For several years, the governing bodies that regulate the safe use of refrigerants in the U.S. have been evaluating the prospect of increasing charge limits in the flammable A3 refrigerant propane (R-290) and an emerging class of mildly flammable A2L refrigerants. In 2021, the Underwriters Laboratories (UL) approved the second edition of its UL 60335-2-89 standard, which included higher charge limits that would expand the potential uses of R-290 and A2Ls in commercial refrigeration.
R-290 charge limit increases
With a long-held maximum charge limit of 150g, R-290 has primarily been used in smaller, self-contained units that don’t need large refrigeration loads. Designing larger-capacity, R-290 based refrigeration equipment has required the use of multiple R-290 based compressors or condensing units.
The updated UL standard raises the charge limits on these commercial stand-alone displays based on whether they have an open or closed design:
• 500g maximum charge limit in open appliances (without doors)
• 300g maximum charge limit in closed appliances (with doors or drawers)
From an application design perspective, these higher charge limits will help to increase system capacities while capitalizing on R-290’s high efficiency and low-GWP rating (GWP = 3).
Ensuring the safe use of A2L refrigerants
Mildly flammable A2L refrigerants have also been identified as low-GWP alternatives for complying with emerging refrigerant regulations. Because of their potential flammability, to date A2L refrigerants have been used globally in relatively small refrigeration architectures, such as: self-contained systems, indoor/outdoor condensing units (OCUs) and distributed systems.
Per the recently updated UL 60335-2-89 safety standard, new A2L charge limit guidelines have been established for self-contained and remote refrigeration systems. For self-contained equipment, charge limits are determined on whether equipment is open or has doors or drawers. Degrees of flammability will vary among different A2L refrigerants, so it’s important to calculate charge limits based on the specific A2L characteristics.
For example, since R-454C has a lower flammability limit (LFL) of 0.291 kg/m3:
• A closed-door case can be charged with up to 2.33 kg (5.1 lbs.) of R-454C.
• An open case with R-454C can be charged with up to 3.78 kg (8.3 lbs.) of R-454C.
In remote or field-erected systems, UL 60335-2-89 supports R-454C charge sizes up to 75.7 kg (166 lbs.) per circuit.
Per the UL 60335-2-89 standard, remote A2L systems must be designed with requisite safety strategies and mitigation measures to keep gas concentrations below flammable thresholds. This includes the ability to detect refrigerant leaks at various points of the refrigeration circuit — from the compressor to the condensing unit to the case — and then take immediate action to mitigate flammability risks. In human comfort applications, similar UL standards are also in place.
Safety standard updates set the stage for wider approvals
The UL 60335-2-89 second edition update is only the first step in a larger series of regulatory approvals needed to enable higher charges of R-290 and the use of A2Ls in U.S. commercial refrigeration. The following supporting regulatory and policy changes will also need to be approved:
• EPA Significant New Alternatives Policy (SNAP) approval of specific A2L refrigerants and increased R-290 charge limits
• ASHRAE 15 safety standard update for refrigeration systems
• Model code updates in the upcoming code revision cycle, such as: Uniform Mechanical Code (UMC), International Mechanical Code (IMC) and International Fire Code (IFC)
• State and local building code updates
Industry stakeholders are optimistic that the ASHRAE 15 update and EPA SNAP approvals (for at least some A2Ls) will yet take place in 2022. Although the next model code update is planned for 2024, select states have legislated or adopted provisions of the safety standards directly into their building code updates to allow for the use of all EPA-approved substitutes. Thus, our industry could begin to see some A2Ls used in late 2022 or early 2023, with more widespread use expected in 2024. In the meantime, installing an A2L-based refrigeration strategy would typically require the approval of local authorities having jurisdiction (AHJ), such as fire marshals and/or building inspectors.