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Blog 8: CO2 System Architectures: Opportunities in Food Retail

AndrePatenaude_Blog_Image Andre Patenaude | Director Food Retail, Growth Strategy

Emerson Commercial & Residential Solutions

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Food retailers seeking to make the move to CO2 refrigeration have two primary system types from which to choose: CO2 transcritical booster and cascade systems. A closer look at each option may help you decide which is a better fit for your operations.

CO2 transcritical booster

A complete R-744 system, CO2 transcritical booster utilizes direct expansion (DX) for low- and medium-temperature suction groups. This system is called transcritical because it is designed to operate at pressures above CO2’s critical pressure (1,500 psig). Heat produced from low-temperature case compressors is rejected into the medium-temperature suction group’s compressors. The medium-temperature compressors are the workhorses of the system and must be sized to handle:

  • The total heat of rejection of low-temperature loads
  • 100 percent of the medium-temperature load
  • The flash tank bypass load

Only one condenser or gas cooler is needed for all low- and medium-temperature cases. CO2 pumped technology — where CO2 is used as a secondary fluid — is also available on both low- and medium-temperature stages.

CO2 cascade

CO2 cascade systems utilize two distinct refrigeration circuits: a CO2 circuit for the low-temperature suction group, and an HFC-based circuit (such as HFC-134a) for the medium-temperature needs. It’s called cascade because the heat produced from the low-temperature circuit is discharged into the suction stage of the medium-temperature circuit via an intermediate heat exchanger. Medium-temperature compressors send gas to an air-cooled condenser on the roof. Like a standard refrigerant, CO2 is maintained below its critical point (or subcritical mode) of 88 °F.

For an all-natural cascade alternative, some retailers have even experimented with using NH3 (ammonia) as the medium-temperature refrigerant. These low-charge ammonia circuits are typically housed on the facility roof, far removed from the store’s occupied spaces.

Evolution of electronics

Unlike traditional HFC systems, CO2 system architectures introduce the requirement for additional electronic components, including: case controllers, pressure transducers, temperature sensors and electronic expansion valves. While these components may contribute to increased system costs, they’re necessary for optimizing the refrigerant quality and pressures to the cases. From an end user and servicing perspective, these case controllers provide quick access to precise temperature controls and ongoing, optimized energy efficiencies.

The benefits of going green

For those U.S. retailers who have experimented with CO2 refrigeration, the benefits are obvious. New Seasons is a Northwestern grocer whose first CO2 system earned a GreenChill Platinum Certification award for green refrigeration. Their CO2 transcritical booster system delivered the following improvements:

  • Up to 30 percent lower total equivalent warming impacts (TEWI)
  • 95 percent fewer refrigerant emissions
  • Smaller refrigeration footprint

The retailer is currently planning additional CO2 installations.

  1., pg. 3

Read the full Accelerate America article on CO2 system architectures [pg.16].

Blog 7: CO2 Leaves a Smaller Carbon Footprint in Large-Format Food Retail Market

AndrePatenaude_Blog_Image Andre Patenaude | Director Food Retail, Growth Strategy

Emerson Commercial & Residential Solutions


Market drivers and refrigerant regulations in recent years have placed an increased focus on sustainability for large-format retailers. Among the natural refrigerant alternatives suitable for these centralized applications, CO2 (or refrigerant name R-744) leads the pack. Offering zero ozone depletion potential (ODP) and a global warming potential (GWP) of 1, CO2 is often considered the benchmark for environmentally friendly refrigerants. In terms of customer-facing peace of mind, CO2 has neither the flammability nor toxicity challenges posed by other natural refrigerant alternatives. And, as energy efficiencies and the reliability of CO2 refrigeration systems rise, system costs have fallen to levels typically found in traditional hydrofluorocarbon (HFC) systems.

Increasing global CO2 adoption

For all these reasons, CO2 has become the preferred natural refrigerant option for large-format food retailers. A recent Shecco study1 on CO2 adoption confirms this trend, showing a growing number of CO2 transcritical stores worldwide:

  • Canada: 150+
  • United States: 260+
  • Japan: 2,400+
  • Europe: 9,000

The number of CO2 stores in the E.U., Norway and Switzerland has tripled in the last three years, representing 8 percent of the overall food retail market share in these regions. In North America, retailers are still in an experimental “trial” phase to see how CO2 — and other natural refrigerants for that matter — can be used in their facilities and across varying climatic zones.

As older systems age and require upgrading or replacement, many large-format food retailers will be seizing the opportunity to transition from higher-GWP, HFC refrigeration architectures to lower-GWP systems. This trend toward eco-friendly refrigeration is being driven by multiple forces: 1) global regulatory efforts to phase down HFCs; 2) industry organizations like the Consumer Goods Forum that advocate the use of these systems; and 3) many retailers are stating corporate sustainability objectives.

Economies of scale reduce operating costs

The steady increase in global CO2 refrigeration adoption has led equipment and component manufacturers to not only increase production, but also make continued investments in research and development to refine CO2 technologies. These economies of scale are helping to lower CO2 system costs and reduce complexities for end users and service technicians alike.

CO2 training — both formal and hands-on types — has greatly improved as the industry becomes much more familiar with CO2 architectures and performance characteristics. Even refrigeration consultants are becoming well-versed in CO2 systems and can make more educated recommendations.

While the U.S. is still in the early phases of trials and experimentation, every successful implementation increases the likelihood of more stores making the transition to CO2. Safe, environmentally friendly, economical and reliable: CO2 has all the characteristics that make it a candidate as the large-format refrigerant of the future.

Read the full Accelerate America article on the large-format refrigerant of the future [pg.16].

[Webinar Recap] Factors in Evaluating and Selecting Refrigerants

AndrePatenaude_Blog_Image Andre Patenaude | Director Food Retail, Growth Strategy

Emerson Commercial & Residential Solutions

This blog is based on our most recent E360 Webinar, “Top Retailer Trends for Refrigeration, Controls and Facility Optimization.”


I recently participated in an E360 webinar where we explored trends in refrigeration systems and controls and discussed how they continue to evolve to keep up with changes in consumer preferences, global regulations and market dynamics. The webinar also featured John Wallace, Emerson’s director of innovation, and Andrew Knight, vice president of Henderson Engineers. Together, we presented insights into the factors driving refrigerant selection, controls architectures and design strategies.

The first of these trends is the continuing global transition toward the use of more environmentally friendly refrigerants. When we look at the market dynamics behind this movement, refrigerant selection is one factor among a long list of considerations for food retailers — but one that impacts system architectures, controls and long-term operational goals.

It’s important to keep in mind that food retailers are making refrigerant decisions within an increasingly complex cold chain. As the product journey from farm to fork requires many handling and transportation steps involving multiple intermediaries, the objective of maintaining consistent temperature remains paramount. But, once food arrives in their stores, retailers then face a combination of consumer-driven and operational requirements, including:

  • Producing consistently fresh, high-quality foods
  • Appealing to the growing demand for “experiential retail”
  • Meeting energy efficiency and sustainability objectives

As a result, retailers are making investments in improved shopping experiences, new refrigeration systems and facility management controls.

Natural Refrigerant Architectures

The current regulatory climate has paved the way for the resurgence of natural refrigerants — largely due to their ultra-low global warming and ozone depletion potentials. Commercial and industrial refrigeration manufacturers continue to develop systems that utilize the potential of these gases while mitigating their operating challenges. Among the leading natural refrigerant architectures used in supermarkets are:

  • CO2 booster transcritical — large-capacity system based completely on CO2; ideal for low ambient conditions; high ambient strategies are becoming more viable
  • Indirect chiller with cascade — niche application delivers a fully natural solution for large commercial or industrial applications; capable of utilizing multiple, low-charge refrigerant options, including: naturals, HFOs or A2Ls
  • Distributed — well-suited for smaller applications; allows for multiple refrigerant options (including CO2) and the flexibility to deploy individual systems for low- and medium-temperature suction groups
  • Integrated case (or micro-distributed) — integrates the refrigeration system into the case, typically using a low charge of R-290 (propane); unit condensers connect to a shared water loop for heat management

In our next blog, John Wallace will discuss the crucial role of controls in these systems and how refrigerants influence controls architectures.

Blog 6: New Natural Refrigerant Equipment and System Architectures Come to Small-format

AndrePatenaude_Blog_Image Andre Patenaude | Director, CO2 Business Development

Emerson Commercial & Residential Solutions

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Over the past several years, a dynamic regulatory climate has prompted original equipment manufacturers (OEMs) to develop new equipment and system architectures for small-format retailers. The transition from hydrofluorocarbons (HFCs) with high global warming potential (GWP) to new refrigerant alternatives is underway. These new alternatives must simultaneously offer lower GWP levels and performance efficiencies that meet new environmental and energy targets. Natural refrigerants propane (or R-290) and CO2 (or R-744) are part of a very short list of refrigerants capable of meeting both of those criteria.

R-290 applications

R-290’s flammable (A3) classification and current 150g charge limit have largely restricted its use to smaller systems that utilize fractional horsepower compressors or condensing units. Efforts are currently underway to increase its charge limits. Here’s a look at some of the new R-290 equipment and system architectures.

Stand-alone — R-290 is most commonly found in self-contained display cases that feature a built-in condensing unit in each refrigeration fixture. These cases have been in service for more than a decade in Europe and have become increasingly popular in the U.S. in recent years.

Integrated cases — deployed as an alternative to centralized systems, these large refrigeration cases integrate multiple R-290 compressors on individual 150g circuits. Each compressor has its own supporting system components (e.g., fans, valves, piping, etc.). An increase to the 150g charge limit would greatly simplify equipment design and expand R-290’s application potential.

Micro-distributed architecture — like stand-alone cases, each fixture is designed with its own condensing unit. The difference is, micro-distributed systems are designed to remove exhaust heat from the building through a shared heat rejection/water loop system that extracts the heat from each unit and diverts it to a condenser/cooler on the roof. While store comfort is optimized, operators may expect higher first costs and a slight energy penalty due to the secondary heat exchange design. However, in warmer climates, the removal of exhaust heat from a facility — and the load reduction on its HVAC system — may offset this penalty.

Ice machines — the EPA recently listed R-290 as acceptable for use in ice machines. Choosing which type of ice machine (cuber or flaker) to use is a key design consideration for OEMs, but component manufacturers are offering fractional horsepower compressors to integrate with both types and help with evaporator design.

R-744 applications

R-744 is effective alternative to HFCs in both low- and medium-temperature applications. Its high operating pressure (around 1,300 psig or 90 bar) and low critical point require refrigeration strategies to account for these unique characteristics. Although CO2 is more common in large-format grocery stores, OEMs have begun manufacturing systems and components sized for smaller equipment.

Small, centralized CO2 systems — appropriately sized for small-format applications, these systems are based on existing CO2 architectures (such as cascade and transcritical booster). A typical small system relies on four compressors to supply the complete refrigeration needs of the retailer.

Remote condensing units — many OEMs are manufacturing CO2 condensing units that can serve small-format needs, such as walk-in freezers and coolers. These recently developed solutions will likely become increasingly used in applications in the coming years.

Read the full Accelerate America article on small-format refrigeration applications [pg.18].

Blog 5: Natural Refrigerants Make Inroads in Small-format Refrigeration Applications

AndrePatenaude_Blog_Image Andre Patenaude | Director, CO2 Business Development

Emerson Commercial & Residential Solutions

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Small-format retail and foodservice markets are making significant changes in their refrigeration architectures. President Obama-era regulations, environmental initiatives by industry organizations, and the desire to adhere to corporate sustainability objectives are driving these sectors away from hydrofluorocarbon (HFC) refrigerants and toward natural alternatives. Natural refrigerants propane (or R-290) and CO2 (or R-744) are emerging as environmentally friendly, energy-efficient options to help operators achieve their short- and long-term refrigeration objectives.

The broad spectrum of applications in these markets is making this transition especially complex. Whether you operate a small grocery, convenience store or restaurant, you’ll find a dizzying variety of equipment and system architectures, each with unique new refrigerant requirements. Making sense of it all is not easy, but many owner/operators are tasked with selecting refrigeration platforms that will serve as the future of their refrigeration strategies. It’s no surprise then that R-290 and CO2 play an increasingly vital role in these markets.

As it stands today, there are numerous regulatory deadlines from both the Environmental Protection Agency (EPA) and the Department of Energy (DOE) that will take place in the next several years. The EPA has set a phase-out schedule for the use of HFC refrigerants with a high global warming potential (GWP), while the DOE has established new energy consumption guidelines for specific classes of refrigeration equipment. Unfortunately, compliance dates from each agency aren’t necessarily in sync.

While recent actions from the Trump administration suggest that deregulation measures may yet be on the horizon, the specific extent of these revisions is still largely unknown. Even so, the industry has made tremendous progress in recent years developing new equipment that utilizes natural refrigerants with lower GWP; these efforts will continue, regardless of the regulatory decisions of the current administration.

For a little perspective on why there is so much uncertainty and confusion in the small-format sectors, consider all the equipment classes affected by current regulations:

  • Supermarket systems (racks)
  • Walk-in coolers and freezers (remote condensing units)
  • Stand-alone coolers (<2,200 BTU)
  • Stand-alone coolers (>2,200 BTU)
  • Stand-alone freezers
  • Ice machines
  • Dispensing units

It’s important to note that the EPA has listed R-290 acceptable for use in new stand-alone units and ice machines, while R-744 is allowable in each of the above classes. R-290 has a GWP of 3; R-744 has a GWP of 1. And while other synthetic refrigerant options are available, currently none of these alternatives can deliver ultra-low GWP levels below 150 GWP, which is considered the hypothetical threshold for exemption from future regulatory action.

R-290 has proved a viable replacement to R-404A and HFC-134a, delivering well-documented performance efficiencies and superior thermodynamic properties, without compromising capacity. Caveats for R-290 use come down to its flammability (class A3), serviceability concerns and charge limit of 150g. Because CO2 has a high operating pressure (around 1,300 psig or 90 bar) and low critical point, refrigeration strategies must be designed to account for its unique characteristics.

Read the full Accelerate America article on small-format refrigeration applications [pg.18].


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