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CO2 Properties, Best Practices & Benefits [Transcript]

Posted by Super Radiator Coils on Jun 14, 2022 9:36:37 AM

Note: the following is a transcript of a podcast. To listen, check out the SRC Podcast here or wherever you get your podcasts. 

Nate Budryk: Hello and welcome to another SRC podcast. Today, we’re talking about one of the poster children of the natural refrigerant push, which is CO2, also known as R744 or carbon dioxide. Today’s conversation will include a brief overview of CO2, some specifics of the refrigerant & CO2 systems, and some industry general best practices. To help us do that today are two CO2 experts: Will Klick, who serves as sales application engineer for SRC, and Wynand Groenewald, a director at Future Green Now, which is a CO2 consultancy based in South Africa. Will and Wynand, how are you doing, guys?

Will Klick: Doing pretty good today. How about you, Nate?


Nate Budryk: Good, good. Wynand, how’s it going?


Wynand Groenewald: Well, good. Getting to the end of our day here but hopefully, you guys still got a full one ahead of you. All good. Thanks for having us.


Nate Budryk: Absolutely. Absolutely. Thanks for coming along and doing this with us. First off, let’s go into a little background and history of CO2. Its usage can be traced back well into the 1800s where it was used, as I understand it, for things like shipboard refrigeration. It was also commonly used for other applications from the 1920s up until the development of synthetic refrigerants, dichlorodifluoromethane, or R12, around 1935. The synthetic refrigerants were the death knell for CO2, essentially rendering it obsolete. Later on, we learned, of course, that synthetic refrigerants, and HFCs, and stuff like that were harmful to the environment.

Starting around 2008, R744’s popularity started growing in places like Europe and Canada for refrigeration applications like refrigerated food warehouses, supermarkets, stuff like that. Today as Will and Wynand will illustrate, CO2’s place in the market continues to grow and evolve as new technology emerges and environmental regulation moves the refrigerant world away from synthetics. So, now onto some specifics of CO2 and CO2 systems. Well, if you’ve spent any time researching CO2, you’ve likely heard the term subcritical and transcritical, which are obviously some important terminology to be able to define and understand. Wynand and Will, can you guys break down those terms for the listeners and help them understand what each means and the implications on your system?


Will Klick: Certainly. Subcritical CO2 is anything operating below the critical point, so 88.7 Fahrenheit or about 31 Celsius, and 1,0071 PSI, or about 74 bars. When it’s in those conditions, it’s operating more like a traditional refrigerant where you run through your condenser. It condenses to a liquid and operates fairly similarly. It’s a little bit lower pressure as well. At that point, it’s more of what we all understand as refrigerants. However, once you get above those points, which let’s face it, most parts of the world you’re going to get above 88 degrees at some point, that ends up getting into the transcritical phase, which is where it stops acting like a normal refrigerant. You’re going to stay as a gas as it runs through what would be your condenser, which is now a gas cooler. It’s just cooling the gas. You have some large temperature swings in there so you can change 100 to 200 degrees pretty easily in the gas cooler. While a condenser, you would just be a constant temperature and it’ll stay in the gas phase the entire time. The other thing you need to watch with that when you go back to that subcritical is if you drop that pressure too much, you end up forming dry ice if you get anything below about 75 PSI.


Nate Budryk: Got it. Wynand, do you have anything to add to that?


Wynand Groenewald: In transcritical operation, one of the things you need to remember is no pressure temperature correlation. In that case, CO2 flexibility where you can, above the critical point, basically determine or dictate the pressure that your system wants to run to. I think one misconception as well perhaps around subcritical and transcritical systems is that it’s referred to, as Will said, where you’re operating. The same system can operate in a sub or trans critical manner at any time depending on the ambient conditions or where you choose to operate that system. A lot of times, we do get asked, “Is this a trans or a subcritical system?” It’s both depending on where it runs and what your conditions are.


Nate Budryk: Got it. With those properties in mind, Wynand, you mentioned that a subcritical versus trans critical system, that’s not exactly the right terminology, right? It could be both, like you said. I know that there are some different designations of CO2 systems with two of the ones that I hear most about being booster and cascade systems. Do you think you could give a few bullet points about each one of those and just define each one for us?


Wynand Groenewald: Yeah, sure. I mean basically in a summary, cascade versus booster type system is exactly around the sub and trans critical operations. A cascade system is designed to have an alternative refrigerant or medium on the high side. The reason for that is you’re keeping your CO2, which is on the low side, in a subcritical manner all the time. Basically, that’s what a cascade system is. You’re cascading heat in various levels. Typical cascade systems will either be 1 through 4A system condensing the CO2 on the low side or an ammonia system that’s condensing the CO2.

Your ammonia system is subject to the atmospheric conditions, but the evaporation side of the ammonia system is condensing your CO2. Your CO2 refrigeration cycle will see the same conditions all year around. Therefore, operating in a subcritical manner all year round. Your booster type system is where you have CO2 only as a refrigerant. Your LT refrigerant or your LT application would discharge into the suction of your medium temperature compression group. From here, your medium temperature compressive group will go into a gas cooler, and you will be subject to ambient conditions. One thing that brings an element around this is now you start introducing your high-pressure valve, flash gas valves. You start introducing some additional control valves that’s not predominantly found in HFC-based systems or even ammonia systems but that you do find in CO2 systems. Then obviously, that system can operate in a trans critical manner because it’s subject to ambient conditions.


Nate Budryk: Applying some of those booster and cascade systems. Let’s shift over to an application focused discussion. When we were talking earlier in some prep for this recording, you mentioned that supermarkets tend to be a market’s entry point into CO2. What kind of system would be in a supermarket? Would that be booster or cascade?


Wynand Groenewald: In a supermarket, you would see both. Let me put it this way. Traditionally what I can say in history, you would have seen a medium temperature refrigerant that’s HFC based serving all the medium temperature applications. CO2 on the freezer applications would be cascaded off that system. This would be a way to introduce CO2 to the contractors and service technicians and get everybody comfortable. Today, predominantly your booster system is what you will find in a supermarket system.

The main reason for that is it is a 100% natural refrigerant. It’s difficult to use an ammonia refrigerant on the high side due to regulations and because of the toxicity and ASHRAE classification of ammonia. Therefore, if you want to have a carbon neutral refrigerant system, you need to put a CO2 transcritical booster-type system in. Whereas the cost associated with cascade system, predominantly also looking at retail where your cooling capacitor requirement is not as high as industrial. It does become costly to look at a cascade-type system. Your cascade-type system is still found more in your industrial applications. A lot of industrial applications where you can have your ammonia, I call it as a secondary medium just for your high temperature and medium temperature applications. You might have CO2 being either a liquid overfeed or a TX type system but being condensed by the ammonia system. Technically, maintaining your ammonia in your plantroom or machine room and you’re using glycol/CO2 as a secondary medium to do your additional cooling at lower temperatures.


Nate Budryk: And that’s a well understood application market at this point for CO2. So much so that recently, Target announced that, I think, by 2040, it would be moving all of its supermarkets. I think that referred to display cases. It would be moving all to CO2 by that year, or they were going to develop a plan to get there by 2040. That’s pretty crazy to see because before, I think, 2008 we said, it wasn’t really much of a blip on the radar. CO2 is definitely getting some legs under it as a refrigerant in the mainstream. Let’s go non-mainstream then. I know both of you guys have done some work in some less commonly understood applications. Wynand, what are some interesting or cutting-edge applications you’ve seen CO2 used for that you think make a lot of sense and could maybe catch on?


Wynand Groenewald: I mean we’re seeing a lot of suppliers bringing out ways to make these refrigeration systems more energy efficient. From an application point of view, definitely one of the biggest requirements or the biggest applications I do see coming up for CO2 as a refrigerant is in the heat pump industry. Especially I know a lot for argument’s sake California is trying to move away from gas heating to electrified heating. Then your electrified heating needs to be done with a CO2 heat pump. Your refrigerant that you need to use, it’s going to have to be below a certain GWP value. That leaves the CO2 heat pumps as your almost only or one of few solutions for heating applications. One benefit of CO2 in the heat pump applications is the high temperatures you can get out of it. I mean you can 180+ temperatures out of it. That, all of a sudden, puts heat pumps in not just domestic situations and applications but also food processing, boiler preheating, drying requirements. It puts CO2 right up into those applications where even standard heat pump systems are not always capable of serving those applications.


Nate Budryk: I think it’s a lot more versatile than people think, right.


Wynand Groenewald: Yeah.


Nate Budryk: Will, what about you?


Will Klick: We’ve also been seeing a huge influx of inquiries about heat pump systems. A lot of the water heaters seems to be a big market right now. Again, as Wynand was pointing out, California and Washington as well have both started pushing to get rid of fossil fuels in any new construction. Something’s got to take their place. CO2 has been a great application for that. As you were saying with the high pressures you can run at high temperatures. We’re seeing a lot of people where they are trying to do large apartment complexes or even some light industrial applications that they can heat up the water with that CO2 system using essentially an evaporator on the roof and a plate and frame exchanger inside the building. That’s how they’re controlling their entire building. It’s going to be a big push here soon.

We’re seeing a lot of it now. To my knowledge, there’s not too many people in the market that have the system currently available but they’re coming soon. We’ve all seen a customer that both Wynand and I have worked with, they actually built a chiller system that is used in a heat recovery as well. They're chilling down a process system, whether it’s dairy or brewery, and then they’re taking that waste heat and they’re actually recovering that into storage water for washdown. They can clean their facility with the heat that they’re pulling out of the product. It ends up being substantially more efficient and helps drive down the costs of the equipment.


Wynand Groenewald: There’s another one. This just comes back to the properties again like we touched on right in the beginning of what I said. When you’re operating a CO2 system in transcritical mode, you do not have a pressure-temperature correlation. This is quite important to understand when you design a system for heat reclaim or if you incorporate heat reclaim on a standard system. The main difference is, without getting too technical, with a standard phase change refrigerant or an HFC based refrigerant, the discharge pressure is determined by what you condense. You can force yourself to condense at a higher temperature but by doing that, you need to increase your condensing temperature, which means you’re paying a very big penalty from a power usage point of view.

With CO2, because we incorporate a high-pressure valve, in the transcritical mode there’s no pressure-temperature correlation. We can still reject as much heat as we want but we can choke the system to run at a very high discharge pressure or higher discharge pressure, which allows us to get maximum heat out of that refrigeration system. The benefit of this is even in your colder areas where predominantly heat reclaim off of an HFC based system, when you need it the most in the winter, it’s not as successful as it should be with a CO2 system. In the winter you can get maximum heat and 98% of the time, the heat you can get out of a CO2 refrigeration system is enough to suffice for all the heating requirements with a typical supermarket.


Nate Budryk: From cost savings obviously by some efficiency gains. There’s also another pro of cost saving from a refrigerant cost. In the research I did, I saw typically six to eight dollars a pound for HFCs, like R404A, and then anywhere from $12 a pound and up for newer HFOs R-1234yf or R-1234ze. And then CO2 conversely, sells for typically between $1 and $2 a pound. Does that sound about right to you, Wynand, Will?


Will Klick: Sounds about right. The refrigerants have actually been going up a lot though. Last time I had looked at R404A we’re actually looking around $20 a pound. It’s been a pretty substantial jump over the last few years. With the phase temps coming, that’s only going to increase greater. CO2 is going to become much more cost competitive with just the refrigerant costs alone.


Wynand Groenewald: Yeah. Will, you mentioned in the beginning the GWP peak level one potential of CO2 is one. Never mind is it cheap to change CO2. We also need to understand basically the reason why CO2 has a GWP of one is because it’s used as the benchmark. Basically, at the end of the day, we are borrowing CO2 from the atmosphere and we’re putting it in a system for a short period. If we release it, we basically just back to where we were at square one. That’s basically the explain the GWP of one. If carbon dioxide was not used as the benchmark for all other refrigerants, it probably would have had a GWP of zero because it’s a natural occurring refrigerant.


Nate Budryk: Got to set up our frame of reference, right, somewhere?


Wynand Groenewald: Yup.


Will Klick: To tie in with that too, it makes it a great benefit when you go to work on your systems because if you’re releasing most HFCs or all HFCs, you’ve got to do recovery operations and there’s a lot of very stiff fines and penalties if you have any release of those refrigerants. CO2, you can open the valve theoretically and just dump the atmosphere if you really just want to get rid of it.


Nate Budryk: Those are some of the reasons behind the popularity of CO2, the pros of the refrigerant. Now, moving onto the con side of things. Some of the reasons behind either industry skepticism or hesitancy around adoption. Wynand, in your experience, what have been some of those barriers to adoption - either founded or less founded? Some reasons that you hear of people being hesitant to adopt CO2.

Wynand Groenewald: The main reason is the unknown. People are set in ways. A lot of guys do not want to change. It’s a big change. I mean we’ve had changes over the last few years. We had drop in refrigerants. Worst case scenario, you need to change some seals. You need to change oil. Do a few tweaks on the settings on the valves and stuff like that. I mean with CO2 you are really changing big-time. Number one is the reluctance. Number two, I mean the pressure side of it. Everybody perceives it as a high-pressure especially if you use on the HFC side of life operating there. Then again, I don't know. I’m always looking at a silver lining. I see it as a benefit to CO2 because all of a sudden, your quality of your system and componentry has gone way up.

You guys will know from a manufacturing point of view, there’s no shortcuts and no one is going to give you a fake gas cooler or product for CO2 in the market. It won’t last. Workmanship has gone up. That is the benefit that come with higher operating pressure. It’s not really that high. I mean what people sit on forklifts every day. You’re sitting on much higher pressures below your bum than what’s in a CO2 refrigeration system. There are misconceptions as well. Fear of the unknown and then looking for misconceptions. I know one that’s definitely coming up is the one that a lot of guys do require is say that CO2 is not as efficient as other refrigerants available on the market and predominantly in high ambient conditions. This is something that we’ve tried, and tested, and showcased over a lot of time.

South Africa is definitely a high-ambient climate zone. We’ve been running CO2 systems here efficiently for years and all over the world. I mean Australia, even the Middle East has CO2 refrigeration systems operating. The misconception of that is you need to look at CO2 on an annual basis. There’s a lot of benefits from CO2 in terms of better heat transfer, which you don’t see or perceive with you look at COP (coefficient of performance). One of my tips to people would be do not look at COP and do not look at your worst case 0.5% ASHRAE designs if you want to see how a CO2 system performs against another one. Look at an annual basis. Design fresh. Return on invest for annual. I guess that’s what I would like to say.


Nate Budryk: I guess both you guys can probably chime in on this one. We had talked about general immaturity of the supply chain of componentry for CO2 systems. What are some of the componentry that is harder to find?


Will Klick: Sometime for the coils that we run into, they then use a special alloy for your tubes, or you’ve got to use a fairly heavy wall copper that isn’t as standard as some of the systems you see out there. It’s certainly nothing that’s insurmountable and obviously, we’ve been working on it for a long time. On the header side, you also run into some issues with the large diameter pipes you’ve got to use for your header. You need to use a HXP or a stainless type of material to be able to stand those pressures of the larger diameters. Again, it’s nothing that’s hard to come by at this point. The market there has really stepped up. Beyond that, there’s actually not a huge difference in the component makeup of it. The overall materials are the same. They’re built the same.

You’ve just got to focus on the design side of it where you need to compensate for the different temperatures and being a gas the entire time rather than condensing. On the greater system side, you’re running into a lot of issues, at least in the US, where manufacturers, distributors, and compressors are still working to get up to the point of having everything they need particularly in the TXV valves seem to be hard to come by at the pressure rating. What we found though in working with a number of different customers, many of those valves are actually able to withstand the pressure. There just hasn’t been the demand to have a new UL listed to it. I know I’ve seen some companies where they were actually getting their own UL listing on a manufacturer’s TXV valve or different components. It’s just a matter of getting those certifications up to the level that they need to be.


Nate Budryk: That speaks to some of the newness I think of the market overall, right? It sounds like the supply chain is a lot more mature over in your neck of the woods and Australia. Places like that. Does that jibe with your experience for American jobs and stuff? Have you seen that in the supply chain too?


Wynand Groenewald: Yeah, there’s two things. Let’s put it this way. Doing a few projects and stuff in the US, what we can use outside of the US, and the European market, or South African market that we know is fairly available is not always UL registered or listed already in the US. Another thing as well is the problem is a lot of the componentry is pressure rating gets derated when they go into UL. I know a lot of plate heat exchangers especially on the discharge side where they are 130 bar rated in Europe are now 120 bar rated in the US because of the UL pressure factors and the way they list it in the UL side of life. One thing we need to understand, where the supply chain will catch up, is although CO2 is really a hot topic, it’s still also one of the biggest potentials that coming up.

Like you said it earlier right in the beginning, Nate you said, the supermarket chains and there’s a lot of guys putting their hands up and saying they want to be 100% CO2 when, what, 2040, 2050. That’s around the corner. Forget the industrial. If you only look at retail, worldwide less than 2% of the market is actually, of the install market, is only on CO2 and 98% of what is installed currently in the US, outside of the US worldwide basically needs to be converted to some sort of natural refrigerant if we want to all go to being natural. I mean that’s massive. That means the supply chain with CO2 is still supplying the minority, sadly.

I think this is really starting to change. It’s getting more and more there. It’s a trend that we’ve been following. In Europe specifically you can see it. Majority of the European market is utilizing CO2 at the moment where the usage of CO2 is outweighing the usage of HFC based and also the taxation on that. We’ve seen the trend of CO2 component keeping a very stable cost over the last two, three, four, five odd years. Where the cost of HFC based equipment has just skyrocketed. I don’t want to speak out of turn for Europe, but I actually think in certain countries in certain areas within Europe, it’s actually more cost effective to put a CO2 system down than an HFC based system.


Nate Budryk: Yeah, I think that’s the idea, right? They want to make this stuff that they’ve deemed environmentally harmful expensive, hard to get, and then they want to funnel folks into finding creative ways of using CO2 to make them more applicable across a wider range of circumstances is the idea.


Wynand Groenewald: True.


Nate Budryk: Got it. Well, I think with that, we can move towards wrapping up. Wynand, if they’re interested in working with you, how can they reach you?


Wynand Groenewald: Sure, thanks. I mean they can get us on a I can share email addresses if you want to maybe put it. People don’t need to try and learn how to spell my name to get my email address.




Nate Budryk: I’ll put it on screen.


Wynand Groenewald: [Laughs] Cool. I mean basically, what we as a company do is we’re a consulting-based company. Like I said, we work a lot in the US, Australia, Middle East, Europe, Africa. Our specialty is CO2. We do everything from product development, to application development, to install turnkey solutions. We work with contractors, OEMs. We basically want to support the industry as much as possible and anybody that wants to go to CO2. Support them by either developing a product or helping them to design, install, drawings, and requirements, and commissioning all startup. A lot of our projects involve converting current HFC based refrigeration products over to CO2 for certain OEMs and stuff like that. Yeah, definitely willing to help the industry. A lot of what’ll happen, or at least with our experience with yourself and Super Radiator, is you guys in your consulting work you’ll have need for CO2 coils for your systems that you’re developing. That’s where SRC and a guy like Will will come in.


Nate Budryk: Will, tell the folks something about your experience and how customers can benefit from working with a company like SRC.


Will Klick: We’ve dealt with systems all across the board. Everything from water heaters we just talked about, to large chiller systems. You name it, we’ve touched on it here. We have a great research department where we’ve designed our software based on substantial testing in our wind tunnel, our refrigerant test labs. When you work with us, we know what the results are, and we know they’re accurate. We test most systems to get good baselines and we tend to be the most accurate people out there. At least, we like to believe we are.


Nate Budryk: Then in the coming years and decades down the road as CO2 usage expands into more industrial type stuff in the United States and just different applications, SRC has nearly 100 years of experience designing heat exchangers for all sorts of markets, from commercial to industrial, to nuclear. We can handle it all. By the time that comes, we’ll probably have a pretty good handle on designing the new stuff as well too.


Nate Budryk: With that, I think we can wrap up. Wynand, Will, appreciate you guys doing this with us. Maybe we’ll come at you with a new podcast down the road. Maybe 2040 when Target finally puts all of their systems in.




Wynand Groenewald: That’s still far off. Yeah, sounds like a deal. [Laughs]


Nate Budryk: Thanks, everyone.


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