NATE Low-GWP cheat sheet

Low GWP Refrigerants (LGWP)

• GWP is a 100-year time-integrated radiative forcing of 1 kg of a gas relative to 1 kg of CO2; CO2 is defined as GWP 1 and values come from IPCC assessment reports (AR4, AR5, AR6), so always state which report a number is drawn from.

• Representative 100-year GWP values (AR4 unless noted): R-744 (CO2) = 1; R-717 (ammonia) = 0; R-290 (propane) = 3; R-600a (isobutane) = 3; R-32 = 675; R-134a = 1430; R-410A = 2088; R-404A = 3922; R-22 = 1810; HFO-1234yf < 1 (about 4 by AR5); HFO-1234ze(E) < 1.

• ASHRAE 34 classifications to memorize: A1 = lower toxicity, no flame propagation; A2L = lower toxicity, lower flammability (R-32, R-1234yf, R-1234ze(E), R-452B, R-454B); A2 = lower toxicity, flammable (R-152a); A3 = lower toxicity, higher flammability (R-290, R-600a); B2L = higher toxicity, lower flammability (R-717 is B2L).

• A2L refrigerants burn only in a narrow concentration band and need high ignition energy: burning velocity is roughly 5-10 cm/s versus about 40 cm/s for propane, minimum ignition energy is on the order of 1-10 mJ, and the lower flammability limit is typically above 100,000 ppm (about 0.3-0.4 kg/m3 in air).

• R-454B is a zeotropic blend of R-32 (68.9%) and R-1234yf (31.1%) with GWP about 466 (AR4); R-452B is R-32/R-125/R-1234yf (67/7/26) with GWP about 676; both are A2L and are drop-in-system replacements for R-410A with similar volumetric capacity. Blends must be charged as liquid because of glide.

• HFO refrigerants (R-1234yf, R-1234ze(E)) are mildly flammable, have near-zero GWP, and are chemically similar to HFCs, but they can form trifluoroacetic acid (TFA) as an atmospheric degradation product and are mildly flammable A2L, so leak detection and ventilation rules still apply.

• Natural refrigerants: R-744 operates at high pressure (critical point 31 C / 73.8 bar, triple point -56.6 C / 5.2 bar), has very high volumetric capacity, low critical temperature, and needs transcritical or cascade designs; R-717 is toxic and slightly flammable (B2L), has excellent efficiency, and is incompatible with copper; R-290 has high latent heat and low charge limits in many codes.

• Regulatory drivers: the Kigali Amendment to the Montreal Protocol phases down HFC production/consumption (baseline 2011-2013 for most Article 5 parties), the US AIM Act implements that phase-down, and the EU F-gas Regulation bans high-GWP refrigerants in new equipment by application; EPA SNAP lists acceptable substitutes and use conditions (charge limits, A2L requirements).