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Jul 13, 2021






Air conditioning is the process of treating air so as to control simultaneously its temperature, humidity, purity and distribution to meet the requirements of the conditioned space, such as comfort and health of human beings and other needs of the situation.


a. To improve the quality of the products in industrial processes such as artificial silk and cotton cloth. In the case of other industries, it helps in providing comfortable working conditions for the workers, resulting in the increase of production.

b. In commercial premises such as theatres, offices, banks, shops and restaurants, air conditioning is done to improve the working the atmosphere and maintain comfort within these concerns.

c. To give comfort to the residents of private buildings. The air-conditioning system in this case serves a small number of persons.

d. In travel by air, railway, road and water, air conditioning imparts facility and comfort by conditioning the quality of air in aeroplanes, railway coaches, road cars, buses, ships, etc.


The principle involved in air conditioning is:

a. Sucking the air through a filtering media.

b. Cooling it (in summer) or heating it (in winter).

c. Dehumidifying, if it is to be cooled, or humidifying if it is to be heated.

d. Forcing it into the rooms for proper circulation.

e. The used air is collected through exhaust and mixed with some outside fresh air and sucked again through the filtering medium, thus completing the cycle.



Comfort feeling is a good indication of a healthy atmosphere and it depends upon the temperature, air motion or air velocity and humidity changes for different seasons of the year.

The principle of air conditioning should involve proper control of temperature, humidity and air velocity

a. Temperature control: Comfortable zone is the temperature range suitable for the majority of the people. The comfortable zones are different for summer and winter due to the clothing worn in these two seasons. The effective temperature zone for summer is 20–23°C and for winter is 18–22°C. A temperature of 21–25°C is required for comfort conditions regardless of the outside temperature.

b. Air velocity control: Air velocity control is also an important factor. The increase in velocity results in the decrease of inside effective temperature below the outside temperature. Therefore, the velocity of air is generally taken as 6–9 m/sec, which is considered as relatively still air.

c. Humidity control: Dry air imparts great strain on the human body. Due to this reason, moisture is added to the heated air (i.e., humidification) in case of winter air conditioning and moisture is extracted from the cooled air (i.e., dehumidification) in case of summer air conditioning. An average value of relative humidity between 40 per cent and 60 per cent is considered desirable. During the summer season 40–50 per cent is comfortable and for winter 50–60 per cent is suggested.



Depending on the location of air-conditioning equipment, the system of air conditioning is classified as follows:

a. Central system: In this system, all the equipment pertaining to air conditioning are installed at one focal or central point and then the conditioned air is distributed to all the rooms or enclosures by ducts. This type of system requires less space for installation and the maintenance is also easy. It proves to be economical. Due to the presence of ducts, it requires large space.

b. Self-contained or unit system: In this system, special portable attractive cabinets which fit in with the decoration of modern rooms are placed inside the room near the ceiling or window. They are self-contained in every respect and conditioned air is formed inside the unit itself. The conditioned air is then directly thrown into the room without the help of any ducts.

c. Semi-contained or unitary central system: In this system, every room is provided with an air-conditioning unit and the room unit obtains its supply from the central system. Such a system results in a smaller size of ducts. Another form of this system is adopted in which conditioned air may be supplied from a central unit but for the heating or cooling maybe carried out in the room itself.

d. Combined system: A combined system may consist of

(i) central and self-contained system

(ii) central and semi-contained system and

(iii) self-contained and semi-contained system

The choice of a particular system of air conditioning depends upon several factors such as the size of the structure, method of heating, volume and type of air conditioning unit, period of the year for which air conditioning is required and a number of rooms to be served.

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