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Natural Refrigerants Remain Viable Among Emerging Options

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

Emerson Commercial & Residential Solutions

I was recently asked by the editor of Accelerate America to offer my opinion on the viability of natural refrigerants, including CO2 (R-744), propane (R-290) and ammonia (R-714). Among the many emerging refrigerant alternatives, natural refrigerants check important boxes for owners and operators who are preparing for the rapidly changing commercial refrigeration landscape. View the full article here and read a summary of its key points below.

For more than a decade, natural refrigerants have factored prominently in the search for environmentally friendly refrigeration in both commercial and industrial sectors. We’ve seen the introduction of R-290 in micro-distributed, self-contained cases; increased global adoption of CO2 in centralized systems; and the emergence of ultra-low-charge ammonia, by itself as well as integrated with CO2 in cascade systems. As we kick off a new decade, we will likely continue to see these refrigerants progress along those established lanes.

Drivers for natural refrigerant adoption

Since their introduction, the drivers for natural refrigerant adoption have not changed. Most legacy refrigeration strategies rely on the use of high global warming potential (GWP) hydrofluorocarbon (HFC) refrigerants, and companies with sustainability objectives or regulatory mandates were among the first to make the transition to natural refrigerants — which by many are considered immune from regulatory-mandated GWP caps.

In 2020, the phase-down of HFCs remains a focus of global environmental regulations. From the Kigali Amendment to the Montreal Protocol and the European F-Gas regulations to the California Air Resources Board (CARB) and Environment and Climate Change Canada (ECCC), many countries, states and regions share the goal of an HFC phase-down.

It’s often said that there’s no such thing as a perfect refrigerant — and that’s certainly the case with natural options. But natural refrigerants are among the very few alternatives capable of meeting some of the more aggressive GWP targets. R-290 has a GWP of 3; CO2 has a GWP of 1; and ammonia has a GWP of 0. So from environmental and regulatory perspectives, this puts them in a class by themselves.

Characteristics and caveats

With decades of field use and research to draw from, the performance characteristics of natural refrigerants are well known. But each option has operating caveats that equipment owners must carefully consider before investing in a long-term refrigeration strategy.

  • R-290 offers excellent energy efficiencies, but as an A3 (flammable) refrigerant, safety regulations limit its use to small charges globally from 150g to 500g. R-290 is a natural fit for small-capacity, self-contained cases that require a lower charge and are hermetically sealed at the factory.
  • CO2 is a high-pressure refrigerant with a low critical point (87.8 °F) that determines its modes of operation (subcritical, or below the critical point; transcritical, or above the critical point). It also has a high triple point where the refrigerant will turn to dry ice. Systems must be designed to manage these characteristics, and operators must have access to qualified technicians.
  • Ammonia has been used in industrial refrigeration for the past century, but its toxicity (B2L classification) presents challenges to equipment owners. Tightening safety regulations and the risk of exposure have led to system architectures designed to lower charges and move it out of occupied spaces.

Selecting a natural architecture

When evaluating natural refrigerant architectures, store formats and application requirements will often dictate the refrigerant choice. R-290 is well-suited for either smaller-format stores or as a spot merchandising option for larger stores. CO2 makes the most sense in larger stores seeking a centralized architecture alternative to HFCs. Ammonia is relatively rare in commercial applications but is finding its way into innovative architectures designed to mitigate its risks and benefit from its excellent performance characteristics.

R-290, from integrated cases to micro-distributed — For nearly a decade, manufacturers have worked within the 150g charge limit to create self-contained, integrated cases, in which the refrigeration system (compressor and condensing unit) is built into the display case. These evolved into a micro-distributed approach for small stores, where multiple units share a water/glycol loop to remove excess heat. This approach provides very low-GWP, total-store cooling while keeping charges low, typically operating with 90% less refrigerant than a centralized system.

CO2 transcritical booster — CO2 came into prominence more than a decade ago in large supermarkets where centralized architectures are preferred. CO2 transcritical booster system technology continues to improve today, offering an all-natural solution for both low- and medium-temperature cooling. Compared to centralized HFC systems, CO2 transcritical boosters represent a completely different approach to system operation and servicing. Operators must acquire technicians that are trained to service CO2 systems and implement strategies for power outages in order to mitigate “stand-still” pressure while the system is off.

CO2/ammonia hybrid subcritical (cascade) — CO2 cascade systems are designed to utilize CO2 in the low-temperature (LT) suction group where the refrigerant stays below its critical point and operates at lower pressures, much like a traditional HFC. Typically, an HFC (or HFO/HFC blend) is used in the medium-temperature (MT) circuit, where heat produced from the LT circuit is discharged (i.e., cascaded) into a heat exchanger and into the suction stage of the MT circuit. However, the recent introduction of ammonia as the MT refrigerant has transformed this configuration into an all-natural refrigerant option.

Safety first

With each of these natural refrigerant options, safety must be the primary consideration. Manufacturers have poured a great deal of effort into ensuring the safe operation and maintenance of natural systems with a variety of strategies, including pressure relief valves, specially designed components, leak detection devices, and proper guidance to owners and operators.

The global regulatory climate and trend toward environmentally friendly refrigeration will help natural refrigerants to proliferate along these well-established paths of least resistance. Still, there is much to consider for system operators, who must weigh the opportunity costs for selecting a natural refrigerant option.

 

More Food Retailers Opt for Natural Refrigerant Systems

AndrePatenaude_Blog_Image Andre Patenaude | Director, CO2 Business Development

Emerson Commercial & Residential Solutions

This blog summarizes an article from our most recent E360 Outlook, entitled Natural Selection.” Click here to read it in its entirety.

9760-E360_Outlook_September-2017-Natural_Selection_Facebook-1200x630_v2

One of the most complex decisions food retailers have today is selecting which refrigerant will serve as the basis of future refrigeration platforms. While there are very few refrigerants that can deliver regulatory compliance and align with corporate sustainability goals, three natural options are at the top of this short list: carbon dioxide (CO2 or refrigerant name R-744); the hydrocarbon propane (refrigerant name R-290); and ammonia (NH3 or refrigerant name R-717).

In recent decades, as synthetic chlorofluorocarbon (CFC) and hydrofluorocarbon (HFC) refrigerants were found to have either ozone depletion potential (ODP) or global warming potential (GWP), natural refrigerants have made their way back into the commercial refrigeration conversation — even being listed by the Environmental Protection Agency (EPA) as acceptable for use in most commercial refrigeration applications (subject to use conditions).

Make no mistake: these refrigerants are by no means perfect — each has its own caveats — but in terms of thermodynamic properties, operational efficiencies and eco-friendliness, natural refrigerants are often referred to as “future proof”.

Innovative installations

As modern refrigeration technologies continue to improve, equipment manufacturers are working closely with early adopters to develop innovative solutions. This has resulted in several creative natural refrigeration applications that belie their traditional uses — like ammonia being used in supermarket systems and CO2 playing a larger role in industrial process cooling.

Ammonia trials in food retail
In September 2015, the Piggly Wiggly supermarket company opened a new 36,000 square-foot store in Columbus, Ga., that utilizes an NH3/CO2 cascade system manufactured by Heatcraft Worldwide Refrigeration. The all-natural refrigerant system uses an ultra-low charge of ammonia (53 pounds) located away from occupied spaces (on the facility’s roof).

CO2 adoption in industrial cooling
In cold storage applications, where ammonia has been the preferred refrigerant for decades, companies are also seeking to lower ammonia charges. As older ammonia systems near replacement, many operators are determining the best option to expand their facility’s low-temperature capabilities. They’re accomplishing this by adopting NH3/CO2 cascade systems that not only utilize very low charges of ammonia, but also keep the R-717 circuit out of occupied spaces.

Propane in food retail
When major retailers like Target publicly announce their intentions to use only propane in their self-contained units, it’s an indication that the perceptions about the mainstream viability of R-290 are shifting. The smaller charge limits make R-290 a logical fit for Target’s smaller, stand-alone refrigerated display cases and coolers.

While efforts are needed to mitigate their associated risks and ensure their safe use, natural refrigerants represent true sustainable alternatives that do not sacrifice performance. As regulatory bodies and industry organizations work to refine these standards, natural refrigerants will continue to play a key role in the future of commercial and industrial refrigeration

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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