Which refrigerant is commonly used in residential air conditioning systems?

R-22 is a refrigerant that has historically been widely used in residential air conditioning systems due to its efficiency and effectiveness in heat transfer. It is a hydrochlorofluorocarbon (HCFC) that has been favored for many years because of its favorable thermodynamic properties, which help in achieving effective cooling.

In addition to being commonly used, it is important to note that R-22 has been phased out in many regions due to environmental concerns regarding ozone depletion. Although it was prevalent, newer systems have shifted toward alternatives that are more environmentally friendly, such as R-410A. However, up until its gradual phase-out starting around 2010, R-22 was a dominant refrigerant in existing residential systems, making it a significant option in this context.

The other refrigerants listed, while they may be used in various applications, do not have the historical prevalence in residential air conditioning systems like R-22. For example, R-12 was largely phased out due to its ozone-depleting properties, and R-134a, while used in some applications, has not been as commonly used in traditional residential AC units as R-22 was before the phasing out began. R-410A is increasingly used in new