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Freezer_case_Lidl-West_Babylon_Russell_Redman.jpg Russell Redman
Throughout the food retail industry, stakeholders are rethinking their approach to refrigeration and promoting the use of refrigerants with lower global warming potential (GWP).

CO2 refrigeration on the rise

Reviewing the regulatory, market and technological trends behind increased adoption of CO2 refrigeration in the U.S.

Andre Patenaude is Director – Solutions Integration at Emerson and is responsible for supporting system-related innovation and leveraging Emerson’s global cold chain to drive adoption of integrated solutions in North America. He most recently led marketing efforts pertaining to Emerson’s food retail and chiller markets. Prior to that, he had managed Emerson’s global CO2 development. The views expressed here are those of the author.



For the past decade, CO2 refrigeration systems in the U.S. have been perceived as exceptions to the accepted norms of commercial refrigeration. Mostly championed by a small subset of sustainably minded supermarket operators, CO2 installations have been deployed often as proofs-of-concept — and more sparingly as a retailer’s primary refrigeration strategy. Although the U.S. has seen steady increases in CO2 adoption in recent years, it still hasn’t experienced the industry-wide acceptance taking place in Europe.

But that appears to be changing. The global hydrofluorocarbon (HFC) refrigerant phasedown and subsequent environmental regulations have generated renewed interest in CO2 refrigeration and set the stage for its likely widespread adoption in the U.S.

Throughout the food retail industry, stakeholders are rethinking their approach to refrigeration and promoting the use of refrigerants with lower global warming potential (GWP). Among the environmental strategies identified to combat climate change, the greening of commercial and industrial refrigeration equipment has been recognized as an essential tactic of decarbonization plans and corporate sustainability initiatives. Retailers are seeking long-term refrigeration strategies that support:

  • Environmental, social and governance (ESG) efforts
  • Energy efficiency and emissions reductions targets
  • Net zero goals

With zero ozone depletion potential (ODP)and a GWP of 1, the natural refrigerant CO2 (refrigerant name R-744) has become a proven viable alternative to higher-GWP HFC refrigerants. In addition, the proliferation of CO2 refrigeration systems around the globe has given equipment manufacturers opportunities to improve compression, controls and valve technologies — simplifying system management and bringing system costs into parity with traditional HFC systems. Let’s look more closely at some of trends driving the increased adoption of CO2 refrigeration in the U.S.

Regulations drive down GWP levels

Global, federal and state regulations are steering the industry away from HFCs and toward lower-GWP alternatives. The Kigali Amendment to the Montreal Protocol — which has been ratified by 129 countries — serves as the regulatory framework supporting a variety of these efforts in the U.S. and abroad.

Per its HFC production and consumption phasedown schedule, the next step will be a 40% reduction in 2024 (compared to the baseline established in 2011–2013). Refrigerant regulations in the U.S. have been constructed to follow this mandate.

AIM Act established federal mandate

The passing of the American Innovation and Manufacturing (AIM) Act in 2020 restored the Environmental Protection Agency’s (EPA) authority to enforce HFC mandates and establish sector-based guidelines. As the EPA implements the Kigali Amendment’s HFC refrigerant phasedown guidelines and supplies are reduced, the industry can expect an increase in HFC refrigerant prices.

CARB mandates

For many years, the California Air Resources Board (CARB) has led efforts to phase down HFCs in the state of California. Its current 2022 proposal has set 150 GWP as the refrigerant benchmark for its state-wide mandates. Thus, all new refrigeration systems containing more than 50 pounds of refrigerant installed in new facilities will be required to use refrigerants with less than 150 GWP.

Existing facilities will factor in the refrigeration footprint of equipment greater than 50 pounds in a retailer’s entire fleet of stores in California, including: existing stores, new construction, retrofits and remodels. Many industry insiders consider what’s happening in California as a potential preview of what’s to come for the rest of the U.S.

As regulatory targets appear to be driving GWP levels near or below the 150 GWP threshold, many retailers are actively exploring their lower-GWP system options.

Global adoption trends

CO2 refrigeration has been used widely in Europe for more than a decade. Today, that trend continues with adoption steadily increasing in the U.S. and other countries. Per recent industry data, nearly 46,500 CO2 transcritical booster systems are currently installed worldwide.

  • 900 in the U.S. (1,400 in North America with the inclusion of Canada)
  • 40k in the E.U.
  • 5k in Japan

Industry estimates show that the E.U. and U.S. have experienced significant growth in CO2 refrigeration from 2020–2021. In the U.S., Emerson expects CO2 adoption to increase up to 50% by 2025. This growth trend is expected to continue at a similar trajectory throughout the next decade, with the possibility that the U.S. could potentially mirror E.U. levels of adoption.

Technological improvements and emerging applications

CO2 refrigeration technologies are continuously evolving. Thanks to increased global adoption and investments in research and development (R&D), equipment manufacturers continue to refine CO2 components, overcome known challenges, and simplify system operation.

CO2’s inherent energy efficiency in most climates allows it to deliver direct and indirect emissions reductions, or lower total equivalent warming impact (TEWI). System technologies are evolving to enhance these benefits and mitigate CO2 refrigerant and system complexities.

Electronic system controllers

To effectively manage CO2’s high pressures and system volatilities, CO2 transcritical booster systems have benefited greatly from improvements in electronic controls designed to simplify installation, commissioning and system management during standard operation. These types of improvements minimize system complexities, alleviate the burden from technicians, and provide peace of mind to end users.

Emerson217-I-CO2 Diagram-4.jpg

CO2 transcritical booster systems (diagram above) continue to be the most widely adopted CO2 refrigeration systems and are preferred in medium- to large-format food retail stores.

Integrated CO2 transcritical booster system components

Today, CO2 transcritical booster systems continue to be the most widely adopted CO2 refrigeration systems and are preferred in medium- to large-format food retail stores. One key system advantage is that both medium- (MT) and low-temperature (LT) circuits run on R-744. System design requires the seamless integration of all components, including: compressors, electronic expansion valves (EEVs), high-pressure valves and an electronic controller.

Warm ambient strategies

CO2 transcritical booster systems are subject to declining efficiencies in warm ambient climates, but manufacturers have developed a variety of strategies to maintain efficiency levels.

  • Adiabatic gas coolers — keep the refrigerant below its critical point for as long as possible to maximize system efficiencies
  • Parallel compression — compresses excess flash gas at higher pressure via a dedicated intermediate stage compressor, resulting in 810% annualized efficiency gains
  • Mechanical sub-cooling — provides increased refrigerant enthalpy
  • Gas ejectors, liquid ejectors — optimize efficiency
  • Low superheat of MT evaporators — delivers year-round efficiency improvements


CO2 transcritical booster systems are subject to declining efficiencies in warm ambient climates, but manufacturers have developed a variety of strategies to maintain efficiency levels.

Distributed CO2 condensing units (CDUs)

Operators in the E.U. are beginning to utilize CO2 CDUs to support distributed refrigeration system architectures. Although this approach is ideal in smaller-format stores, it can also potentially support larger store retrofits by allowing operators to decommission sections of their HFC systems and replace them with CO2 CDUs.

A distributed CO2 CDU approach provides a smaller, lighter and simpler alternative to centralized CO2 systemsby offering true “plug and play” characteristics. One type of CO2 transcritical scroll compressor recently launched in the E.U. is designed to support distributed CO2 CDUs. It features dynamic vapor injection (DVI) that eliminates the need for parallel compression, thereby lowering system costs and increasing energy efficiencies. It leverages integrated controls that manage system operation and improve ease of use.

The release of similar CO2 transcritical scroll compressors are expected to be extended globally over the coming years.

Preparing for a more sustainable future

The increased focus on sustainable refrigeration and ongoing efforts to improve CO2 equipment and system technologies will position CO2 for much wider global adoption over the next decade. As the market for CO2 refrigeration continues to expand, the proliferation of new products is creating economies of scale, which lower the costs and complexities of implementing CO2 technologies.

Watch for technological enhancements and new product offerings in CO2 systems, giving end users and contractors the confidence to move forward with this environmentally friendly, natural refrigerant.

To access a full kit about CO2 in refrigeration, click here.

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