The Defense Commissary Agency has installed transcritical CO2 systems in three existing military-base stores as part of its exploration of natural refrigerants.
John Stuit, DeCA
The Defense Commissary Agency (DeCA), the “supermarket to the U.S. military,” with 240 stores worldwide, has been experimenting with different natural refrigerant systems since 2014, including transcritical CO2 and ammonia/CO2 cascade.
The agency is trying “to find out what the end game is going to be,” said John Stuit, its chief of design and construction, at the ATMOsphere America conference last month. “It’s certainly going to be some kind of natural refrigerant."
So far, DeCA has focused its efforts on existing store retrofits – in contrast to the rest of the U.S. food retail industry, which favors new-store installations for natural refrigerants. Over the past year, DeCA has retrofitted transcritical CO2 systems in three stores – in Newport, R.I., Mojave, Calif. (Edwards Air Force Base), and Mountain Home, Idaho. The climates of the three stores are marine, hot/dry and cool/dry, respectively.
All three installations use adiabatic condensers and parallel compression, both designed to enable transcritical systems to operate efficiently in hot weather.
At one site, which used installers who had not worked on a CO2 installation before, “they managed to blow the entire charge right into the sales area,” Stuit said. “But it’s working well now.”
““The results look promising; it looks like we’re meeting our energy goals.”
– John Stuit, DeCA
The three DeCA retrofit stores required significant case loads (from 30% to 50%) for system start-up, said Stuit, adding, “Store operations don’t like giving up display cases [for a retrofit]; they want to keep selling groceries.”
Stuit provided preliminary energy results for the transcritical system at the Newport, R.I., store over a six-month period (October 2016-April 2017), when there was 14% less energy consumption compared to the previous HFC system. “The results look promising; it looks like we’re meeting our energy goals,” said Stuit.
However, he said the first-cost premium for the transcritical systems, according to his contractor, “is probably $200,000 for the typical store.” Depending on energy costs, the ROI for that ranges from five to 10 years for a system that will run for 15-20 years, he added.
DeCA has also installed a transcritical CO2 booster system at a new store in Spangdahlem, Germany – a cool climate – that opened in May, 2016. Preliminary data shows that the system consumes 23% less energy than a comparable HFC system. The agency plans to deploy a transcritical system in Northern Italy that will be the first to include an ejector, which will help with efficiency in the warmer climate.