ET25SWE0005 - Comparative Field Assessment of CO₂ System Performance vs. HFC Refrigeration in Supermarkets
Refrigeration systems in commercial facilities, such as supermarkets and grocery stores refrigerated display cases and cooler/freezer rooms, can account for up to 50% of these facilities' total electricity consumption. In California, most refrigeration systems rely on HydroFluoroCarbon (HFCs), which have high global warming potential (GWP). With increasing regulatory and policy pressure, the demand for California's refrigeration end-users to transition to low-GWP refrigerants is growing. However, there are limited field assessments that focus on the use of CO₂ for commercial refrigeration in grocery stores. It is important for customers to understand the CO₂ system’s performance including energy and demand use.
The previous lab assessment (ET19SCE7070), conducted by SCE, produced positive results for a small CO₂ system, supporting the need for this field assessment to evaluate energy savings and operational benefits at much larger actual customer sites. This proposed project will compare CO2 to HFC based refrigeration in at least two California Climate Zones (CZ), gather required operational data to analyze the unit’s performance, and obtain customer feedback on the use of CO₂ as a refrigerant.
While CO₂ refrigeration is gaining traction among some key customers due to the need to avoid high-GWP refrigerants, it still lags the use of traditional refrigerants. This project will deepen the understanding of the energy and operational benefits of CO₂ system refrigeration refrigerated cases and multiplex rack systems at the selected customer sites at one of the largest national grocery store chains and identify market barriers and inform utility programs.
This assessment will focus on CO₂ as the refrigerant. The project will conduct stakeholder meetings, recruit locations, conduct site selections and audits, evaluate the requirements and specifications of the customer’s refrigeration systems, select the sites, perform (M&V) and report the results and recommendations. Customer/stakeholder feedback will also be gathered to help inform utility efforts to increase market adoption of CO₂ refrigeration systems in the retail food refrigeration market. This project’s focus on (CO₂) systems aligns directly with the listed 2024 Process Loads TPM Refrigeration- Commercial area, where ETP has the lead role and the priority is high. The sub-family Refrigeration, Commercial & Industrial lists the proposed Research Initiative as having immediate need for performance evaluation.
The project team anticipates that the utility program teams will have no significant challenges in using the data from this project to support future or existing custom incentive programs, as has been done with previous field assessments. Additionally, there is a separate CalNEXT project (ET24SWE0046) underway that updates and refines existing CO₂ analysis and load modeling tools to support utility programs.
Key objectives:
- Field assessment and performance comparison of CO₂ and standard HFC refrigerant units in at least two climate zones (CZs).
- Obtain performance results for the selected systems and determine the benefits of CO₂ systems in retail food refrigeration.
- Review market barriers and feedback from stakeholders.
- Compare the assessed CO₂ systems to a previous lab report as applicable.
- Interview stakeholders on market size, adoption barriers, estimated return on investment (ROI), and end-use market considerations that could impact future market penetration.
Executive Summary
Supermarket refrigeration accounts for nearly half of the electricity consumption in grocery stores, making it one of the largest opportunities for both energy efficiency improvements and greenhouse gas reduction. In California, recent regulations now require new supermarket refrigeration systems with a refrigerant charge greater than 50 pounds to use refrigerants with a global warming potential below 150. This has accelerated the transition away from high-global-warming-potential hydrofluorocarbons, such as R-404A, toward low-global warming potential alternatives, including carbon dioxide (R-744).
Despite strong regulatory drivers, important questions remain about energy performance, operational reliability, and the cost-effectiveness of carbon dioxide systems across California’s diverse climate zones. To help address the knowledge gap, this project, a CalNEXT field study (ET25SWE0005), compared two carbon dioxide and two hydrofluorocarbon supermarket refrigeration systems located in Climate Zones 10 and 11.
Approach
The project team installed calibrated three-phase power monitoring and temperature logging equipment to collect detailed performance data over a four-month period. Using this data, the team developed regression models to correlate refrigeration system energy use with outdoor temperature. Annualized results were produced by applying the models to historical weather data. In parallel, the team’s on-site engagement with store personnel and corporate stakeholders provided insights into operational practices, perceived risks, and market adoption considerations.
KEY FINDINGS
- Energy: After adjusting for system load and equipment efficiency, the carbon dioxide systems showed little to no net energy savings compared with hydrofluorocarbon systems in these warmer climate zones. Above ~95°F, carbon dioxide system efficiency can diminish due to transcritical operation, limiting performance gains.
- Economic: Installed costs for carbon dioxide systems were approximately 30 percent higher than for hydrofluorocarbon systems. With minimal avoided energy, simple payback calculations were unfavorable when based solely on energy savings.
- Environmental: While the carbon dioxide systems experienced 7 to 19 percent annual leak rates, their climate impact was minimal (global warming potential of 1). By contrast, even modest leaks of R-404A would generate substantial carbon dioxide emissions, given its global warming potential of 3,922.
- Operational feedback: Store personnel at carbon dioxide sites described the two systems assessed as more complex, sensitive, and less reliable to restart after outages. One location experienced a major outage caused by a high-pressure leak and associated product loss. Hydrofluorocarbon systems, by contrast, were viewed as reliable and easy to restart.
- Stakeholders: The grocery store chain’s corporate refrigeration management emphasized that, despite uncertain return on investment, compliance with California regulations and alignment with company sustainability goals are the primary drivers for carbon dioxide refrigeration system adoption. However, field-validated performance data were consistently highlighted as essential for informing future capital investment and incentive participation.
Conclusions
This limited field assessment suggests that in warmer California climates, adoption of carbon dioxide refrigeration systems may not be justified by direct energy or cost savings alone. Instead, regulatory compliance, corporate greenhouse gas reduction commitments, and potential utility incentives are the leading motivators. The findings underscore the need for broader field studies across additional climate zones and store configurations to provide a more representative dataset on energy performance, leak rates, and operational reliability.
By producing objective, field-based evidence, this study provides information to inform Investor-owned utility program design, policy alignment, and industry decision-making as California advances its transition to low-global-warming-potential refrigeration.
Recommendations
Based on the findings from this limited field assessment, the project team suggests the following recommendations to assist in future utility research, program design, and market development efforts:
- 1.Expand Field Data Across More Climate Zones and Store Types
Conduct additional monitoring of CO₂ refrigeration systems in cooler and coastal California climate zones (CZ 3–6) as well as in larger-format and small-footprint stores. Broader datasets will enable more representative comparisons of energy use, leak performance, and reliability. - 2.Develop Targeted Incentive Frameworks
Because CO₂ system adoption is primarily compliance- and sustainability-driven rather than energy-cost-driven, consider incentive approaches that reflect carbon reduction value, refrigerant avoidance benefits, and lifecycle emissions rather than only kWh savings. - 3.Support Workforce Training and Commissioning Best Practices
The higher leak rates and restart challenges observe in this assessment, suggest a need for enhanced technician training, standardized commissioning protocols, and expanded service infrastructure to ensure reliable operation and lower maintenance costs. - 4.Encourage Manufacturer and End Use Customer Collaboration
Utility programs and CalNEXT can convene online presentations and discussion for manufacturers, OEMs, and retailers to share performance and reliability data, identify common failure modes, and review potential system designs for transcritical CO₂ operation in warm climates. - 5.Continue Market Transformation Research
Track CO₂ refrigeration deployment costs, leak rates, and energy trends over time as the market matures. Longitudinal studies will help quantify cost reductions, performance improvements, and carbon benefits as systems evolve. - 6.Integrate CO₂ Findings into Future Emerging Technology and Custom Program Pathways
Incorporate these field results into the CalNEXT Technology Priority Map and custom measure development to support consistent evaluation criteria for low-GWP refrigeration technologies.