Compendium

Refrigerants — Family Index

28 min read

Refrigerants — Family Index

Working fluids for vapor-compression and absorption refrigeration cycles, organized by generation: CFC → HCFC → HFC → HFO → natural. Regulatory pressure (ozone depletion, then global warming) has driven five distinct waves of chemistry since 1930. Selection today is a four-way trade among thermodynamic performance, safety (flammability + toxicity), environmental impact (ODP + GWP), and regulatory eligibility per jurisdiction.

0. Quick reference card

GenerationEraKey examplesODPGWP rangeStatus 2026
CFC1930–1996R-11, R-120.85–1.04750–10900Banned production
HCFC1970–2030R-22, R-1230.02–0.1179–2310Service phase-out
HFC1990–2050R-134a, R-410A, R-32, R-404A0124–3985Kigali stepdown
HFO / HCFO2010–presentR-1234yf, R-1234ze, R-1233zd0–0.00034< 1–10Current new equipment
Natural1850–presentR-744, R-717, R-290, R-600a, R-71800–3Long-term option

1. At a glance

Five generations, each displacing the last under regulatory pressure:

  • CFC (chlorofluorocarbons) — R-11, R-12, R-113, R-114, R-115. High ODP. Montreal Protocol 1987 phased out production by 1996 (developed countries).
  • HCFC (hydrochlorofluorocarbons) — R-22, R-123, R-141b. Lower ODP than CFC but non-zero. US new-equipment ban 2010 (R-22), service-only with reclaimed material post-2020, full phase-out 2030.
  • HFC (hydrofluorocarbons) — R-134a, R-32, R-410A, R-407C, R-404A. Zero ODP but high GWP. Kigali Amendment 2016 (entered force 2019) initiated global stepdown.
  • HFO (hydrofluoroolefins, 4-digit) — R-1234yf, R-1234ze, R-1233zd. Zero ODP, GWP < 10, mostly A2L. Current frontier for new equipment 2020+.
  • Natural — R-744 (CO₂), R-717 (NH₃), R-290 (propane), R-600a (isobutane), R-1270 (propylene), R-718 (water). Zero ODP, GWP ≤ 3, no regulatory phase-down risk.

ASHRAE 34 R-numbering (saturated halocarbons): hundreds-digit = (number of C atoms − 1), tens-digit = (number of H atoms + 1), ones-digit = number of F atoms; remaining bonds filled by Cl. Alphabetic suffix denotes isomer (e.g., R-134a). For four-digit HFO designators, the leading digit denotes unsaturation count + 1 (so R-1234yf is one C=C double bond, derived from propene backbone with appropriate F substitution). Blends: R-4xx (zeotropic) and R-5xx (azeotropic), with composition-suffix letters distinguishing different blend ratios (e.g., R-410A vs R-410B).

2. Key environmental metrics

  • ODP (Ozone Depletion Potential) — referenced to R-11 = 1.0. R-22 = 0.05. All HFCs, HFOs, and naturals = 0. HCFO R-1233zd has a tiny residual ODP ≈ 0.00034 (negligible, accepted under Montreal).
  • GWP (Global Warming Potential) — relative to CO₂ = 1, 100-year horizon. Reference is IPCC AR5 in most regulations; AR6 (2021) tweaked many values but AR5 numbers remain in force in EU F-Gas and AIM Act schedules. Cut-off thresholds in common use: GWP < 150 for new mobile AC (EU MAC Directive 2006/40/EC, in effect since 2017); GWP < 150–300 for new commercial supermarket racks (EU F-Gas 2024/573); GWP < 700–750 for residential split AC (US EPA SNAP + AIM Act, force 2025).
  • TEWI (Total Equivalent Warming Impact) = direct (leak × GWP) + indirect (energy × grid CO₂ intensity). Often more honest than pure GWP for hermetic equipment because indirect dominates. Annual leak rate for stationary AC is typically 2–5 %/yr, supermarket racks 15–25 %/yr (old style) down to < 5 % for new CO₂.
  • LCCP (Life Cycle Climate Performance) = TEWI + manufacturing + end-of-life. EU F-Gas pushes LCCP-style accounting.
  • Atmospheric lifetime — drives GWP. CFC-12 = 102 years, HCFC-22 = 11.9 years, HFC-134a = 14 years, HFC-32 = 5.4 years, R-1234yf = 11 days, R-744 = effectively immortal once added to the atmospheric pool but GWP defined as 1 by convention.
  • Other gauges — ALT (atmospheric lifetime, years), RF (radiative forcing, W m⁻² ppb⁻¹), GTP (global temperature potential — alternative time-integrated metric, less common in regs).

Two derived performance metrics dominate technical comparison once environmental criteria are met:

  • Volumetric capacity (kJ/m³ at standard evap conditions) — drives compressor displacement. NH₃ ≈ 2330, R-410A ≈ 2080, R-32 ≈ 1900, R-22 ≈ 1280, R-134a ≈ 600, R-744 transcritical ≈ 8400. Higher = smaller compressor + smaller pipes.
  • Coefficient of Performance (COP) at standard cycle (e.g., 0/40 °C). Most halocarbons cluster 4.5–5.5; NH₃ 5.5–6.5; R-744 transcritical 2.5–3.5 below 25 °C ambient but suffers above 30 °C without ejector or parallel compression.

3. CFC (banned)

Discovered by Midgley at Frigidaire/GM in 1928 as a safe replacement for SO₂ and NH₃ in domestic refrigeration. Three decades of unchallenged dominance until Molina & Rowland (1974) linked stratospheric chlorine to ozone destruction; Antarctic ozone hole confirmed by Farman 1985. Montreal Protocol signed September 1987, in force January 1989.

  • R-11 (CCl₃F, trichlorofluoromethane) — GWP 4750, ODP 1.0 (reference), A1, ALT 45 yr. Low-pressure centrifugal chillers (Carrier 19E, Trane CenTraVac legacy fleet) and rigid polyurethane foam blowing agent. NBP +23.7 °C — operates with evaporator at sub-atmospheric pressure (vacuum-pulldown required, air leakage is a typical fault).
  • R-12 (CCl₂F₂, dichlorodifluoromethane) — GWP 10900, ODP 1.0, A1, ALT 100 yr. Auto AC (universal pre-1994), domestic refrigerator (universal pre-1993), centrifugal chillers, MDI propellant for asthma inhalers (post-Montreal “essential use” exemption now lifted). NBP −29.8 °C.
  • R-113 (C₂Cl₃F₃) — GWP 6130, ODP 0.85. Solvent for electronics + dry cleaning, centrifugal chillers.
  • R-114 (C₂Cl₂F₄) — GWP 10000, ODP 1.0. Specialty chillers, US Navy submarine AC (replaced post-2000).
  • R-115 — component of R-502 (R-22/R-115 azeotrope), the supermarket low-temp standard before R-404A.
  • Production banned: Montreal Protocol Article 2A — 1996 in developed countries (Article 2), 2010 in Article 5 (developing). Service of existing equipment used reclaimed and stockpiled stocks; most equipment now retired or retrofit. Trace illegal production of R-11 in East Asia 2013–2018 caused a documented atmospheric concentration anomaly, since closed.

4. HCFC (transitional, mostly phased out)

Added hydrogen atom shortens atmospheric lifetime by tropospheric OH-radical attack — most molecules destroyed before reaching stratosphere. ODP cut to 2–11 % of CFC. Always intended as a transitional class; the Montreal Protocol set HCFC phase-out from the outset.

  • R-22 (CHClF₂, chlorodifluoromethane) — GWP 1810, ODP 0.05, A1, ALT 11.9 yr. The North American residential AC workhorse 1965–2010; commercial chiller, supermarket medium-temp, heat pump. NBP −40.8 °C. Production phase-out in developed countries (Article 2): new equipment ban 1 Jan 2010, service with virgin material banned 1 Jan 2020, reclaimed-only post-2020, complete phase-out 2030 (Montreal accelerated schedule under the 2007 Adjustment). Reclaimed R-22 prices spiked 2018–2022; supply now exceeds demand as fleet retires.
  • R-123 (CHCl₂CF₃, dichlorotrifluoroethane) — GWP 79, ODP 0.02, B1 (low flammability, OEL 50 ppm TWA). Low-pressure centrifugal chillers (Trane CenTraVac), particularly large-tonnage (> 500 ton). NBP +27.6 °C. Production phase-out: 2020 new, 2030 service. Direct R-123 replacement is R-1233zd(E) HCFO.
  • R-141b (CH₃CCl₂F) — GWP 725, ODP 0.12. Foam blowing, solvent. Phased out 2003 (US).
  • R-142b (CH₃CClF₂) — GWP 2310, ODP 0.07. Specialty chillers, foam.
  • R-124 — component of R-401A and R-409A retrofit blends for R-12.

5. HFC (current generation, being phased down)

No chlorine, zero ODP — the post-Montreal answer. But high GWP made them a climate problem, triggering Kigali Amendment (2016).

  • R-134a (CH₂FCF₃, 1,1,1,2-tetrafluoroethane) — GWP 1430, A1. Auto AC 1994–2017 (EU mandate forced switch to R-1234yf 2017; US OEM transition ~2014–2020), domestic refrigerator post-1993, medium-temperature commercial refrigeration, centrifugal chillers. NBP −26.1 °C. Direct R-12 replacement.
  • R-32 (CH₂F₂, difluoromethane) — GWP 675, A2L (mildly flammable, burn velocity < 10 cm/s). Single-component HFC (not a blend) used in Asian residential AC since Daikin launched it commercially 2012, EU adoption ~2018, available US 2024+. NBP −51.7 °C. Higher discharge temperature than R-410A (~10–15 K hotter), often paired with vapor injection on the compressor.
  • R-410A (R-32/R-125 50/50 wt, near-azeotrope) — GWP 2088, A1. North American + EU residential AC and heat pump standard 2000–2024. NBP −51.6 °C. Higher operating pressure (1.5× R-22) drove thicker copper and beefier coils.
  • R-407C (R-32/R-125/R-134a 23/25/52, zeotrope, glide ~7 K) — GWP 1774, A1. R-22 replacement for retrofit; lower performance penalty than R-410A swap but glide complicates flooded evaporators.
  • R-404A (R-125/R-143a/R-134a 44/52/4, near-azeotrope) — GWP 3922, A1. Supermarket low-temperature (frozen) and transport refrigeration 1990s–2020s. Among the highest-GWP HFCs in widespread use, prime target of Kigali.
  • R-507A (R-125/R-143a 50/50, azeotrope) — GWP 3985, A1. Supermarket low-temp, similar role to R-404A.
  • R-407F (R-32/R-125/R-134a 30/30/40) — GWP 1825, A1. Lower-GWP R-404A retrofit for medium-temp supermarket; about 10–15 % better COP than R-404A.
  • R-417A, R-417B, R-422D, R-427A, R-438A — R-22 retrofit blends (typically R-125 + R-134a + small mineral-oil-miscible component like R-600). GWP 1900–3140. Service-life solution for the R-22 fleet, not the replacement strategy.
  • R-23 (CHF₃, trifluoromethane) — GWP 12400, A1. Ultra-low-temp cascade low-stage (−40 to −80 °C); high-GWP target of the next phase-down round. Alternative R-508B (R-23/R-116) GWP 13400 also targeted.
  • R-152a (CHF₂CH₃, difluoroethane) — GWP 124, A2 flammable. Limited HVAC use; aerosol propellant; component of R-500 retrofits.

6. HFO and HFCO (current frontier)

Adding a C=C double bond gives a tropospheric reactive site, atmospheric lifetime collapses to days/weeks, GWP drops to single digits. Most are mildly flammable (A2L) — burn velocity below 10 cm/s and minimum ignition energy orders of magnitude above hydrocarbons.

  • R-1234yf (CF₃CF=CH₂, 2,3,3,3-tetrafluoropropene) — GWP 4, ODP 0, A2L. EU mobile AC mandate (MAC Directive) since 2017, US OEM voluntary adoption 2014+. NBP −29.5 °C. Drop-in performance for R-134a (~5 % capacity penalty). Manufactured by Chemours (Opteon YF) and Honeywell (Solstice yf).
  • R-1234ze(E) (trans-CHF=CHCF₃) — GWP 7, A2L. Centrifugal chillers (Trane Sintesis, Carrier AquaForce), cabinet refrigeration, foam blowing. NBP −19 °C — slightly less volatile than R-134a, suits low-pressure designs.
  • R-1233zd(E) (trans-CHCl=CHCF₃, HCFO) — GWP 1, A1 (non-flammable!), ODP 0.00034 (de minimis, accepted under Montreal). Low-pressure centrifugal chillers (new Trane CenTraVac, Carrier 19DV). NBP +18.3 °C — direct R-123 replacement.
  • R-1336mzz(Z) (HFO, cis-CF₃CH=CHCF₃) — GWP 2, A1 non-flammable. High-temperature heat pumps, ORC (organic Rankine cycle), centrifugal chillers. NBP +33.4 °C.
  • R-1224yd(Z) (HCFO) — GWP < 1, A1, ODP 0.00012. Low-pressure chillers, R-123 replacement (AGC Asahi Glass AMOLEA).
  • R-1132a (CH₂=CF₂, 1,1-difluoroethylene) — GWP < 1, A2 lower-flammability. Component of next-generation blends under development.
  • R-1336mzz(E) (trans isomer) — GWP 18, A2L. Higher-temp variant for heat pumps.

Trifluoroiodomethane (CF₃I, R-13I1)

GWP ≈ 0.4, A1 non-flammable, ODP ≈ 0.011 (tropospheric photolysis-limited). Strong knock-out agent and blend modifier; small component in R-466A. Concerns about iodine release under thermal stress have slowed adoption.

7. HFO/HFC blends — low-GWP

Pure HFOs are expensive ($30–80/kg) and many are A2L. Blending with HFC R-32 or R-125 reduces cost, can move flammability classification or capacity to target value, but reintroduces non-trivial GWP.

  • R-454B (R-32/R-1234yf 68.9/31.1) — GWP 466, A2L. Carrier and Trane chose R-454B for US residential AC and heat pump replacement of R-410A, effective with 2025 model year (US EPA SNAP + AIM Act force). Drop-in pressure profile within ~10 % of R-410A.
  • R-454C (R-32/R-1234yf 21.5/78.5) — GWP 148, A2L. Sub-150 GWP variant for jurisdictions with stricter limits (commercial). Lower capacity than R-454B; larger compressor displacement needed.
  • R-454A (R-32/R-1234yf 35/65) — GWP 239, A2L. Medium-temp commercial refrigeration.
  • R-452B (R-32/R-1234yf/R-125 67/26/7) — GWP 698, A2L. Daikin “Puron Advance” for US residential AC alternative to R-454B.
  • R-466A (R-32/R-1234yf/R-125) — GWP 733, A1 non-flammable! Honeywell Solstice N41 — would be the holy grail (A1 + low GWP) but US-EPA SNAP listing delayed by stability concerns under fault conditions (iodine catalysis).
  • R-455A (R-744/R-32/R-1234yf 3/21.5/75.5) — GWP 148, A2L. Light commercial refrigeration, monoblock heat pumps. CO₂ added to suppress flammability and raise glide for refrigeration duty.
  • R-447A, R-447B — R-32/R-1234ze/R-125 variants, GWP ~580–740, A2L.
  • R-448A (Honeywell Solstice N40, R-32/R-125/R-1234yf/R-134a/R-1234ze) — GWP 1387, A1. Supermarket medium- and low-temperature, R-404A retrofit, A1 classification retained.
  • R-449A (Chemours Opteon XP40) — GWP 1397, A1. Same role as R-448A.
  • R-513A (R-1234yf/R-134a 56/44) — GWP 631, A1. R-134a chiller replacement keeping A1 (non-flammable) — Carrier 23XRV, Trane Series E and S CenTraVac.
  • R-513B (R-1234yf/R-134a 58.5/41.5) — GWP 596, A1.
  • R-515B (R-1234ze/R-227ea 91.1/8.9) — GWP 293, A1. Low-pressure centrifugal, R-134a chiller successor with A1 retained.
  • R-450A (R-1234ze/R-134a 42/58) — GWP 605, A1. Medium-temp commercial refrigeration retrofit.
  • R-1233zd, R-515B, R-513A, R-450A are the “A1 low-GWP” option set when flammability classification is contractually mandated (typical for occupied chiller plants in some US AHJ).

7a. Secondary refrigerants and heat-transfer fluids

When the primary refrigerant is restricted by safety class or charge limit, a secondary loop is added: the primary cycle chills a heat-transfer fluid that circulates to the load.

  • Glycol-water — ethylene glycol (toxic) or propylene glycol (food-safe) at 30–50 % concentration; freeze protection to −20 to −40 °C. Most common secondary in supermarket and ice-rink installations behind NH₃ or CO₂ primary.
  • CaCl₂ brine — historic ice-rink fluid; corrosive and being phased out for propylene glycol or CO₂ direct.
  • K-formate / K-acetate (Tyfoxit, Pekasol) — low-viscosity at low temperature, lower pumping power, food-safe.
  • HFE / HFO secondary (3M Novec) — single-phase or two-phase for electronics immersion cooling.
  • Direct-expansion CO₂ as secondary — primary loop chills CO₂ that boils in load coils at constant temperature; common in supermarket cascade.

8. Natural refrigerants

Fluids found in nature — no fluorine, no phase-down exposure. Each has a fundamental safety trade-off (toxicity for NH₃, flammability for HC, pressure for CO₂).

  • R-744 (CO₂) — GWP 1, ODP 0, A1 non-flammable, non-toxic at refrigeration concentrations (TLV 5000 ppm). Triple point 5.18 bar / −56.6 °C, critical point 73.8 bar / 31.1 °C. Transcritical operation common (heat rejection above critical point): discharge 90–120 bar, suction 25–40 bar. Heat-rejection control via high-side pressure (no condensation, only gas cooling). Applications: commercial supermarket racks (Carrier CO2OLtec, Hillphoenix Advansor, Danfoss Multi-Ejector since ~2010; EU Multi-Pack Centaur is the de-facto standard for new EU supermarkets), industrial cascade low-stage with NH₃ high-stage, automotive heat-pump (VW ID Buzz, Mercedes EQS — small but growing). Auto AC: Daimler + VW seriously evaluated R-744 1990s–2010s, dropped for R-1234yf for cost and complexity reasons.
  • R-717 (NH₃ ammonia) — GWP 0, ODP 0, B2L (toxic + low flammability). NBP −33.3 °C. Highest volumetric capacity of any common refrigerant and very high COP. Industrial process refrigeration (food processing, cold storage, ice plants, ice rinks, pharmaceutical, brewing) — overwhelmingly dominant in industrial-scale (> 200 kW) systems. Code-restricted in occupied spaces: ASHRAE 15 + IIAR 2 limit charge per occupancy class; supermarket direct-expansion essentially prohibited, so NH₃ is used in chiller plant with secondary loop (glycol). Compatible with steel (not copper) — system construction differs entirely from halocarbon.
  • R-290 (propane, C₃H₈) — GWP 3, A3 (highly flammable, LFL 2.1 vol%, MIE 0.25 mJ). NBP −42.1 °C. Small self-contained commercial refrigerators and freezers (US EPA SNAP charge limit 150 g for hermetic retail commercial), residential heat pumps (EU Daikin Altherma 3 R-290, Mitsubishi Ecodan, Bosch Compress 5800i AW — explosive growth since 2022). Monoblock outdoor units sidestep indoor flammable charge by routing only hydronic water inside. Charge limit per IEC 60335-2-89 (commercial) and IEC 60335-2-40 (heat pump) — 500 g typical limit for installed heat pumps with safety mitigation.
  • R-600a (isobutane, i-C₄H₁₀) — GWP 3, A3. NBP −11.7 °C. Domestic refrigerator since 1990s in EU (Greenfreeze 1993, supported by Greenpeace), US EPA SNAP-approved 2011 with 57 g charge limit (raised to 150 g 2021). Now standard in virtually all new domestic refrigerators globally.
  • R-1270 (propylene/propene, C₃H₆) — GWP 2, A3. NBP −47.7 °C. Industrial process refrigeration; rare in commercial.
  • R-718 (water) — GWP 0, ODP 0, A1. NBP 100 °C, freezing point 0 °C limits cycle to chilled-water above 5 °C duty. Very low vapor density at sub-atmospheric evaporator pressures means very large compressor displacement — uneconomic for vapor compression at small scale. Dominant in absorption (LiBr-H₂O for chilled-water generation from waste heat, e.g. Yazaki, Trane Horizon, Carrier 16NK) and adsorption (silica-gel water, e.g. Mayekawa AdRef-Noa) chillers, where the heat source (cogen, solar, district steam) provides cycle driver and electricity demand is minimal. NH₃-H₂O absorption (Robur) covers sub-freezing duty.

Natural refrigerant trade-offs at a glance

  • CO₂ wins on safety + GWP + cost; loses on cycle efficiency above 25 °C ambient unless ejector / parallel compression mitigates supercritical penalty.
  • NH₃ wins on COP + volumetric capacity; loses on occupied-space restriction and material compatibility (no copper).
  • HC (propane, isobutane) wins on cycle efficiency + low cost; loses on charge limits from A3 flammability — restricts to small or sealed systems.
  • Water wins on environmental neutrality + non-toxicity; loses on freezing point + huge displacement, so used only in absorption / adsorption thermal cycles.

Refrigerant fundamentals quick-reference

RefrigerantFormulaNBP (°C)Critical T (°C)Critical P (bar)GWPSafetyNotes
R-11CCl₃F+23.719844.14750A1Banned CFC
R-12CCl₂F₂−29.811241.410900A1Banned CFC
R-22CHClF₂−40.89649.91810A1HCFC phase-out
R-123CHCl₂CF₃+27.618436.679B1Low-P chiller
R-134aCH₂FCF₃−26.110140.61430A1Auto AC legacy
R-32CH₂F₂−51.77857.8675A2LAsian AC
R-410AR-32/R-125−51.67149.02088A1NA AC legacy
R-454BR-32/R-1234yf−50.97853.8466A2LNA AC 2025+
R-1234yfCF₃CF=CH₂−29.59533.84A2LAuto AC
R-1234ze(E)CHF=CHCF₃−1911036.37A2LChiller
R-1233zd(E)CHCl=CHCF₃+18.316636.21A1Low-P chiller
R-744CO₂−78.5 (sub)31.173.81A1Transcritical
R-717NH₃−33.3132113.30B2LIndustrial
R-290C₃H₈−42.196.742.53A3HP, small ref
R-600ai-C₄H₁₀−11.7134.736.43A3Domestic ref
R-718H₂O+100374220.60A1Absorption

9. Safety classifications (ASHRAE Standard 34)

Two-character code: letter = toxicity (A lower, B higher), digit = flammability (1 no propagation, 2L lower flammability with burn velocity < 10 cm/s, 2 lower flammability, 3 higher flammability).

ClassToxicityFlammabilityExamples
A1lownoneR-22, R-134a, R-404A, R-410A, R-1233zd, R-1336mzz, R-466A, R-448A, R-449A, R-744
A2Llowlower (BV < 10 cm/s)R-32, R-1234yf, R-1234ze, R-454B, R-454C, R-452B, R-455A, R-447A
A2lowlowerR-152a
A3lowhigherR-290, R-600a, R-1270
B1highernoneR-123
B2LhigherlowerR-717 (NH₃)

A2L matters because it requires leak-detection + ventilation per ASHRAE 15 and IFC 605, charge size limits per IEC 60335 by occupancy class, and updated brazing/service practice — but it does not preclude indoor residential AC, unlike A3 which generally requires monoblock or sealed-system designs.

10. Phase-down timeline

Kigali Amendment (2016, entered force 2019) — global HFC stepdown via Montreal Protocol mechanism. Developed countries (Group 1): baseline = avg 2011-2013 HFC + 15 % of HCFC baseline; reductions 10 % by 2019, 40 % by 2024, 70 % by 2029, 80 % by 2034, 85 % by 2036. Article 5 Group 1 (most developing): freeze 2024, stepdown beginning 2029, 80 % cut by 2045. Article 5 Group 2 (high-ambient — India, Pakistan, Gulf states): freeze 2028, 85 % cut by 2047.

US — AIM Act (American Innovation and Manufacturing Act, 2020) — EPA-administered, aligned with Kigali Group 1. Production + import allowances issued annually: 10 % cut 2022, 40 % cut 2024–2028, 70 % cut 2029–2033, 80 % cut 2034–2035, 85 % cut 2036+. Sector-specific Technology Transitions rules (final 2023): residential AC + heat pump GWP < 700 from 1 Jan 2025; supermarket racks GWP < 300 (medium-temp) / 150 (low-temp) phased 2027–2030; mobile AC R-1234yf already.

EU F-Gas Regulation (2024/573) — tighter than Kigali; quota-based phase-down via CO₂-equivalent allowance market. New domestic refrigerator GWP < 150; commercial standalone unit GWP < 150 by 2025; centralized commercial refrigeration > 40 kW: GWP < 150 (low-temp circuit), < 1500 (medium-temp) by 2029; split AC < 12 kW: GWP < 750 from 2027, < 150 from 2032; monoblock heat pumps < 12 kW: GWP < 150 from 2027. Service bans on virgin HFC > 2500 GWP since 2020 (essentially R-404A retrofit-only).

Japan, China, Australia — implementing Kigali. Japan METI Fluorocarbons Act (revised 2019); China MEE HFC phase-down began 2024 Group 1 freeze. Australia OPSGGM Act (2022) imports quota system. India ratified Kigali 2021 with 2032 freeze (Group 2 high-ambient).

Standards bodies and how they fit

  • UNEP Ozone Secretariat — Montreal Protocol parent body; tracks ODP-weighted production.
  • IPCC — supplies GWP values; AR5 in regulatory use, AR6 published but lag in adoption.
  • ASHRAE (Atlanta) — Standards 34 (designation/safety class), 15 (system safety), 90.1 (energy in buildings), 147 (refrigerant emission reduction).
  • AHRI (Air-Conditioning, Heating, and Refrigeration Institute) — equipment certification 210/240 (unitary), 550/590 (centrifugal chillers), 700 (refrigerant specifications).
  • IIAR — ammonia-specific standards 2 (design), 5 (start-up), 6 (inspection), 7 (operating procedures), 9 (compliance).
  • EN / ISO — EN 378 mirrors ASHRAE 15 in EU; ISO 817 mirrors ASHRAE 34.
  • UL — UL 60335-2-40 + UL 60335-2-89 are the US/Canadian electrical-safety harmonizations of the IEC base standards adding A2L-specific provisions.
  • IEC — 60335-2-40 + -89 international electrical safety for heat pump + commercial refrigeration.
  • EPA SNAP — US “Significant New Alternatives Policy” approval listing.

11. Application / refrigerant matching

ApplicationPreferred 2026Legacy / transitionalNotes
Domestic refrigeratorR-600a (R-290 small)R-134a, R-12 (banned)< 150 g charge; near-universal globally
Auto ACR-1234yfR-134a (R-12 banned)EU mandate 2017; US OEM full transition by ~2020
Auto / EV heat pumpR-744 (some), R-1234yfR-134aPump-up cabin heat from cold-ambient; VW ID Buzz, Mercedes EQS
Residential split AC + heat pumpR-32 (Asia/EU), R-454B (US)R-410A, R-22 (banned)A2L charge + leak-detect rules apply
Residential heat pump (EU monoblock)R-290R-410AOutdoor charge isolation simplifies A3 compliance
Commercial chiller, centrifugalR-1233zd, R-1234zeR-123 (phase-out), R-134aNew Trane CenTraVac, Carrier 19DV
Commercial chiller, screwR-32, R-454B, R-1234ze, R-717R-134a, R-410AIndustrial-scale screws favor NH₃
Commercial chiller, scrollR-454B, R-32R-410AMost package rooftops
Supermarket medium-tempR-744, R-448A, R-449A, R-454CR-404A, R-22Transcritical CO₂ now dominant in EU
Supermarket low-temp / frozenR-744 transcriticalR-404A, R-507ACascade or booster
Cold storage industrialR-717 NH₃, R-744 cascadeR-22, R-404ANH₃ dominant > 200 kW
Ice rinkR-717 (NH₃)R-22Indirect glycol or CaCl₂ loop
Heat-pump tumble dryerR-290R-134a< 150 g sealed
Vending machine / coolerR-290, R-600aR-134a< 150 g (or 500 g per new IEC 60335-2-89)
Mobile transport refrigerationR-452A, R-744R-404ACarrier Vector eCool, Thermo King
Absorption chiller (waste heat)LiBr-H₂O (R-718), NH₃-H₂O—Driven by 90–180 °C heat

11a. Sizing and design implications

Switching refrigerants is rarely a “drop-in” — pressure ratios, mass-flow, latent heat, viscosity, and oil miscibility all shift.

  • Pressure — R-22 to R-410A retrofit not viable (R-410A operates ~1.5× higher pressure); R-22 to R-407C is closer in pressure but requires oil change MO → POE. R-410A to R-454B is near-drop-in pressure-wise but flammability class changes A1 → A2L, mandating service procedure updates and indoor leak-detection sensors per UL 60335-2-40 if charge exceeds threshold.
  • Glide — zeotropic blends have non-zero temperature glide between bubble and dew points. R-407C glide ≈ 7 K, R-448A ≈ 5.7 K, R-454B ≈ 1.5 K (near-azeotrope), R-410A ≈ 0.1 K (effective azeotrope). Glide complicates flooded evaporators and TXV setting; counter-flow evaporators can leverage glide to reduce LMTD penalty.
  • Compressor displacement — for fixed cooling duty, displacement scales inversely with volumetric capacity. R-744 transcritical needs ~25 % of R-134a displacement; R-1234yf needs ~5 % more than R-134a; R-454C needs ~30 % more than R-454B.
  • Heat exchanger sizing — CO₂ transcritical needs a gas cooler (sensible heat rejection) not a condenser, sized for outlet approach temperature to ambient (lower = better COP).
  • Pipe size + insulation — NH₃ uses steel pipe (welded), not copper. CO₂ uses thick-wall copper or stainless. HFC/HFO uses standard refrigeration-grade copper.

12. Lubricants

Refrigerant oil pairing is non-negotiable. Wrong oil = compressor failure within hours.

  • Mineral oil (MO) — R-12, R-22, R-717 (NH₃), R-290, R-600a, R-1270.
  • Alkylbenzene (AB) — R-22 retrofit blends, often a 50/50 with MO. Good miscibility, intermediate price.
  • POE (polyolester) — R-134a, R-404A, R-407C, R-410A, R-32, R-454B, R-1234yf (stationary), R-1234ze, R-1233zd. Highly hygroscopic — drying and vacuum to 500 µm before charging is mandatory. POEs vary in viscosity (ISO 22/32/68/100/170) — pick per compressor manufacturer spec.
  • PAG (polyalkylene glycol) — auto AC R-134a and R-1234yf (mobile only). PAG and POE are not cross-compatible — never mix.
  • PVE (polyvinyl ether) — newer alternative to POE, similar miscibility, less hygroscopic. Daikin uses PVE in R-32 systems.

R-744 (CO₂) uses POE or PAG with high-temperature, high-pressure additive packages (transcritical discharge temperatures can exceed 130 °C). NH₃ industrial systems use synthetic-PAO or naphthenic MO; the oil must be drained from low spots periodically because NH₃ and oil are largely immiscible.

12a. Compressor type matching

Refrigerant choice and compressor type are coupled.

  • Reciprocating — oldest, robust. Used with NH₃ (industrial single- and two-stage), HFC small-to-medium, HC small. Discharge temperature high, suited to low-pressure-ratio cycles.
  • Scroll — dominant in residential and light-commercial AC and heat pump 5–30 kW. Used with R-410A, R-32, R-454B, R-22 legacy. Hermetic; oil-flooded; tolerates A2L with electrical-spark mitigation.
  • Rotary — small Asian residential AC under 7 kW. R-410A, R-32. Twin-rotary common in inverter-driven systems.
  • Screw — industrial chiller and large commercial 100–2000 kW. Used with NH₃, R-134a, R-1234ze, R-513A. Liquid injection for cooling on high pressure ratio.
  • Centrifugal — large chillers > 500 kW. Used with R-134a, R-123/R-1233zd, R-1234ze, R-515B. Magnetic-bearing oil-free (Danfoss Turbocor, Smardt) becoming common.
  • CO₂ semi-hermetic reciprocating + transcritical — Bitzer 4-MTC, Dorin CDS series; built for 130-bar discharge.
  • Linear / free-piston — niche (LG inverter linear) for hermetic appliance; pairs with R-600a.

13. Service notes

  • A2L handling — leak detection mandatory per ASHRAE 15 + IFC 605; refrigerant detection sensors required in occupied space if charge exceeds RCL (refrigerant concentration limit) per ASHRAE 34. Charge size capped per IEC 60335 by occupancy class.
  • Brazing — for halocarbon HVAC, BCuP-2 (Cu-P) for copper-to-copper, BAg-7 (silver) for copper-to-steel or steel-to-steel. Nitrogen purge at 0.1–0.2 bar mandatory during brazing to prevent black copper oxide scale that would later plug TXV / electronic expansion valve and capillary tubes.
  • Evacuation — pull vacuum to 500 µm (Hg) absolute or below for HFC + HFO + HCFO systems. Triple-evacuation procedure for moist or long-line systems. Standing-vacuum test 10 minutes < 100 µm rise.
  • Recovery — required by US EPA Section 608 (Clean Air Act) for any halogenated refrigerant. Certified technician required (Type I, II, III, or Universal). Recovery cylinder must be DOT-rated and partially evacuated.
  • Charge — most systems require subcooling-target or superheat-target charge, weighed in by mass. Zeotropic blends (R-407C, R-454B etc.) must be charged as liquid only to preserve composition; charging as vapor fractionates the blend.
  • Leak detection — bubble solution (low-tech), electronic halogen sniffer (heated diode or corona discharge for HFC), ultrasonic, infrared absorption (specific to refrigerant fingerprint, best for HFO/HCFO). UV trace dye optional. Per EN 378 / ASHRAE 15 thresholds, scheduled checks scale with system charge: more often as charge increases past 5 kg, 50 kg, 500 kg CO₂-eq thresholds.
  • Decommissioning — refrigerant must be recovered to certified cylinder; cylinder returned to reclaimer or destruction facility (rotary kiln incineration at > 1100 °C with HF scrubber). Burning refrigerant in open atmosphere creates toxic phosgene-type byproducts.
  • Logbook — EU F-Gas + EPA Section 608 require logbook for any system > 3 kg charge: each service event recorded with date, technician ID, refrigerant identity, mass added/removed.

14. Selection heuristics

  • New commercial building chiller 2026 — R-1233zd (HCFO, A1, GWP 1) for low-pressure centrifugal, or R-1234ze for mid-size; variable-speed magnetic-bearing options widespread.
  • New residential AC, US 2025+ — R-454B (Carrier, Trane, Lennox) or R-32 (Daikin, LG). Both A2L; both require updated installer training and leak-detect provisions per UL 60335-2-40.
  • New auto AC, 2026 — R-1234yf for conventional cabin AC; R-744 heat-pump for EV thermal-management on high-end (VW MEB, Mercedes EVA).
  • Deep-freeze supermarket 2026 — CO₂ transcritical with parallel-compression and multi-ejector (Carrier CO2OLtec Evo, Hillphoenix Advansor SuperPack). At high ambient (> 35 °C), parallel compression + ejector restores efficiency lost in supercritical heat rejection.
  • Industrial ice / cold storage — NH₃ flooded evaporator with screw or reciprocating compressors; or NH₃/CO₂ cascade (NH₃ high-stage, CO₂ DX low-stage) when NH₃ charge minimization is the priority.
  • Small portable refrigerator — R-290 hermetic, ≤ 150 g charge.
  • Replacement for R-22 existing system — drop-in retrofit to R-407C or R-422D for limited service life; or full system replacement to R-454B / R-32 with new compressor and metering devices (preferred — R-22 system pressures and oils don’t match HFO blends well).
  • High-temperature heat pump (process heat 80–150 °C) — R-1336mzz(Z), R-1233zd, or R-744 transcritical depending on temperature target. R-1234ze for 80–100 °C, R-1336mzz for 100–160 °C, butane/pentane for > 120 °C in industrial ORC-style.
  • Data center cooling — R-134a or R-1234ze in centrifugal chillers; or direct evaporative + adiabatic cooling avoiding refrigerant entirely above part-load; or two-phase immersion (engineered fluorinated dielectric like 3M Novec, separate from refrigerant scope).
  • Ultra-low temperature freezers (−80 °C lab, vaccine cold chain) — cascade R-170 ethane / R-1150 ethylene low stage with R-290 or R-404A high stage; growing interest in R-23 alternatives due to high GWP (R-23 GWP 12400 itself a phase-down target).

14a. Pitfalls + failure modes

  • Mixing refrigerants — even small contamination (5 % R-22 in R-410A) shifts pressure-temp curve and destroys system performance; non-condensables push head pressure. Always recover and reclaim, never top-up an unknown system.
  • Oil hygroscopy — POE absorbs water 10× faster than mineral oil; opened POE drum unusable within hours of humid exposure. Bottle dryness < 50 ppm water before charge.
  • A2L ignition — minimum ignition energy two orders higher than HC, but real fault scenarios (failed solenoid arc, brazing flame on charged line) can still ignite. ASHRAE 15 mitigation = leak detection + ventilation + dilution + charge limit.
  • CO₂ transcritical over-pressure — high-side relief at 130–140 bar; thermal expansion of trapped liquid CO₂ in service-isolated section reaches 200+ bar rapidly. Pressure-relief valves on every isolatable volume mandatory.
  • NH₃ release — IDLH 300 ppm; chronic exposure damages mucous + respiratory. Mandatory water deluge on roof of machinery room (NH₃ is hygroscopic, water absorbs spill plume).
  • TXV / EEV mismatch — every refrigerant has a different P-T curve; using R-22 TXV on R-410A under-feeds the evaporator catastrophically. EEV with refrigerant-aware firmware preferred.
  • Lubricant return — long suction lines on low-temp HFC systems need oil traps + risers sized for vapor velocity > 5 m/s to carry oil back; oil starvation kills hermetic compressors silently.

14b. Emerging research directions (2025–2030)

  • Ultra-low-GWP supermarket — CO₂ transcritical with parallel compression + ejector + adiabatic gas cooler now sub-1.0 TEWI vs HFC baseline even at 40 °C ambient. Multi-ejector control becoming standard.
  • R-290 high-charge residential heat pump — IEC 60335-2-40 amendment 2 (2022) raised allowable charge for monoblock; sealed-circuit cassettes (Mitsubishi Ecodan R290, Bosch CS6800iAW) deploying widely in EU.
  • Solid-state cooling — magnetocaloric (Cooltech, Camfridge), thermoacoustic, elastocaloric, electrocaloric — niche today but no refrigerant at all. Still 5–10 years from competitive COP at HVAC scale.
  • Trans-critical R-290 + R-1270 — research into propane / propylene above critical point for high-temp heat pumps to 150–180 °C.
  • NH₃ small-charge / micro-channel — Mayekawa, Star, Johnson Controls offer < 15 kg NH₃ packaged chillers, opening commercial applications previously closed by occupied-space ASHRAE 15 limits.
  • PFAS regulatory pressure — HFOs are technically PFAS (per-and polyfluoroalkyl substances) by some definitions; pending EU ECHA universal PFAS restriction (proposal 2023) could threaten HFO production. Industry argues HFO atmospheric breakdown produces trifluoroacetic acid (TFA), already detected in rainwater. This is the most significant medium-term uncertainty for the refrigerant industry.

15. Cross-references

  • [[Engineering/refrigeration-cycles]] — vapor-compression, absorption, transcritical cycle thermodynamics
  • [[Engineering/thermodynamics]] — Carnot, p-h diagrams, exergy
  • [[Engineering/hvac-fundamentals]] — building heating/cooling load, system design
  • [[Engineering/heat-transfer]] — evaporator + condenser design, two-phase flow
  • [[Engineering/environmental-engineering]] — atmospheric chemistry, Montreal + Kigali context

15a. Frequently confused points

  • R-410A vs R-410B — R-410B is a different blend ratio of the same components (R-32/R-125). Not interchangeable. R-410A dominant.
  • R-134a vs R-1234yf — both auto AC, but R-134a is HFC (GWP 1430), R-1234yf is HFO (GWP 4). New fittings (different SAE J639 service ports) prevent cross-charging.
  • R-32 single vs R-32 in blends — R-32 alone is the Daikin / Asian standard; R-32 in R-410A is paired with R-125. Performance, oil, and service procedures differ.
  • “A2L = explosive” — false. A2L burn velocity is < 10 cm/s, two orders of magnitude below hydrocarbons. Ignition requires sustained ignition source (electrical arc, open flame); a hot wire or static spark typically insufficient.
  • “CO₂ refrigerant = climate solution” — true on direct emissions (GWP 1), neutral on indirect; the question is total TEWI relative to alternatives, which depends on grid CO₂ intensity and cycle COP at site ambient.
  • “All HFOs are A2L” — false. R-1233zd, R-1336mzz, R-466A are A1 non-flammable. The 4-digit designator says nothing about flammability — the double bond reactive to OH does not necessarily make the molecule flame-propagating.

16. Citations

  • ASHRAE Standard 34 — Designation and Safety Classification of Refrigerants, latest 2022 ed. Defines R-numbering and A/B 1/2L/2/3 classification.
  • ASHRAE Standard 15 — Safety Standard for Refrigeration Systems, 2022. Sets charge limits, ventilation, machinery room rules.
  • ASHRAE Handbook — Refrigeration, 2022 ed.
  • IPCC AR5 (2014) Working Group I, Ch. 8 Anthropogenic and Natural Radiative Forcing — GWP100 values in regulatory use.
  • IPCC AR6 (2021) Working Group I — updated GWP100; not yet adopted in F-Gas / AIM Act.
  • Montreal Protocol on Substances that Deplete the Ozone Layer (1987), Kigali Amendment (2016) — UNEP Ozone Secretariat https://ozone.unep.org/.
  • Regulation (EU) 2024/573 on fluorinated greenhouse gases (F-Gas Regulation, recast 2024).
  • US EPA SNAP (Significant New Alternatives Policy) program — listings under Clean Air Act §612.
  • US AIM Act (American Innovation and Manufacturing Act of 2020) — Subtitle B of Title LXII, NDAA FY2021.
  • IIAR Standards 2, 5, 9 (International Institute of Ammonia Refrigeration) — design, start-up, inspection of NH₃ systems.
  • IEC 60335-2-40 — household + similar electrical appliances, heat pumps and AC.
  • IEC 60335-2-89 — commercial refrigerating appliances.
  • UL 60335-2-40 — US adoption of IEC 60335-2-40 with A2L provisions.
  • EN 378-1 through -4 — European refrigeration system safety standards (mirrors ASHRAE 15 in EU).
  • ISO 817 — Refrigerants designation and safety classification (mirrors ASHRAE 34 internationally).
  • AHRI Standard 700 — Specifications for refrigerants purity for new and recovered fluorocarbons.
  • NIST REFPROP — reference equation-of-state library; thermophysical properties source for all major refrigerants.
  • Calm, J.M. (2008) The next generation of refrigerants — historical review, considerations, and outlook, International Journal of Refrigeration 31:1123–1133 — canonical generational summary.
  • McLinden, M.O. et al. (2017) Limited options for low-global-warming-potential refrigerants, Nature Communications 8:14476 — formal proof that thermodynamic + safety + low-GWP constraints exclude all but a small set of candidate molecules.
  • Domanski, P.A. & Brignoli, R. (2017) NIST/AHRI refrigerant comparison studies — performance benchmarking of low-GWP refrigerants in standardized cycles.
  • UNEP TEAP Refrigeration AC and Heat Pumps Technical Options Committee — biennial assessment of refrigerant alternatives by sector, drives Montreal Protocol policy.
  • Honeywell Solstice + Chemours Opteon — vendor technical bulletins are the practical reference for HFO blend properties, oil compatibility, and retrofit procedures.
  • Linde, Air Products, Air Liquide — industrial gas supplier handbooks for CO₂ and NH₃ system design.
  • Bitzer Refrigerant Report — biennial industry survey of refrigerant trends, free PDF.

17. See also (external)

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