NATE Low-GWP key terms

A number that compares how much heat a gas traps in the atmosphere over a set period, usually 100 years, to the same mass of carbon dioxide, which is assigned a value of 1.

A common unit for expressing total climate impact, calculated by multiplying the mass of a refrigerant released by its GWP so different gases can be compared on one scale.

A relative score for how strongly a substance destroys stratospheric ozone compared with CFC-11, which is set at 1.0. HFCs and HFOs have zero ODP.

A refrigerant family containing only hydrogen, fluorine, and carbon. HFCs do not deplete ozone but many carry high GWP values, which is why they are being phased down.

A refrigerant family with a carbon-carbon double bond that makes the molecule break down quickly in the atmosphere, giving very low GWP and zero ODP. Often mildly flammable.

A safety classification for refrigerants that are mildly flammable, burn slowly, and need a higher concentration and energy to ignite than A3 refrigerants. Common low-GWP HFOs and blends carry this rating.

A safety classification for highly flammable refrigerants such as propane and isobutane. They ignite easily and require stricter charge limits and ignition-source controls than A2L products.

The standard safety grouping that assigns refrigerants a letter for toxicity (A or B) and a number for flammability (1, 2L, 2, or 3), such as A1, A2L, or B2.

The minimum concentration of refrigerant vapor in air, expressed as a percentage by volume or in kilograms per cubic meter, that will support combustion at standard test conditions.

The highest concentration of refrigerant vapor in air that will still burn. Above this level the mixture is too rich to ignite, which matters when evaluating leaks in small enclosed spaces.

The smallest spark energy, measured in millijoules, needed to ignite a flammable refrigerant-air mixture. A2L refrigerants generally need far more energy than A3 products.

Design and service practices that remove sparks, hot surfaces, open flames, and energized switching devices from areas where flammable refrigerant could collect, reducing the chance of ignition during a leak.

A single-component HFC refrigerant with a GWP of about 675, roughly one-third that of R-410A. It is classified A2L and is widely used in small split systems.

A zeotropic blend of R-32 and R-1234yf with a GWP near 466, designed as a lower-GWP replacement for R-410A in residential and light commercial equipment. Classified A2L.

A low-GWP HFO refrigerant with a GWP of less than 1, used mainly in automotive and some commercial cooling. It is classified A2L and has zero ozone depletion potential.

An HFO refrigerant with a GWP below 1, used in chillers and some commercial systems. It is classified A2L and is often chosen where a very low climate impact is required.

A near-azeotropic HFC blend of R-32 and R-125 with a GWP of about 2,088, long the standard for residential air conditioning and now the target of low-GWP replacements.

A single-component HFC refrigerant with a GWP of about 1,430, once common in chillers, vehicles, and appliances. Its high GWP has driven replacement with lower-impact alternatives.

A refrigerant mixture whose components boil at different temperatures, so its composition and properties shift as it evaporates or condenses. Charging must be done as a liquid.

The difference between the bubble point and dew point of a zeotropic blend at a given pressure. It affects superheat, subcooling, and coil performance calculations.

The tendency of a blend's components to separate when it leaks or is charged as a vapor, because the more volatile component leaves first. This can change the remaining mixture's composition and performance.

Adding refrigerant to a system as a liquid rather than a vapor, required for zeotropic blends so the cylinder contents stay at the intended composition and glide is preserved.

The temperature at which the first bubble of vapor forms in a liquid refrigerant mixture at a given pressure. It is used as the saturated liquid reference for zeotropic blends.

The temperature at which the first drop of liquid forms as a refrigerant vapor mixture is cooled at a given pressure. It is the saturated vapor reference for zeotropic blends.

The number of degrees a refrigerant vapor is above its saturation temperature. With blends, superheat is measured from the dew point rather than a single saturation value.

The number of degrees a liquid refrigerant is below its saturation temperature. With blends, subcooling is measured from the bubble point, and it confirms a solid liquid seal at the metering device.

The 2020 U.S. law that directs the EPA to phase down production and consumption of HFCs on a national schedule and to manage refrigerant recovery, reclaim, and leak reporting rules.

An amendment to the Montreal Protocol that sets a global schedule for cutting HFC production and consumption, with different phase-down steps for developed and developing countries.

A scheduled reduction in the amount of high-GWP HFCs produced and consumed, measured in CO2e against a baseline year, which pushes the market toward lower-GWP refrigerants and equipment.

The international treaty that first phased out ozone-depleting substances and now also governs the HFC phase-down through its Kigali Amendment.

The part of the U.S. Clean Air Act rules covering refrigerant handling, leak repair, recovery, and technician certification for stationary refrigeration and air-conditioning equipment.

The credential a technician must hold to buy or handle regulated refrigerants and to service stationary equipment, obtained by passing a proctored exam on refrigerant rules and safe practice.

Removing refrigerant from a system into a container for reuse, recycling, or destruction instead of venting it to the atmosphere, as required by law and by good environmental practice.

Reprocessing used refrigerant to meet new-product purity specifications, verified by chemical analysis, so it can be returned to service in any system, including those under warranty.

Cleaning recovered refrigerant by removing oil, moisture, and particulates, usually on site, without restoring it to new-product purity. Recycled refrigerant is typically reused in the same owner's equipment.

A measure that adds the direct global warming effect of refrigerant leaked over a system's life to the indirect effect of the energy used to run it.

A broader analysis than TEWI that also counts emissions from manufacturing, transporting, and disposing of the equipment and refrigerant, giving a fuller picture of climate impact.

The ratio of cooling delivered to energy consumed. Lower-GWP refrigerants can change efficiency, so equipment design and charge size must be balanced against climate impact.

The maximum mass of flammable refrigerant allowed in a space or system, set by safety standards based on room volume, LFL, and whether mitigation is provided.

Engineering or procedural measures, such as ventilation, refrigerant detection, or shutoff valves, that reduce the risk or concentration of a flammable refrigerant leak in an occupied space.

Sensors and controls that sense a flammable refrigerant leak, then alarm, ventilate, or shut off equipment to keep concentrations below hazardous levels in occupied or enclosed spaces.