So the power generation cost is economical.
❖ This power plant has easy maintenance cost.
❖ Steam power plant can be installed in any area where water sources
and transportation facility are easily available.

Disadvantages

❖ The life and effectiveness of the steam power plant are more concise
when compared to Hydel power plant.
❖ Transport of fuel is a major problem.
❖ The cost of power generation is higher than hydropower.
❖ Air pollution is a major difficulty.
❖ Coal may be depleted by gradual use.
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2. Diesel Power Plant

Chemical Energy of Diesel Heat Energy Mechanical Energy Electrical Energy

Main Components of Diesel Power Plant:
1.Diesel Engine 5. Engine Cooling System
2. Engine Fuel Supply System 6. Engine Lubrication System.
3. Engine Air Intake System 7. Engine Starting System.
4. Engine Exhaust System 8. AC or DC Generators 9
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Working Principle of Diesel Power Plant

In a diesel power station, diesel engine is used as the prime

mover. Air is compressed as the compression stroke begins
and the fuel enters the cylinder at the end of compression
stroke. Heat of compression is used for ignition of fuel. In
diesel engine, air is compressed to about 30 bars, which
increases the temperature when finely atomised diesel fuel oil
is sprayed into the heated air, it ignites and diesel burns
inside the engine. The products of this combustion act as the
working fluid to produce mechanical energy. The diesel
engine drives generator which converts mechanical energy
into electrical energy.

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As the generation cost is considerable due to high price of
diesel, therefore, such power stations are only used to
produce small power. Although steam power stations and
hydroelectric plants are invariably used to generate bulk
power at cheaper costs, yet diesel power stations are finding
favour at places where demand of power is less, sufficient
quantity of coal and water is not available and the
transportation facilities are inadequate. These plants are also
standby sets for continuity of supply to important points such
as hospitals, radio stations, cinema houses and telephone
exchanges.

Advantages of Diesel Power Plant

❑ Very simple design also simple installation.

❑ Limited cooling water requirement.

❑ Standby losses are less as compared to other Power plants.

❑ Low fuel cost.

❑ Quickly started and put on load.

❑ Smaller storage is needed for the fuel.

❑ Layout of power plant is quite simple.

❑ There is no problem of ash handling.

❑ Less supervision required.

❑ For small capacity, diesel power plant is more efficient as compared to

steam power plant.

❑ They can respond to varying loads without any difficulty.

 Disadvantages of Diesel Power Plant

1. High Maintenance and operating cost.

2. Fuel cost is more, since in India diesel is costly.

3. The plant cost per kW is comparatively more.

4. The life of diesel power plant is small due to high maintenance.

5. Noise is a serious problem in diesel power plant.

6. Diesel power plant cannot be constructed for large scale.

Applications of Diesel Power Plant

✓ They are quite suitable for mobile power generation and are widely
used in transportation systems consisting of railroads, ships,
automobiles and aeroplanes.

✓ They can be used for electrical power generation in capacities

from 100 to 5000 H.P.

✓ They can be used as standby power plants.

✓ They can be used as peak load plants for some other types of
power plants.

✓ Industrial concerns where power requirement are small say of the

order of 500 kW, diesel power plants become more economical
due to their higher overall efficiency.
 3. Hydro-electric Power Plant

Hydro projects are

developed for the
following purposes:
1. To control the
floods in the rivers.
2. Generation of
power.
3. Storage of irrigation
water.
4. Storage of the
drinking water supply.

Working Principle of Hydro-electric

power plant
When rain water falls over the earth’s surface, it
possesses potential energy relative to sea or ocean
towards which it flows.
The water falls through an appreciable vertical height,
this energy can be converted into shaft work.
As the water falls through a certain height, its potential
energy is converted into kinetic energy and this kinetic
energy is converted to the mechanical energy by
allowing the water to flow through the hydraulic turbine
runner.
This mechanical energy is utilized to run an electric
generator which is coupled to the turbine shaft.

The power developed in this manner is given as:

Power = W.Q.H.η watts
where, W = Specific weight of water, N/m3
Q = rate of water flow, m3/sec.
H = Height of fall or head, m
η = efficiency of conversion of potential energy into mechanical
energy.
 Advantages of Hydro power plant

1. The plant is highly reliable and its maintenance and

operation charges are very low.
2. The plant can be run up and synchronized in a few
minutes.
3. The load can be varied quickly and the rapidly
changing load demands can be met without any difficulty.
4. The plant has no stand by losses.
5. No fuel charges.
6. The efficiency of the plant does not change with age.
7. The cost of generation of electricity varies little with the
passage of time.
 Disadvantages of hydro power plant
1. The capital cost of the plant is very high.
2. The hydro-electric plant takes much longer in design and execution.
3. These plants are usually located in hilly areas far away from the load
center.
4. Transformation and transmission costs are very high.
5. The output of a hydro-electric plant is never constant due to vagaries
of monsoons and their dependence on the rate of water flow in a river.

4. Nuclear Power Plant

• Uranium was discovered in 1789 by Martin Klaproth, a German chemist, and
named after the planet Uranus.
• The science of atomic radiation, atomic change and nuclear fission was
developed from 1895 to 1945, much of it in the last six of those years.
• Over 1939-45, most development was focused on the atomic bomb.
• From 1945 attention was given to harnessing this energy in a controlled fashion
for naval propulsion and for making electricity
• Since 1956 the prime focus has been on the technological evolution of reliable
nuclear power plants.
• The energy in one pound of highly enriched Uranium is comparable to that of
one million gallons of gasoline.
• One million times as much energy in one pound of Uranium as in one pound of
coal.
• Nuclear energy annually prevents 5.1 million tons of sulfur 2.4 million tons of
nitrogen oxide 164 metric tons of carbon.
• First commercial power plant, England 1956.
• 17% of world’s electricity is from nuclear power.
 Nuclear Reactions
• Nuclear reactions deal with interactions between the nuclei of atoms
including of nuclear fission and nuclear fusion
• Both fission and fusion processes deal with matter and energy
• Fission is the process of splitting of a nucleus into two "daughter" nuclei
leading to energy being released
• Fusion is the process of two "parent" nuclei fuse into one daughter nucleus
leading to energy being released

Working of Nuclear Power Plant

 Nuclear Reactors
The pressurized water reactor overcomes the problem of a slightly radioactive
steam circuit by having an intermediate heat exchanger to separate the reactor
coolant circuit from the turbine steam circuit. Steam is generated in this steam
generator and is sent to the turbine as saturated steam under conditions similar to
those in the boiling water reactor. The reactor coolant circuit is maintained at high
pressure to prevent any boiling in the reactor and operates at a slightly higher
temperature than the BWR to promote heat transfer to the secondary steam
circuit. Because no boiling occurs in the reactor core, it is more compact and does
not require channels. The fuel rods of the individual elements form a continuous
vertical matrix in the core. This is flooded with an upward flow of circulating light
water which serves as coolant and moderator.

The Pressurized
Water Reactor
(PWR)

Nuclear Reactors
The boiling water reactor consists of a pressure vessel containing the fuel
rods in vertical elements, with each element surrounded by a channel. The
channels are flooded with light water which serves as the moderator and
coolant. Pumps circulate water upwards through the channels, and steam
is generated within the channels. The exit steam quality is about 13%, and
the steam is separated from the water in cyclone separators above the
reactor core. This saturated steam is sent directly to the steam turbines.

Boiling Water
Reactor (BWR)
 The Pressurized
Water Reactor
(PWR)

Boiling Water
Reactor (BWR)

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Nuclear power stations in India

(i) Tarapur Nuclear Power Station. It is India’s first nuclear power plant. It has
been built at Tarapur 60 miles north of Bombay with American collaboration. It has
two boiling water reactors each of 200 mW capacity and uses enriched uranium as
its fuel. It supplies power to Gujarat and Maharashtra.
(ii) Rana Pratap Sagar (Rajasthan) Nuclear Station. It has been built at 42 miles
south west of Kota in Rajasthan with Canadian collaboration. It has two reactors
each of 200 mW capacity and uses natural uranium in the form of oxide as fuel and
heavy water as moderator.
(iii) Kalpakkam Nuclear Power Station. It is the third nuclear power station in
India and is being built at about 40 miles from Madras City. It will be wholly
designed and constructed by Indian scientists and engineers. It has two fast
reactors each of 235 mW capacity and will use natural uranium as its fuel.
(iv) Narora Nuclear Power Station. It is India’s fourth nuclear power station and is
being built at Narora in Bullandshahar District of Uttar Pradesh. This plant will
initially have two units of 235 mW each and provision has been made to expand its
capacity of 500 mW. It is expected to be completed by 1991.
(v) Kakarpar Nuclear Power Plant. This fifth nuclear power plant of India is to be
located at Kakarpar near Surat in Gujarat. This power station will have four reactors
each of 235 mW capacity.
 Advantages of Nuclear power plant

1. Space requirement of a nuclear power plant is less as compared to

other conventional power plants are of equal size.
2. A nuclear power plant consumes very small quantity of fuel. Thus fuel
transportation cost is less and large fuel storage facilities are not needed.
Further the nuclear power plants will conserve the fossil fuels (coal, oil,
gas etc.) for other energy need.
3. There is increased reliability of operation.
4. Nuclear power plants are not effected by adverse weather conditions.
5. Nuclear power plants are well suited to meet large power demands.
They give better performance at higher load factors (80 to 90%).
6. Materials expenditure on metal structures, piping, storage mechanisms
are much lower for a nuclear power plant than a coal burning power
plant.
7. It does not require large quantity of water.

Disadvantages of Nuclear power plant

1. Initial cost of nuclear power plant is higher as compared to hydro or
steam power plant.
2. Nuclear power plants are not well suited for varying load conditions.
3. Radioactive wastes if not disposed carefully may have bad effect on
the health of workers and other population. In a nuclear power plant the
major problem faced is the disposal of highly radioactive waste in form of
liquid, solid and gas without any injury to the atmosphere. The
preservation of waste for a long time creates lot of difficulties and
requires huge capital.
4. Maintenance cost of the plant is high.
5. It requires trained personnel to handle nuclear power plants.
 Comparison of Nuclear power plant with
steam power plant
(i) The number of workman required for the operation of nuclear power plant is much less
than a steam power plant. This reduces the cost of operation.
(ii) The capital cost of nuclear power plant falls sharply if the size of plant is increased. The
capital cost as structural materials, piping, storage mechanism etc. much less in nuclear
power plant than similar expenditure of steam power plant. However, the expenditure of
nuclear reactor and building complex is much higher.
(iii) The cost of power generation by nuclear power plant becomes competitive with cost of
steam power plant above the unit size of about 500 mW.

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Charan boiler

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Working Principle of Babcock and Wilcox Boiler

Coal is introduced into the grate through the fire door and ignited, causing the
resulting hot exhaust gases to rise and flow across the left side of the water tubes.
Baffles strategically guide these flue gases in a zig-zag pattern over the water
tubes and the superheater. Eventually, the exhaust gases exit through the
chimney.
The section of water tubes situated just above the furnace experiences a higher
temperature than the rest. Water ascends into the drum through the uptake
header, where both steam and water are evenly distributed. Being lighter, steam
collects in the drum's upper region, while water from the drum descends through
the down header into the water tubes.
This continuous movement of water from the drum to the water tubes, and vice
versa, is sustained by convective currents, commonly referred to as "natural
circulation." Steam is drawn from the steam space through tubes leading to the
superheater, where it undergoes further heating.
For the secure operation of the boiler, essential fittings and devices are
incorporated. On the left end of the boiler, you will find the water level indicator
and pressure gauge. The stop and steam safety valves are positioned on the
upper side of the drum, ensuring safety. Additionally, a blow-off cock is provided to
remove accumulated mud and sediment from the mud box periodically.
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A LaMont boiler is a type of forced circulation water-tube boiler

in which the boiler water is circulated through an external pump
through long closely spaced tubes of small diameter. The
mechanical pump is employed in order to have an adequate
and positive circulation in steam and hot water boilers.

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The primary importance of a heat
engine is to produce mechanical
energy with the help of heat energy.
There are two primary
classifications of heat engines.

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Internal Combustion Engine As the name suggests, the burning of fuel,

commonly known as combustion, occurs inside the system. It is commonly
known as IC engines. An IC engine is a type of heat engine that uses working
fuel such as petrol and diesel as a heat energy source. The working principle is
that it produces work by burning fuel and creating a high-pressure
environment. This high pressure is then used to run a turbine or a piston, which
converts the heat energy to mechanical energy. The internal combustion engine
is classified into three major types, and they are as follows.

Petrol engine or Spark-ignition engine: The basic principle is that a piston is

moved up and down by burning the fuel using a spark.
Diesel engine or Compression ignition engine: It has the same principle as
the spark-ignition engine. The only difference is that the fuel (diesel) is made
to combust by producing high pressure. It is commonly used in heavy-duty
vehicles.
Gas turbines: It uses steam as a medium to produce mechanical energy
instead of fuel. Gas turbines have high power output, but it also requires a lot
of space as the engines are massive.
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The Advantages of IC Engines

❑ It requires a low initial cost.

❑ It has better mechanical simplicity.
❑ It can produce higher power output per unit weight of the fuel.
❑ These units are very compact and require less space.
❑ It has a better brake thermal efficiency, as only a small amount of
thermal energy is lost.
❑ It is easy starting from cold conditions.

The Disadvantage of IC Engines

❑ It cannot use solid fuels such as coal which are far cheaper than
petrol or diesel.
❑ The IC engines have a lot of moving parts; therefore, it requires a
lot of maintenance
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Internal Combustion Engines (I.C. Engines)

In this case, combustion of the fuel with oxygen of the air
occurs within the cylinder of the engine. The internal
combustion engines group includes engines employing
mixtures of combustible gases and air, known as gas engines,
those using lighter liquid fuel or spirit known as petrol engines
and those using heavier liquid fuels, known as oil compression
ignition or diesel engines.

Internal combustion engines may be classified as given below :

1. According to cycle of operation:
(i) Two-stroke cycle engines (ii) Four-stroke cycle engines.
2. According to method of ignition :
(i) Spark ignition (S.I.) engine(ii) Compression ignition (C.I.)
engine.

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BASIC ENGINE COMPONENTS

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THE WORKING PRINCIPLE OF ENGINES

The credit of inventing the spark-ignition engine goes to
Nicolaus A. Otto (1876) whereas compression-ignition engine
was invented by Rudolf Diesel (1892). Therefore, they are
often referred to as Otto engine and Diesel engine.

In a four-stroke engine, the cycle of operations is completed in

four strokes of the piston or two revolutions of the crankshaft.
During the four strokes, there are five events to be completed,
viz., suction, compression, combustion, expansion and
exhaust. Each stroke consists of 180° of crankshaft rotation
and hence a four-stroke cycle is completed through 720° of
crank rotation.

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Four-Stroke Spark-Ignition Engine

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Four-Stroke Compression-Ignition Engine

The four-stroke CI engine is similar to the four-stroke SI engine
but it operates at a much higher compression ratio. The
compression ratio of an SI engine is between 6 and 10 while
for a CI engine it is from 16 to 20. In the CI engine during
suction stroke, air, instead of a fuel-air mixture, is inducted.
Due to higher compression ratios employed, the temperature
at the end of the compression stroke is sufficiently high to self
ignite the fuel which is injected into the combustion chamber.
In CI engines, a high pressure fuel pump and an injector are
provided to inject the fuel into the combustion chamber. The
carburetor and ignition system necessary in the SI engine are
not required in the CI engine. The ideal sequence of
operations for the four-stroke CI engine as shown in Fig.

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Otto Cycle Diesel Cycle

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Refrigeration
Refrigeration is the science of producing and
maintaining temperatures below that of the surrounding
atmosphere. This means the removing of heat from a
substance to be cooled. Heat always passes downhill, from a
warm body to a cooler one, until both bodies are at the same
temperature. Maintaining perishables at their required
temperatures is done by refrigeration. Not only perishables
but today many human work spaces in offices and factory
buildings are air-conditioned and a refrigeration unit is the
heart of the system.

In simple, refrigeration means the cooling of or removal

of heat from a system. The equipment employed to
maintain the system at a low temperature is termed as
refrigerating system
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Important refrigeration applications:

1. Ice making
2. Transportation of foods above and below freezing
3. Industrial air-conditioning
4. Comfort air-conditioning
5. Chemical and related industries
6. Medical and surgical aids
7. Processing food products and beverages
8. Oil refining and synthetic rubber manufacturing
9. Manufacturing and treatment of metals
Types of refrigeration Systems
The various refrigeration systems may be enumerated as below:
1. Ice refrigeration
2. Air refrigeration system
3. Vapour compression refrigeration system
4. Vapour absorption refrigeration system
5. Special refrigeration systems
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VAPOUR COMPRESSION REFRIGERATION SYSTEM
In a simple vapour compression system fundamental processes are
completed in one cycle.
These are :
1. Compression
2. Condensation
3. Expansion
4. Vaporisation

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The flow diagram of such a cycle is

shown in Fig. 1.The vapour at low
temperature and pressure (state ‘1‘)
enters the “compressor” where it is
compressed isentropically and
subsequently its temperature and
pressure increase considerably (state
‘2‘). This vapour after leaving the
compressor enters the “condenser”
where it is condensed into high
pressure liquid (state ‘3‘) and is
collected in a “receiver tank”. From
receiver tank it passes through the
“expansion valve”, here it is throttled
down to a lower pressure and has a
low temperature (state ‘4‘). After
finding its way through “expansion
valve” it finally passes on to
“evaporator” where it extracts heat
from the surroundings or circulating
fluid being refrigerated and vaporizes
to low pressure vapor (state ‘1‘).
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Co-efficient of Performance (C.O.P.)
The performance of a refrigeration system is expressed by a term
known as the “co-efficient of performance‘‘, which is defined as the
ratio of heat absorbed by the refrigerant (Rn) while passing through
the evaporator to the work input (W) required to compress the
refrigerant in the compressor ; in short it is the ratio between heat
extracted and work done (in heat units). C.O.P. = Rn/W
Air-conditioning:
“Air-conditioning” is the simultaneous control of
temperature, humidity, motion and purity of the
atmosphere in confined space. Thus the important factors
which are involved in a complete air-conditioning installation
are (i) Temperature control;(ii) Humidity control ;(iii) Air
movement and circulation and (iv) Air filtering, cleaning and
purification. Complete air conditioning provides simultaneous
control of these factors for both summer and winter.
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An air-conditioning system is defined as an assembly of

different parts of the system used to produce a specified
condition of air within a required space or building.

The basic elements of air-conditioning systems (of

whatever form) are:

1. Fans for moving air.

2. Filters for cleaning air, either fresh, recirculated or both.
3. Refrigerating plant connected to heat exchange surface,
such as finned coils or chilled water sprays.
4. Means for warming the air, such as hot water or steam
heated coils or electrical elements.
5. Means for humidification; and or dehumidification.
6. Control system to regulate automatically the amount of
cooling or warming.
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Summer air conditioning systems
This involves cooling of air, removal of excess moisture,
removing the pollutants, dust and introducing fresh air to dilute
the odours and the carbon dioxide level. Cooling is done by a
refrigeration system and the removal of moisture is also done
by the cooling coil. In extreme cases, dehydration by silica gel
or other chemicals may be required.

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