Low-GWP Refrigerants

Context and Urgency

Hydrofluorocarbons (HFCs), the dominant class of refrigerants in modern air-conditioning and heat pump systems, are potent greenhouse gases with high global warming potentials (GWPs). Although their current share of total climate impact remains modest, their projected contribution is expected to surge in line with rising demand for space cooling and heating globally. This trajectory has prompted decisive regulatory action: many governments have mandated an HFC phase-down and a global HFC reduction agreement was reached under the Montreal Protocol's Kigali Amendment in 2016. These policy shifts signal a clear imperative for transitioning away from high-GWP refrigerants toward safer, more sustainable long-term alternatives.

Defining the Challenge

Replacing HFCs is technically complex. Unfortunately, very few refrigerants meet all these criteria. Thermodynamic modeling and chemical database screening show that the pool of viable single-component, low-GWP fluids is limited, and nearly all exhibit mild flammability. A viable alternative must offer:

Very low or zero GWP

Zero ozone depletion potential (ODP)

Chemical and thermal stability

Compatibility with existing system materials

Non-toxicity and manageable flammability

Appropriate thermodynamic properties

HFOs and the Tradeoff Triangle

Hydrofluoroolefins (HFOs) like R-1234yf and R-1234ze(E) have emerged as key alternatives. These unsaturated compounds break down rapidly in the atmosphere, resulting in ultra-low GWP values. However, their reduced chemical stability brings a tradeoff: increased flammability and lower volumetric cooling capacity. As a result, HFOs are often blended with traditional HFCs to achieve an acceptable balance of performance, safety, and GWP.

The Return of “Natural” Refrigerants

As synthetic options face regulatory pressure, natural refrigerants are re-entering the mainstream despite the same issues that once led to their decline. For example:

CO2 (R-744) is now widely used in commercial refrigeration and increasingly in HVAC

Ammonia (R-717) offers high efficiency but presents toxicity risks

Propane (R-290) and other hydrocarbons offer ultra-low GWP but highly flammable

Water (R-718) is gaining attention for niche applications, despite complex system

Each natural refrigerant comes with trade-offs in cost, efficiency, and system design complexity. Options are not universally applicable and require application-specific evaluation.

Industrial Perspectives and Market Readiness

Danfoss and other manufacturers anticipate that vapor-compression systems will remain dominant, with refrigerant choice becoming increasingly nuanced. They emphasize that new refrigerants must optimize parameters: affordability, safety, and environmental impacts. Achieving this balance requires:

Investment in new system designs

Updated safety codes

Training and education for safe handling

Region-specific product development

The HVACR industry is entering a decade of accelerated innovation and regional differentiation. While blends and new formulations may serve as interim solutions, the ultimate shift will require infrastructure upgrades and market transformation.

Policy and Market Implications

With legacy refrigerants like R-134a, R-407C, and R-410A being phased out, stakeholders face narrowing options. The industry must navigate a rapidly changing refrigerant landscape, safety standards and building code revisions, and incremental costs for system redesigns. Policy makers and manufacturers alike must consider the full refrigerant lifecycle including supply chain availability, global infrastructure readiness, and end-of-life management to support a just and effective refrigerant transition. The industry is facing a pivotal shift: one that prioritizes climate responsibility while ensuring performance and safety in real applications.

Conclusion

There is no one-size-fits-all refrigerant. Low-GWP options require trade-offs between flammability, toxicity, efficiency, cost, and availability. Navigating this landscape will demand coordinated action across the value chain—manufacturers, regulators, designers, and installers.