Examining ignition risks when flammable refrigerants meet poor design or maintenance.

My father, Dr. S. Forbes Pearson, known to everyone as Forbes, died in March of this year. At his memorial service in April, I reflected on the fact that there are at least half a dozen things that are now commonplace in the industrial refrigeration world but that had not been done, or at least had not been commercialized, until he did them.

I likened this to a backroom songwriter who creates a tune for someone else and then hears it all over the place—on the radio, in a pub or a football stadium—without anyone connecting him to the music that they love so much. I was thinking of someone like American songwriter Otis Blackwell. Otis who? Well, he’s only the guy who wrote “All Shook Up,” “Return to Sender” and “Don’t Be Cruel” for Elvis, and of course “Great Balls of Fire” for Jerry Lee Lewis.

I wrote about one of the innovations commercialized by Forbes in last month’s column: reverse cycle defrost. Two of his other innovations relate to the use of carbon dioxide (CO₂) as a refrigerant. CO₂, as a volatile secondary refrigerant, where the circulating coolant evaporates and recondenses without a compressor, was first done for a supermarket installation in Kilmarnock, Scotland, in 1991 and has subsequently been used for chill stores, air-conditioning systems and blade server cooling around the world. The concept of parallel compression was developed in 2003 for single compressor applications in transcritical systems to improve capacity and efficiency in warm weather, although it is now much more commonly used in multiple compressor systems—a much easier proposition!

One of the most widely commercialized ideas led by Forbes, among others, was the use of zeotropic mixtures in refrigeration systems. This work in the 1980s was done in parallel with several other researchers, particularly in America. This led to lifelong friendships with many of them, including Dave Didion of National Bureau of Standards (which later became NIST) and Don Bivens of the DuPont Company. The insight that Forbes brought to this work was invaluable. He knew, for example, that a good service technician, when faced with oil return problems in an industrial R-22 system, might add a small amount of R-12 to improve miscibility, even though the boiling points of the two refrigerants were very different.

Searching for a substitute for R-502 in the mid-1980s, Forbes decided to add some propane to R-22 in order to improve oil return in the same way and set up his own “great balls of fire” to establish how much propane would make the mixture flammable. “Hardly any” was the disappointing answer following a series of flammability tests, but by adding a third component, R-218, he managed to get the propane proportion of his blend up to 5% without the mixture being flammable.

The realization that mixing components could provide beneficial characteristics was a game-changer. The hydrocarbon improved oil compatibility and the perfluorocarbon, as well as providing some fire suppression, gave an extremely low discharge temperature, which was an essential factor in the replacement of R-502.

There are now over 100 recipes for zeotropic blends following this principle registered with ASHRAE SSPC 34, and we have all learned that temperature glide does not prevent systems from operating reliably and efficiently.

Forbes believed firmly in sharing information, reckoning that he always gained more than he gave in these exchanges. Any invention, whether technical or musical, starts out as your own private thought but with the hope that it will become public property; enjoyed by millions to whom its origins are unknown.