Refrigeration Systems Chillin’ With Carbon Dioxide

Thinking Differently

Some U.S. retailers believe the solution to the emissions of HFC refrigerant is not to replace the refrigerant with CO₂ or another low-GWP gas, but to simply tighten the refrigeration system so that the leak rate approaches zero. Retailers in the GreenChill program, for example, have succeeded in lowering their leak rates dramatically. But Bérubé questions how long a leak-tight system can remain that way. “I have stores with a 0.5% leak rate, but over the next 20 years that will increase by 100% for sure because of the  aging of piping and the vibrations,” he said.

Sobeys decided to commit to transcritical systems “to find a solution for our increasing maintenance costs and leak costs,” he said. “We had tried a lot of things, such as improving the leak tightness of the system. But we decided we have to think differently.”

Sobeys initially tested cascade systems, partly to quiet the fears of upper management about making the leap to a new technology and refrigerant. But cascade systems, which pump glycol or CO₂ through the cases as a secondary refrigerant and holds CO₂ to a low pressure and temperature, “don’t meet our expectations on the energy consumption side,” Bérubé said.

The vision Sobeys has for its transcritical  system — which it began realizing two years ago — encompasses a simpler, smaller design with far fewer compressors. It uses no HFCs, and has half the maintenance costs, lower energy consumption and an equal or lower initial cost, Bérubé said. It takes advantage of a less expensive refrigerant in CO₂ ($1 or less per pound, compared with $12 per pound for many HFCs), uses almost half as much refrigerant and also leaks less because of the simplicity of the system.

The installation cost is less because the copper piping has a smaller diameter (an inch or less compared with three inches). It uses electronic valves and controls that meet the needs of the cases — temperature, defrost and energy management — in real time, improving the quality of product on display and helping to moderate the temperature of the store. The electronic valves add to the initial cost of the system, but bring energy cost savings in the long term.

The transcritical system also generates a large amount of heat, all of which can be reclaimed for space and water heating, adding to the efficiency of the overall system. Heat reclaim is a definite advantage of the transcritical system, said Honeywell’s Vogl. “If you can use all the heat that the system makes, it does give you a little benefit.”

Sobeys has received $15 million in rebates from Hydro-Quebec, and $125,000 per project in grants from Canada’s Office of Energy Efficiency to support its transcritical implementation, but that was “the cherry on top,” not part of the cost calculation, said Bérubé, adding, “We still have some subsidies but it won’t last forever.”

Last fall, Sobeys was able to directly profit from its green refrigeration initiative by selling 15,000 tons of carbon credits to the National Bank of Canada. “It was an interesting transaction for the bank and us — we’re both happy,” said Bérubé, who declined to cite the cost of the carbon credits. “It’s another added value for us to go to these new technologies.” All told, Sobeys, which is a participant in the Western Climate Initiative, has 100,000 tons of carbon credits it could put on the carbon market, he added.

Not everyone concurs with Bérubé’s assessment  that the initial cost of the transcritical system is equal to or less than that of a conventional system. Fresh & Easy’s Hagen regards the cost of transcritical systems as a drawback, “but with more acceptance and volume, costs will decline and the lifecycle cost could become comparable.”  And Carnot’s Lesmerises said that retailers will “pay more for the transcritical rack, but less for installation.” With the energy savings, lower maintenance costs and cheaper refrigerant, “they will save in a short period of time,” he added.

Bérubé acknowledges that CO₂ can’t be simply “dropped in” with a few modifications as a replacement for R-22, which is being phased out in the U.S. and Canada. (See the R-22 refrigerant shortage story here.) Sobeys still uses R-22 in more than 100 stores. But the retailer is determined to make the investment in retrofitting aging refrigeration systems with CO₂-based transcritical technology.

Sobeys plans to keep stores open during the retrofit process. It can do that because the transcritical compressor rack is compact enough to be installed in the machine room next to the original rack so that the changeover can be made “one line at a time,” Bérubé said. A retrofit requires upgrading the evaporator and valves in the chilled and frozen cases, as well as installing narrower copper piping in the store, though Sobeys is “challenging our suppliers” to do the retrofit with the original piping. Standard cases can be used as long as they are rated for 600 pounds per square inch (psi), said Simard.

Sobeys has used another natural refrigerant — ammonia — to refrigerate its warehouses, switching in 2008 to a smaller quantity of ammonia in a new energy-efficient warehouse in Trois-Rivieres (Three Rivers), Quebec, in concert with glycol. “At Three Rivers, I was able to demonstrate to my top management that since we built a big warehouse with no HFCs, so why not build a store with no HFCs?” said Bérubé.