The principal mechanism of Adiabatic Air Conditioning (AAC) is to produce cool air by adiabatic saturation process that reduces the air temperature as moisture is absorbed. It is evaporative-type humidifiers one of which that uses a spray of water. The system pumps water from a collection basin under the sprayer and sprays water over a sprayer in the air stream. (Nelson, G., 2000)

          Adiabatic expansion, in thermodynamic, is any physical process in which quantities such as pressure and volume are varied without any significant of heat energy to or from the surrounding. The process happens too quickly for the last heat to be replaced from the surroundings, hence the drop in temperature. (Microsoft Encarta Encyclopedia, 2001)

          Cooling & humidifying can be accomplished by spraying water into the air. Such a process is called adiabatic in as much as no heat is added or extracted. It is also known as evaporative cooling when an unsaturated stream of air is passed through a re-circulated water spray, water is evaporated: if the spray is adequate, the air will be saturated with no heat added in the process, the heat required to evaporate the water can only come from the air, thus reducing air temperature while increasing moisture content. (Canadian Building Digest, 1968)

          In documented tests of transit buses, AAC systems provide more cooling faster than refrigerant air conditioning systems. The cooling agent is water, there are no refrigerants, no compressors, no pressurized piping. Unitary AAC systems consist of a pump, blowers as a result it is simple and more reliable. (VehiCool, 1999)

          AAC technology has zero ozone depleting impact. Substituting water based AAC for refrigerant units. Unlike refrigerant air conditioning systems that re-circulate stale inside air, AAC systems supply fresh-filtered outside air. Water-based AAC is non-flammable and non-toxic, thus eliminating the need for recycling & recovery and safety concerns, training and liability associated with toxic refrigerants. AAC systems are less expensive than comparable refrigeration units, typically as much as 25% less expensive. (VehiCool, 1999)

          An evaporative cooler/adiabatic cooler is completely different type of air conditioner that works well in hot, dry climates. These units cool outdoor air by evaporation achieved through adiabatic saturation and blow it inside the building, causing a cooling effect. When operating an adiabatic cooler, windows are opened part way to allow warm indoor air to escape as it is replaced by cooled air. (National Renewable Energy Laboratory, 1999)

          Adiabatic cooling is 100% fresh air cooling. This means that all the air being cooled is brought in from outside. It is also necessary to force approximately 90% of all the air coming into the building, out of the building, leaving a nice 10% positive pressure. Today, the term “Sick Building Syndrome” exemplifies the result of continuously re-circulating the air inside the building. The old saying that you can get sick in a hospital is true. The air containing contaminants of all sorts is being breathe in by everyone. Fresh air would exhaust these contaminants quickly and harmlessly. US Federal guidelines in building construction now require a percent of all air in the building be fresh air. (Premier Industries Inc., 1996)

          Frost, et. al. (1996) mentioned that AAC technologies are growing worldwide, however they are still widely underutilized and often even unknown in many parts of the world. Through AAC cooling can be provided with minimal energy consumption and without the use of Chlorofluorocarbons or other similar ozone-depleting chemicals. AAC can provide comfort cooling throughout the many arid and semi-arid regions of the world, as well as a relief cooling for commercial and industrial applications such as greenhouse, buses, laundries, warehouse, factories, kitchens, and poultry houses. 

Apte, et. al. (2002) conducted a study comparing two HVAC, one is heat-pump air conditioner system and the other a direct evaporative cooler (DEC). The study was to compare their performance by running the standard and advanced systems in the same classrooms on alternate weeks. The study aims to provide energy-efficient structures that can help school districts lower their energy bills, and structures designed with good air quality in mind that help students and teachers stay healthy and sharp in the classroom. The researchers found out that since it has a quieter fan and no compressor, a DEC’s noise is lowered. DEC had lower CO₂ concentrations compared to standard systems and was also better at reducing the average formaldehyde concentrations, as well as those of other targeted volatile organic compounds. Finally, the energy use of the DEC system was considerably lower than that of the standard system.

          Gordian Associates Research Organization  (2002) studied whether evaporative air-cooling works on hot weather countries. They concluded that in large areas of the United States, evaporative air-cooling can provide essentially equivalent comfort conditions to a residential. They also said that evaporative coolers consume considerably less primary or resource energy than mechanical air conditioners. They added that with evaporative cooling, a complete air change occurs every one-to-three minutes. Which offers a great health advantage over traditional refrigerated air conditioning, which employs a complicated “closed” system that re-circulates the same stale dry air over and over.