Since 2012, a new refrigerant has been taking over the automotive air conditioning industry. The whole reason for the switch was a decision of the European Parliament back on May 17, 2006. They decided to prohibit refrigerants that had a 100 year global warming potential greater than 150. I'll forego discussing global warming in this post.
DuPont and Honeywell developed R-1234yf to meet the global warming potential (GWP) requirements. But this new refrigerant was worse than R-134a in several very important categories. It's more flammable, more toxic, and more expensive. The main reason why R-1234yf has such a low GWP number is because of the short atmospheric lifetime of 11 days. It quickly decomposes into trifluoroacetic acid (TFA).
If the goal was to find a refrigerant safer for the environment, they failed. It's no safer than R-134a. Unfortunately, the target metric was GWP, and that's about all they got.
Check out what happened when engineers at Mercedes-Benz tested it.
This video shows both R-134a and R-1234yf leaking onto a hot turbo. The R-1234yf catches fire, while the R-134a does not.
R-1234yf alone is hardly flammable at all. But it is when it's mixed with refrigerant oil, as is the case when used in air conditioners.
The fire isn't what worries me. It's the deadly fluorine compounds released as combustion by-products. These gasses are so reactive, they etch glass. The IDLH for HF is 30 ppm. That means that 30 ppm is immediately dangerous to life or health. This is an accident waiting to happen. Someone is going to get a very serious injury or die from an accident where this refrigerant is burned.
To compensate for the fact that R-1234yf is flammable, auto makers re-designed the evaporators to be more sturdy to prevent leaks into the passenger compartment.
Since it seems we're now ok with refrigerants that are toxic to the environment and release deadly gasses when burned, I propose we switch to a different refrigerant that is much safer for the environment, has virtually no toxic combustion by-products, and runs at about the same pressures as existing automotive A/C systems. It's only worse than R-134a in one category. It's highly flammable. We've seen that it is economically feasible to build better evaporators for R-1234yf, so why not do the same for R-600a?
R-600a has already been legal in the United States for use in stand-alone refrigeration units since July 31, 2013 (link).
Here are some other refrigerants used in or since the early 20th century.
Sulfur Dioxide is toxic. The IDLH is 100 ppm. It's corrosive, which means it will eventually leak out of the refrigeration unit. Who wants their refrigerator to smell like rotten eggs?
Ammonia is also toxic. The IDLH is 300 ppm. But it's cheap and an efficient refrigerant, which is why it's still used in some large-scale commercial systems today.
Chloromethane (aka methyl chloride) IDLH is 2000 ppm. It's carcinogenic. With a flash point of -20C, chloromethane is extremely flammable. It is no longer used as a refrigerant.
Methylene Chloride (aka dichloromethane) IDLH is 2300 ppm. No flash point, but can be flammable above 100C.
Methyl Formate (C2H4O2) IDLH is 4500 ppm, meaning it's toxic. It has zero GWP and zero ozone depletion. But it's highly flammable, with a flash point of -19C.
Propane is a simple asphyxiant (too much propane means not enough oxygen) so other than that, no symptoms from inhalation.
Carbon Dioxide has a GWP of 1 (which might as well be zero). It's safe, non-toxic, and non-flammable. CO2 refrigeration was patented in 1867 by Thaddeus Lowe (British patent 952), and used to cool an office building in 1906. The main disadvantage is the high pressures required.
We converted over to R-134a was because it was better for the environment and I do agree that it is a better alternative than R-12, but the move to R-1234yf was supposed to be because it was even better for the environment. The only reason it has a lower GWP number is because it decomposes faster. It decomposes quickly (11 days) in air into trifluoroacetic acid (TFA), which is harmful if inhaled, and toxic for aquatic organisms, even at low concentrations. TFA is not biodegradable in water. It's worth noting that R-134a also decomposes into TFA, but at a slower rate than R-1234yf.
In this table, I compare several refrigerants to R-134a. A green background means it's better than R-134a in that category, and red is worse.
* The maximum possible AEL number is 1000, so that isn't a fair comparison.
Comparing the refrigerants, it appears that R-134a is the best non-flammable option. Otherwise, R-600a is the best choice. I didn't include carbon dioxide in this table since it isn't compatible with typical automotive compressors. But the technology is available to use it.
