Natural refrigerants include which of the following?

• A. R-290 (Propane), R-600a (Isobutane) and R-744 (CO2)
• B. R-404A
• C. R-22
• D. R-134a

Answer: (A)

Natural refrigerants are substances that occur in nature or are not primarily synthesized for cooling, and they typically have very low or zero ozone depletion potential and low global warming potential. Propane (R-290) and isobutane (R-600a) are hydrocarbons, and carbon dioxide (R-744) is another natural refrigerant. Together they exemplify natural refrigerants used in various cooling applications. The other options are synthetic refrigerants, which generally have higher global warming potential or ozone depletion potential: R-404A is a blend of HFCs, R-22 is an HCFC, and R-134a is an HFC. So the list that includes propane, isobutane, and carbon dioxide best fits natural refrigerants.