Using carbon dioxide (CO2) as a refrigerant began in early industrial times and has been revived in the past couple of decades. But what is CO2 refrigeration? And why is CO2 a good thing when it comes to refrigeration? It is, after all, common knowledge that CO2 emissions from fossil fuel consumption are one of the main drivers of climate change.
CO2 and all other refrigerants used in air conditioning, heat pumps and refrigeration systems have been given a Global Warming Potential (GWP) value. The GWP explains the magnitude of its effects on the climate over a period of time, traditionally 100 years. As the main greenhouse gas, CO2 — also called R744 when used as a refrigerant — has been given a GWP value of 1. This is to make comparisons between different refrigerants easier.
So why is CO2 refrigeration a good thing?
This becomes apparent when looking at synthetic refrigerants promoted by the chemical industry. These have GWPs that, in many cases, are thousands of times higher. Two of the most popular synthetic refrigerants around the world, currently, are called R410A and R32. R410A has a GWP of 2,100 and R32 has a GWP of 771, calculated over a period of 100 years. In other words, R410A’s GWP is more than two thousand times higher than R744’s, meaning that while CO2 that escapes from cooling or heating equipment does have a small impact on the climate, the alternatives are thousands of times worse.
These values are even higher when looking at short term effects. If calculated over a period of 20 years, the GWP values for R410A and R32 becomes 4,400 and 2,530, respectively. This is relevant because many of these fluorinated synthetic refrigerants break down in the atmosphere much quicker than 100 years – with atmospheric life times closer to 20 years (or even less). (For more information about GWP values and how they are calculated, click here.)
This doesn’t mean that CO2 emissions from burning fossil fuels are suddenly unproblematic, most certainly not. We should still do our best to minimize those emissions as much as possible. However, in the cooling and heating industries, CO2 refrigeration is a very environmentally friendly option compared to synthetic refrigerants. So using CO2 can actually help reduce the effect these industries have on the climate – significantly.
Moreover, because it is benign to the environment, CO2 can be considered a “future-proof” refrigerant, which will never be encumbered by the regulations that have targeted fluorinated refrigerants.
Other refrigerant options
CO2 is not the only refrigerant with a low GWP. Other natural refrigerants1 like ammonia and hydrocarbons (propane and isobutane), have even lower GWPs, less than 1. For more information about ammonia and hydrocarbons, visit Ammonia21.com and Hydrocarbons21.com.
The newest generation of synthetic refrigerants (called HFOs) also have low GWPs compared to their predecessors. However, these HFOs have other concerns. They are flammable, and there are growing environmental concerns that they are damaging to the environment, and to human health.
Scientists are looking at byproducts created when HFO refrigerants break down in the atmosphere. These byproducts can enter water bodies and drinking water supplies and be consumed by humans and other animals.
One of the main concerns is about trifluoroacetic acid, or TFA, because some HFO refrigerants (especially R1234yf) produce TFA when broken down in the atmosphere. According to a definition used in Europe, TFA belongs to a group of chemicals better known as forever chemicals (or PFAS) because they are very persistent and don’t break down any further once in the environment. So any problems will only increase over time as more HFOs are released. The issue with TFA is that a growing number of peer-reviewed studies are providing evidence that it is, among other things, damaging to the liver and thyroid function in humans.
In other words, the conclusion is that using CO2 for refrigeration is one of the safest and most environmentally friendly options we currently have.
1 Natural refrigerants are non-synthetic and naturally occurring substances, as opposed to synthetic refrigerants, which are compounds created by chemists in a laboratory.