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Posts tagged ‘R-744’

Evaluating Sustainable Supermarket Refrigeration Technology

AndrePatenaude_Blog_Image Andre Patenaude | Director, Food Retail Marketing & Growth Strategy, Cold Chain

Emerson Commercial & Residential Solutions

Progressive Grocer recently interviewed me about Emerson’s and the commercial refrigeration industry’s efforts to help promote the emergence of more sustainable, refrigeration technologies. The complete article can be found here.

Evaluating Sustainable Supermarket Refrigeration Technologyd

It’s not news that supermarkets are under continuous regulatory pressure to not only lower the energy demand of their refrigeration systems, but also to make the transition to low global warming potential (GWP) and zero ozone depletion (ODP) systems. The permanent ban on R-22, long the industry standard, becomes official on January 1, 2020.

What is news is how intensely suppliers and retailers are focused on and sharing information on sustainability initiatives intended to sharply reduce the costs and impact of their refrigeration systems, both in anticipation of future regulations and to attain long-term economic and environmental sustainability.

As different manufacturers approach these issues with a variety of new technology options, the challenge becomes defining new standards for sustainable products and systems, so that the industry can converge on proven, synergistic solutions.

Taking a full system’s approach to sustainability

At Emerson, our approach to sustainability is based on a multi-faceted goal. First, sustain the environment through lower-GWP refrigerant and technology choices. Second, sustain companies financially from a total cost of ownership perspective. And third, focus on energy efficiency as a path to sustainability through forward-looking engineering and the implementation of new monitoring and control technologies, particularly Internet of Things (IoT) capabilities.

At Emerson, we take a full system approach to evaluate the sustainability of new and existing technologies in the context of multiple key selection criteria. This is part of Emerson’s “Six S’s” approach to refrigeration sustainability: simple, serviceable, secure, stable, smart and sustainable.

(To learn more about the rationale, methodology, application and impact of Emerson’s “Six S’s” philosophy, read the blog found here.)

Exploring the potential of natural refrigerants

One area of Emerson’s focus is our work to better understand and then implement emerging natural refrigerants, such as R-744 (carbon dioxide) and R-290 (propane) for different types of applications.

Recent innovations include the development of an integrated display-case architecture. This R-290 system is designed to use one or more compressors and supporting components within cases, removing exhaust heat through a shared water loop — incorporating our expertise in R-290 compressors and our experience with stand-alone condensing units. We’ve also developed a full range of CO2 system technologies, including valves and controls for both small and large applications. For cold storage applications, our modular refrigeration units utilize both CO2 and ammonia-based refrigerant configurations.

Early adopters pave the road to the future

Over the past decade, there have been many retailers committed to testing sustainable refrigeration technologies and low-GWP refrigerants in their stores. For example, the article quoted Wayne Posa of Ahold Delhaize USA, who discussed the company’s transition from R-22, stating: “Food Lion has been committed to zero-ODP and low-GWP refrigerants for several years.”

Different manufacturers are taking different approaches to studying and applying refrigerants and technologies to reach that goal, from the use of hydrofluoroolefin (HFO) refrigerants (such as R-448A and R-450) in distributed refrigeration systems to proven CO2-based system architectures.

In the area of refrigerants — let alone technologies in development for increased energy efficiency and remote monitoring and control — the refrigeration industry continues its search for a new standard. As Brian Beitler of Coolsys, a consulting and contract engineering firm explains, “Between transcritical, ejector systems, NH3 over CO2, cascade, propane, multidistributed and hybrid gas coolers, the jury is still out.”

As we move closer to the most sustainable standard for refrigerants, Emerson continues its work on total refrigeration system sustainability — in refrigerants, energy efficiency, and control — as guided by our “Six S’s” philosophy. This work is our road map to the future.

 

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.


To read all posts in our series on CO2 as a Refrigerant, click on the links below:

  1. Series Introduction
  2. Criteria for Choosing Refrigerants
  3. Properties of R744
  4. Introduction to Trancritical Operation
  5. Five Potential Hazards of R744
  6. Comparison of R744 with Other Refrigerants
  7. R744 Advantages / Disadvantages
  8. Introduction to R744 Systems
  9. Introduction to Retail Transcritical Systems
  10. Retail Booster Systems
  11. Introduction to Retail Cascade Systems
  12. Introduction to Secondary Systems
  13. Selecting the Best System

 

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.


To read all posts in our series on CO2 as a Refrigerant, click on the links below:

  1. Series Introduction
  2. Criteria for Choosing Refrigerants
  3. Properties of R744
  4. Introduction to Trancritical Operation
  5. Five Potential Hazards of R744
  6. Comparison of R744 with Other Refrigerants
  7. R744 Advantages / Disadvantages
  8. Introduction to R744 Systems
  9. Introduction to Retail Transcritical Systems
  10. Retail Booster Systems
  11. Introduction to Retail Cascade Systems
  12. Introduction to Secondary Systems
  13. Selecting the Best System

 

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.


To read all posts in our series on CO2 as a Refrigerant, click on the links below:

  1. Series Introduction
  2. Criteria for Choosing Refrigerants
  3. Properties of R744
  4. Introduction to Trancritical Operation
  5. Five Potential Hazards of R744
  6. Comparison of R744 with Other Refrigerants
  7. R744 Advantages / Disadvantages
  8. Introduction to R744 Systems
  9. Introduction to Retail Transcritical Systems
  10. Retail Booster Systems
  11. Introduction to Retail Cascade Systems
  12. Introduction to Secondary Systems
  13. Selecting the Best System
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