US retailer Piggly Wiggly’s ammonia/CO2 experiment
US retailer Piggly Wiggly has recorded energy savings averaging 28.5% over a seven-month period in a Georgia store, thanks mainly to its NH3/CO2 refrigeration system.
Piggly Wiggly operates over 750 self-service grocery stores in 18 states across the Midwestern and Southern regions of the United States.
When Keith Milligan received the first utility bill for his new 36,000-square-foot Piggly Wiggly store in Columbus, Georgia last year, he was flabbergasted at how low it was.
“I called the lady at the power company [Georgia Power] and said, ‘I just want to make sure you got this right,’” said Milligan, CIO for the JTM Corp., Phoenix City, Alabama, a US family-owned retailer that operates 19 Piggly Wiggly stores along the border separating central Alabama and Georgia. He chuckled at the memory. “I didn’t want her to come back in two years and say, ‘I billed you wrong and you owe us $200,000.’ But she checked it, and it was correct.”
The store, opened in September 2015, is just the fourth in the US to use an NH3/CO2 refrigeration system. But its superior energy efficiency, even in a warm climate like central Georgia, makes NH3/CO2 one of the more promising natural refrigerant technologies in the world.
The Piggly Wiggly store uses an ultra-low charge (53 pounds) of ammonia –– less than any of the other NH3/CO2 stores – which is confined to the roof in the ammonia rack.
The ammonia condenses the CO2, which circulates throughout the store; cooling low-temperature cases via direct expansion and medium-temperature through pumped liquid overfeed. For energy comparison purposes, an HFC (R407A) rack alternates every few weeks with the ammonia rack in condensing the CO2.
Milligan’s data comes from a comparison between the Columbus store’s power consumption and an R407A Piggly Wiggly store in La Grange, Georgia. For the period ranging from October 2015 to April 2015, the new Piggly Wiggly consumed 23% to 33% less energy than the conventional outlet, for an average energy savings of 28.5% ($33,170 in total).
The new store was equipped with a number of other energy-saving elements, including LED lights, skylights, occupancy and daylight controls, doors on display cases, and heat reclaim for hot water. But the NH3/CO2 system, accounting for 60% of the store’s electricity consumption, was by far the most impactful on efficiency.
Ammonia’s big potential
Milligan said he considered installing a transcritical CO2 system, offered by Heatcraft, Hillphoenix and other OEMs, instead of the NH3/CO2 system, but decided not to because of central Georgia’s warm climate. “The [transcritical] technology is improving [for warm climates] but at the time it would have increased my power bill.”
By contrast, ammonia systems are unaffected by high ambient temperatures. “The ammonia system has worked very well,” Milligan said. “Ammonia has been around forever as a refrigerant, though not in such tiny quantities.” Ali added that in warmer climates, the NH3/CO2 system offers “the biggest bang for the buck”.
Now he would like to see more supermarkets follow his lead. “Every store you change makes a big difference.” To that end, he invites other retailers, including competitors, to tour his Columbus store.
Milligan intends to use an NH3/CO2 system in future stores. As for existing outlets, he is hoping Heatcraft will come up with a retrofit solution that encompasses natural refrigerants.