The National Institute of Standards and Technology (NIST) has identified more than a dozen chemical blends as alternatives for current refrigerants.
According to the NIST, these blends do not heat the atmosphere as much as today’s refrigerants do, nor do they catch fire.
The study identified the 22 best nonflammable or marginally flammable blends with lower global warming potential (GWP) than the current standard refrigerant for vehicle air conditioning (AC) called R-134a (tetrafluoroethane).
Though the research was conducted primarily for the U.S. military, the results could be extended to civilian applications too, says study lead author Ian Bell.
The researchers chose 13 fluids within a range of pressure, flammability, and GWP values that might produce a blend with the desired characteristics.
All fluids were low in toxicity and commercially available. Once this was ascertained, the researchers conducted an extensive evaluation of all possible combinations of two or three of the 13 fluids.
The team however did not find any blends that met all desired constraints of nonflammability, low GWP, high efficiency – and overall cooling capacity similar to R-134a baseline systems.
The study identified 14 nonflammable blends that offer a reduction in GWP of, at most, 51% compared to R-134a’s GWP of 1300.
An additional eight blends that were marginally flammable were also identified with GWP reductions of as much as 99%.
The researchers then simulated the performance of these 22 blends in a detailed refrigeration cycle model.
According to the scientists, the most promising nonflammable blends have slightly lower efficiency compared to R-134a.
These nonflammable blends have a lower GWP limit of 640; this is due to the need for a lot of R-134a in the mixture to suppress the flammability of low-GWP fluids.
Other blends containing a significant amount of carbon dioxide were also nonflammable, but these had very low efficiencies compared to R-134a and were not considered viable alternatives.
Shedding light on this trade-off, Bell remarked that it was not easy to find both nonflammability and efficiency in a single blend, and one had to make sacrifices when it comes to choosing an alternative.
Image and content: Jimmie D. Pike-U.S. Air Force photo/NIST