Contrary to how it sounds, when carbon dioxide (CO2) is used as a refrigerant, this doesn’t mean that it’s being used as the fuel source, “I didn’t think that was something we actually needed to specify until we had a customer ask, “Wait, so I’m burning the CO2?” joked Andrew Macaluso, product manager of systems solutions for Watts Water Technologies, and Brian Cummings, product manager of decarbonization solutions for Watts Water Technologies.
CO2 has been used in modern refrigeration for around 100 years. But the resurgence of R744 as a refrigerant has been during the last 10 to 20 years. Over in Europe, it has been used for around 50 years.
Often found in supermarkets and transport refrigeration, this type of technology has begun to branch out into hydronic practices, with the introduction of CO2 heat pump water heaters into the Canadian market. There are several available on the market, including Lync’s Aegis heat pump water heater and Mitsubishi’s City Multi QAHV. “Heat pumps are meant to provide space comfort where you need heating in winter and cooling in summer,” explains Pushpinder Rana, senior manager of commercial products and industry relations, HVAC division for Mitsubishi Electric Sales Canada Inc. “Now heat pumps are also getting into hydronic solutions. You can use heat pump technology to provide hot water or chilled water as well. This is different from our traditional electric water heater.”
This is one of the fundamental shifts currently occurring within the market. There is an expectation within the industry that more and more solutions will be offered. “I think it’s the best solution because its global warming potential is so low and that has become a hot topic for our industry anyway. It is non-flammable, plus, it has a high heat transfer coefficient,” said Rana. This also means that CO2 performs quite well in Canada’s cold weather climate. “It’s kind of what separates the CO2 products from most of the typical refrigerants because HFCs have already seen a lot of adoption in warmer climates,” explains Macaluso and Cummings. “CO2 will work well in a warm climate, but it’s one of the only ones that will also work in a cold climate and that’s really where it differentiates itself. I would say that generally speaking, it’s going to work better than what’s available on the market today for cold climates.”
Refrigerant benchmark
As previously mentioned, CO2 refrigerant has a GWP of one—it is commonly referred to as the benchmark for comparing GWP values against other refrigerants. “There are so many refrigerants in the market. But it’s CO2 which is used as a benchmark to calculate the GWP for all other types of refrigerant available in the market,” explains Rana.
While it’s difficult to compare natural refrigerants based on its environmental impact, the decarbonization trend within the industry has been a driving force for the adoption of R744 refrigerant. Each type of natural refrigerant, whether it may be ammonia, CO2, or propane, has its place for when it should be used for a project. Nowadays, CO2 lends itself well to domestic hot water production and supermarket applications, while refrigerants like ammonia work well in industrial applications. But because of safety concerns, it isn’t as commonplace within commercial or residential applications, explains Macaluso and Cummings.
Although CO2 has been making some headway in the commercial sector as companies are looking to decarbonize the grid, “Your warehouses are now looking at CO2 as well. Your meat processing plants, or smaller processors are going to look to CO2, especially the ones that are part of large organizations that have sustainability goals. They’re the ones that are going to look at it first,” explains Andre Patenaude, director of solution strategy, cold chain for Emerson Commercial & Residential Solutions.
It could even penetrate into the residential market and commercial applications, such as hotels or office buildings, adds Rana.
Electronically charged
There may be many individuals that will turn to carbon dioxide for their refrigeration solutions solely due to its energy savings, but as the technology becomes more commonplace, more people will likely turn to it for other reasons. As Macaluso and Cummings put it, “I think what we’re going to see is people looking at them for other reasons… maybe it’s just an energy cost savings or maybe beyond that. They’re looking to not only electrify but shift their electrical load and storing energy in water versus storing it in a battery gives them a lot more flexibility in how they do that. I think that as this starts to become more and more commonplace, you’ll see more people looking at it for a variety of reasons beyond just, ‘hey, I want to be the green guy on the block.’”
This brings something important to light regarding carbon dioxide systems—everything is electronic, reports Patenaude. There are no mechanical valves other than shut-off valves. Since it is operated at such a high pressure and it is an extremely reactive refrigerant to pressure and temperature changes, electronics are the only type of product that can react quickly enough to changes within the system.
In addition to high-pressure concerns, there are other safety concerns to keep in mind, which include asphyxiation, trapped liquid, dry ice, and freeze burns, explains Patenaude. Keeping up to date on the latest training will help ensure that no one gets injured on the job.
Knowledge is power
When asked what advice he’d give to contractors working with CO2 systems, Patenaude stated that he’s been giving the same advice since he started working with CO2 back in 2014, which was to start learning now. “It is never going to go away, and it will become a larger part of your daily life sooner than you think. One of the things about CO2, which is also a concern, is the fact it’s electronics based—everything is controlled by electronics. No longer can a good refrigeration mechanic get away with doing a good job because he’s not that savvy on controls. Controls is a major part of CO2 systems and will continue to be.” In addition, it’s important to understand the difference between natural refrigerants, like CO2, and HFCs.
Most manufacturers will offer some type of training to keep up to date. At Emerson they designed and built a Mobile CO2 Training Unit back in 2015 to provide the industry with transcritical booster training.
Looking to the future, carbon dioxide has lots of opportunities at finding itself in other sectors of the industry, including residential applications. “With time I think natural refrigerants, like carbon dioxide, have a good future. We expect more and more innovation or product range should be available in the heat pump format so that we can even work in our typical commercial and residential application where heat pumps have a great fit,” explains Rana.
As more products are available in the market, this will help drive adoption and drive down the price, “I’m looking at my whiteboard right now and you know, I’ve got four different consulting engineering firms working with us already on heat pumps for CO2 for various reasons (water heaters, air space, light industrial) because of new compression technology that Emerson has developed,” explains Patenaude. “It’s not out yet, it’s still in the development phase. But those are the things that are going to move the mark towards more CO2 adoption, as OEMs continue to design and refine and improve efficiencies and take cost out and simplify architectures. That’s going to drive adoption and drive down the price.”