Air conditioning means the cooling of indoor air for thermal comfort. It refers in a broader sense; any form of cooling, heating, ventilation, or disinfection that modifies the condition of air. Any appliance, system, or machine that is designed to stabilize the air temperature and humidity within an area (used for cooling as well as heating depending on the air properties at a given time), is referred to as an air conditioner. Typically this uses a refrigeration cycle but sometimes evaporation, which is commonly for comfort cooling in buildings and motor vehicles.
Modern air conditioning emerged from advances in chemistry during the 19th century, and it was recorded that the first large-scale electrical air conditioning was invented and used in 1902 by Willis Haviland Carrier in Buffalo, New York. The first air conditioners and refrigerators employed toxic or flammable gases like ammonia, methyl chloride, and propane which could result in fatal accidents when they leaked.
Air conditioning is broadly divides to comfort and process applications. In Comfort Applications it aims to provide a building indoor environment that remains relatively constant in a range preferred by humans despite changes in external weather conditions or in internal heat loads, whereas in Process Applications it aims at providing a suitable environment for a process being carried out, regardless of internal heat and humidity loads and external weather conditions. In addition to buildings, air conditioning can be used for many types of transportation – motor-cars and other land vehicles, trains, ships, aircraft, and spacecraft. Although often in the comfort range, it is the needs of the process that determine conditions, not human preference. In both comfort and process applications, the objective may be to not only control temperature, but also humidity, air quality and air movement from space to space.
Though built for man’s comfort, air conditioning can constitute air pollution. Air pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or damages the natural environment into the atmosphere. Since the atmosphere is a complex dynamic natural gaseous system that is essential to support life on planet Earth, its pollution will drastically affect human health as well as the Earth‘s ecosystems.
Since chronic, low-level exposure to various chemicals, e.g., lead exposure – even at relatively low levels – may result in a number of adverse outcomes, continuous exposure to air conditioning appliances can have severe effects, such as anaemia, malaise, and damage to the nervous system. Children are particularly vulnerable to the neurotoxic effects of lead. Relatively low levels of exposure can reduce their IQ scores, cause learning disabilities, poor school performance, and violent behaviour, all of which may contribute to reduced lifetime earnings.
Apart from the problem of stratospheric ozone depletion, indoor air pollution and urban air quality are listed as the world’s worst pollution problems in the 2008 Blacksmith Institute World’s Worst Polluted Places report. Though atmospheric pollution can be caused by other combustible materials such as open burning of refuse, old tyres, old vehicles, exhaust pipes of engines and other locomotives which pollute the environment, yet pollution from air conditioners are very dangerous. Prevention of atmospheric pollution is very important because a lot of diseases like respiratory tract infections can occur from them and the major constituent of these gases which is carbon-monoxide can prevent the free flow of blood in the body by impairing the oxygen carrying capacity of the hemoglobin. A poorly maintained air-conditioning system can occasionally promote the growth and spread of microorganisms, the infectious agent responsible for Legionnaires’ disease, but as long as the air conditioner is kept clean these health hazards can be avoided.
Conversely, air conditioning, including filtration, humidification, cooling, disinfection, etc., can be used to provide a clean, safe, hypoallergenic atmosphere in hospital operating rooms and other environments where an appropriate atmosphere is critical to patient safety and well-being. Air conditioning can have a positive effect on sufferers of allergies and asthma. In serious heat waves, air conditioning can save the lives of the elderly. Some local authorities have even set up public cooling centers for people without home air conditioning.