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Refrigeration and Air Conditioning |
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Refrigeration : It is a combination of mechanical equipment wherein a refrigerant is circulated for cooling or
extracting heat from spaces or bodies. Compression system is more popular than absorption system.
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Refrigeration Effect : The cooling effect which is produced by a machine.
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Coefficient of Performance : The ratio of the heat energy extracted by the
heat engine at the low temperature to the work supplied to operate the cycle.
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Capacity of a Refrigerating Machine : A machine having capacity to produce cooling effect of 50 kcal/min is said
to have one ton capacity of refrigeration.
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Refrigerants : The heat carrying medium which is used in a refrigerating system. An ideal refrigerant should
liberate all the heat which it is capable of absorbing.
- Primary Refrigerants : Those refrigerants which cool the substances by absorption of latent heat. These are
used in vapor compression systems. Such as, Ammonia, Carbondioxide, Sulphur dioxide, Methyl chloride, Methylene
chloride and fluorinated hydrocarbons.
- Secondary Refrigerants : Those refrigerants which cool substances by absorbing their sensible beat. Such as, air,
water, calcium chloride brine, sodium chloride, brine, glycol etc.
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Psychometry : It is the branch of science which deals with the study of the mixture of dry air and water vapor.
In air conditioning estimations air is taken as a mixture of dry air and water vapor.
The principles of psychometry apply to any physical system consisting of gas-vapor mixtures.
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Moist Air : The mixture of dry air and water vapor. The quantity of water vapor present in air is known as
moisture.
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Saturated Air : When moist air contains maximum amount of water vapor that it can hold, it is called saturated
air.
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Unsaturated Air : Moist air which is not saturated.
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Humidity Ratio : The weight of water vapor per unit weight of dry air in a vapor air mixture. It is also called
Specific Humidity.
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Degree of Saturation : The ratio of the prevailing humidity ratio of moist air to the humidity ratio of
saturated air at the same temperature and pressure.
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Relative Humidity : The ratio of actual weight of water vapor in a given volume to the weight of water vapor
contained in the same volume at the same temperature when the air is saturated.
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Dry-bulb Temperature : The temperature which is recorded by a thermometer whose reading is not affected by the
humidity ratio or by thermal radiation.
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Wet-bulb Temperature : The temperature which is recorded by a thermometer when its bulb is covered with wet
cloth and is exposed to a current of moving air. The difference between dry-bulb temperature and wet-bulb temperature
is known as wet-bulb depression.
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Dew Point Temperature : The saturation temperature which corresponds to the existing humidity ratio and
barometric pressure. Generally dew point temperature is taken to be the temperature at which condensation will just
begin when the moist air mixture under consideration is cooled at constant pressure.
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Psychometric Chart : The graphical representation of various thermodynamic properties of moist air. In this
abscissa represents dry bulb temperature and ordinate represents specific humidity.
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Psychometric Processes : The various processes which are involved in air conditioning to change the psychometric
properties of air according to requirement.
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British Thermal Unit (BTU) : The unit of heat energy and equals to the heat required to raise the temperature
of 1 lb of water by one degree Fahrenheit. It is used in the power, steam generation, heating and air conditioning
industries.
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Bypass Factor : The inefficiency of the heating coil or cooling coil in not being able to heat or cool the
incoming air to the temperature of cooling coil.
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Sensible Heat Factor : The ratio of space sensible heat to space total heat. It is used for air-conditioning
calculations.
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Grand Sensible Heat Factor : The ratio of total sensible heat to the grand total which the cooling coil should
handle.
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Effective Surface Temperature : The assumed uniform surface temperature of heating/cooling coil which would
produce same conditions of leaving the coil as the actual non-uniform surface temperature of the coil varying
through-out as air passes over it.
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Humidifying Efficiency : The air from spray wash will come out at 100% relative humidity, the extent to which
humidification is affected depending on the velocity of air and the depth of showers etc.
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Air Conditioning : Simultaneous control and purification to suit specific requirement of conditioned space. For
human comfort the temperature requirement is around 20oC and relative humidity 60%.
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Cooling Loads : The total quantity of heat which is required to be pumped out from the space to be kept at the
desired level of temperature by the refrigerating equipment. The total load determines the size of plant needed.
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Insulating Materials : These are used to minimize heat conduction through structures. These are bad conductors
of heat. Even air is not a good conductor of heat. Commonly used insulating materials are Cork board, Foamable
Polystyrene, Thermocole, Glass wool, Hair felts, Celotex etc.
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