While CO2 transcritical refrigeration systems are slowly being adopted in the U.S. food retail industry, two other natural refrigerants – ammonia and propane – are also beginning to attract interest among food retailers.
All three refrigerants were addressed in a session on commercial refrigeration at the ATMOsphere America conference in Chicago on June 16.
Ammonia/CO2 at four U.S. stores
Whole Foods Market’s store in Dublin, California, is one of four examples in the U.S. of a supermarket ammonia/CO2 cascade system, which uses ammonia as the primary refrigerant and CO2 as the secondary cooling agent.
In this application, recirculated CO2 goes to (750 KBTU) medium-temperature cases while DX CO2 is employed in (120KBTU) low-temperature cases, noted Dan O’Brien, national sales manager for Zero Zone, which supplied the system. The total load is 70TR.
O’Brien described the year-old project as “overall successful,” though data on energy consumption has not yet been collected.
Environmental and regulatory changes, especially in California, were a driver of the project, he noted.
Among the challenges posed by the NH3/CO2 system: isolating ammonia from occupied areas, and keeping costs justifiable “in markets accustomed to cheaper systems using synthetic refrigerants,” said O’Brien.
The Whole Foods store has the ammonia equipment, including 200 pounds of ammonia, on the roof with controlled access to the equipment area and leak detection with local and remote alarms. DC Engineering, which worked on the project, and Whole Foods “dealt with the local municipality” to gain approval for the system, said O’Brien.
In the “worst-case” scenario that all 200 pounds of ammonia were to leak, it would be contained on the roof, according to an Environmental Protection Agency study. Calculations like this are needed to educate retailers and overcome “misconceptions of ammonia leak potential,” O’Brien said.
At the Whole Foods store, shaft-seal leaks released “minute amounts of ammonia” to no effect, and the seals were replaced, he said.
To compensate for the absence of an on-site operator and to minimise service requirements, the system incorporates near-total automation, including extra sensors for monitoring, automatic shut-down/restart, remote monitoring, and an automatic oil recovery and return system.
The Whole Foods NH3/CO2 system also employs a BAC TrilliumSeries condenser, which increases operating efficiency and improves lifecycle costs, while capturing compressor heat for facility heating and hot water.
Joe Sanchez, engineering manager for Bitzer U.S., pointed out that the four U.S. supermarket installations of NH3/CO2 – Whole Foods, Piggly Wiggly, Defense Commissary Agency (DeCA) and Albertsons – are “extremely different,” with varied approaches to ammonia charge, efficiency, cost and maintenance. “There’s no clear winner – and there will be no perfect system in the future,” he said.
One difference is the compressor configuration. The Albertsons store (in Carpinteria, California, uses a single pack, whereas the Piggly Wiggly and Whole Foods stores employ multi-compressor parallel racks, and the DeCA commissary has a modular design with nine rooftop units.
Though the Whole Foods store uses an automatic oil recovery and return system, Sanchez said the cost of that system “is one of the cost drivers hampering the success of ammonia/CO2 [installations]”. He noted that in industrial refrigeration, manual oil draining is a longtime practice. “Why not consider draining oil in supermarkets?” he said. He suggested having grocery technicians drain the oil once every six to twelve months.
Sanchez described the danger of ammonia in a supermarket setting “very, very low.” But he acknowledged that in a supermarket even the smell of ammonia presents a “social” issue. But it doesn’t have to be perceived as scary, he said. “Maybe one day we will smell ammonia in a supermarket and say ‘that’s not a big deal; it’s probably something with the refrigeration’.”
More than 1,000 propane cases
According to Howell Feig, sales director for strategic accounts at AHT Cooling Systems USA, AHT’s self-contained propane (R290) cases – including spot bunker units and narrow, wide and jumbo island cases – have been installed in more than 1,000 locations in the U.S.
In addition, a number of retailers are exploring AHT’s R290 self-contained units as a “full-store solution,” with some projects to be completed “in the near term,” he said.
Though R290 cases are approximately 10% more expensive than HFC cases, utility rebates – based on superior energy efficiency – are available to offset that initial premium, Feig said. Thirteen-foot R290 cases with lids were found to be much more efficient than open cases, consuming 4,672 kWh annually compared to 7,640 kWh (remote 12-foot) and 10,741kWh (self-contained 10-foot).
All propane cases contain a maximum of 150g, but “maybe it can get up to 300-500” with regulatory changes, said Feig.
Technician training and getting permission from local authorities were barriers when AHT introduced self-contained R290 units in the U.S. in 2010-2011. However, there are now many certified technicians and no issues with local authorities, said Feig.
Paul Delaney, senior engineer for Southern California Edison (SCE), described a study of propane-case efficiency that the utility conducted in its labs. The propane “coffin” cases were found to offer 20% energy savings compared to R404A cases, with an annual savings of about 500-600 kWh. “The propane and variable-speed drives contributed to the efficiency,” he said.
SCE is offering a custom incentive to a new group of 39 stores entering Southern California for these R290 cases. In addition, the utility will be monitoring the efficiency of the new stores in an effort to develop a deemed (prescriptive) incentive that is easier to implement, said Delaney.
CO2 in supermarkets and ice rinks
Carnot Refrigeration has brought energy-efficient CO2 refrigeration to a range of applications. At ATMOsphere America, CEO Marc-Andre Lesmerises described two types of application – ice rinks and supermarkets.
Two ice rink installations of Carnot’s CO2 systems using glycol as a secondary fluid saved 29% and 18% in energy compared to previous systems, he said. The energy expended in pumping glycol is recovered in heat recovery from the system. The facility with 29% savings – the Cynthia-Coull Arena, Greenfield Park, Quebec – received an ASHRAE Best Technology Award in 2015.
Carnot has installed CO2 transcritical systems in 65 supermarkets, including 15 retrofits. In two examples, the stores were found to save 23% and 14% in energy compared to prior systems. To enhance energy savings at these stores, Carnot deployed software to improve heat reclaim capabilities.
Daniel Clark, founder of UK-based Hamilton-Clark Refrigeration Design & Management, described the implementation of CO2 transcritical systems by Booths, a 28-store grocery chain in Northwest England. Starting in 2010, Booths now has these systems in 40% of its stores. “Transcritical CO2 is the new norm,” said Clark.
Each Booths store uses two independent transcritical booster CO2 systems encompassing Advansor racks, Bitzer compressors, Hauser cabinets, Wieland tubing and Resource Data Management controls.
The CO2 racks offer 12% energy savings, and in Booths’ northern climate, can take advantage of free cooling. Doors on the multi-deck cases add 38% savings, while heat recovery contributes 5% savings, said Clark.
Cost of the system is “getting nearer” to that of HFC systems. But because of CO2’s higher pressures, which require more metal, “you are never going to get to cost parity,” he said. However, capital cost uplift is “dwarfed by life cycle savings”.
Clark also noted that the total equivalent warming impact (TEWI) of Booths’ CO2 system is 82% less than that of an R404A system with open multi-decks and no heat recovery.
U.S. food retailers installing CO2 transcritical systems can benefit from the “intensive development of CO2 refrigeration technology over the past 10 years,” said Clark. “CO2 is the ‘New Normal’ in Europe.”