Introduction to Refrigeration,
In air refrigeration, the air is used as a refrigerant. In olden days, air was widely used in commercial applications because of its availability at free of cost. Since air does not change its phase i.e. remains gaseous throughout the cycle, therefore the heat carrying capacity per kg of air is very small as compared to vapour absorbing systems.
The air-cycle refrigeration systems, as originally designed and installed, are now practically obsolete because of their low coefficient of performance and high power requirements; however, this system continues to be favoured for air refrigeration because of the low weight and volume of the equipment.
Refrigeration essentially means continued abstraction of heat from a substance (perishable foods, drinks and medicines etc.) at low temperature level and then transfers this heat to another system at high potential of temperature.

The basic elements of an air cycle refrigeration system are as follows:
1. Compressor
2. Cooler or heat exchanger
3. Expander
4. Refrigerator

Introduction to Air- Conditioning,
The air conditioning is that branch of engineering science which deals with the study of conditioning of air i.e. supplying and maintaining desirable internal atmospheric condition for human comfort, irrespective of external condition. This subject, in its broad sense, also deals with the conditioning of air for industrial purpose, food processing, storage of food and other materials.
Air conditioning refers to the simultaneous control of temperature, humidity, cleanliness and air motion within a confined region or space.

The basic elements of an Air-Conditioning system are as follows:
1. Circulation fan
2. Compressor
3. Condenser
4. Dryer
5. Evaporator
6. Supply Duct
7. Supply outlet
8. Return outlet
9. Filters