Air-conditioning primarily consists of refining air in order that it may be utilised to the best advantage of the user. The user may be human beings, materials, equipment, etc. Thus conditioned air would mean an atmosphere having controlled temperature, humidity and velocity condition with dust-free cleanliness to meet the requirement.
Purposes of Air-Conditioning
Air-conditioning of any building or space is adopted to satisfy one of the objects mentioned below.
1. Residential Buildings
For human beings living in residential buildings, the conditioned air is expected to give a better health or to preserve and maintain the health, comfort and convenience.
2. Industrial Premises
Industrial air-conditioning may be required to preserve the quality of industrial product and at the same time to create, control and maintain the working of different processes such as artificial silk, cotton cloth or preservation of fruits, etc.
3. Commercial Premises
Commercial premises such as theatres, offices, banks, restaurants, shops, stores, etc., are air-conditioned to improve their working conditions and to maintain comfort within the concerns.
4. Transport Vehicles
Air-conditioning plays an important role in providing facility and comfort in transport vehicles such as aeroplanes, railway coaches, road-cars, buses, ships, etc.
28.2.2 Terminologies
Following terminologies are used in air-conditioning:
1. Psychometrics
It is the branch of science that deals with the study of mixture of dry air and water vapour and is also the subject connected with the study of the behaviour of moist air.
2. Dry Air
It is a mechanical mixture of gases comprising of oxygen, nitrogen, carbon-dioxide, hydrogen, argon, neon, helium, ozone and xenon. In nature, a complete dry air does not exist but some quantity of water vapour is diffused in it.
3. Moist Air
It is the mixture of dry air and water vapour.
4. Dry Bulb Temperature
Temperature of air recorded by an ordinary thermometer is known as dry bulb temperature.
5. Wet Bulb Temperature
Temperature recorded by a mercury thermometer when its bulb is covered with a wet cloth and is exposed to a current of moving air at a velocity of 300 ml min is known is wet bulb temperature.
6. Due Point Temperature
Temperature at which liquid droplets just appear when the moist air is cooled continuously is known as dew point temperature.
7. Relative Humidity
It is the ratio of partial pressure of water vapour to the partial pressure of saturated water vapour at that temperature or the ratio of mass of water vapour to the mass of saturated water vapour.
8. Specific Humidity
It is the ratio of mass of water vapour to the mass of dry air in a given volume of the mixture.
9. Degree of Saturation
It is the ratio of prevailing specific humidity to the saturated specific humidity. Degree of saturation is a measure of the capacity of air to absorb moisture.
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