Globally and domestically, more and more end users are interested in adopting natural refrigerant solutions. As CO₂ continues to emerge as a formidable option, questions arise regarding system improvements and the changes necessary to implement R-744 solutions.

Recently, Trevor Matthews, founder of Refrigeration Mentor, spoke with Andre Patenaude, CET, director of solution strategy at Copeland, about the emergence of CO₂ and the requirements surrounding its architecture. We’ve transcribed a portion of that interview below. To watch the interview in its entirety, click here or watch below.

Patenaude: More and more retailers know they have to do something. They recognize they have to decarbonize.

One of the first things they need to ask themselves is where exactly is this CO₂ store is going to be located, and how does the climate impact that technology? If the store is in California, there are targets that need to be hit by 2026. There are additional GWP-reduction targets that need to be met by 2030. Retailers know they have to do something.

Location is key. Accordingly, they need to take a look at the ambient temperatures. CO₂’s basic system architecture is quite efficient in low-ambient areas. In most of Canada, for example, 90% of the hours of operation occur below 60°F. Humidity is also important. It can play to your advantage with a CO₂ system, because the wet bulb effect can help reduce condensing temperatures and keep the pressure as low as possible.

Retailers also need to evaluate the technicians in the area. As CO₂ continues to ramp up, service techs will be needed to satisfy the demand. Right now, we're a little bit challenged to get service techs into any refrigeration field. So, when they’re questioning putting a CO₂ store in a region, they need to ask, “Can I find service technicians that have CO₂ experience in that area?” If there aren’t any experienced techs, the fear is that the learning curve may cost them maintenance dollars, high service bills, and CO₂ losses through pressure relief valves, which all add to the total cost.

Matthews: At some point, I’m confident the lack of technician issue is going to be resolved. There are a lot of the schools that are still teaching R-404, or -22, but I know, in the next 10 years, this is not going to be an issue because the new people coming in are going to be learning these technologies and equipment. We find ourselves at a transition point. This one is just a little more drastic than those such has R-12 and R-404, because there are more controls and complexity to it.

Patenaude: Right now, the lack of technicians is a concern — that's the feedback we're getting from our customers. We sit in front of a lot of end users on a weekly basis to talk about low-GWP refrigerants, CO₂, R-290, and even A2L options, and all of these things kind of bubble up in their minds. They're most interested in selling groceries and keeping their costs as low as possible. Those are things to think about. Another thing is what kind of complex add-ons do I need to include on my CO₂ system in order to mitigate the ambient requirements of that specific zone or region?

Matthews: This is important because there is a lot to it. Starting a new store is ‘easy.’ When we talk about retrofits, that’s a different conversation. For example, if a store doesn’t have the right power supply coming into the building, and the CO₂ system is going to require more distribution, retailers are worried about the disruption this may cause. It’s not about techs or the equipment anymore; they're worried about shutting their stores down for a week or more.

Patenaude: Regarding retrofits, you're absolutely right. I've seen some retrofits go on for very long periods of time. We’ve gotten much better at planning and retrofitting on the go, but it can be disruptive, there's no doubt about it. The retrofit model is a different conversation, and we’re starting to see customers develop a strategy now where, if they have a lineup of cases that have reached the end of their lives, instead of ripping and replacing everything at once and having a full store disruption, they're thinking about doing lineups and having distributed CO₂ equipment. They’ll first focus on the low-temp loads or medium-temp loads, and then, maybe a little while later, look at adding another piece of distributed CO₂ equipment to try to keep the disruption as low as possible. But, most have a strategy to transition over time to a full natural solution. When you initiate a plan, you can optimize your suction pressures, giving you an energy advantage.

Matthews: Regarding the total cost of ownership, what should a retailer be looking at?

Patenaude: We did a total cost of ownership study a couple of years ago, and we looked at basically comparing a CO₂ system to a legacy system. A lot of retailers, when trialing natural solutions, want to know how they compare to HFCs, centralized 448 racks, etc. So, we looked at that. We actually had a consulting engineering firm design eight different stores from scratch, including CO₂ — one with adiabatic — and compared them all to a centralized system. We looked at different areas, factors, and climates. We considered the number of compressors, whether you're using an adiabatic gas cooler or a dry gas cooler, how do these factors impact your peak energy, etc.

We focused on annualized energy and peak energy usage because, when CO₂ is operating supercritically, above the critical point of 87.8°F, it can boost total energy costs. During the hot summer months, you may pay a peak demand charge in certain areas. It’s important to consider capex, capex maintenance, and, of course, energy.

Different regions can have different influences on a 20-year total cost of ownership. When you compare CO₂ to other technologies — condensed units, R-290 micro distributed with water-cooled units, and a few other systems — CO₂ fared pretty well overall, especially with adiabatic, when you can mitigate that peak.

Matthews: With parallel compression has been proven to save energy in CO₂ systems. Despite its widespread use globally, why aren’t we seeing more parallel compression units in North America?

Patenaude: We will. Parallel compression is an added complexity, and many end users were waiting to get a good feel from their manufacturers and suppliers about the technology and assurance that they can manage these systems. A parallel compressor is really being fed by an excess of flash gas at a suction pressure that's typically 100 psi higher than the medium-temp suction. So, really, that compressor has more net compressor capacity because the suction is higher, resulting in a lower compression ratio. So, that's a good thing, because the total heat of rejection going into the gas cooler is lower, and the energy is less because compression ratios are less. OEMs may look at it and say, “OK, well, I can downsize this compressor, and my parallel compressor will give me the same capacity as the medium temperature, because I want to bring it 100 psi higher. So, there are net advantages to parallel compressors that digest excessive blast gas from flash tanks in the summer.

When we compared results in 13 climate zones across 166 cities throughout the U.S., there are nine climate zones that see an energy advantage using parallel compression annualized versus adiabatic. For that reason, you’re going to start seeing more parallel compression very soon.

visit the Refrigerant Mentor landing page on YouTube for more.