REFRIGERATION AND AIR
CONDITIONING SYSTEM
AIRCONDITIONING
• Air-conditioning
Air conditioning may be defined as the simultaneous
control of temperature, humidity, motion and purity
of air within an enclosed space, irrespective of
external conditions.
Unit of Refrigeration / Air conditioning:
Ton of refrigeration is the term used to indicate the
capacity of the refrigeration and air conditioning system.
One Ton of Refrigeration is defined as the amount of
cooling produced by melting one ton of ice from and at
0oC in 24 hours.
• One Ton of Refrigeration= = 12,660 KJ/hr.
• One Ton of Refrigeration (1 TR) = 12,660 KJ/hr.
= 210 KJ/min.
= 3.5 KJ/sec. or KW.
Convert °F to °C
• Convert °F to °C. Use the following formula:
• °C = 5/9 (°F−32)
• EXAMPLE:
• Convert °C to °F. Use the following formula:
• °F = 9/5 (°C) + 32
Types of Air conditioning
• According to the purpose
Comfort air conditioning
Industrial air conditioning
According to the season of year
Winter air conditioning
Summer air conditioning
Year round air conditioning
According to the equipment arrangement
unitary system
Central air conditioning system
Difference between Comfort and industrial air conditioning
Sl.N Comfort air conditioning Industrial air conditioning
o
1 The main object of this to The main object of this to
produce comfortable and provide a suitable
healthy conditions for human atmosphere for a specific
beings industrial process
2 This is adopted for small This is applied to photo
cabins, office hall or big halls film industries, tool rooms,
like cinema theaters, electronic industries,
automobiles, trains, hotels textile mills, computer
etc. industries etc.
PSYCHROMETRY
Psychrometry is the branch of science
which deals with the study of the mixture
of dry air and water vapour.
• Psychrometer
– It is an Instrument to measure the
properties of air. Psychrometer has two
thermometres. One is wet bulb and the
other is dry bulb thermometer.
PSYCHROMETRY
• Psychometric Terms
• Dry air
It is the mixture of oxygen, Nitrogen, argon, corbon di oxide
and traces of other gases in atmospheric air excluding water
vapor. It is generally considered as a mixture of nitrogen (77 % by
wt.) and oxygen (23 % by wt).
• Moist air
• It is a mixture of dry air and water vapor
• Saturated air
• When the air contains the maximum amount of water vapor
that it can hold at that particular temperature, then it is called
saturated air. For saturated air , all the three temperatures i.e.
dry, wet, dew point temperatures have same value.
Dry bulb temperature (DBT)
Dry bulb temperature (DBT) is the temperature of the moist air
as measured by a standard thermometer or other temperature
measuring instruments.
Wet bulb temperature (WBT)
The temperature recorded by a thermometer when its bulb is
covered with wet cloth and exposed to a current of air moving with
a velocity of 270 m/min is known as Dry bulb temperature (DBT)
Dew point temperature (DPT)
Dew-point temperature: If unsaturated moist air is cooled at
constant pressure, then the temperature at which the moisture in
the air begins to condense is known as dew-point temperature (DPT)
of air. An approximate equation for dew-point temperature is given
by:
DPT = 4030(DBT+235) _ 235
4030-(DBT+235) Inφ
• where Φ is the relative humidity
Wet Bulb Depression
The difference between the dry bulb temperature and wet bulb
temperature is called wet bulb depression.
Relative humidity (Φ)
It is defined as the ratio of the mass of water vapour in a given
volume of moist air to masss of water vapour in same volume of
saturated air at the same temperature and pressure.
Specific humidity or Humidity ratio (w)
It is the mass of water vapour present in 1 kg of dry air. It is
generally expressed in term of kg per kg of dry air
W= mv/ma
W= .622 x pv
Pb-pv
Pv = partial pressure of water vapour
Pb = barometric pressure
Degree of saturation or Saturation ratio (µ)
It is the ratio of specific humidity of moist air
to the specific humidity of saturated air at same
temperature.
Enthalpy of moist air (h)
Total enthalpy of moist air is the sum of the
enthalpy of dry air and enthalpy of water vapour
associated with dry air.
H = Cp td+ w hg
• Dew point depression. It is the difference
between the dry bulb and dew point
• temperatures (tdb – tdp).
• Daltons Law
– The total pressure exerted by air and water vapour
mixture is equal to barometric pressure
Pb = Pa + Pv
PSYCHROMETRIC CHART
PSYCHROMETRIC CHART
• A Pychrometric chart is
a graphical
representation of the
various thermodynamic
properties of moist air
Psychrometic processes
• PSYCHROMETRIC PROCESSES
• 1. Mixing of air streams
• 2. Sensible heating
• 3. Sensible cooling
• 4. Humidification
• 5. De humidification
• 4. Cooling and dehumidification
• 5. Heating and humidification
SENSIBLE COOLING
• Sensible cooling is cooling of air without any change
in its specific humidity.
• The cooling is done by passing the air over cooling
coil of tubes such as evaporative coil of the
refrigeration cycle.
• Cooling of air decreases the dry bulb temperature
and decreases the enthalpy.
SENSIBLE COOLING
SENSIBLE HEATING
• Sensible heating is heating of air without any
change in specific humidity.
• The heating is done by passing the air over a
heating coil of tubes such as electrical heating
or steam.
• The heating of air rises the dry bulb
temperature and increases the enthalpy.
SENSIBLE HEATING
BY PASS FACTOR
BY PASS FACTOR
• Heating coil
• The temperature of coming out of the
apparatus td2 will be less than the
temperature of heating coil
• Cooling coil
• The temperature of coming out of the
apparatus td2 will be more than the
temperature of cooling coil
• Let 1 kg of air be in inlet point and x kg of air to be by pass
unaffected and (1-x) kg of air is direct contact with the coil.
• This By pass process of air is measured in terms of by pass
factor.
• BPF = td3-td2 for heating coil
td3-td1
BPF = td2-td3 for cooling coil
td1-td3
Where
td1 = temperature of inlet air
Td2 = Temperature of outlet air
Td3 = temperature of coil
HUMIDIFICATION AND DEHUMIDIFICATION
• Humidification
Addition of water vapour in the air is known as humidification.
• Dehumidification
Removel of water vapour in the air is known as
Dehumidification.
Sensible Heat factor
The ratio of sensible heat to total heat is known as Sensible
heat factor or Sensible heat ratio
SHF = Sensible heat = SH
Total heat SH+LH
SH= Sensible heat
LH= Latent heat
HEATING AND HUMIDIFICATION
HEATING AND HUMIDIFICATION
• This process is used in winter air conditionong to
heat and humidify the air. It is the reverse
process of cooling and de humidification.
• The air is passed through the humidifier.
• The spray water temperature is higher than the
dry bulb temperature of the entering air.
• Now the unsaturated air will reach saturated
condition. Thus the air becomes hot.
• The heat of vaporization of water is absorbed
from the spray water itself and hence its cooled.
In this way the air is heated and humidified.
COOLING AND DEHUMIDIFICATION
COOLING AND DEHUMIDIFICATION
• This process is generally used in summer air
conditioning to cool and dehumidified the air.
• To achieve this process a cooling coil is used.
• Its temperature is maintained below the dew
point temperature of entering air.
• When the air is passed over it the air is cooled
and condensation of moisture takes place.
• That the moisture is removed or dehumidified.
• Thus the cooling and dehumidification is
achieved.
Mixing of Air Streams
• When two quantities of air having different enthalpies and different
specific humidity are mixed the final condition of the air mixture
depends upon the masses involved and on the enthalpy and
specific humidity of the each constituent which enter the mixture.
M1 = mass of entering air 1
H1 = enthalpy of air entering 1
W1 = specfic humidity of air entering 1
Similarly
• M2, h2, w3 corresponding values of air entering 2
• M3, h3, w3 corresponding values of air mixture leaving 3
We know that
• Mass balance m1 + m2 = m3
• Mass balance of water vapour m1W1 + m2W2 = m3W3
• Energy balance m1h1 + m2h2 = m3h3
Mixing of Air Streams
Requirements of Comfort air conditioning
1. Temperature of air
The temperature of air should be controlled.
Temperature control means maintaining any desired
temperature within and enclosed space even though the
outside air is above or below the desired room
temperature.
The human being the comfortable temperature is 21C
with 56% relative humidity.
2. Motion of air
The circulation of air must be controlled to maintain
sufficient carbon di oxide and oxygen for human breathing
and keep constant temperature through out the
conditioned room.
Requirements of Comfort airconditioning
3. Humidity of air
The humidity should be controlled.
Humidity of air control means the increasing or decreasing of
moisture contents of air during summer or winter.
This is done in order to produce comfortable and healthy
conditions. This also increase the efficiency of workers.
For summer conditioning the relative humidity should not be less
than
60 %. Whereas for winter air conditioning it should not be more
than 40 %.
4. Purity of air
people do not feel comfort when breathing contaminated air.
So the air is supplied to conditioned room should be clean and
free from odour, dust, toxic gases and other impurities.
PSYCHROMETERS
• The psychrometers may be classified as
follows :
• 1. Laboratory psychrometer
• 2. Sling psychrometer
• 3. Aspirating psychrometer
• 4. Continuous recording psychrometer..
Sling psychrometer
Aspirating psychrometer
• The Aspirating
psychrometer is a
portable battery
powered and motor
aspirated
psychrometer. It has
many important
advantages over
conventional sling type
psychrometers.
HYGROMETER
• A hygrometer is described as an
instrument used to measure the
amount of moisture in the air. If a
moist wick is placed over a
thermometer bulb the evaporation
of moisture from the wick will lower
the thermometer reading
(temperature).
HUMIDITY CONTROL
• Hygroscopic elements such as strand of hair can
be used for humidity control. A simple
arrangement is shown in fig. elongation of hair
due to an increase in relative humidity results in a
clockwise turning of roller, moving lever to the
left. The movement of lever will operate a switch.
• Recently the hygroscopic nature of same salts,
(CaCl2, LiCl2) has also been used in humidity
control devices. Their electric resistance changes
with change in humidity.
HUMIDITY CONTROL
