Transcritical CO2 (R744) is now the refrigeration specification for new stores in California for Emeryville, California-based discount retailer Grocery Outlet, with a goal of expanding the application to other regions in the U.S.
This decision comes after a two-year monitoring program at an East Sacramento, California, Grocery Outlet store that opened in January 2020, which found that its transcritical CO2 booster system with an adiabatic condenser uses 27% less energy compared to the R404A-based system of a similar store under the same brand.
The R744 system, manufactured by OEM Hillphoenix, also resulted in a reduction of energy costs by 23% and CO2e emissions by 27%. The East Sacramento store is the first Grocery Outlet store to use transcritical CO2 refrigeration; two more new stores in California, in Murrieta and Atwater, will be installing the system by the end of the year.
Details of the installation and Grocery Outlet’s plans were presented by Frank Davis, Senior Director of Refrigeration and Sustainability at Grocery Outlet, during the “Measuring Performance of Natural Technologies” session at the North American Sustainable Refrigeration Council (NASRC)’s Sustainable Refrigeration Summit, which took place virtually October 24–28.
Results from the monitoring program were shared at the session by Safdar Chaudhry, Senior Engineer Manager at ADM Associates, which conducted the measurement and verification (M&V) analysis for the project.
R744 vs HFCs
Grocery Outlet, which oversees 430 independently owned and operated stores across eight states, installed the CO2 system in a 2,200m2 (24,000ft2) store in East Sacramento with funding from the Sacramento Municipal Utility District (SMUD) and the American Public Power Association (APPA)’s Demonstration of Energy and Efficiency Developments (DEED) program.
The CO2 system uses 190kg (420lbs) of R744 and includes four compressors with a total capacity of 139.8kW (39.7TR) and one condenser with a capacity of 160.3kW (45.6TR). According to Davis, an adiabatic condenser was chosen to try to capture better energy efficiency to reduce energy costs. The total refrigeration load of the store’s refrigeration equipment is 118.6kW (33.7TR).
During his presentation, Davis noted that Grocery Outlet opted for an R448A-based HVAC system for the store due to financial constraints, even with the incentive rebates and grants available.
To assess the benefits of the transcritical CO2 booster system, its performance was compared to the HFC-based direct expansion (DX) system of a 2,155m2 (23,200ft2) Grocery Outlet store in the Pocket section of Sacramento.
The DX system uses 272kg (600lbs) of R404A – which has a 20-year GWP of 6,600 – and includes five compressors with a total capacity of 83.3kW (23.7TR) and five air-cooled rooftop condensers that have a total capacity of 127.1kW (36.1TR). The total refrigeration load of the store’s 23 refrigeration cases of varying sizes and temperatures is 70.6kW (20.1TR).
Following a monitoring period from July 2020 until March 2022, the CO2 system was found to be “superior to the conventional HFC system” in terms of energy use, energy cost and CO2e emissions impacts, said Chaudhry during the NASRC event.
The R744-based system used 27% less energy and reduced energy costs and CO2e emissions by 23% and 27%, respectively.
During the M&V period, no leakage was reported for either system, which Chaudhry noted is very rare. However, if there was leakage at these stores, “the natural systems advantage would have increased significantly to a 93% reduction [in CO2e emissions],” he added.
Analysis also found that while the installation and equipment cost for the CO2 system was about 24% higher than a comparable conventional HFC system, operating costs of the former are estimated to be lower than for the latter.
California’s GWP regulations
Under California Air Resource Board (CARB) regulations, as of January 1, 2022, new stationary refrigeration systems with more than 22.7kg (50lbs) of refrigerant must use refrigerants with a GWP of less than 150.
According to Davis, this was a significant driver for Grocery Outlet’s CO2 pilot project. The supermarket brand was also interested in gathering data to inform future decisions regarding refrigeration systems for new stores, he added.
In total, Grocery outlet received US$217,000 (€216,960) in funding for the project: approximately US$79,000 (€78,985) came from SMUD’s natural refrigerant incentive fund, US$13,000 (€12,997) came from the utility’s energy efficiency incentive fund, and US$125,000 (€124,977) came from an APPA DEED grant.
The money received was just enough to cover the additional cost of the transcritical CO2 system versus a typical R448A DX rack, noted Davis.
“We probably wouldn’t have done this project at this time without the financial incentives,” he added.
The project has helped reduce the GWP of the Grocery Outlet store, which is now in alignment with CARB requirements.
In addition to the transcritical CO2 store, there are five Grocery Outlet stores that use propane (R290) micro-distributed systems – four in California and one out of state. There is also interest in A2Ls, said Davis.
NatRef technicians needed
According to Davis, the shortage of technicians with experience in natural refrigerants has been a challenge.
“In Southern California, there are a lot of these types of systems, so the technicians are getting more familiar with the technology,” he said. “But in some smaller regions, it’s still difficult to find a refrigeration rack technician, let alone a CO2 mechanic.”
“In Southern California, there are a lot of these types of systems, so the technicians are getting more familiar with the technology. But in some smaller regions, it’s still difficult to find a refrigeration rack technician, let alone a CO2 mechanic.”Frank Davis, Grocery Outlet
To overcome this barrier, Davis said that more training is needed and that the retail industry needs to encourage engagement and collaboration to show the service industry that natural refrigerants are the future.
Incentivizing the NatRef transition
In March 2017, SMUD – a community-owned, not-for-profit electricity service – launched a pilot incentive program designed to reduce the energy consumption of, and direct GHG emissions from, new or retrofitted refrigeration systems. Customers could get up to US$250,000 (€249,941) in funding for projects.
According to Kathleen Ave, Senior Climate and Ecosystem Strategist, Customer and Grid Strategy at SMUD, who spoke at the NASRC session, the objective of the program is to “create a cost-effective pathway for natural refrigerants” and to build a network of manufacturers, engineers, technicians and customers.
Ave emphasized that the program, which received APPA’s National Energy Innovator Award in June 2022, specifically supports natural refrigerants, not just low-GWP options.
“We understand that the impact of HFOs is not yet well studied or understood, and there are concerns about by-products and potential restrictions as a PFAS ‘forever chemical,’ so we decided to make it support natural refrigerants only,” she said.
“We understand that the impact of HFOs is not yet well studied or understood, and there are concerns about by-products and potential restrictions as a PFAS ‘forever chemical,’ so we decided to make it support natural refrigerants only.”Kathleen Ave, SMUD
While its incentive program has concluded, SMUD is discussing internally to see how it can continue the work, said Ave. It is also talking with other utilities to encourage them to roll out similar programs.
Raley’s ammonia/CO2 system
As well as funding the R744 system at Grocery Outlet, SMUD’s program also funded a two-stage ammonia/NH3 (R717) and CO2 system at a Raley’s supermarket in Sacramento. The store received US$150,000 (€149,965) from the utility’s natural refrigerant incentive fund and US$56,000 (€55,986) from its energy efficiency incentive fund.
The system was compared to a R404A-based two-stage system at a similar-sized BelAir store in the city.
In this instance, analysis found the ammonia/CO2 system to be “inferior to the HFC system” in terms of energy use, energy cost and capital cost. It used 18% more energy due to the heat transfer inefficiencies compared to a single-fluid system, and the installation and equipment costs were approximately 18% higher than the HFC alternative.
“Although emissions associated with energy use were higher, the low GWP of Raley’s natural refrigerant enabled it to maintain lower overall emissions when leakage was considered,” concluded Chaudhry during his presentation. “Overall, Raley’s ammonia/CO2 system reduced CO2 emissions by 74% compared to BelAir’s HFC-based system.”
While this ammonia/CO2 system wasn’t able to compete in terms of energy use and cost, he noted that other benefits could be realized by adopting such as system.
A study has been commissioned by energy provider Southern California Eddison (SCE) to look at the wider environmental benefits of the Raley’s system. This will go beyond just energy consumption and direct emissions to look at other factors such as water and natural gas consumption.
Other stores in the U.S. using ammonia/CO2 systems have found them to be more efficient than conventional systems.
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