Transcritical CO2 (R744) refrigeration “seems to be the way of the future for us,” said Doug Milu, Manager, Refrigeration & Energy Program for Publix Super Markets, a Lakeland, Florida (U.S.)-based food retailer that operates 1,284 stores in seven Southeastern states,

Milu imparted that message during the end users session at the ATMOsphere America conference, held online on November 3. ATMOsphere America was organized by ATMOsphere (formerly shecco), publisher of

Publix has so far installed transcritical CO2 systems at a store in Longwood, Florida, which opened in June 2020, and a store in Tampa, Florida, which opened in August 2021. A third store opening on November 17 in Chattanooga, Tennessee, will also employ a transcritical CO2 system.

Publix has adjusted two of its seven store prototype designs to accommodate transcritical CO2, including at a multilevel retail/residential location. “We see transcritical CO2 in more of our prototypes moving forward,” said Milu.

Prior to the COVID-19 pandemic, Publix was opening 30 new stores annually as well as another 20 stores acquired from other companies and remodeled to its specifications; that pace slowed somewhat in 2021.

Milu noted that the shift to transcritical CO2 is “not only about meeting compliance with environmental regulations, it’s truly about trying to get to a carbon-neutral position in the future.”

Publix began using CO2 as a working refrigeration fluid 11 years ago at a store in Conyers, Georgia, in a cascade R407/CO2 cascade system. In July 2019, the chain opened its first store with DX CO2 for low-temperature cases and liquid CO2 overfeed, linked to a small R449A topside system, for medium-temperature cases; it now operates about 78 stores with this configuration.

Transcritical CO2 is now Publix’s latest R744 system iteration. Publix’s CO2 systems are “predominantly” supplied by U.S. OEM Hillphoenix. The initial three stores employ two split-suction racks but future stores will use four racks “to maintain redundancy if there is an issue,” said Milu.

Some smaller future stores will use Hillphoenix’s AdvansorFlex, a downsized version of its standard Advansor rack, Milu noted, adding that rooftop installations of the AdvansorFlex could serve expansions of existing stores.

Getting closer to energy parity

Publix operates in a warm part of the U.S., where basic transcritical CO2 systems are challenged to run efficiently. To improve their efficiency, the chain’s transcritical systems work with adiabatic gas coolers from Baltimore Aircoil (BAC).

While the energy consumption for the CO2 DX and CO2 liquid overfeed systems is close to parity with air-cooled HFC DX systems, the transcritical CO2 systems have so far been 12-14% higher, Milu said. However, Publix is working with its suppliers at the first transcritical store in Longwood, Florida, to optimize the system “and get closer to parity.”

“We’re not quite there yet,” he said, “but with other innovations surrounding R744 in retail grocery, I think that we’ll get there relatively soon.”

In regard to energy-improvement innovations, he mentioned ejectors as well as a pressure exchanger device recently introduced for transcritical CO2 by Energy Recovery, which he called “intriguing.”

Milu still sees “a lot of skepticism” about transcritical CO2 in the U.S. marketplace. “I was skeptical as well when I first started reading about the pressures, different components and safety protocols,” he said. However, once Publix started up a transcritical CO2 system he realized, “OK, that wasn’t that big of a deal.”

The same applies to technicians working with the technology. “We know not to isolate the refrigerant within a system, and always allow an escape route back to the suction side,” he said. At its headquarters in Lakeland, Florida, Publix is developing a training center for CO2 geared to outside technicians and its own employees.

His message to retailers and technicians in regard to transcritical CO2: “Don’t fear it.”

The biggest challenge Publix has faced with CO2 is finding a ready supply of the gas. “We’re used to HFCs, where you can call any supplier and get the gas delivered 24/7, 365,” he said. “That’s not necessarily the case with [CO2].” Publix is working with its larger CO2 suppliers to overcome any supply issues.

In addition to transcritical CO2, Publix has committed to using propane (R290) refrigerant in all of its small self-contained cabinets in new stores as well as in replacement units in existing stores.

“We see transcritical CO2 in more of our prototypes moving forward.”

Doug Milu, Publix

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