Refrigerants are cool, I’m telling you!
This is the story of how your ice cream might be hurting the environment.
You would be forgiven for not knowing what a refrigerant is. For many of us, things like air conditioning, freezers, and refrigerators are just boxes that make things cold. Yet, on the inside happens a bit of magic, where a fluid we call a refrigerant absorbs heat on the side we don’t want it and expels it on the other side. Unfortunately, the impact on global warming between one type of refrigerant and another may as well be compared to the difference between buying an old diesel and a new electric vehicle. Unlike with cars, however, we have readily available replacements that are much more environmentally friendly. Despite this, many countries still haven’t signed on to the 2016 Kigali Amendment, whose main goal is to phase out refrigerants that cause global warming. While on an individual level there probably isn’t much you can do, the issue of refrigerants is one that more people should be aware of, so that collectively we can ask our governments to do better.
A short history
For a few decades at the end of the 20th century, the depletion of the ozone layer was all over the news. This was because scientists in the 1970s had discovered that chlorofluorocarbons (CFCs), a set of chemicals commonly used in refrigeration and aerosols, were contributing to the depletion of the ozone layer. Research showed humans were slowly creating a hole in the “roof” above their head, and pressure mounted to find a resolution to the issue. This led to the 1987 Montreal Protocol, where the world came together and agreed that the predicted hundreds of millions of cases of skin cancer was something to avoid. The first international treaty universally signed by all countries was a success. The use of ozone-depleting chemicals dropped drastically following the agreement, and not only did we avoid further damages to the ozone layer, we are now starting to see it gradually healing itself. As an added bonus, we also avoided further impacts to climate change, something we only started to understand in recent years.
Unfortunately, this is not the end of the story when it comes to harmful chemicals used for refrigeration. As it turns out, common replacement refrigerants for CFCs are HFCs (hydrofluorocarbons), and while they do not endanger the ozone layer, they have an enormous climate change potential. With HFCs expected to contribute up to 19% of all greenhouse gases emissions by 2050, there have been multiple attempts to cut back their usage. In 2016, the Kigali Amendment to the aforementioned Montreal Protocol was laid out, with the aim of phasing out HFCs and financially supporting developing countries in their objective to do so. Unfortunately, while the Montreal Protocol was a success, being signed by the entire world, less than half of the initial signatories signed on to the Kigali Amendment, including major players such as the United States and China.
Refrigerants? Heat pumps?
Now, we’ve established that it’s not every day that you’re asked to think about the inner workings of your refrigerator or air conditioner, and so it’s worth looking at what refrigerants do for us.
- Your refrigerant starts its cycle as a liquid.
- As it enters the space you are trying to cool, it passes through an expansion valve (1) that, given the sudden drop in pressure, lowers its temperature.
- As the refrigerant travels through an evaporator (2), it absorbs the radiant heat, eventually reaching its boiling point, turning it back into a gas.
- The gas then enters a compressor (3), which raises the pressure of the refrigerant, further increasing its temperature.
- This heated gas then enters a series of coils (4) that allow it to cool, pushing the heat away from the system, and transform back into a liquid, bringing us to the original step in the cycle.
Essentially, the refrigerant allows us to cool one side of the system by pumping the heat to the other side; hence why we call them heat pumps.
As you can imagine, not every fluid is a suitable refrigerant, since you need to find one that has properties that won’t hinder the system. For instance, the fluid freezing during the expansion phase would rapidly hinder the system’s operation. Similarly, requiring large amounts of energy to convert the fluid from one phase to another, such as water with its high boiling point, makes for a system that is typically too inefficient for most applications. Aside from the required thermodynamic properties, you need one that isn’t toxic or flammable, doesn’t damage your refrigeration unit, is easy to find or make, is affordable enough to put into systems that are sold in mass, and, ideally, doesn’t threaten the environment. As a result of this, it’s quite hard to find a fluid that ticks all the right boxes, and we end up looking for a compromise of all the requirements.
Thankfully, there are a lot of fluids that can potentially work in the system described above, but most of them come with a set of compromises on the ideal characteristics for a refrigerant. Still, let’s have a look at some of the replacements:
- Isobutane: A common refrigerant used in domestic refrigeration in Europe. Its downside is its flammability.
- Propane: Used in some commercial applications, and is also flammable.
- CO2: While it used to be more common in industrial applications, it is now making a comeback in many sectors. As part of our atmosphere, this is one of the most harmless refrigerants you could think of, but its requirement for high working pressure means that you often need a more expensive system to make it work.
- Ammonia: Having been a popular choice for industrial and commercial applications for some time now, this refrigerant has two problems that often deter from its use. First, while the refrigerant itself is relatively cheap, the equipment required to use it is many times more expensive than other refrigerants, due to how ammonia reacts to air and water. Second, a leak can prove fatal to humans.
- HFCs: While still having a higher global warming potential than a natural refrigerant like CO2, some HFCs have a much lower impact, allowing them to continue being used.
- HFOs: An up-and-coming replacement for HFCs, these are typically much more expensive. In addition to this, they tend to be highly flammable. On the positive side, their impact on global warming is but a fraction of typical HFCs.
A common trend is the cost associated with the replacements for HFCs. Either the system ends up costing more upfront, or it has to receive periodic maintenance to ensure it won’t suddenly kill everyone in the vicinity, raising its cost over time. While this isn’t necessarily a major problem in affluent countries, it quickly becomes one in developing nations.
While the Kigali Amendment does acknowledge this by having wealthier signatories help poorer ones, it also makes it a tougher sell to nations that will now have to shell out to help the rest of the world transition. In other words, the reasons we are not transitioning away from refrigerants that are causing us long-term harm are the same as for a lot of things: money and politics.
To conclude, it’s worth pointing out that not everything is doom-and-gloom. For instance, while not every nation has signed the Kigali Amendment, many still try to take action. The United States, for example, hasn’t signed the agreement, but has been moving towards reducing the use of HFCs with high global warming potential. At the same time, many companies, perhaps sensing the long-term trend, are also making a voluntary transition to more environmentally friendly refrigerants. We are headed the right way in many sectors, let’s just make sure we stay on track, and perhaps remind our governments that their role is to help the transition happen.