Don’t Forget R744

Cheryl Hogue’s Government & Policy article “Replacing the Replacements” failed to mention the possible use of CO₂ (aka R744) as a replacement for hydrofluorocarbons such as R134a (C&EN, Dec. 5, 2011, page 31). R744 does not deplete stratospheric ozone and has a global-warming potential (GWP) of 1 (by definition), a factor of 4–7 times less than the GWPs of the HFC replacement candidates (HFC-1234yf, HFC-1234ze, and HFC-1233zd) discussed in the article.

The American Society of Heating, Refrigerating & Air-Conditioning Engineers (ASHRAE) has classified R744 into safety group A1, the safest classification for both toxicity (A) and flammability (1). As mentioned in the article, different refrigerants will likely emerge as the best solution for different applications, but any discussion of HFC replacements certainly should include R744 as an attractive candidate for many applications.

By Matthew Eisaman
Port Jefferson, N.Y.