Air conditioning refers to the cooling of indoor spaces for comfort during hot and humid days. The term can also be used for cooling, ventilation, heating which modifies the temperature of air inside. Air conditioners are appliances or systems used to maintain the temperature and humidity of an area using a refrigeration cycle. Conditioning can be either cooling or heating depending on the existing temperature and the desired one. Air conditioning is mostly used for cooling buildings and transportation vehicles. Huge conditioners called chillers are used for large scale manufacturing units and industries.



Romans in olden days used water through the walls of houses to cool them. As water was scarce then, only the wealthy afforded them. Persians used wind towers and cisterns to cool buildings during dry and hot seasons. Cisterns are large open pools in court yards. Michael Faraday, a British inventor discovered that compression of ammonia could cool air when it is allowed to evaporate, in the year1820. John Gorrie in 1842 used compressor system to create ice which he used to provide cool air for his patients. He was granted a patent in 1851 though his machinery performed abnormally. After his death, his vision of air conditioning went under the wraps for 50 years. The first modern electrical air conditioner was invented by Willis Haviland Carrier in the year 1902. His machine not only lowered temperature but also humidity. Later Carrier formed The Carrier Air Conditioning Company of America to increase productivity in the work places. Later it was used in homes and automobiles also. An American, Cramer coined the term ?air conditioning? to combine moisture with ventilation to condition the air in his factory so that he can control the humidity needed in textile plants. Carrier adopted the term and used it in his company. This process of evaporating water into air to provide a cooling effect is called evaporative cooling.

There are two different types of applications of conditioners namely process applications and comfort applications. Comfort applications provide conditioning for indoor environments which remain constant as desired by humans irrespective of the climatic changes outside. Research states that highest performance can be exhibited by a person seated in an office at around 22 ?C. SO in order to maintain the temperature, conditioners have become a must now a days. Conditioners are typically used in Commercial buildings, Industrial spaces, High and low-rise residential buildings, Institutional buildings like schools, colleges, hospitals and universities. Air conditioners are also used in vehicles like trains, cabs, ships, and aircrafts.

Process applications try to provide an apt environment for a process to be carried out, regardless of the internal heat, external weather conditions and humidity. Here it is not the desire of the humans, but the demand of the process that has to be given preference. Typical areas like Hospital operating theatres where air is supposed to be maintained at a certain level to reduce the risk of infection (operations such as an open heart surgery need a temperature of 18 ?C), Facilities for the breeding of laboratory animals, clean rooms for the production of pharmaceuticals and integrated electronic circuits, aircraft air conditioning (due to low pressure area outside the craft), Nuclear facilities, Farms and Plant growing areas, Data processing centers, Chemical and biological labs, Mines, Food processing units, Industrial areas and other significant places. It is not only the comfort, but also the humidity, air motion, air pressure, air quality that determines the cooling effect required.

Air conditioning systems usually lower the air humidity of the area. The relatively colder evaporator coil condenses vapor from the processed air, there by sending water to a drain and removing vapor from the cooled area and lowering the relative humidity of the space. A comfort conditioner is designed to provide 40 to 60% humidity in the present space. Some conditioners dry the air without cooling it and are known as dehumidifiers. A heat exchanger is placed between the exhaust and the intake in these systems. These dehumidifiers are energy efficient since they consume about one third of electricity compared to a normal air conditioner.