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CO2 as a Refrigerant — R-744 Advantages/Disadvantages

This is post number seven of a series.

Weighing the Advantages and Disadvantages of R744

Table 1 outlines the advantages and disadvantages of R744 as a refrigerant. The list of disadvantages appears smaller than the advantages list, but these issues should not be overlooked, as they have a significant impact on the safety and reliability of R744 systems.

Table 1: Advantages and disadvantages of R744 as a refrigerant

Table 1: Advantages and disadvantages of R744 as a refrigerant

Future articles in this series will cover additional topics concerning R744 in more detail, including the general aspects of R744 systems; more specific information about the design of R744 cascade, transcritical booster and secondary systems; and key points about their commissioning, operation and service.

Andre Patenaude
Director – CO2 Business Development, Emerson Climate Technologies

Visit our website for additional information on CO2 Solutions from Emerson. 
Excerpt from original document; Commercial CO2 Refrigeration Systems, Guide for Subcritical and Transcritical CO2 Applications.

What Are E360 Forum Attendees Saying?

We launched our E360 initiative last year with the intention of creating a dialogue that would address the many issues facing the HVACR industry today. Our hope was that by incorporating the perspectives of every segment of the industry we could achieve consensus and collectively shape the future of refrigeration and A/C. So far, we’ve hosted three daylong E360 Forum events in the U.S. and Canada to provide a format where information can be shared and this dialogue can take place.

We hope you’ve been able to attend a complimentary E360 Forum and make your voice heard. Our next event will take place in Dallas on Thursday, Sept. 3; we encourage you to register today and make plans to attend. If you’re wondering if it’s worth the effort, we thought we would share a few testimonials we’ve gathered from previous sessions. Based on what past E360 Forum attendees have said, these informative events have provided many valuable, timely insights.

E360 Forum Testimonials

Here are just a few recent testimonials.

  • “Some of the biggest takeaways were learning about the changes happening in the foodservice industry, and how energy and environmental challenges are playing huge roles. Seeing how these things are interconnected was an eye-opening experience.”
  • “I would absolutely recommend these E360 Forums to everyone in the industry who wants to grow their business.”
  • “Whether you’re an OEM manufacturer, wholesale distributor, contractor or a consultant, these events have fantastic information for everybody involved.”

We’ve also compiled a video of testimonials from our E360 Forum events so you can see for yourself what your peers are saying.

Join Us This September in Dallas

Make plans now to attend our next E360 Forum on Thursday, Sept. 3 at The Westin Dallas Fort Worth Airport in Irving, Texas. Register today at, and be sure to invite all of those on your team who could benefit from this important industry event. You don’t want your team to miss out on these insights for the road ahead.

Making Sense of Servicing CO2 Transcritical Booster Systems

Amidst increasing regulations to phase-down hydrofluorocarbon-based (HFC) refrigerants, global adoption of CO2 (R744) as a natural alternative is on the rise. But to successfully perform service on a CO2 system, mechanics will need proper training and a deep understanding of the refrigerant’s unique properties.

Seven Keys to Servicing CO2 Systems

Our 13th Making Sense webinar, Seven Keys to Servicing CO2 Systems, offered a basic primer on CO2-based refrigeration and discussed the many implications of servicing a CO2 transcritical booster system. The webinar was presented by Andre Patenaude, director of CO2 business development for Emerson Climate Technologies.

Andre introduced common CO2 system architectures — secondary, hybrid cascade and transcritical booster; the latter is the only system that relies completely on CO2 as its only refrigerant. He explained that CO2’s global adoption has largely been driven by its effectiveness in cooler climates due to its low critical point of 87.8 °F. This is primarily the reason that subcritical systems (where the ambient temperature is typically below 87.8 °F) have been successful to date. It’s also the reason that CO2 transcritical booster system technology (above 87.8 °F) is evolving to enable operation in warmer climates.

In addition to low critical point, Andre explained two other primary differences between CO2– and HFC-based systems:

  • High triple point (where three phases of refrigerant co-exist) — the triple point temperature for CO2 is -69.8 °F, but the pressure is relatively high at 60.4 psig. Technicians need to avoid approaching that point, or the CO2 refrigerant will turn to dry ice in the system. This is why systems need to be charged with vapor CO2 first in order to reach sufficient pressure (145 psig) before switching to its liquid form to complete the charge.
  • High pressure — historically, CO2’s high pressure has been the primary concern for adoption. At supercritical mode, on a hot day above 87.8 °F, the pressures on the roof (condenser) could be as high as 1,400 psig, with temperatures approaching 240 °F. To handle those conditions, stainless steel piping is required. A pressure-reducing valve is also needed to lower the pressures to a point where it’s similar to working with an HFC system (400–500 psig).

Because CO2 transcritical booster systems lose efficiency in warmer climates, several techniques are used to offset the impacts of high ambient air temperatures.

  • Spray nozzles — condenser that mists water to cool air across condenser coils
  • Adiabatic gas cooler — wet pads lining the outside of condenser are used to cool air and keep the system from going into transcritical mode
  • Parallel compression — flash tank feeds an independent compressor with increased suction pressure and smaller motor
  • Subcooling — cools the gas to increase efficiency
  • Ejectors — a means of using high-pressure gas energy to reduce evaporator superheat and increase suction temperature

Andre stressed the importance of having a plan to deal with power outages, including designing systems with generators and standby condensing units to keep CO2 pressures from building up during system shutdown. In fact, retailers should test the effectiveness of their response by performing a trial power outage.

Most importantly, service technicians should be well-trained to understand the intricacies of dealing with CO2-based refrigeration systems.

To hear this webinar in its entirety, please visit the webinar archives on our MAKING SENSE website.

CO2 as a Refrigerant — Comparison of R744 with Other Refrigerants

This is post number six of a series, and compares CO2 to both traditional and new refrigerants.

R744 vs. Other Refrigerants

Table 1 shows a simple comparison of R744 with other types of refrigerants, including those that are currently commonly used and those that are currently being evaluated for future use. It uses a simple “traffic light” system and employs the common HFCs, such as R404A and R134a as a baseline.

This provides a simple introduction to the options — the situation varies globally, especially in the availability of refrigerants, components and expertise.

For retail applications a well-designed and installed R407A/F system generally has better efficiency than R744 systems. However, the overall environmental performance of R744 systems is better, primarily because of the low GWP in the event of leakage.

Table 1: Comparison of R744 with other refrigerants

Table 1: Comparison of R744 with other refrigerants

Blog post seven in this series will weigh the advantages and disadvantages of R744.

Andre Patenaude
Director – CO2 Business Development, Emerson Climate Technologies

Visit our website for additional information on CO2 Solutions from Emerson. 
Excerpt from original document; Commercial CO2 Refrigeration Systems, Guide for Subcritical and Transcritical CO2 Applications.

Compressor Diagnostics Save Merchandise and Reputations

Imagine: you close your market at the end of the day, and the next morning you return to find your merchandise spoiled because your refrigeration system failed overnight. Though it doesn’t happen often, it takes just one failure to cause catastrophic losses for large and small businesses alike.

For one small-town meat market, this nightmare nearly happened due to a faulty defrost timer on the walk-in cooler. On an ordinary system, a series of events would occur, eventually ending with spoiled meat and possibly ruined equipment. But because the market’s cooler had a scroll compressor with CoreSense™ technology, quick action from staff saved both the meat and the equipment.


While the timer is not part of the compressor itself, the diagnostic technology was still able to save the cooler from failing. It sent an alert to the facility manager, who brought in a qualified contractor to identify the issue with the timer, repair it and reset the compressor. More than $10,000 in food was saved, and the compressor and cooler weren’t damaged. And since store managers became aware of the issue as it occurred, they were able to closely monitor product integrity and ensure they maintained the quality their customers expect.

Ideally, like in the meat market situation, personnel would respond quickly to the notification and address the cause of the failure. If no one responds, however, the technology directs the system to reset for up to four hours. At the end of this four-hour time period, it shuts down the compressor and waits for a manual reset. Although the food would begin to spoil at that point, the equipment would be saved.

This blog is a summary of “Nightmare on Steak Street: Saved in the Nick of Time” in the latest edition of Emerson Climate Technologies’ E360 Outlook. Read the column in its entirety and download the digital edition.


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