Refrigeration Systems Chillin’ With Carbon Dioxide

Managing Change

Bérubé cited “change management” as the biggest challenge in the implementation of the transcritical system. “You have technical people, middle management and marketers who retain their way of doing business,” he said. “That will change over time.” It helps that top management “wants this solution to be deployed,” he added. Simard noted that training technicians to handle the electronic components of the system can be a challenge.

Bérubé downplayed the often-expressed concerns about the high pressures that the transcritical system operates under when cooling medium temperature cases, particularly in warmer weather when the outside temperature reaches 88 degrees Fahrenheit (the critical point of CO₂), with a pressure of 1,067 psi. In the parts subject to the higher pressure, which ranges from 800 to 1,300 psi, the system is protected by stainless steel piping that can withstand seven to eight times the operating pressure, he noted.

When the temperature reaches 88 degrees, CO₂ enters the “supercritical” or transcritical state in which it no longer operates like a normal gas in that it no longer condenses directly to a liquid. The system is designed with a gas cooler, gas bypass valve and high-pressure valve that bring the temperature of the CO₂ down so that it can become a liquid and then enter the normal evaporation phase that chills and freezes food. The energy penalty in the system largely occurs as the system grapples with the supercritical state.

Simard noted that there have been at least three pressure-related accidents in transcritical systems in European stores. But the accidents were related to the use of compression settings that are not used in North America. “There was a big boom, but it just gave out dry ice that looked like snow and nobody was hurt,” he said.

“In 2012, 2,000 pounds of pressure is nothing,” added Simard. “The hydraulic power steering in your car has pressure like that — around 1,500 psi.”

In order to maintain the high pressures in the event of a power failure, a back–up generator is considered necessary for a transcritical system. Sobeys uses a large generator in most of its stores to accommodate the entire store. The CSC system only needs a 7-kilowatt generator, which costs around $2,000, said Simard.

By contrast, traditional DX refrigeration technology is notable for its compressor redundancy, said Vogl. “You could have multiple compressor failures and you’re still in the frozen/refrigerated food business.”

In a presentation he made at FMI’s Energy & Store Development Conference, Bérubé concluded by pointing out that a major leak in a conventional synthetic refrigerant system would have the same GWP as driving 1,200 cars on the road for a year; on the other hand, a major leak in a CO₂ system would have the same GWP impact as a “solitary fisherman using his motor boat on the lake.”

He encouraged the retailers in the room to “change the world” by looking into the new CO₂ transcritical refrigeration technology, which he insisted was “not the technology of the future — it’s today’s technology.”