ASHRAE Standard 15 Offers Contractors Guidance and Flexibility When Working with A2L Refrigerants
Key Takeaways
- ASHRAE Standard 15 offers flexible options for equipment placement, detection, and mitigation, allowing contractors to tailor solutions to specific applications.
- Systems with less than 4 pounds of refrigerant are considered safe and do not require detection or mitigation, simplifying compliance.
- Upcoming regulations will impact larger VRF systems, prompting redesigns with smaller circuits or alternative refrigerants to meet flammability limits.
A2L low global warming potential (GWP) refrigerants are here, and that’s changing how to monitor HVAC equipment for potential leaks and how to mitigate them. Contractors will have to change a few things to adapt to the new rules.
Under the U.S. Environmental Protection Agency (EPA) mandates, new HVAC installations and replacements will require equipment that uses low-GWP refrigerants, mostly A2Ls. This creates a new dynamic because A2L refrigerants are moderately flammable. While the ignition risk isn’t great, this is a significant change from previous non-flammable refrigerants, such as R-134a and R-410A. Non-flammable refrigerants have been in use for the past 90 years.
As a result, contractors will have to mitigate potential fire risks and understand what the A2L rules do and do not cover.
System Location and Leak Mitigation
ASHRAE Standard 15 outlines the different mitigation efforts that must be in place to manage possible refrigerant leaks. A2Ls must be significantly concentrated to ignite, and they burn quite slowly, but are flammable nonetheless. The standard is specifically designed to help protect people from the risks posed by A2L refrigerant leaks or ignition. These rules govern where to place HVAC units and where leak detection and mitigation will be necessary.
The guidelines are largely dependent on the unit’s chemical charge and location, stating that the minimum refrigerant charge — under 4 pounds — is always considered safe, and no mitigation or detection is required. If the refrigerant leaked out, it would not be concentrated enough, even in a relatively small space, to pose a fire risk.
Units with A2L charges greater than four pounds must ship with factory-installed refrigerant detectors placed on the evaporator connected to the indoor space. If a leak reaches 25% of the lower flammability concentration limit, the detector raises the alarm, shutting down the cooling and turning on fans to disperse the refrigerant.
Contractors will become quite familiar with the effective dispersal volume calculation (EDVC), which determines the maximum allowable charge for the space(s) in which refrigerant might disperse.
The EDVC is based on the volume of the vulnerable spaces and the circuit with the largest charge. For example, an appliance might have 75 pounds of charge, divided into four circuits. The EDVC would be calculated based on the largest charge, say, 25 pounds. Contractors have a lot of flexibility to subdivide charges and help ensure they are under the dispersal limit. In most cases, allowable EDVC refrigerant charges are high enough for A2Ls that only certain applications will run into that limit, like VRFs, chillers, and large split systems.
High- and Low-Probability Systems
Another critical issue, described in the guidelines, is probability. If the HVAC system is deemed high-probability, leaked refrigerant will likely enter an occupied area. Low-probability systems, like chillers, are often located in machinery rooms and would be unlikely to leak into occupied spaces.
When installing a low-probability system in a machinery room, contractors will need to add external detectors to the room. The in-room detection system must provide audible and visual alarms during a leak. In addition, units in a machinery room will need a remote HVAC system shutoff outside the room and automatic electrical disconnection in the event of a leak.
A high-probability system with A2L refrigerant must automatically generate an alarm within 30 seconds of leak detection and begin mitigation within 15 seconds of the alarm. These various mitigation efforts can engage circulation fans, open zone dampers and set them to full airflow, activate mechanical ventilation and safety shutoff valves, and turn off potential ignition sources, including electric resistance heat in ducts. According to ASHRAE Standard 15, none of these systems need to be connected to a fire board.
If everything is arrayed properly, according to the standard, the only negative consequence of a refrigerant leak would be loss of cooling or heating (if the unit is a heat pump) and the fans coming on for a few minutes. Management will also have to call in a technician to repair the leak.
Take Advantage of the Standard’s Flexibility
Contractors will appreciate that ASHRAE 15, in many respects, is quite flexible. For example, there are various equipment options. If one system would exceed the lower flammability limit (LFL) during a leak, and require extra mitigation, there are almost certainly equipment choices that would meet the LFL without the extra work.
Also, the standard describes what a contractor cannot do, but doesn’t say what they can do (that book would be quite lengthy). While it’s not okay to put a continuous refrigerant pipe across a space that’s not being air conditioned, it is acceptable if the pipe is contained within a fire-rated chase. There are always options.
Get Ahead of the Revised VRF Standards Coming Next Year
The first EPA deadline for A2Ls, which went into effect on Jan. 1, 2025, encompassed most chillers, packaged units, split systems, window air conditioners, small, variable refrigerant flow (VRF) — less than 65,000 Btu per hour — and other small systems.
Starting in January 2026, these changes will affect larger new and existing VRF systems. VRF systems use refrigerant piping throughout a building. As a result, the system’s design must take into account the amount of refrigerant that could potentially leak into any one space. The new rules reduce the amount of refrigerant allowed in a room by roughly a factor of four compared to non-flammable refrigerants, like R-410A. As a result, when retrofitting existing R-410A or R-22 VRFs, those systems may have to be pulled and redesigned to transition to A2Ls.
However, as previously stated, the standard is flexible. Contractors installing a new VRF system next year can use multiple, smaller circuits. Three VRF condensers, instead of one, can reduce the charge and keep the system LFL-compliant. In addition, some newer systems use water, along with refrigerants, reducing the total amount of refrigerant required by the system and the risk of refrigerant exposure.
While regulatory changes can be difficult to manage at first, over time, they simply become the water in which everyone swims. The most important thing to remember about ASHRAE Standard 15 is that it is generally flexible. There are creative solutions for every problem, and most of them will not be difficult to implement.
Learn more about the A2L refrigerants:
About the Author
Steve Kujak
Steve Kujak has over 30 years of experience in the development of new refrigerants, lubricants, and HVACR system designs. He is currently an incoming director at large for the ASHRAE Board of Directors and the director of Next Generation Refrigerants Research at Trane Technologies.
Kujak holds over 40 patents, many related to the safe and effective use of next-generation refrigerants. In collaboration with influential organizations ASHRAE and AHRI, and events such as the International Refrigeration and Air Conditioning Conferences, he has authored or co-authored more than 50 published articles about refrigerants and HVAC technology.
He has been a Distinguished Lecturer for ASHRAE and serves on Standard 34 Designation and Safety Classification of Refrigerants committee for the past 20 years, various Section 3 Technical Committees on refrigerants, and has chaired its Refrigeration Committee for Comfort, Process and Cold Chain.
He holds a bachelor's degree in chemistry from the University of Wisconsin-La Crosse.