R-744, or Carbon Dioxide, is quickly becoming one of the most popular refrigerants in the world. As the usage of this refrigerant grows I can’t help but laugh as we have now come full circle. You see, if you go back one-hundred years Carbon Dioxide was one of the main refrigerants used but its usage declined in the 1930’s with the invention of synthetic refrigerants such as CFCs and HCFCs.
These new synthetic refrigerants were safe, cheap, and reliable. Because of this they took over the marketplace. It wasn’t until it was found that CFC/HCFC refrigerants actively harm the environment that we began to see more R-744 applications appears. In this article we’re going to take a look the various R-744 applications that can be found in the world today:
Let me first start out by saying that R-744 is a very unique refrigerant, more so then others. R-744 is a natural refrigerant. But, unlike other natural refrigerants, there is not a safety concern. With hydrocarbons you have the flammability risk, with Ammonia you have the toxicity risk, but with CO2 the safety risk is minimal. Along with it being a safe natural refrigerant it also is very versatile. It is mainly used in a transcritical refrigeration system but it can also be used in subcritical systems when done through a cascade. On top of that R-744 can be used as a secondary fluid refrigeration system.
Between these different types of refrigeration there are a wide a range of applications such as vending machines, supermarket refrigerators/freezers, industrial refrigeration, refrigerated transport, automotive air conditioning, heat pumps, and even in sports arenas for ice rinks. In this section we are going to take a look at each of these applications:
One of the first targets in the global HFC phase down was R-404A. As you know, 404A was used in a variety of applications including vending machines. In the early 2010’s there was a push from a variety of companies, including Coca-Cola, to switch their vending machines away from 404A and over to R-744 Carbon Dioxide. Now, as I write this article CO2 vending machines are found all over the United States. One of the initial struggles of these systems was finding qualified technicians as these vending machines operate as a transcritical system rather then subcritical. The good news is that as the years go by and the amount of these transcritical machines grow then the technicians will become more seasoned and experienced with working on these kinds of systems.
The grocery store refrigerators and freezer market didn’t switch over as fast as vending machines but there is significant progress being made. While R-744 isn’t necessarily the preferred refrigerant to use in these applications there are some companies moving forward. Depending on the application supermarkets will either use a stand alone plug-in unit that is very similar to a vending machine or they will use one system that connects to all of the various refrigerators and freezers.
When it comes to using R-744 the type of application will determine if the unit will be a subcritical cascade or a transcritical system. If we look at a stand alone refrigerator/freezer then we would be dealing with a standard transcritical system. This would operate very similar to how vending machines do. On the other hand, if we look at some of the larger systems that are all connected then we would be looking at a cascade system. A cascade system uses two or more refrigerants. In the example of R-744 we would find R-744 on the low temperature side of the cycle. By having R-744 isolated to the low end of the system we can prevent the refrigerant from going past the critical point and keep it subcritical. The other refrigerant used for the high side of the system can vary. It could be Ammonia, Propane/Isobutane, or even an HFC or HFO refrigerant.
The term industrial refrigeration can be quite vague and can encompass a variety of applications from chillers, to chilled warehouses, to heat extraction, and so much more. In the past, before R-22 was phased out it was one of the top refrigerants used in these larger scale operations. When R-22 was phased out some companies switched over to the HFC R-404A/R-134a only to find that these refrigerants were going to be phased out soon as well.
In Europe, in Canada, and in other countries R-717 or Ammonia is one of the top picks when it comes to industrial refrigeration such as meat packing plants. Ammonia is chosen as it is highly regarded as the most energy efficient refrigerant out there. The downside, of course, is that Ammonia is toxic and can also be slightly flammable. Whenever you see a story in the new stating that a plant had to be evacuated due to a refrigerant leak the chances are that it is Ammonia is quite high. There are many instances of this occurring here in the United States and in most cases everyone is fine. We just have to ensure that the proper precautions are followed.
While R-744 may not be as efficient as Ammonia it has another thing going for it. It’s not toxic. That being said though it appears that the use of R-744 plants and chillers is still quite rare. I spent some time looking around online trying to find stories on R-744 plant usage but wasn’t able to find anything. It seems that Ammonia still has a strong hold on the industry but as technologies change and as HFCs become completely phased out we may begin to see more active R-744 industrial applications. If you know of some active R-744 plant applications please reach out to me and let me know.
When I hear the words refrigerated transport I instantly think of trucking. That’s most likely because I came from the trucking industry. I remember going through pallets of R-404A for our carrier refrigerated trucks. In the case of R-744 though the refrigerated transport we are discussing is naval transport or refrigerated shipping containers. It’s not just produce or meat being refrigerated on cargo ships though. No, in some cases cruise liners have installed CO2 systems to cool their larger refrigerators and freezers. Again, I looked around for any mention of R-744 being used in refrigerated cargo transport on trucks but saw no mention of it. This may still be down the road.
Automotive Air Conditioning
This one is definitely unique. If we rewind about ten years ago there were two refrigerants to choose from for automotive air conditioning. The first was the ever popular HFC R-134a. I am sure most of you are familiar with this refrigerant. You can buy cans of it at your local O’Reillys. At this time though a new refrigerant was introduced to the automotive sector. This refrigerant known as R-1234yf, was an HFO refrigerant invented between a partnership of DuPont and Honeywell. YF was to be the refrigerant of the future. It would replace R-134a and it would be used in every car from now on.
Most of the world was on board except for Germany. The German automakers had tested with YF and found that it was flammable. In one instance during a simulated collision the lines ruptured and spilled the refrigerant onto the hot engine block. The refrigerant ignited and caused a fire. This one test scared the German automakers, especially Daimler, away from using YF. While the rest of the world pushed forward with YF Daimler set off on their own to create the first automotive R-744 application.
Years later they achieved their goals and we now have German made cars using CO2 as their refrigerant. There is now no risk of flammability with their cars and they are still being environmentally friendly. I love hearing this story again and again as it’s a prime example of forging your own way and still coming out on top.
Japan has put forth a lot of focus on R-744 heat pumps. CO2 heat pumps can produce a much higher temperature output then a traditional HFC heat pump system. This is thanks in part due to the transcritical process. These heat pumps can heat water all the way up to one-hundred and ninety-four degrees Fahrenheit (source). The adaption of CO2 based heat pumps is moving forward, but it has been slowed due to the extremely high operating pressures and the breakage of components. (The same story we have seen in other CO2 applications.) In the future we will most likely begin to see CO2 heat pumps in mini-split air conditioner systems. Perhaps, down the road, we may even see them in traditional split air conditioning systems.
From my experience a typical ice rink uses either Ammonia, R-22, or an HFC such as R-134a or R-404A. What refrigerant is used seems to depend on what country you are in. Outside of America the standard refrigerant has been Ammonia. As we discussed earlier in this article Ammonia is widely seen as the most efficient refrigerant. When dealing with such a large application like an ice rink efficiency is a must. The downside of course, is the toxicity. The toxicity is especially important when it comes to a public area like ice rinks. It’s not just technicians or employees who are at risk but you also have the general public.
Here in America we are always hesitant to use the more ‘dangerous’ refrigerants such as Ammonia or Hydrocarbons. Because of this hesitation we instead went the route of R-22 for our ice rinks and hockey arenas. Now though, with R-22’s phase out coming to a close in 2020 ice rink owners are looking for alternative refrigerants. Sure, there are HFC and now even HFO alternatives that can be used in these applications but each of these alternatives still have a higher then neutral Global Warming Potential (GWP). The problem with these refrigerants is that they will not stand the test of time when it comes to climate impact and phase outs.
If I was an arena owner or manager I would only seriously be considering two options. The first is Ammonia like I discussed earlier. This comes with it’s own risks but you get the low cost and energy savings. The alternative is R-744 Carbon Dioxide. R-744 has it’s own Pros and Cons which I’ll get into in our next section, but the big selling point is that you get a climate neutral refrigerant that is safe to the public in case a leak occurs. While R-744 systems aren’t widely found in the world today, they are growing. An article I was reading from 2016 had this quote, ”
“Today the number of CO2 ice rinks is growing rapidly. There are now 25-30 CO2 ice rinks in the world,” he says. 20-25 of these CO2 ice rinks are in North America, 20 of which are in Canada (mostly in Quebec) and three in Alaska, according to EKA.”
As you can see Carbon Dioxide refrigerant is quickly being adapted across various applications here in the United States and across the world. While R-744 does have it’s downsides such as high pressure and more complex systems we have now become to overcome these challenges with new technology and adaptions. Out of all of the refrigerants that are available today I specifically advocate for R-744. This is for two reasons. The first is that it will never be phased out as it is what I like to call ‘Climate Neutral.’ Secondly, Carbon Dioxide is safe. It is non-toxic and non-flammable. These two factors alone make for a great refrigerant.
For more information on R-744 please check out our R-744 Refrigerant Fact & Info Sheet.