1. Temperature of air: In air conditioning, the control of temperature means the maintenance of any desired temperature within an enclosed space even though the temperature of the outside air is above or below the desired room temperature. This is accomplished either by the addition or removal of heat from the enclosed space as and when demanded. It may be noted that a human being feels comfortable when the air is at 210C with 56% relative humidity. 2. Humidity of air: The control of humidity of air means the decreasing of increasing of moisture contents of air during summer or winter respectively in order to produce comfortable and healthy conditions. The control of humidity is not only necessary for human comfort but it also increases the efficiency of the workers. In general, for summer air conditioning the relative humidity should not be less than 60% whereas for winter air conditioning it should not be more than 40%. 3. Purity of air: It is an important factor for the comfort of a human body. It has been noticed that people do not feel comfortable when breathing contaminated air, even if it is within acceptable temperature and humidity ranges. It is thus obvious that proper filtration, cleaning and purification of air is essential to keep it free from dust and other impurities. 4. Motion of air: The motion or circulation of air is another important factor which should be controlled, in order to keep constant temperature throughout the conditioned space. It is therefore, necessary that there should be equi-distribution of air throughout the space to be air conditioned.