Which of the following is a common refrigerant used in HVAC systems?

R-410A is a common refrigerant used in many modern HVAC systems due to its efficiency and effectiveness in cooling applications. It is a hydrofluorocarbon (HFC) blend that does not deplete the ozone layer, making it an environmentally friendly alternative to older refrigerants such as R-12. The use of R-410A has become prevalent since it can operate at higher pressures, which allows for improved performance and energy efficiency in air conditioning systems.

Furthermore, R-410A is favored for its thermodynamic properties, making it suitable for both residential and commercial applications. Its widespread adoption has been partly driven by regulatory changes and initiatives to phase out substances that harm the environment, such as CFCs and HCFCs, which included compounds like R-12.

In contrast, other refrigerants listed, while used in specific situations or applications, are not as common in standard HVAC systems. Ammonia, for instance, is typically used in industrial refrigeration systems due to its high efficiency but poses safety concerns. Carbon dioxide is used in some applications but has unique operational requirements that make it less common in traditional HVAC settings.