The gas commonly used in air conditioning systems is called refrigerant. Refrigerants are substances specifically chosen for their ability to undergo phase transitions, changing from a gas to a liquid and vice versa, at low temperatures. This characteristic allows them to absorb heat from the indoor environment and release it outside, thereby cooling the air.
Over the years, different types of refrigerants have been used in air conditioning systems. One of the most widely used refrigerants in the past was chlorofluorocarbons (CFCs), such as R-12 (also known as Freon-12). However, due to their harmful impact on the ozone layer, CFCs have been phased out and are no longer used in most modern air conditioning systems.
Currently, the most common refrigerants used in air conditioners are hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs). Some of the popular HFC refrigerants include R-410A and R-134a, while a commonly used HCFC refrigerant is R-22. These refrigerants have lower ozone depletion potential compared to CFCs, but some HFCs are still known to have high global warming potential.
It's important to note that there is ongoing research and development of new refrigerants with even lower environmental impact, such as hydrofluoroolefins (HFOs) and natural refrigerants like hydrocarbons (HCs) and carbon dioxide (CO2). These alternatives aim to reduce the environmental impact of air conditioning systems and comply with regulations regarding the use of refrigerants.