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CO2 as a Refrigerant — Five Potential Hazards of R744

This is post number five of a series, and continues our overview of CO2 as a refrigerant by touching on the potential hazards associated with handling systems where R744 is present.

R744 Hazards

R744 is not flammable, but its high pressures, toxicity at high concentration, and potential for dry ice formation must be taken into account when applying and handling. This post explains some of the hazards and provides very general guidance on reducing them.

1. Asphyxiation

R744 is odorless, heavier than air, and is an asphyxiant. The practical limit[1] of R744 is lower than hydrofluorocarbons (HFCs) because of its potential for high toxicity (HFCs are non-toxic):

  • Practical limit of R744: 0.1 kg/m3 (56,000 ppm);
  • Practical limit of R404A: 0.48 kg/m3 (120,000 ppm)

Note: The practical limit is defined in EN378 but may vary in regional regulations.

CO2 TLV Threshold Limit Value is 5000PPM (0.5%), and Ammonia TLV is 25 PPM (0.0025%), which is the highest concentration for an eight-hour limit.

Table 1 summarizes the effect of CO2 at various concentrations in air.

Table 1: Effects of CO2 at various concentrations in air

Table 1: Effects of CO2 at various concentrations in air

If a leak of R744 could result in a concentration exceeding the practical limit in an enclosed occupied space such as a cold room, precautions must be taken to prevent asphyxiation. These include the use of permanent leak detection, which activates an alarm in the event of a leak.

2. High Pressures

R744 systems operate at significantly higher pressures compared to conventional systems, especially when ambient temperatures cause the system to operate above the critical point. As a result, system components, pipe work, tools and equipment must be rated to safely operate at these higher pressures (see Table 2 for more details). It should be noted that the standstill pressure on some systems (e.g., cascade systems) is higher than the maximum rated suction pressure PS (hence, the pressure-relief valve setting). The pressure-relief valve will discharge in the event of a fault such as a power failure.

Table 2: R744 standstill and typical system operating pressures

Table 2: R744 standstill and typical system operating pressures

To ensure the pressure does not rise to the relief pressure in the event of a power failure or sudden system shutdown, these systems can be fitted with a small auxiliary cooling system. This typically runs on an auxiliary (uninterruptable) power supply and will switch on when the pressure rises above a set point (this is lower than maximum allowable suction pressure PS, but higher than the normal operating pressure). The auxiliary cooling system is sized to remove sufficient heat to keep the standstill pressure below the safe low side limit when there is no load on the system (apart from heat absorbed from the ambient).

Care must be taken when charging R744 systems. The maximum operating pressure of some systems (such as cascade systems and parts of transcritical systems) is normally below the R744 cylinder pressure. These systems must be charged slowly and carefully to prevent pressure relief valves discharging. This topic will be covered in greater detail in a future article.

3. Trapped Liquid

The coefficient of expansion for R744 is significantly higher than for other refrigerants. The practical impact of this on liquid R744 trapped between closed valves is shown in the graph in Figure 1.

Figure 1: Relationship between temperature and pressure of trapped liquid R744.  Source: Danish Technological Institute

Figure 1: Relationship between temperature and pressure of trapped liquid R744.
Source: Danish Technological Institute

The example shows the effect of a 20 °C (36 °F) temperature rise on liquid that is trapped at an initial temperature of -10 °C (14 °F). The pressure will increase from 44 bar (638 psi) to approximately 240 bar (3,480 psi). This condition could potentially occur in a liquid line of a cascade system, and similar situations can arise in other parts of the system and in other R744 systems. As a rule of thumb, trapped R744 liquid will increase in pressure by 10 bar (145 psi) for every 1 °C (1.8 °F) temperature increase.

The pressure of trapped liquid refrigerant always increases, but the pressure increase of R744 is much greater than for other refrigerants. This is exacerbated by the potential to trap R744 at low temperatures and hence for the liquid temperature to rise more than for other refrigerants.

Systems should be fitted with pressure-relief protection wherever liquid could be trapped, either during operation or service. Methods of providing this protection will be covered in upcoming articles on the design of R744 systems.

4. Dry Ice

Dry ice (solid R744) is formed when R744 pressure and temperature are reduced to below the triple point (4.2 bar/60.9 psi, -56 °C/-68.8 °F). This will not occur within a properly working refrigeration system, but can occur when:

  • A pressure-relief valve discharges if it is venting vapor R744
  • Venting R744 during service (component change or replacement, for example)
  • Charging a system which is below 4.2 bar/60.9 psi (e.g., an evacuated system)

Dry ice does not expand when it is formed, but dry ice will become gas as it absorbs heat (e.g., from ambient). If the dry ice is trapped within the system, it will absorb heat from the surroundings and turn into gas. This will result in a significant pressure increase.

Dry ice can block vent lines, so care must be taken to ensure that this cannot occur:

  • Appropriate pressure-relief valves should be used — see the upcoming articles on system design for more information about these and how safety valves should be applied;
  • When R744 is vented from a system during service it should be vented as a liquid, and the pressure in the system monitored. R744 should always be vented outside a building.

5. Freeze Burns

Contact with solid or liquid R744 will cause freeze burns and should be avoided. Suitable gloves and goggles should always be worn when working with R744. (The surface temperature of dry ice is -78.5 °C [-109.3 °F]).

My next blog post will compare R744 to both traditional and new refrigerants.

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.

[1] EN378 Refrigerating systems and heat pumps — Safety and environmental requirements
ISO 5149 mechanical refrigerating systems used for cooling and heating — Safety requirements.

Connecting Kitchen Equipment for a Competitive Edge

In today’s competitive foodservice environment, quick service restaurants (QSRs) are only as good as the last meal they’ve served. But unfortunately, cold French fries, warm soda, and over- and under-cooked menu items are all too common. It only takes a few of these negative experiences to tarnish a brand’s reputation in consumers’ eyes.

ConnectedKitchen-Cvr Fast casual restaurants that offer fresher, healthier menus appeal to increasingly discriminating consumer preferences. While fast food restaurants may wish to tap into these changing trends, they struggle to introduce new menu items. And the reality is, there are enough options to make it all too easy for consumers to permanently avoid a particular establishment (or even franchise) altogether.

For nearly a decade, connected equipment technology has been embraced in food retail to optimize facility operations. In foodservice, the concept of connected, communicating kitchens and facility systems is relatively new. Many foodservice operators don’t even realize that the technology exists today to help protect their brand and gain a competitive advantage.

This technology is often referred to as the Internet of Things (IoT) because it combines machine to machine (M2M) connectivity with Internet and/or cloud services to store enterprise data and leverage that data for analytics. It often relies on a supervisory system controller as the “brain” that monitors and controls nearly every aspect of a facility’s operational infrastructure.

Thirty-five percent of total energy consumption in a QSR is directly attributed to food preparation, representing the largest factor contributing to overall energy usage in a restaurant. Restaurant chains can no longer afford to ignore the opportunity to improve energy efficiencies in food preparation.

Another promise of kitchen connectivity is the ability to broadcast new menu items across an enterprise of stores in real time. We refer to the equipment and personnel that make up the food assembly line as the “food factory.” Traditional food factories are currently not equipped to quickly respond to menu changes. In most QSRs, menu changes take place approximately every six months and are notoriously difficult to implement. A connected kitchen that can roll out changes across entire regions or districts in near real time — and do so with greater accuracy with feedback — has a much has a much higher probability for successful menu management.

To make this scenario a reality, foodservice equipment manufacturers are utilizing Emerson’s controls into their systems. Multi-purpose ovens, grills, fryers, holding stations and the like are all being designed with M2M and IoT connectivity in mind. The ultimate goal is to capture data points from nearly every piece of equipment in the restaurant — all in an effort to improve food quality and preserve brand reputations.


Finally, by compiling data on every piece of equipment in the food factory, the connected kitchen maximizes store uptime by preventing critical points of failure. And to ensure safety, it even provides hazard analysis and critical control points (HACCP) monitoring.

This blog is a summary of Paul Hepperla’s column in the latest edition of Emerson Climate Technologies’ E360 Outlook. Read the column in its entirety and download the digital edition.

Get Answers to Tough Questions at Our Next E360 Forum

Countless changes over the last few years have left our industry in uncharted waters. Unlike any time in recent history, we’re confronted with a convergence of regulatory motions and market trends that challenge our basic notions of conducting business. This perfect storm is prompting food retailers and foodservice operators alike to rethink long-held market preconceptions, adapt to changing consumer preferences, and prepare for an uncertain future of EPA and DOE compliance.

There are as many questions as there are answers about how we will weather this storm. That’s why Emerson Climate Technologies created its E360 Forums — to facilitate a dialogue that will answer these questions and help shape the future of HVACR. Our next E360 Forum will take place on Thursday, Sept. 3 at The Westin Dallas Fort Worth Airport in Irving, Texas.

Session Highlights

This free, daylong event will feature timely keynote addresses and interactive breakout sessions to allow you to engage in these important discussions. The keynote addresses will provide information about the latest trends and rulings, while the breakout sessions will allow you to share your concerns and get answers to the questions that keep you up at night. Here are just a few of the highlights:

  • Keynote address: Refrigerant and Energy Regulations Update — As the EPA moves closer to announcing its final rule in refrigerant delisting, Emerson’s Dr. Rajan Rajendran will explain the many potential scenarios and their far reaching implications.
  • Breakout session, food retail track: Trends in Refrigeration System Architecture & CO2Andre Patenaude and Mitch Knapke will explore the trends in supermarket refrigeration system architecture that are helping cut energy consumption and reduce carbon dioxide equivalents (CO2e).
  • Breakout session, foodservice track: Enterprise Management & Communicating Kitchens — Paul Hepperla will lead an informative session on the potential to connect kitchen equipment and enable communication for a variety of benefits.

For more details about E360 Forums, registration information and the complete agenda, please visit our website: As an industry, we feel it’s important that we address the tough issues head-on today, so that we can collectively create a realistic path for our future. But, to achieve that goal, we need everyone’s contribution. We look forward to you lending your voice to this important dialogue at our E360 Forum in Dallas.

Is It Time to Make the Transition to Intelligent, Connected Stores?

Today, food retailers and foodservice operators are making the move toward more intelligent, connected stores to gain insights into all areas of operations. Not only are they looking for ways to reduce energy consumption, equipment and system downtime, or general maintenance costs, but also deliver improved performance levels to maintain a competitive edge. The prospect of connected stores takes the guesswork out of performance benchmarking by offering stakeholders real-time and reliable access to the data that matters most.  Is It Time to Make the Transition to Intelligent, Connected Stores? | Climate Conversations While they share the same objective of improving performance levels, supermarket food retailers and foodservice personnel have vastly different day-to-day business challenges. Food retailer challenges include:

  • Creating a great in-store shopping experience
  • Providing a variety of quality foods and brands
  • Reducing energy consumption — driven mostly by HVAC, refrigeration, lighting and maintenance costs

The drivers in foodservice equipment and building connective are unique:

  •  Providing quality meals with speed and accuracy during breakfast, lunch and dinner
  • Improving the efficiency of the food service processes
  • Ensuring the reliability of the equipment that makes up the “food factory”
  • Maintaining access to qualified local service technicians

In terms of technology adoption, supermarket retailers have led the way in connectivity for years, employing electronic store and system controls to better manage and control their equipment. And, they’ve integrated these controls with their IT networks to gain access to real-time performance data. But this hasn’t happened across the board, and particularly in older stores, the opportunity to drive better store performance still exists. Unlike food retail, foodservice operators have not integrated store controls to enable an intelligent, connected environment. Even though a typical store utilizes 40–45 pieces of equipment with embedded electronic controls, most operators have not enabled the technology to connect them. The few early adopters in foodservice have numerous operational advantages:

  • Remotely managing equipment to ensure reliable operation and consistent foodservice
  • Predicting failures and resolving equipment issues before they occur
  • Programming new menu options in real-time

There are several reasons why the connected kitchen concept has taken off in foodservice:

  1. A store needs both facility and equipment controls that can communicate with each other. Most store controls for small-format retailers have been overdesigned and are too expensive.
  2. The IT infrastructure necessary for connectivity and communication (i.e., WiFi, LAN, GSM, etc.) has not been developed.
  3. Contractors have not supported the move to electronic controls, because it represents new technology and a learning curve.

Emerson’s new ecoSYS site supervisory control platform addresses these foodservice challenges and helps small-format retailers enable communication between embedded equipment in the store. We’ve designed it to be easy to install and operate, and it’s affordable. We believe that the connected foodservice store is coming soon, and we are excited to help the industry make this transition. This blog is a summary of Bill Bosway’s column in the latest edition of Emerson Climate Technologies’ E360 Outlook. Read the column in its entirety and download the digital edition.

New MAKING SENSE Webinar Covers Seven Keys to Servicing CO2 Systems

When it comes to refrigerants, a change is in the air. The EPA’s pending SNAP ruling to delist R-404A and other commonly used refrigerants is yet another reminder of the uncertainty that permeates the refrigeration industry. But in this regulatory climate where refrigerants with high global warming potential (GWP) are being phased down, CO2 (R-744) is emerging as a viable natural alternative.


For food retailers seeking to circumvent ongoing regulatory compliance challenges, R-744 represents one of the few future-proof refrigeration options available today. With a GWP of one, virtually zero ozone depletion potential and the technology in place to support broader adoption, R-744 has a tremendous upside. But, its high pressure and unique refrigeration properties will mean a change in typical operating and maintenance procedures. As a result, service technicians will need to educate themselves and become familiar with R-744’s characteristics.

Our next MAKING SENSE webinar will address these considerations. Presented by Andre Patenaude, Emerson Climate Technologies’ director of CO2 business development, “Seven Keys to Servicing CO2 Systems” will take place on July 14 at 2 p.m. EDT. This informative session will explore the many operating implications of CO2-based refrigeration systems from a service technician’s perspective and help them prepare to effectively deal with the refrigerant’s unique properties. In this complimentary webinar, you’ll learn about:

  • Dealing with the high pressure of R-744
  • Understanding R-744’s critical and triple points
  • How to improve CO2 system efficiencies in warm ambient environments
  • Managing power outages
  • Dealing with the standstill pressures of R-744
  • Preparing the service technicians with the proper equipment (gauges, hoses, etc.)
  • R-744 cylinder storage, charging and maintenance best practices

To make sure your service team is prepared to handle CO2 in refrigeration, register now to join us July 14 from 2–3 p.m. EDT. We’ll help you MAKE SENSE of CO2 and allow you to take advantage of the industry’s most future-proof refrigerant alternative. Learn more and register by visiting our website at:


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