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. 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. 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. 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. 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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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. Winter air conditioning system
These systems are used to heat the air and
increase the humidity to acceptable levels.
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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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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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14. Essentials of air conditioning systems
Temperature control
Effective temp = 200C to 230C in summer
Effective Temp = 180C to 220C in winter
For Indian conditions 250C with 60%
relative humidity to 300C with 45 % relative
humidity, with air velocity not exceeding
10 m/min
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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. Air velocity control
High velocity of conditioned air
may cause greater temperature
difference between outside and
inside.
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17. Air quality control
Air should be free from
odour, toxic gases, bacteria
and other micro-organisms
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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. 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. 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. 3. Cooling (in summer)
Cooling
of incoming air is
necessary in summer.
Principle of mechanical refrigeration
is used.
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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. 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. 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. 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. 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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