Fig 9.1 Content of this post 
Air conditioning:

It is the process in which temperature, humidity(moisture content), air motion, purity etc. of air in an enclosed space is controlled.As per discussed above there are 4 important factors in air conditioning:
1. Temperature
2. humidity
3. purity
4. Air motion
Air conditioning required for two aspects;
1. Human comfort
2. Industrial air conditioning
Objectives of air conditioning:
1. To produce healthy conditions and comfort for people in houses, theaters, offices, hospitals, railways, aeroplanes,cars and buses etc.
2. In factories to increase efficiency of workers air conditioning is very important.
3. In industries air conditioning is required for manufacturing process such as textile industry,Drug Company, printing industry, computers etc. This type of air conditioning is called industrial air conditioning.

Factors in air conditioning:
Air conditioning provides complete automatic control of below given factors for all types of outdoor conditions.
1. Remove the dirt,dust, soat, germs etc
2. Control the temperature cool in summer and hot in winter.
3.Decrease the humidity in summer and increase the humidity in winter.
4. To evenly distribute the air conditioning air for pleasure of people.
5.Ozonet or ionized to eliminate bad smell.


Terminology/Nomenclature:

1. Water vapour: it is the moisture content in the air. 
2. Saturated and superheated water vapour: The maximum water vapour contained in the air is called saturated water vapour and corresponding temperature is called saturation temperature. 
If the temperature of air and water mixture is higher than saturation temperature then the vapour is called superheated vapour. 
3. Partial pressure: the mixture of air and water when is constituent occupies the total volume then constitution constituent will give some pressure which is called partial pressure of that constituent. 
4. Air or moist air: dry air along with water vapour is known as air or moist air. The water vapour present along with dry air in superheated state but very low pressure. 
5. Dry air : it is the only mixture of dry gases like nitrogen, Oxygen, carbon dioxide Helium, neon etc. 
6. Dry bulb temperature: it is the temperature recorded by ordinary thermometer when its bulb is exposed to surrounding. 
7. Wet bulb temperature: it is the temperature of air measured by ordinary thermometer when its bulb is wrappd by Porus wet cloth and one end of cloth is emerged in the bottle which is located below the bulb and always filled with water. Due to evaporation wet bulb temperature is always lower than dry bulb temperature. By knowing dry bulb temperature and wet bulb temperature relative humidity can be calculated. The difference between dry bulb temperature and wet bulb temperature is called wet bulb depression.
8.Psychrometer :
It is a device or instrument used to measure the psychometric properties of the air. The psychrometer consist of two thermometer as shown in figure.
This two thermometers are mounted on same stand if provision is made to rotate the the psychrometer it is called sling type psychrometer.
It is used to measure dry bulb temperature and wet bulb temperature.
For correct measurement of wet bulb temperature rotate the psycho metre in the air by keeping handle in hand for a minute. we get accurate wet bulb temperature.
9.Degree of saturation:
It is the ratio of mass of water vapour in unit mass of air at pressure P1 and temperature T1 to the the mass of water vapour in unit mass of air at temperature T1 and pressure P1 but the air is in saturated condition.
10.Humidity/humidity ratio/specific humidity:
It is the mass of water vapour present along with 1 kg of dry air.
11.Absolute humidity:
Mass of water vapour present along with 1 m3(metre cube) of dry air.
12.Relative humidity:
It is the ratio of mass of water vapour in a given volume, at pressure P1 and temperature T1 to the the mass of water vapour in the same volume and at same temperature T1 and pressure P1, when air is in saturated condition.It is always expressed in %.