The concept of mechanical refrigeration starts back in the 1750s. Researchers knew nothing about cooling except that pressure and gasses somehow played a key roll in absorbing and removing heat. In these early days, everything was tried as a refrigerant: ammonia, alcohol, air, carbon dioxide, and more. It was the days of trial and error to create the robust understanding of physics and chemistry we have today.
Low Temperature Boiling
The first experiments in refrigeration used Ether and Alcohol, which are readily evaporated. At sea level, Ether boils at 94F and Alcohol can boil as low as 151F, depending on the exact chemical form. Sea level is important here, as pressure changes the boiling point. Lowering the pressure causes a decrease in the boiling point. These gasses with low boiling points were ideal for early experiments.
The first experiments used vacuum chambers and potentially some custom hardware. There isn’t a lot needed to build a basic vacuum chamber. A jar with a good seal, a hose, and a pump can create a vacuum. An observable refrigeration can be done with almost no special equipment at all.
At this scale, cooling was possible, but not feasible. Alcohol, Ether, and other chemicals were common and easy to acquire, but no one was going to put a chunk of meat in a vacuum chamber, cover it in alcohol, wait for it to freeze, and try to store it somewhere. There had to be something better.
Ammonia, Sulfur, and Chloromethane
As early refrigeration developed, the early 1800s brought the first major, practical innovations. There was the vapor-compression cycle which would allow for a continuous cooling process, and with it the first feasible refrigerant: Ammonia.
Ammonia was first chemically isolated in the 1750s. It’s a gas at room temperature and absorbs a great deal of heat when it boils off. It’s toxic, but easily detected in even the smallest quantity thanks to it’s powerful and distinct scent. Exposure can lead to lung damage and eventually death. For early industrial systems, it was an ideal chemical, with one problem. It was hard to source and isolate. Early production relied on a distillation process not suitable for use at commercial scales.
Sulfur Dioxide however, was a decent refrigerant, and much easier to produce. It was also still incredibly toxic, but these were the early days of refrigerants, beggars couldn’t be choosers. Sulfur was producible at scale, affordable, and good enough for the job. the dangerous part was just inhaling it, which would wreak havoc on the lungs. Prolonged exposures could cause premature death. Strangely, it is harmless to ingest.
There was lastly Chloromethane. This was a gas produced from Methane, Sodium Chloride, and Sulfuric Acid. It was first produced in 1835, worked great as a refrigerant, is incredibly toxic, and it’s incredibly flammable. Exposure to Chloromethane produces nervous system effects similar to intoxication, can lead to death, can cause birth defects, and will cause issues with chronic exposure. By comparison, Sulfur Dioxide seems downright benign.
The First Modern Refrigerants
Refrigerators became more widespread in the 1900s, but they immediately faced a public-relations nightmare: they were killing people. Design and manufacturing defects made it incredibly easy for a leak to develop. Refrigerants like Ammonia could literally eat away the seals that kept the gasses trapped inside. Once lose in the home, death was all but guaranteed.
This issue was so widespread that even Albert Einstein, the genius behind some of our most foundational concepts of physics, looked into fixing the modern refrigerator. The young refrigeration and air conditioning industry dove in on developing safer alternatives.
The answer at the time was a new class of chemicals: Chloro-Fluoro-Carbons, CFS. These included atoms from Chlorine, Fluorine, and Chlorine. The major product was R12, Freon. It was incredibly stable, non-toxic, and a highly efficient refrigerant. These properties would make it a dominant part of the 1900s. Most of the older refrigerants would die off in the new era, except for Ammonia, which was finally commercially viable.
There was however, a catch we wouldn’t discover until decades later. Freon was harmless to humans and most living things. It wasn’t harmless to the environment. The incredibly stable chemical broke down when exposed to Ultraviolet radiation. When F12 breaks down, it releases its constituent components into the air. In the air, they broke up the earth’s ozone, O3. Without the ozone, more ultraviolet light could reach the Earth’s surface. In time, this would have lead to mass extinctions. The sunlight in orbit creates temperatures higher than 400 degrees fahrenheit. The Ozone is a key part of that intense heat not baking us to death.
With all these developments, there is some limbo going on in the refrigeration world. R12 was replaced with R22, but it turns out R22 is still not good for the ozone. It’s not as bad, but it needed to be phased out. There are a number of possible replacements, but work is ongoing to find better solutions. Just as in the 1800s, nothing is quite perfect.
R-134a is one of the more common replacements. It is denser than air, causing it to replace the air in rooms where it leaks and to replace the air in lungs, leading to asphyxiation and death. It has a low impact on the ozone, but it has extreme global-warming potential. It too, is slowly being reduced and possibly removed from mainstream production altogether.
R-410a is another newer solution. It is a key component in high SEER rated systems, is harmless to the ozone, but it is as bad for global warming as R22. It’s extreme efficiency however is a redeeming factor. By reducing the electricity required to run an air conditioner, it has a net-benefit. It’s a pollutant itself, but can reduce the presence of other, worse pollutants.
Ammonia has actually become very prominent in refrigeration. It’s generally not suitable for home use due to its potentially lethal effects, but it has become a common component in industrial equipment. It’s an effective refrigerant, is readily detected, and thanks to advancements in manufacturing around WWI, it’s easily produced in bulk.
Refrigerants in the Future
New chemicals are being created and tested every day. We don’t know what the next refrigerant will be, but we are sure there will be another king of industry. There is even potential that refrigerants will be outmodded altogether. Researchers have been looking into ways to create solid state cooling equipment. Silicon chips and other compounds which transfer heat without the need for refrigerants and compressors in the first place. We already use this type of technology in computer cooling, but there are indications that a revolutionary advance is on the way. We are just about over-due for one.