Basic Mechanical Engineering - Air conditioning

1. Prepared by
M.S.Steve
Assistant Professor
Dept. of Mechanical Engineering
Amal Jyothi College of Engineering
Kanjirapally.

Air conditioning
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2. Page 2
Definition
Process of treating the air so as to control simultaneously its
temperature, humidity, purity and distribution to meet the
requirements of controlled space.

Requirements of a conditioned space

1.Comfort and health of occupants
2.Needs of certain industrial processes
3.Efficient working of commercial premises/offices

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3. Page 3
Air conditioning
For human comfort ,air should have the following
properties :
1. Temperature -22 °C to 27 °C
2. Humidity - 55% to 65% Relative Humidity
3. Velocity - 0.3 -0.5 m/s.

Air conditioning systems cool/heat the air,
humidify/dehumidify the air to the above human
comfort conditions depending on the temperature
and humidity of the outside atmospheric air.

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4. Page 4
Applications
Industrial applications- To control chemical & bio
chemical reactions .

Commercial applications- Theatres, hotels, banks
etc.

Transport applications – automobiles, aircrafts,ships
etc

Special applications – T .V centres , hospitals,
computer centres etc.
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5. Page 5
Classifications
Depending up on the processes required for conditioning of
outside air ,air conditioning system are classified in to :

1. Summer air conditioning- it involves Cooling &
Dehumidification process.
2. Winter air conditioning – it involves Heating &
Humidification process
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6. Page 6
Winter air conditioning
In winter outside temperature is low hence heating of air is
needed for comfort.
Cycle of operations consists of
1. Air cleaning
2.Air heating
3.Humidification
4.Air distribution/circulation

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7. Page 7 [email protected]

8. Page 8
Winter air conditioning system
The outside air is sucked in through the damper and is
filtered using an air filter.
The air is then passed through a preheat coil to heat the
air to control the evaporation of water in the humidifier.
Steam is mixed with the air in required quantity to
increase the humidity to 55% RH.
The air is then passed through a reheat coil to bring it to
the comfort temperature of 22 °C.
The conditioned air is then supplied to the conditioned
space by a blower.
Cold polluted air is discharged out and outside air is
again sucked to repeat the cycle.
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9. Page 9
Winter air conditioning system





These systems are used to heat the air and
increase the humidity to acceptable levels.
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10. Page 10
Summer air conditioning

 In summer outside temp is more and hence cooling of air is
required
Consists of
1.Air cleaning
2.Air cooling
3.Dehumidification
4.Air distribution/circulation

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11. Page 11 [email protected]

12. Page 12
Summer Air Conditioning
In this system air is cooled & dehumidified.
The outside air flows through the damper and is filtered
using the filter.
The air is then passed through a cooling coil and the air
gets cooled below the required temperature and is also
dehumidified.
The cooled air is then passed through the water
eliminator and water is collected in the sump.
After that air is made to pass through a heating coil to
reach the desired comfort condition.
The conditioned air is now supplied to the space using
the blower.


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13. Page 13
Summer Air Conditioning
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14. Page 14
Essentials of air conditioning systems
Temperature control
Effective temp = 20
0
C to 23
0
C in summer
Effective Temp = 18
0
C to 22
0
C in winter
For Indian conditions 25
0
C with 60%
relative humidity to 30
0
C with 45 % relative
humidity, with air velocity not exceeding
10 m/min

15. Page 15
 Humidity control
During summer dehumidification
is done so that relative humidity is
40 to 50%

During winter humidification is
done so that relative humidity is
50 to 60 %

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16. Page 16
Air velocity control
High velocity of conditioned air
may cause greater temperature
difference between outside and
inside.

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17. Page 17
Air quality control
Air should be free from
odour, toxic gases, bacteria
and other micro-organisms

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18. Page 18
Essentials of air conditioning systems
1.Filtration
2.Heating (in winter)
3.Cooling (in summer)
4.Humidification
5.Dehumidification
6.Air circulation or distribution

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19. Page 19
1.Filtration

Should be capable of removing dust, ash, smoke
,
bacteria etc
Should be capable of holding moderate amount of
dust without affecting the efficiency
Should offer low resistance to flow of air
Workable under sufficient range of velocities.
Should afford easy cleaning manually or
mechanically

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20. Page 20
2. Heating (in winter)

Heating is necessary in winter so as to
compensate heat loss from room.
Pre heating of incoming air may be done by
passing over air furnaces or coils through
which hot water is circulated
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21. Page 21
3. Cooling (in summer)

Cooling of incoming air is
necessary in summer.
Principle of mechanical refrigeration
is used.

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22. Page 22
4. Humidification

Humidification or addition of water is
necessary in winter because of low
temp has less humidity.
Incoming air is passed through pans of
water or wet cloth strips

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23. Page 23
5. Dehumidification

In this process certain amount of
water is extracted from air.
This is done in summer where
incoming air is cooled
.
Adsorbents can be used to adsorb
excess moisture from air .

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24. Page 24
Psychrometry
The properties of moist air are called as
pshychrometric properties .
Although the principles of pshychrometry
can be applied to any physical system
consisting of gas vapour mixtures,the most
common system of interest is the mixture of
water vapour & air.
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25. Page 25
Terms used in psychrometry
Dry Air : Dry air is a mixture of oxygen, nitrogen, carbon
dioxide, hydrogen, argon, neon ,helium etc.
Moist Air : It is an ordinary air, which is a mixture of dry
air and water vapour.
Saturated Air : It is the air which contains maximum
amount of water vapour which the air can hold at a given
temperature and pressure.
Relative Humidity (RH) : It is the ratio of mass of water
vapour in a given volume of moist air at a given
temperature to the mass of water vapour contained in the
same volume of moist air at the same temperature when
the air is saturated.
Dry Bulb Temperature (DBT) : It is the temperature of air
measured by an ordinary thermometer.
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26. Page 26
Terms used in psychrometry

Wet Bulb Temperature (WBT) : It is the temperature
recorded by a thermometer, when its bulb is covered by a
wet cloth and is exposed to a current of moving air.
Dew Point Temperature (DPT) : It is the temperature at
which the condensation of moisture begins when the air
is cooled at constant pressure.
Sensible Heat of Air : It is the enthalpy of dry air, which
can be calculated by measuring its dry bulb temperature.
Total Heat : It is the sum of sensible heat of dry air and
sensible plus latent heat of water vapour present in it.


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27. Page 27
Psychrometric chart

28. Thank You
M S Steve
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@msstevesimon

2m.s.steve
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