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Trane Engineers Newsletter: A2L Refrigerants and ASHRAE® Standard 15

In this Engineers Newsletter (EN), Trane applications engineer John Murphy explains the nuanced refrigerant updates in ASHRAE® Standard 15-2022.

The global scrutiny of the environmental impact of refrigerants has resulted in the development of newer refrigerants with a lower global warming potential (GWP). Some of these are under consideration to be designated as having “lower flammability” (Class 2L), indicating they can ignite under certain conditions. Building codes and industry standards (such as ASHRAE® Standard 15) have been updated to include safety requirements reflecting the less-flammable nature of Class 2L refrigerants.

In the Q3-2023 Engineers Newsletter (EN), Trane applications engineer John Murphy shares an overview of Standard 15’s requirements for the safe design, installation, and operation of systems using this class of refrigerants.

ANSI/ASHRAE® Standard 15, Safety Standard for Refrigeration Systems, applies to a broad range of systems, from a small window air conditioner to a large, water-cooled chiller. Its requirements are intended not only for newly installed systems, but also for replacements or alterations that change the function or capacity of the system, as well as conversions to a different type of refrigerant.

The standard classifies a refrigeration system as either:

  • High-probability systems are those in which the basic design or location of components is such that leaked refrigerant from a failed connection, seal, or component has a high probability of entering an occupied space. Some common examples include a direct-expansion (DX) split-system, a packaged DX rooftop unit, a water-source heat pump, a variable refrigerant flow (VRF) system, or a packaged terminal air conditioner (PTAC).
  • Low-probability systems are those in which the basic design or location of components is such that leaked refrigerant from a failed connection, seal, or component has a low probability of entering an occupied space. A typical example is a water-cooled chiller, located either outdoors or in a “machinery room,” that delivers chilled water to one or more remote air-handling units or terminal units.

Safety requirements for Class 2L (lower flammability) refrigerants were first added to Standard 15 in its 2019 published version. For high-probability systems, these requirements underwent major revisions in the 2022 version in an attempt to better harmonize with the requirements in UL 60335-2-40/CSA C22.2 No. 60335-2-40. For low-probability systems, these requirements are largely unchanged in the 2022 version, with one exception being a reduction in the “Level 2” ventilation rate when a Class 2L refrigerant is used.

Manufacturers of HVAC equipment are likely to follow the requirements of UL 60335-2-40/CSA C22.2 No. 60335-2-40 strictly to ensure their products are “listed”—this listing is a requirement of Standard 15 if a Group A2L refrigerant is used in a “high-probability” system for human comfort. Depending on the application, it’s possible that a specific requirement of Standard 15 may be more stringent than what is required by the UL/CSA standard.

Download the latest issue of the Engineers Newsletter (EN) to read it now.

UPDATED: Trane Applications Engineering Manual on ASHRAE Standard 15

The recently-revised Trane application manual (Literature # APP-APM001F-EN) explains how the requirements in the 2022 version of Standard 15 apply to all types of refrigeration systems—from packaged rooftop units to VRF systems to large water chillers—and all refrigerant safety groups, including Group A2L. It also includes examples of how to calculate the releasable refrigerant charge and effective dispersal volume charge (EDVC) limit for several commonly used system types.

Click to download – FREE copies available only for a limited time!

More about Trane Engineers Newsletters

Engineers Newsletters are topical, informative articles that provide engineering professionals who design HVAC systems with reliable, objective, and technologically current information in a non-commercial format. They've been published by Trane’s Applications Engineering team since 1972 and have long been a trusted technical resource throughout the industry. Subjects range from HVAC system configurations to acoustics to interpretation of ASHRAE standards.

Engineers Newsletters are provided to customers free-of-charge. Current and past issues can be viewed on, and you can even subscribe to receive e-mail notification when a new issue is published.

To learn more about refrigeration management, visit

John Murphy, Applications Engineer

About the Author

John Murphy, Applications Engineer


John has been with Trane since 1993. His primary responsibility as an applications engineer is to aid system design engineers and Trane sales personnel in the proper design and application of HVAC systems. His main areas of expertise include energy efficiency, dehumidification, air-to-air energy recovery, psychrometry, ventilation, dedicated outdoor-air systems, VAV systems, and ASHRAE Standards 62.1 and 90.1. He is the author of numerous Trane application manuals and Engineers Newsletters and is a frequent presenter on Trane’s Engineers Newsletter Live program series.

John is an ASHRAE Fellow and past chair of that society’s “Mechanical Dehumidifiers” technical committee. He has authored many articles for the ASHRAE Journal, presented at ten previous ASHRAE Winter or Summer conferences, and was a featured presenter on ASHRAE’s international webcast, “Dedicated Outdoor Air Systems.”