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Seven Keys to Servicing CO2 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 Keys to Servicing CO2 Systems.” Click here to read it in its entirety.

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From a service technician’s perspective, CO2 has unique performance characteristics and operating peculiarities that dictate system design and impact maintenance requirements. Following are seven key considerations to be aware of when servicing CO2 systems.

  1. Low critical point (subcritical vs. transcritical) — R-744 has a relatively low critical point (1,055 psig or 87.8 °F) that determines its modes of operation. Subcritical mode refers to systems operating in regions with colder climates and lower ambient temperatures where the refrigeration cycle takes place below 87.8 °F. Transcritical mode takes place above this point (also referred to as supercritical) such as in warmer regions or periods during the summer heat.
  2. Higher operating pressure — one of the common reservations when using CO2 is its relatively high operating pressure. But, it’s important to realize that high pressure only takes place in the beginning stages of the refrigeration cycle while the rest of the refrigeration cycle operates at pressures like that of a traditional R-410A high-side system. Stainless steel piping is typically used to handle these pressures, although high-pressure ferrous alloy copper piping has recently been introduced.
  3. High triple point (possibility of dry ice formation) — triple point is the point at which the three phases of CO2 coexist (60.4 psig or -69.8 °F). While the temperature seems low, the pressure is relatively high by refrigerant standards. As the pressure approaches that point in CO2 systems, the refrigerant will turn to dry ice (an unusable state that’s neither a vapor nor a liquid). This can occur during maintenance when a contractor mistakenly thinks the lines are clear, taps the system and discovers the formation of dry ice.
  4. System charging — the high triple point affects R-744’s charging procedures. After pulling a vacuum, the internal pressures of the system will be well below 60.4 psig. Since standard atmospheric pressure is 14.696 psig, the process cannot start with liquid charging. Instead, contractors must vapor-charge the system (roughly to around 145 psig), and then wait until the system has equalized with 145 psig of vapor before charging with liquid.
  5. Managing scheduled shutdowns and power outages — when a CO2 system shuts down for longer periods of time, pressures will build more quickly than in an HFC system. To preserve the system charge, the most reliable method is to install a generator with a standby condensing unit. When the power goes out, the generator powers a condensing unit that has a loop within the flash tank (i.e., receiver) designed to cool the volume of liquid within the tank and keep pressures down.
  6. Resumption of power — the electronic expansion valve (EEV) on every CO2 case utilizes a stepper motor or a pulse-width modulated type of valve. When the power goes out, the stepper motor is frozen in that exact position, leaving the system’s CO2 evaporators susceptible to flooding. R-744 naturally migrates quickly to these cold evaporators, and when the system resumes, this can cause considerable damage to compressors. To avoid this, liquid line solenoids placed upstream of the EEV, supercapacitors or battery backups are often used on case controls to force the valves closed during a power outage.
  7. Form a refrigerant plan — managing CO2 is different from what contractors may be accustomed to with traditional HFCs. Operators and contractors alike need to understand the local codes for storing R-744 cylinders (inside or outside the building), and develop an appropriate strategy.

Grocer’s New CO2 Refrigeration System Earns EPA GreenChill award

 AndrePatenaude_Blog_Image Andre Patenaude | Director, CO2 Business Development

Emerson Commercial & Residential Solutions

This blog summarizes a success story in our most recent E360 Outlook, entitled Natural Born Chillers.” Click here to read it in its entirety.

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Natural refrigerant adoption is on the rise in the U.S., and forward-thinking supermarket retailers are leading the charge. Driven by corporate sustainability objectives and the desire to achieve EPA and DOE regulatory compliance, some operators are turning to eco-friendly options like CO2 to reduce their carbon footprint. Such is the case with New Seasons Market, a northwestern U.S. grocer that was recently awarded the EPA’s GreenChill Platinum Certification in its newest store for installing a transcritical CO2 booster system.

In many ways, sustainability is in New Seasons’ DNA. They partner with local farmers, ranchers and producers to offer the best of the region, and sell homegrown, organic favorites along with traditional grocery store staples. With 20 locations in the states of Washington, Oregon and California, the chain’s recently launched 37,000-square-foot store in Mercer Island, Wash., was the first to earn this distinction from the EPA.

New Seasons partnered with its engineering firm to develop a natural refrigeration system that would meet the sustainability objectives for the new location. The system, which is based on the Hussmann Purity platform, features Emerson’s compression and system controls technology, including:

  • Transcritical CO2 rack — consists of six compressors — three of which are low-temperature Copeland Scroll Digital™ CO2 compressors — with digital capacity modulation to provide energy-efficient refrigeration for the entire store. The system is charged with 1,100 pounds of CO2 (R-744).
  • Roof-mounted gas cooler — a gas cooler utilizes energy-efficient, low-velocity, variable-frequency drive (VFD) fans to reduce overall energy usage.
  • Controls — An E2 RX refrigeration controller manages the system in conjunction with Emerson case controls in the store fixtures. These tools enable the ease of system setup while ensuring ongoing performance optimization, maintaining consistent temperatures throughout the store, minimizing product shrink and preserving food quality.

The EPA GreenChill Platinum Certification recognizes New Seasons’ efforts in revamping the store’s refrigeration system — an HFC system installed by the previous retailer at this location — to a CO2 architecture that reduced refrigerant emissions by at least 95 percent.

The success of the Mercer Island store has opened the door for additional CO2 systems. Their leadership is currently planning the construction of two new stores in 2018 that will also rely on transcritical CO2 booster system architectures.

This blog summarizes a success story in our most recent E360 Outlook, entitled Natural Born Chillers.” Click here to read it in its entirety.

[E360 Webinar Recap] R-290 and CO2 Are Natural Choices for Small-Format Refrigeration

AndrePatenaude_Blog_Image Andre Patenaude | Director, CO2 Business Development

Emerson Commercial & Residential Solutions

VIEW our latest E360 Webinar on demand, Opportunities for Natural Refrigerants in Small-Format Applications.

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Today’s small-format retail and foodservice operators face difficult decisions about which refrigeration architectures — and refrigerants — will be the bases of their next generation of refrigeration platforms. Whether they’re motivated by global regulatory actions to reduce the use of hydrofluorocarbons (HFCs) with high global warming potential (GWP), or simply stating sustainability objectives to improve energy efficiencies and minimize their carbon footprints, operators have a variety of lower-GWP refrigerant options at their disposal.

Natural refrigerants carbon dioxide (CO2, or refrigerant name R-744) and propane (R-290) are currently the only true “future proof” options that hold the potential to take compliance and sustainability concerns out of the equation. But their unique characteristics also introduce new safety and servicing considerations with which operators must become familiar.

In our most recent E360 Webinar, my colleague Allen Wicher, director or refrigeration marketing, and I explored the many factors small-format operators must consider when selecting a natural refrigerant system. I kicked off the presentation by reviewing the long history of natural refrigerants in commercial refrigeration and discussed the market and regulatory forces that are now driving their broad global resurgence.

In particular, I explained how the global F-gas reduction strategy to protect the environment, in combination with voluntary efforts of private industry organizations, were driving the transition away from HFC refrigerants toward lower-GWP options like CO2 and R-290. At the same time, the trend for smaller retail formats in urban areas persists, while the millennial generation continues to shape the consumer desire for convenience and more importantly, fresh, natural and organic food offerings from local, sustainable sources.

Making this decision even more complicated is an increasingly wide variety of equipment and system architectures at play. For CO2 options, I explained how smaller-format systems were scaled down versions of larger-format retail refrigeration architectures. For example, CO2 cascade and transcritical booster architectures can be effectively scaled for use as smaller, centralized systems. And for even smaller convenience store or restaurant applications — such as walk-in freezers and coolers — OEMs are now manufacturing CO2 remote condensing units.

While higher first costs can be a barrier to entry for small-format CO2 refrigeration, I demonstrated how the total cost of ownership is reduced with improved energy efficiencies, performance and lower maintenance.

Allen provided an update on the active regulatory landscape, including:

  • Safety (ASHRAE/UL) and charge limit standards (UL 427) currently underway for flammable refrigerants classified as A3 (R-290) and A2L (synthetic blends)
  • Summary of EPA refrigerant listings (currently no A2Ls are listed as acceptable for use)
  • California Air Resource Board’s aggressive stance on HFC phase-down

Allen then talked about the architectures where R-290 is currently being utilized, including: stand-alone, integrated cases and micro-distributed systems. To learn more about the use of natural refrigerants in small-format retail, click here to view this webinar in its entirety.

CO2 as a Refrigerant – Selecting the Best System

This is post number 13 of a series.

Selecting the Best System – Booster Versus Cascade Versus Secondary

Table 1 lists the advantages and disadvantages of cascade, transcritical, and secondary retail systems

Table 1

Table 1.2

Table 2

Table 3

Conclusion

Transcritical operation is generally less efficient than subcritical operation, so system type selection is usually driven by the ambient temperature profile:

  • Transcritical systems are normally used in areas where the ambient temperature is generally low (i.e., predominantly below 68 °F to 77 °F (20 °C to 25 °C), such as northern Europe and Canada.
  • Cascade and secondary systems (subcritical R744) are usually used in high ambient areas such as southern Europe, the U.S., much of central and South America, southeast Asia, Africa and Australia. The use of transcritical systems in high ambients generally results in lower efficiency, hence cascade or secondary systems are preferred in these areas.
  • Efficiency improvement for Booster Transcritical system for high ambient conditions is being aggressively developed to allow wider use of these systems.

The next articles in this series will provide more detailed information about the design and components of R744 cascade, transcritical booster and secondary systems.

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 – Introduction to Secondary Systems

This is post number 12 of a series.

Secondary Systems

Figure 6 shows a simple secondary system. The high-stage system cools the liquid R744 in the secondary circuit. The R744 is pumped around the load. It is volatile, so unlike a conventional secondary fluid such as glycol it does not remain as a liquid. Instead it partially evaporates, providing a significantly greater cooling capacity. This reduces the pump power required and the temperature difference needed at the heat exchanger.

Figure 6

Figure 6: Simple cascade system

R744 would typically be cooled to 26.6 °F (-3 °C ) for the MT load, and to -13 °F (-25 °C) for the LT load.
The high-stage system is a simple chiller-type system, typically running on an HFC, HC or Ammonia refrigerant.

In the next article of this series we’ll review the advantages and disadvantages of booster, cascade, and secondary systems. We’ll also review some case studies to determine how to select the correct system for our application.

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

 

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