Global regulations coming into effect in the coming years will require manufacturers to find alternative refrigerants to meet new limitations. These new limitations are determined based on a refrigerant’s determined global warming potential (GWP), a measure of infrared energy the emissions of a gas will absorb relative to carbon dioxide (CO2). Unlike the complete phaseout and ban of chlorofluorocarbon (CFC) refrigerants R-12 and R-22, which went into effect on Jan. 1, in all cases, this new transition to lower GWP refrigerants is a phasedown. Existing products on the market will be able to continue using refrigerants, such as the common HFC, R-410A.

The current objective to comply with new regulations is to find a refrigerant with a GWP of less than 750. Many of the current lower GWP solutions that are desirable among manufacturers have properties that make them mildly flammable. The transition from the current traditional refrigerants to these alternatives requires additional precautions be taken when operating and storing equipment to mitigate hazards associated with refrigerant leaks.

Refrigerant Classifications

ASHRAE 34 provides a system of alphanumeric characters to define a refrigerant’s safety classification in North America. These align with the global classification system under ISO 817. The classification system uses a two-character designation. The first character (A or B) defines the toxicity of the refrigerant, with “A being less toxic than B,” as determined by the occupant exposure limit (OEL). The second character(s) define flammability by an increasing designation from 1-3, where 1 means no flame propagation; 2L denotes a maximum burning velocity ≤ 10 cm/s; 2 means flame propagation, a lower flammability limit (LFL) of more than 0.10 kg/m^3, and heat of combustion < 19,000 kJ/kg; and 3 has flame propagation, an LFL of less than or equal to 0.10 kg/m^3, and a heat of combustion ≥ 19,000 kJ/kg.

For comparison, the traditional refrigerant, R-410A, is classified A1, or no flame propagation. However, it has a GWP of 2,088. Alternatives, while posing a lower GWP, are largely classified as A2L, having a maximum burning velocity of less than 10 centimeters per second. They are thus considered nontoxic and mildly flammable.

Considerations

The differences between the traditional A1 refrigerants and the alternate A2L require several considerations when it comes to product design, use, and overall safety. These include:

• Density — The most popular alternative refrigerant choices are all heavier than air. This increases risks of potential hazards if a leak occurs close to the floor or ground where dilution with air is limited.
   
• Ignition — Many alternatives have a lower flammable limit, making them more quickly and easily ignited. As such, potential sources of ignition (like a brazing torch) must be considered during installation, operation, service, and tear-down.
   
• Physical Risks — If a leak and ignition does occur, some refrigerants produce hydrogen fluoride (HF) as a biproduct of combustion. HF can cause severe burns on skin as well as lung damage leading to respiratory distress or cardiac arrest. 

UL 60335-2-40 and UL 60335-2-89

UL 60335-2-40 is a test-based standard that will become mandatory in January of 2024. It applies to air conditioners, heat pumps, liquid chillers, hydronic fan coil units, hot water pumps, dehumidifiers, supplemental heaters, and equipment with flammable refrigerants. It is replacing safety standards UL 1995, UL 484, and UL 474 for HVAC systems and appliances, room air conditioners, and dehumidifiers respectively.

UL 60335-2-89 is also a test-based standard that will likely come into effect in 2022, once dates are confirmed within the refrigeration industry. It applies to electrically operated commercial refrigeration appliances that have an incorporated compressor, refrigerating appliances that are supplied in two or more units for assembly as a single appliance in accordance with the manufacturer's instructions (split system), and partial units intended for installation in a field-erected system. This includes display cases, service counters, blast freezers, icemakers, and other common commercial refrigeration appliances. When it takes effect, it will cover refrigeration products previously approved under safety standards UL 1995, UL 427, and UL 471.

The latest major changes in both UL 60335-2-40 and UL 60335-2-89 cover flammable refrigerants and the allowed charge limitations depending on product type and refrigerant classification per ASHRAE 34 and ISO 817. For flammable refrigerant systems, these latest updates will have significant new requirements for installation and operation manuals (IOMs), temperature requirements of components and surfaces, safety control sensor locations, flame arrest enclosure verifications, and toxicity charge limits.

Safety requirements for systems with flammable refrigerants will be determined based on the total system refrigerant charge within three charge-level classifications: m1, m2, and m3. This is a calculation based on the lower flammability limit properties of the refrigerant with m1 being the lowest charge designation and m3 the maximum possible charge allowed for most appliances utilizing an A2L-classified refrigerant. The charge designation will determine what additional safety mitigations must be provided with the appliance from the factory or during installation. 

For example, unitary air conditioning systems with a charge less than m1 aren’t required to have additional mitigation safety controls, but if the charge designation is greater than m1, up to and including m3, it must have a mitigation safety control in the event a refrigerant leak occurs. One type of mitigation is an included refrigerant detection system capable of identifying the presence of a leaked refrigerant that shuts down the system and activates a circulation blower to dilute refrigerant concentrations below their flammability limits. The refrigerant detection system may also activate safety shut-off valves to limit the amount of refrigerant lost. Alternatively, the manufacturer can design a system to run continuous airflow circulation through the system in lieu of a refrigerant detection system. Manufacturers will have to declare and provide thorough installation instructions that cover the limitations for areas of the rooms where equipment is installed and used per the requirements set in the safety standards. Minimum allowed room areas are critical to ensure refrigerant concentrations do not exceed set limitations based on the charge level of each independent refrigerant system. 

When testing appliances with flammable refrigerants for certification they must be evaluated to determine what parts within the confines of the equipment could be a refrigerant leak source. These leakage sources are evaluated with the potential ignition sources within the equipment. Critical points to evaluate for a refrigerant leak include a joint in the refrigerant system tubing; a bend more than 90 degrees; or a point judged to be a weak point in the refrigerant containing system due to thickness of the metal, exposure to damage, sharpness of a bend, or the manufacturing process. Ignition sources can be electrical components that produce sparks or arcs such as brush-type motors, switches, and relays. Ignition sources may also be surfaces of components or cabinets that exceed the auto ignition temperature (AIT), such as electric heaters or UV lights. 

Certification test labs are going to simulate all these potential combinations of leak sources and ignition points to verify the components are protected by segregation from the leak source, placed in approved flame arrest enclosures, or the components themselves are designed and listed suitable for use in areas of known flammable vapours, also designated as hazardous locations. Some other general construction and installation requirements specific to flammable refrigerant systems include refrigerant tubing must be enclosed or protected from mechanical damage, low temperature solder alloys with a melting point less than 427C may not be used for pipe connections, and fusible plugs added during installation or provided with the equipment from the manufacturer must be vented to the outdoors.

Appliances utilizing flammable refrigerants must withstand the effects of vibration during transport and the vibrations that occur during the use of the appliance once installed. To simulate transport, they will be tested in final packaging and withstand a 180-minute vibration test to ASTM D4728-06. To test vibration during normal use that could affect connection points of the refrigeration system, vibrations are measured at all critical points while the appliance is in operation to ensure vibrations do not cause excessive resonance in the piping connected to the compressor. Pass/fail criteria are the use of detection equipment having an equivalent sensitivity of 3 g/year of refrigerant shall reveal no leaks.

Systems with flammable refrigerants are going to have new markings to alert professionals and users before any routine service or repairs. Equipment using A2L refrigerants must have the word “WARNING” near all service ports, pipes, hoses, and other devices through which the refrigerant is serviced. A2 and A3 refrigerants will have the word “DANGER” in these same locations. Symbols indicating the use of flammable refrigerants in the product must also be used. Service ports for A2 and A3 refrigerant systems must be painted or colored an easily visible red when they are capable of being serviced.

Evaluating systems that use flammable refrigerants under UL 60335-2-40 and UL 60335-2-89 entails a full assessment of the appliance and its construction as well as a thorough review of markings, instructions, and manual(s). As the standard’s effective date is still years in the future, there will likely be changes and amendments in the coming years. As such, it is important to stay up to date on developments within the standard to ensure continued success in assessing products. Working with a trusted partner to stay on top of changes and complete evaluations can help ensure the process goes smoothly and products get to market efficiently. Proper understanding of the use and safety considerations around these alternate refrigerants will also be key.