Which of the following refrigerants has a GWP closest to "1"?

The refrigerant that has a Global Warming Potential (GWP) closest to "1" is R-1233zd. This refrigerant is classified as an environmentally friendly option because it has a low impact on global warming compared to the other listed refrigerants.

R-1233zd is a hydrofluoro-olefin (HFO) refrigerant and is designed as a replacement for high-GWP refrigerants in many applications, resulting in significantly reduced climate change potential. Its GWP is considered negligible when compared to traditional refrigerants, which typically have much higher values.

In contrast, the other options represent refrigerants that have a much higher GWP. R-22, R-134a, and R-410A are all hydrochlorofluorocarbons (HCFCs or HFCs) with substantially higher GWPs due to their molecular structures, which contribute to greenhouse gas emissions. Understanding the GWP of refrigerants is crucial for selecting environmentally responsible options in HVAC and refrigeration applications.