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.

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