Natural Refrigerants 2026: CO₂, Ammonia, and Hydrocarbons — The Sustainable Future

Why Natural Refrigerants Are Winning in 2026

"Natural refrigerants" are substances that already exist in nature and are used in refrigeration with zero synthetic-chemistry footprint: CO₂ (R-744), ammonia (R-717), propane (R-290) and isobutane (R-600a). All have zero ozone-depletion potential and GWPs of 0–3. Three forces have pushed them from niche to mainstream:

• Regulation. The Kigali Amendment (U.S. AIM Act: −85% HFC production by 2036) and the EU's revised F-Gas Regulation (EU) 2024/573 — which cuts HFC quota by ~80% in CO₂-equivalent terms by 2030 and bans all virgin HFCs in 2050 — are collapsing the economic case for high-GWP refrigerants. The EU has already banned GWP ≥ 750 refrigerants in new single-split AC under 3 kg charge (2025), GWP ≥ 150 in new self-contained commercial refrigeration (2025), all F-gases in domestic fridges (2026), GWP ≥ 150 in self-contained AC (2027), and GWP ≥ 150 in split systems up to 12 kW (2029).
• Economics. HFC quota cuts have made R-404A, R-410A and R-23 prices volatile and trending upward. Natural systems increasingly win on total cost of ownership — especially CO₂ racks and R-290 plug-ins.
• LCCP thinking. Life-cycle climate performance counts direct refrigerant emissions plus indirect emissions from energy use. A low-GWP refrigerant with poor efficiency can lose to a GWP-675 fluid in a highly efficient system — which is why this guide leads with real COP and capacity data, not just GWP badges.

CO₂ (R-744): The High-Pressure Workhorse

CO₂ has GWP 1, is non-flammable (A1), and is chemically stable. Its defining feature is the low critical point — 30.98 °C and 73.8 bar — which means most heat rejection happens in transcritical operation: above the critical point there is no condensation, and the "condenser" becomes a gas cooler. Discharge pressures of 80–120 bar are routine, and system design is a different discipline from HFC practice (hence "CO₂ is a different animal, not a drop-in").

Where it shines: supermarket transcritical racks (now the default in much of Europe), where the massive volumetric capacity shrinks compressors and the high discharge temperature enables free hot-water recovery; CO₂ heat-pump water heaters, which outperform HFC units for high-temperature water; and the LT stage of cascades, where CO₂ stays at 6.8 bar even at −50 °C — no vacuum, no air ingress, no oversized compressors. The honest caveat: in hot climates, transcritical CO₂'s COP trails HFC systems unless the gas-cooler pressure is actively optimized (ejectors and parallel compression close most of the gap). At −10 °C / 30 °C subcritical, CoolProp gives CO₂ an ideal COP of 3.14 vs. 4.90 for R-404A — the efficiency story is application-dependent, which is exactly why you should model it before committing.

Ammonia (R-717): The Efficiency King

Ammonia has GWP 0 and sits at the top of nearly every efficiency table: ideal COP of 5.59 at −10 °C / 30 °C — the best of the ten refrigerants in our COP comparison — and 4.17 at real-world AC conditions, ahead of R-134a, R-290 and every HFC. It has been the backbone of industrial refrigeration for over a century: food processing, cold storage, ice rinks, and district cooling plants from megawatt scale up.

• Safety class B2L — toxic and mildly flammable. Ammonia's pungent odor is a built-in leak detector (humans smell it at ~5 ppm, long before harmful levels), but it demands proper machine rooms, ventilation, and compliance with IIAR standards (Americas) or EN 378 / ISO 5149 (Europe).
• Materials: steel systems only — ammonia attacks copper and brass. Sealed, welded steel piping is the norm, which paradoxically makes ammonia systems among the tightest in the industry.
• Pressures are gentle: 2.9 bar at −10 °C, 13.5 bar at 35 °C — well below CO₂ and similar to R-134a. But below about −35 °C the evaporator goes subatmospheric (0.41 bar at −50 °C), which is why ultralow ammonia plants use cascade or two-stage architectures.
• Watch discharge temperature: 102 °C at 5/45 °C conditions in our model — specify oil cooling or desuperheating on high-lift duty.
• Efficiency trick: flooded evaporators with recirculation and low-pressure receivers outperform DX evaporators by several percent — a classic ammonia advantage.

Hydrocarbons: R-290 and R-600a

R-290 (propane), GWP 3, safety class A3 — highly flammable but thermodynamically superb: ideal COP 5.34 at −10 °C / 30 °C and 4.01 at real 5/45 °C AC conditions, second only to ammonia in our tables. Propane is the growth story of the decade in plug-in commercial refrigeration (beverage coolers, display cabinets), heat pumps, and residential AC (India, Japan, and increasingly the EU, where the F-Gas GWP-150 horizon makes R-32's 675 a stepping stone, not a destination). Pressures are conventional: 2.0 bar at −25 °C, 15.3 bar at 45 °C.

R-600a (isobutane), GWP 3, A3 — the quiet revolution already inside most homes: the overwhelming majority of new European domestic refrigerators run on R-600a charges of 40–80 g. Its low pressures (0.58 bar at −25 °C, 6.0 bar at 45 °C) let manufacturers use thinner-walled, lighter components and low-torque compressors.

Side-by-Side Comparison

Pressures computed with CoolProp 7.2. Volumetric capacity at −10 °C (kJ/m³): R-744 ≈ 18,400 · R-410A ≈ 5,100 · R-404A ≈ 3,800 · R-717 ≈ 3,100 · R-290 ≈ 3,000.

What to Specify in 2026

• Supermarkets & food retail: transcritical CO₂ racks (Europe-standard), CO₂/NH₃ cascades, or R-290 plug-ins for small formats. EPA's GWP-150 supermarket deadlines (2025–2032) make HFC racks a short-lived investment.
• Industrial & cold storage: ammonia — flooded where possible, with two-stage or cascade below −35 °C. R-290 LT stages are viable for −45 °C food duty under A3 rules.
• Domestic refrigeration: R-600a, effectively without exception in new EU product.
• Commercial plug-in: R-290, engineered to the 150 g charge limit or EN 378 room rules.
• Air conditioning & heat pumps: R-32/R-454B (A2L) dominate new residential units today; R-290 and R-744 heat pumps lead the EU's sub-150-GWP trajectory.
• Ultralow temperature (−60 to −80 °C): CO₂ cascade, or ethane/ethylene (R-170/R-1150) stages replacing R-23.