Ahold Delhaize USA - Hannaford Transcritical CO₂ system in Turner, Maine

In 2014, the grocery chain opened a 36,000-square-foot store equipped with a CO₂ transcritical booster system in Turner, Maine - the first in the U.S. at that time. Hannaford’s transcritical booster system has a low-temperature capacity of 259,800 British Thermal Units (BTUs)/hour, generated by 6 UL-approved compressors. It includes a controller as well as glycol heat reclaim technology.

The refrigeration system has a warm gas defrost system and Micro Thermo control systems. As a back-up, one of the compressors and the gas cooler are linked to an emergency generator. “If we lose power we have enough to keep it running for at least four hours, which is enough time to get products taken care of,” said Harrison Horning.

The system is designed with stainless steel piping in high-pressure areas, special evaporators to accommodate higher pressures, and relief valves that are set for pressures ranging from 580 to 1,740 psig. “The relief valves are piped to locations where they pose no danger if they lift,” he said.

The choice of using CO₂ was partly driven by the need to address the EPA-mandated phase-down of ozone-depleting R-22, which has been removed from 75% of its stores.

“We had this need to phase out [R22], knowing full well that the HFCs we were using [in R22’s place] were going to have issues,” said Horning. “The GreenChill Partnership gave us a forum where we could get together with other supermarket operators and government people and suppliers and really start getting our arms around it.”

Another motivation for testing a CO₂-only system is the growing vulnerability of HFCs, given the movement by the U.S. Climate Alliance – a bipartisan coalition of states committed to taking ground action with regards to climate change, including phasing-down the use of HFCs, as well as the possibility of the United States to ratify the Kigali Amendment to the Montreal Protocol, a United Nations-led international agreement phasing down the use of HFCs globally. “I don’t think anybody’s ignoring those signals,” said Horning. “People are paying attention.”

Horning evaluates the energy efficiency of the store by measuring the total energy (electric and gas) used in the store – “the energy bills we pay each month,” he said. On this basis, the Turner supermarket consumes 187 Kilo British Thermal Units (KBTUs)/square foot/year. That is a little higher than at Hannaford’s two most efficient stores of a similar size in a comparable climate (167 and 179) but lower than a similar store in an older format.

“I honestly did not expect it to beat our [best] existing system and it hasn’t, but it’s in the ballpark,” said Horning. “And I’m fully confident that with a little bit of focus on it and a few iterations, we can get it equal to or better than our existing systems.”

Horning looks at the stores’ overall energy consumption – not just that of their refrigeration systems – because of the interaction of the systems’ heat generation with the stores’ HVAC equipment. At the Turner store, for example, the transcritical system supplies considerable heat via a series of heat reclaim component.

On a daily basis, the transcritical CO₂ store’s total energy consumption generally fell between a comparable new DX store, which was more efficient, and an older DX store. The transcritical store’s consumption dipped below even the new DX store in the spring and fall, but spiked above it during the winter “when it was pushing to get heat,” and in the summer “when it’s pushed into the transcritical range [above the critical point] for some hours,” said Horning.

He also separately tracked the daily gas and electric energy usage of the three stores and found a similar pattern, with greater variability in the electric energy consumption at the transcritical store compared to the others. He also recently finished analyzing the kilowatt-hours consumed by the individual compressor racks and found that “the transcritical CO₂ system can be very efficient when condensing temps are not too high.”

Horning added the new standard for new stores is to use transcritical systems. “We may pilot some other things like propane cases or maybe medium-temp glycol, but if we’re just doing a standard new store today, I’d say it’s transcritical CO₂. And we would expect the cost premium to be pretty minimal and something that we would get approval for,” said Horning.