Editor’s Note: Julius teamed up with Daikin Applied’s Phil Johnson, P.E., to author this piece.

The engineering community and the world embraced the ban of chlorofluorocarbon (CFC) as a means of protecting the ozone layer. The 1987 Montreal Protocol was a landmark decision for protection of the environment. The predominant use of CFC was in air-conditioning and refrigerating systems.

The refrigerant industry quickly switched to replacement refrigerants that had a zero-ozone depletion potential. Some of the common replacement refrigerants were R410A for air conditioners, including heat pumps, and R134a for chillers. While these refrigerants were good replacements for CFC, it also was known that these newer refrigerants would have to be changed in the future. While the replacement refrigerants have a zero-ozone depletion potential, they also have a high global warming potential.

The continuation of the Montreal Protocol includes the eventual elimination of high global warming potential refrigerants. The movement to lower global-warming potential (GWP) refrigerants was further quantified by the Kigali Amendment to the Montreal Protocol. See Table 1 for the goals set by the Kigali Amendment. The refrigerant industry selected a value of 750 or less as defining a lower GWP refrigerant.

Article 5 Parties are divided into two groups:   

Group 1: The majority of Article 5 parties; 

Group 2: Bahrain, India, Iran, Iraq, Kuwait, Oman, Pakistan, Qatar, Saudi Arabia and the United Arab Emirates.

Non-Article 5 parties: Later-start countries: Belarus, the Russian Federation, Kazakhstan, Tajikistan and Uzbekistan

Determining GWP of refrigerant: The GWP is a comparison of a chemical to carbon dioxide. Carbon dioxide has a GWP of 1. If a refrigerant has a lower GWP of 750, the release of one pound of refrigerant would be equivalent to releasing 750 pounds of carbon dioxide into the environment. Refrigerant molecules with reduced numbers of fluorine atoms generally have lower GWP, however, that leaves more hydrogen atoms, which increases flammability.

All of the currently accepted (and listed in ASHRAE 34-2019) alternative refrigerants for R410A fall into the category of Group A2L refrigerants. Many of the alternative refrigerants for chillers also fall into the category of Group A2L. See Table 2 of alternative refrigerants.

ASHRAE designation of refrigerants: Group A2L is a new safety classification of refrigerants added to the 2019 edition of ASHRAE 34. Prior to the update of the standard, A2L was considered a subclass of Group A2. The A and B designations indicate toxicity classification, A being lower toxicity while B is a high toxicity. The 1, 2, 3 designation indicates the burning characteristics of the refrigerant. No. 1 indicates “no flame propagation” when tested in accordance with ASTM E681. No. 2 indicates “flammable” and No. 3 indicates “higher flammability.” A typical A3 refrigerant is propane, R290.

The new designation 2L indicates “lower flammability.” In simple terms, a 2L refrigerant can sustain a flame, but it does not burn very well. It also requires a high energy source to ignite. Common A2L refrigerants are R32 and R1234yf. A common B2L refrigerant is ammonia, R717.

A2L refrigerants are included in current blends of A1 refrigerants. R410A is a blend of 50% R32, a lower GWP A2L refrigerant, and 50% R125, a high-GWP A1 refrigerant. The blend of the refrigerants lowers the flammability of the refrigerant into the Group A1 classification.

The misconception with refrigerants is that A1 and B1 refrigerants do not burn and are often called non-flammable refrigerants. However, all but nine refrigerants will burn and provide a fuel source. The A1 and A2L refrigerants just don’t burn well. Of the nine truly noncombustible, nonflammable refrigerants, none are commonly used in refrigerant systems. However, one refrigerant is gaining in popularity, that being carbon dioxide, R744, although not for air-conditioning systems.

Over the last decade, there has been extensive research on Group A2L refrigerants. One of the concerns is the use of a refrigerant falling into a lower flammability classification. Another issue is the type of lubricant that needs to be used with these refrigerants. Of course, compatibility and replaceability are factors that were researched.

Maximum refrigerant charge: ASHRAE 34 establishes the refrigerant concentration limit (RCL) for each refrigerant. For A1 refrigerants, the RCL is based on the toxicity level of the refrigerant. For Group A2L, A2, and A3 refrigerants, the RCL is based either on the lower flammable limit (LFL) or the toxicity level, whichever is lower. For all but a few A2L refrigerants, the RCL is based on the LFL. The RCL is established at 25% of the LFL for the room concentration. Hence, it would require four times the concentration to reach the point where the refrigerant would ignite.

When comparing A1 to A2L refrigerants, the RCL is normally much lower for A2L refrigerants. For example, R410A has an RCL of 140,000 ppm, which equates to 26 pounds per 1,000 cubic feet, while R32 has an RCL of 36,000 ppm, which equates to 4.8 pounds per 1,000 cubic feet. The allowable refrigerant charge of R32 is 18.5% of the charge allowed for R410A.

Engineers have had a tendency to not pay much attention to the RCL for A1 refrigerants. With the move to A2L refrigerants, the RCL will become an important factor in the design of a refrigerant or air-conditioning system. One of the many benefits of A2L refrigerants use is that most are more efficient, requiring a smaller charge size than their comparable replacement refrigerants.

New A2L standard requirements: After more than a decade of research and analysis of Group A2L refrigerants, ASHRAE has published requirements regulating the use of A2L refrigerants in the 2019 edition of ASHRAE 15. This is the standard on which every mechanical and fire code refrigeration requirement is based. ASHRAE 15 includes requirements for the use of A2L refrigerants in high-probability systems used for comfort cooling, and for systems installed in machinery rooms.

High-probability systems include rooftop units, heat pumps, water-source heat pumps, split systems, package terminal air conditioners, mini-splits and multi-split systems. Prior to the changes to ASHRAE 15, all of these systems typically used Group A1 refrigerants. Only systems using less than 3 kg of refrigerant were allowed to use a refrigerant in a safety classification other than Group A1.

The safety requirements added to ASHRAE 15 for the use of A2L refrigerants for comfort cooling include listing of the equipment, refrigerant detection and ventilation (when necessary). The charge limitation, which also is a safety provision, remains the same based on a maximum concentration equal to 25% of the LFL.

The new requirement for listing of the equipment by a nationally recognized testing laboratory is unique to ASHRAE 15. This is the first time the standard is mandating a listing for a given category of products. Previous editions addressed listing, but never mandated that products be listed.

The listing of A2L equipment will be to the 3rd edition of UL/CSA 60335-2-40. This consensus standard, which will be published this month, includes new requirements for refrigerant equipment using A2L refrigerants. The safety requirements of UL/CSA 60335-2-40 mandate that a refrigerant detector be installed internal to the refrigerant equipment. The internal detector is consistent with the requirement in ASHRAE 15 for refrigerant detectors.

Engineers do not typically pay much attention to equipment standards used for manufacturing, testing and listing equipment. UL/CSA 60335-2-40 is about 250 pages in length, with detailed requirements directed to the manufacturer. The standard specifies all the equipment requirements in addition to the safety requirements for using A2L refrigerants. The A2L safety requirements were developed through the international IEC standard process and harmonized for use in North America. Safety requirements were developed after a thorough evaluation of all the major research done on A2L refrigerants.

Early research verified that minor leaks of A2L refrigerant are of no consequence. The vast majority of refrigerant piping leaks are minor leaks. With a minor leak, there isn’t enough refrigerant to cause a fire or toxicity hazard. The real concern is a catastrophic leak of A2L refrigerant.

The committee responsible for the development of the 3rd edition of UL/CSA 60335-2-40 based the safety requirements on a 4-minute leak of refrigerant. This means the entire refrigerant charge will enter a room or space in a period of 4 minutes. It should be noted this rarely, if ever, occurs.

The goal of the UL/CSA committee was to maintain a safe environment even with a catastrophic 4-minute leak. That was accomplished with the published requirements in the updated standard.

While ASHRAE 15 bases the RCL on 25% of the LFL, UL/CSA 60335-2-40 went further in regulating the charge size, basing it on the height of the installation of the refrigerant unit. Knowing that refrigerant is heavier than air and sinks to the floor, the room volume is based on equipment height rather than the actual room volume. This often results in a smaller charge being allowed in UL/CSA 60335-2-40 compared to ASHRAE 15.

Mitigation to maintain safety: Research has also proven that mixing the refrigerant in the room air by use of a fan is all that is necessary to prevent a concentration of refrigerant from reaching the LFL. As a result, the standard requires the fan to activate in the event of a refrigerant leak. The refrigerant will move throughout the building and eventually to the outdoors, not creating a fire or toxicity hazard.

There was research into the possibility of adding odorant to A2L refrigerant similar to natural gas and propane. However, studies have proven that odorant cannot be added to A2L refrigerants. While there is no odorant added, catastrophic leaks will alert building occupants. A 4-minute leak is very loud. The refrigerant at high pressure escaping into the environment can be heard. The leak is also visible because the refrigerant condenses the moisture in the air. Finally, the refrigerant can be felt. Floor temperatures have been measured at -40° F when there is a catastrophic leak. Frostbite of the feet is a concern before there is any fire or toxic hazard.

While there is no odorant for A2L refrigerants, you can hear it, you can see it and you can feel it when there is a catastrophic leak requiring attention. In addition, refrigerant detectors within the unit will start the remediation action to prevent any fire or toxic event.

Switch to A2L refrigerants: Manufacturers have started the transition to A2L refrigerants for high-probability equipment used for comfort cooling. States, including California and Washington, have already passed legislation requiring the use of lower-GWP refrigerants. The mandatory switch to lower-GWP refrigerants will begin in 2023. There are already more than 70 million A2L air-conditioning units installed worldwide.

Other states will soon follow California and Washington. Now that ASHRAE 15 has been updated to address the safe use of lower GWP A2L refrigerants, the global change to A2L refrigerants is inevitable.

Like the ban of CFC, parts, components and refrigerants will continue to be available for existing systems using higher-GWP refrigerants. Refrigerants such as R410A and R134a will remain available for charging existing systems. Existing equipment using higher-GWP refrigerants can remain in use for the life of the equipment and system.

In addition to the environmental benefits of lower-GWP refrigerants, many of the newer refrigerants are more efficient. Smaller charge sizes will produce the equivalent level of cooling. This results in energy savings. Hence, newer systems using lower-GWP A2L refrigerants will be good for the environment and good for energy efficiency.