All About A2Ls 

Legacy refrigerants like R-410A are being phased out and replaced with a new class called A2Ls. There are more than half a dozen A2L refrigerants, including R-454B and R-32. These refrigerants have a low GWP and are non-toxic; however, they are also slightly flammable. 

For decades, the HVAC industry did not have to worry about refrigerant flammability. But with some of the new low-GWP refrigerants, flammability is once again a concern. While any flammability can be concerning, the risk must be put into context. Advanced refrigerants like R-454B can only be ignited by an open flame or a heat source that kicks out 1290°F. In other words, even flammable refrigerants are not that flammable. Still, it’s essential that they be safely contained, particularly when used near people. 

To ensure the industry is using A2L refrigerants safely and consistently across all applications, ASHRAE has updated Standard 15 to provide the HVAC industry guidance on how to comply with the new mandate.  

HVAC systems are classified into two groups, high or low probability, based on the likelihood that refrigerant could affect people. Should a high-probability system leak refrigerant, there is a significant risk those fluids will affect an occupied space, such as an office or an apartment. If a low-probability system were to leak, the refrigerant would go into (mostly) unoccupied, inaccessible areas, like a machinery room in a stand-alone building, posing little risk to occupants.  

These designations also influence the types of refrigerants being used and what mitigating systems must be installed. For high-probability products and systems with A2L refrigerants, this is required. While the rules for low-probability spaces are less stringent, that doesn’t mitigate the need to install leak detection and ventilation in those areas to alert the systems, the building team, or the occupants when there is a problem. 

Leak Detection 

Because occupant safety is the primary goal, ASHRAE has established guidelines to keep everyone in the building safe. As a result, leak mitigation systems on HVAC equipment, and in the rooms where the systems live are required. Trane has added factory-installed leak detection systems to all models that contain more than 3.91 pounds of refrigerant.  

These appliance-based sensors activate when refrigerant concentrations reach 25% of the flammability danger zone. If a leak is detected, the system automatically activates mitigation steps within 15 seconds, including shutting down the compressors in the HVAC unit and increasing airflow. 

To generate the most comprehensive system response and meet the 15-second standard, the HVAC system should be connected to a building automation system. The BAS will initiate any additional mitigation actions and notify building operators if there are any leaks.  

Sometimes, an HVAC system with a factory-installed leak detection system is all a space needs, unless it is in a machinery room. For example, a room that houses a chiller with 1,000 pounds of A2L refrigerant requires additional ventilation and outside air to support the airflow. The room will also need a stand-alone leak detection system mounted on the wall to automatically initiate mitigation if a leak occurs. Contractors also need to identify potential ignition sources in the room, which must also be mitigated during a refrigerant leak. 

While the new EPA rules require significant changes, there are a lot of materials contractors and engineers can reference for the latest information. Application engineering and installation operation manuals explain which approaches work best with different systems and applications. ASHRAE also provides multiple publications to clarify the guidelines. Ultimately, once the rules are thoroughly understood and the appropriate mitigation measures are in place, these new practices will become automatic.