Refrigeration Systems Chillin’ With Carbon Dioxide

Refrigeration can truly be said to be at the heart of a supermarket’s business — not to be trifled with — which makes what Sobeys is doing fairly remarkable.

Canada’s second largest food retailer, Sobeys, Stellarton, Nova Scotia, is in the process of converting all of its refrigeration systems to something that has never been tried before in North America on a large scale — a “transcritical” refrigeration system that uses carbon dioxide as its only refrigerant.

If it succeeds, this closely watched implementation could have a major impact on how food retailers in North America refrigerate food.

Carbon dioxide, or CO₂ (R-744 in refrigeration lingo), is an abundant, cheap and harmless gas that is fundamental to life. It was actually one of the first refrigerants in early-model systems, circa 1900, reaching a peak of utilization during the Roaring ’20s. But as refrigeration evolved, synthetic refrigerants proved more efficient and CO₂ was relegated, seemingly, to the dustbin of history.

Synthetic refrigerants, however, turned out to be detrimental to the environment in commercial applications such as supermarkets, either hurting the ozone layer (CFCs and HCFCs) or contributing to global warming (HFCs), or both, as they leaked into the atmosphere. By the 1990s, refrigeration engineers were revisiting their old friend CO₂.

In the U.S., Food Lion began testing CO₂ as a “secondary” refrigerant in low-temperature applications (frozen cases) at a store in Montpelier, Va., in 2006. Over the next few years, the chain added another secondary-loop test and three stores that employed CO₂ in what are called cascade (or subcritical) systems. Other retailers, such as Price Chopper, Fresh & Easy Neighborhood Market and Stop & Shop, have also tested cascade systems in recent years, and the interest in those systems is growing. But in both secondary and cascade systems, CO₂ is often used in conjunction with synthetic (HFC) refrigerants, albeit in smaller quantities.

Around 2005, the transcritical system made its debut in Europe, with the distinction of using only CO₂, eliminating all other refrigerant gases that, upon leaking into the atmosphere would contribute to global warming or deplete the ozone layer. The system has since been adopted by retailers in the U.K. and other northern European countries. However, the transcritical system operates sometimes at comparatively high pressure — especially in warmer temperatures — which has impeded its adoption in North America. And there are still questions about its relative energy efficiency.

In July 2006, Sobeys decided to try its hand at a CO₂-only transcritical booster refrigeration system at a store in Quebec, the first such deployment in North America. Since then the company, which operates more than 1,300 stores across Canada (some as franchises), has become the de facto leader of transcritical refrigeration in the North American supermarket industry. Sobeys now operates 23 IGA stores in Quebec (out of 260) with transcritical systems, including 20 new stores and three retrofits of existing locations, and the company expects to have about 31 transcritical stores by year’s end, including six retrofits, said Simon Bérubé, senior director of engineering and commercial development for Sobeys Quebec, pictured at right in the photo that also includes Sobey's Luc Duprey during their appearance last fall at Food Marketing Institute’s Energy & Store Developement Conference.

Sobeys also has nine stores with cascade systems, but going forward the company plans to install only transcritical systems in new stores, as well as retrofit all existing stores, with a goal of being deployed chainwide with transcritical in 15 years, said Bérubé. Sobeys’ franchised stores are not obligated to switch to the new system, though so far they have all accepted it.

Sobeys is now at the final stage of its commitment to CO₂-based transcritical refrigeration, having gone stepwise through a series of improvements over the last few years. “This is where we want to stand,” said Bérubé. Its current transcritical design “is the solution for our climate here. It is meeting our entire vision.”