Right now, 20 percent of the world’s electricity goes into refrigeration, the technology behind air conditioning and keeping food and other goods cold. What’s more, refrigeration is responsible for about eight percent of all global greenhouse gas emissions. And as the climate crisis continues, we’re not going to need less cooling, but we might be able to totally reinvent it.
Here’s how: There are two problems with refrigeration. One, the electricity that keeps us cool in a warming world is of course causing emissions that make the problem worse. But the chemicals that make the process work are themselves greenhouse gases too.
The problem is, we’ve been using the same so-called Vapor compression cooling systems since the 19th century, and it’s been a hard habit to break. Vapor compression works by using a chemical called a refrigerant to pull heat out of where you don’t want it and dump it somewhere else. When you get right down to it, heat is just the movement of molecules—something whose molecules are jiggling around is warmer than something where they’re more still, and the difference between phases of matter, like liquid and gas, tend to involve a big jump in molecular motion.
Basically, you can absorb a bunch of heat by making something change phase from liquid to gas, and if it takes that heat from the air in your fridge or your home, that air is going to get correspondingly colder. You could do this with water if you really wanted to, but it needs to be a hundred degrees to change to gas phase, so, fine if you like your apartment real tropical.
Which brings us to Vapor compression refrigerants. When they’re pumped into your fridge at low pressure, they will easily turn into gas at a low temperature. That means they’ll absorb some of the heat from the fridge, even if it was cool to begin with. Outside the fridge, the gas is compressed to pack its molecules tighter again, and it gives away heat as it turns back into a liquid. Pump that liquid into the fridge, and the refrigeration cycle can start again, keeping things cool as long as the cycle continues.
In the 1930s, the refrigerants known as freons came into use. They were great at this Vapor compression heat exchange, they had conveniently low boiling points, and were less unpleasant to use than other known refrigerants, like ammonia. However, decades later, it was discovered that these chemicals were also great at stripping our planet’s protective ozone layer. In 1987, almost all the countries in the world signed the Montreal protocol, which laid out a path to phase out freons. As a result, cooling systems started switching over to a different class of chemicals, hydrofluorocarbons (HFCs). They were also effective refrigerants and didn’t react with the ozone layer.
But fast forward a few more decades and it turned out that the ozone-friendly HFCs were still causing trouble in the atmosphere as a greenhouse gas. They can be up to almost 2,000 times more potent than CO2. Ooops. That discovery led to the Kigali Amendment, added to the Montreal protocol in 2016. needs to be done quite often so it’s not really the most practical option
The Amendment states that signatories must cut HFC use by over 80% by 2047, creating a strong incentive to find new refrigerants. However, the alternatives proposed so far are mostly toxic, inefficient, or flammable. An alternative option is to use Modern Green Refrigeration Technologies, such as Magnetocaloric Refrigeration, Elastocaloric Cooling, and Ionocaloric Cooling. Magnetocaloric Cooling is relatively efficient, reaching up to 60% efficiency in the lab, however, it is costly due to the need for powerful magnetic fields and rare earth elements. Elastocaloric Cooling is more cost effective and can be as efficient as Vapor Compression in the lab, but the materials need to be optimized to be resilient enough for real life refrigeration. Lastly, Ionocaloric Cooling is energy thrifty, but only reaches around 30% efficiency, and the self-cooling process needs to be done often.