As we all know, there is no perfect refrigerant. Each one has its own individual upsides and downsides. It could have a great efficiency but also end up being very flammable. Or, it could be non-flammable and non-toxic but have very high Global Warming Potential. The point I’m making here is that there isn’t a perfect one out there and there may never be. In this section we’re going to take a brief look at the various Pros and Cons of using R-744 as a refrigerant. I pulled this information from all over the web, but one site in particular stuck out to me. This article from Emerson has an entire page dedicated to R-744 Pros and Cons.
Let’s take a look at the Pros and Cons of R-744:
Pros
- Rated as A1
R-744 is seen as the ‘perfect’ natural refrigerant as it is climate neutral and there is not a flammability or toxicity risk. It is rated as an A1 from ASHRAE. While it is non-toxic there is still risk if a leak occurs in an enclosed area as R-744 will displace the oxygen in the room and could cause asphyxiation. It is always best to have a leak detector with you so that you can detect the problem early before anything major occurs. - Energy Efficient
Overall, R-744 is more energy efficient and has better heat exchange then a standard HFC based system. While it may not be as efficient as Ammonia this gap between the two refrigerants is shrunk as the evaporator temperature drops. Carbon Dioxide also has a low compression pressure ratio which can improve volumetric efficiency. In some cases CO2’s volumetric efficiency is four to twelve times better then Ammonia. (Source – under Pressure & Temperature.) - Climate Neutral
I mentioned this earlier, but the biggest selling point of R-744 is that it is climate neutral. It has no Ozone Depletion Potential and it’s Global Warming Potential is one. In fact, R-744 is the zero basis for the whole GWP scale. This is a huge Pro as if there is one thing that business owners are looking for it is stability and consistency. R-744 is never going away due to it being so climate friendly. - Size of parts and components
One Pro to R-744 operating at such a high pressure and being such a dense gas is that the overall size of the parts and components is smaller and the overall charge required for a refrigerant cycle is lessened. In some cases the compressor can be up to ten times smaller than an ammonia compressor. As far as refrigerant charges, one example I read from manufacturing.net stated that to cool a two-hundred thousand square foot warehouse you would need forty-thousand pounds of Ammonia but with CO2 you would need less than seven-thousand pounds. - Readily Available
Carbon Dioxide is readily available and the price for this refrigerant is much less then HFC refrigerants that we see today. This is a welcome relief from the instability of prices on HFCs and HCFC refrigerants that we all know about.
Cons
While R-744 is the ‘perfect’ natural refrigerant in theory there are a lot of downsides.
- Extremely high pressure
The biggest one is for Carbon Dioxide to be used as a refrigerant it has to run under extremely high pressure. As an example, R-744 operates at ten times higher pressure then R-134a. Because of this extremely high pressure everything has to be custom built for an R-744 system so that it can withstand the high operating pressure. This includes the pipes, components, and everything else that goes along with the machine. If lesser components are used then you pose risk of constant failure due to the pressure. - Transcritical System Required
If you wish to use R-744 as a stand alone refrigerant not in a cascade system then you will have to be running it as what’s known as a transcritical system. This is because R-744’s critical temperature point is only eighty-eight degrees Fahrenheit. There are many cases where the ambient temperature could be between eighty to one-hundred degrees. If your critical point for R-744 is only at eighty-eight degrees then how can you expect to remove the heat?
Suffice to say, a transcritical system and a high operating pressure system means two things.- Increased Expense
The first is that there is increased expense for these systems. Not only do you have to pay for high pressure rated materials and parts but you also have to pay for a transcritical system. This setup is different then your standard subcritical system. The good news here is that with each year that passes technology improves and the cost of these higher pressure parts goes down. - Increased Complexity
The second is the increased complexity. The higher the complexity means less available qualified technicians. It may be a struggle to find qualified R-744 technicians, at least here in the United States. Each year though this is getting better as more and more businesses are adopting R-744 systems.
- Increased Expense
- Difficult to have same Efficiency
I mentioned efficiency in our Pros section earlier. The reason I mention it again is that the efficiency of R-744 is highly dependent on the type of system it’s being used in and the surrounding climate. I mean, think about it for a moment. We could have a subcritical cascade system for a supermarket in Miami. Or, we could have a transcritical ice rink in British Columbia. In each example we’re using R-744 but we now have two entirely different systems as well as two entirely different climates. Because of these variety of systems and applications it is difficult to measure one single efficiency measurement.
Conclusion
As you can see from the above synopsis, there is no perfect refrigerant. It all depends on what you are looking for in your refrigerant, what application you will be using it for, and even what part of the world you are in. For more information on R-744 please check out our R-744 Refrigerant Fact & Info Sheet.