Many air conditioning units on the side of a large apartment building.
Technical Summary

Alternative Refrigerants

Project Drawdown defines alternative refrigerants as: the gradual replacement of hydrofluorocarbons (HFCs) used in a variety of applications by alternative refrigerants with significantly lower global warming potential (GWP) including ammonia, carbon dioxide, propane and isobutane among others. 

Refrigerants are used as working fluid in commercial refrigeration systems, in household appliances such as air conditioners and refrigerators, in refrigerated containers used for carrying perishable goods, as air conditioning systems onboard cars, trains, aircrafts, and ships, and in industrial cooling systems, etc. There are various classes of refrigerants.[1] Chlorofluorocarbons (CFCs) are ozone depleting substances and have been phased out under the Montreal Protocol; Hydrochlorofluorocarbons (HCFCs) are also being phased out. HFCs, which do not deplete the ozone, emerged as an alternative to HCFCs and have grown to extensive use. All refrigerants have a high GWP, and their release into the environment contributes to global warming. Considering the large impact which the release of refrigerants has on global warming, world leaders have agreed to phase out HFCs and replace them with natural refrigerants with much less warming potential under the Kigali Accord in October, 2016. Refrigerants are emitted into the environment during the production process, from refrigerant banks[2] due to leakages, and during end-of-life disposal of the appliances.


Measuring the alternative refrigerants solution requires: generating a total addressable market forecast of HFC refrigerant gas emissions for the period 2020-2050 (in kilotons of carbon dioxide-equivalent emissions per year), forecasting an adoption of replacement refrigerants and the resulting decreased emissions from reducing the amount of HFC produces, used and released in the atmosphere for each year from 2020-2050, and then comparing the difference in emissions from the total market and the adoption scenarios to arrive at the results. 

Reducing emissions from refrigerants can be undertaken in five main ways:

(i)         Lowering the demand/use of appliances and thereby production of refrigerants.

(ii)        Replacing refrigerants with low-warming HFCs/new cooling agents/non-HFC substances.

(iii)       Increasing the refrigeration efficiency in appliances, thereby lowering the use of refrigerants.

(iv)       Controlling leakages of refrigerants from existing appliances by good management practices.

(v)        Ensuring recovery, reclaiming/recycling, and destruction of refrigerants at end of life.

This Drawdown solution models the second option.

Total Addressable Market[3]

The model uses available projections for global HFC emissions across various sub-sectors such as commercial, industrial, domestic, and stationary (as opposed to mobile) AC systems. Velders (2015, 2017, 2019) provides refrigerant emissions (measured in kton refrigerant – HFCs).  Velders provides and upper scenario and a lower scenario.  A mean scenario is also calculated.  These forecasts are pre-Kigali accord and show a steadily increasing HFC emissions profile through 2050.  These scenarios become the total addressable market for the alternative refrigerants model. 

Adoption of alternative refrigerants is modeled using forecasts from the literature.

Adoption Scenarios[4]

Velders and others estimate the adoption of alternative refrigerants correlated with two different Shared Socioeconomic Pathways (SSPs) developed by the International Institute for Applied Systems Analysis (IIASA).  The literature presents a low scenario and a high scenario.  A mean scenario is also calculated.  These three scenarios, low, mean and high, determine the PDS 1, PDS 2, and PDS 3 adoption scenarios. These were assessed in comparison to a Reference Scenario where the solution’s market share was fixed at the current levels.

Emissions Model

In the reference case HFC emissions are prognosticated according to the year over year data provided in the literature.  Whereas the exact mix of alternative refrigerants is not determined the average GWP of 10 is used.  This is much lower than the dynamic GWP of HFCs which near an average GWP of 2000.


The total carbon dioxide-equivalent reductions that can be achieved from 2020-2050 in the Scenario 1 are 43.5 gigatons. The Scenario 2 shows a larger reduction of 50.5 gigatons from 2020-2050.


Indirect emissions from powering refrigeration appliances is a significant component of grid emissions and is expected to increase in a warming world.  Adoption of low GWP HFC replacements with new appliances brings the potential for increases in energy efficiency.  Some have estimated that the potential impact on indirect emissions may be half as much or as great as direct emissions reduction.  At this time this model and report does not include a forecast for indirect emissions reduction.

In order to achieve a global phase-down of HFCs, replacement fluids must be identified, and a global refrigerant transition must be implemented. Currently, there is no single replacement fluid, all replacements include trade-offs. The theoretically ideal refrigerant is the one having zero ozone depletion potential (ODP), low GWP nontoxic, non-flammable, has appropriate thermodynamic and heat transfer properties and is compatible with any type of lubricating oil (El-Sayed, El Morsi, and Mahmoud 2018). According to El Sayed et al. Hydrocarbons (HCs) satisfy all the requirements except being highly flammable oil (El-Sayed, El Morsi, and Mahmoud 2018).

Climate-friendly alternatives to HFCs are increasingly available for most uses and fall into two basic categories: “natural” or non-fluorinated substances with low GWPs, and fluorinated substances with low to mid-range GWPs (Borgford-Parnell et al. 2018). Currently, there is an emphasis on natural refrigerants that are gradually being used as a replacement for refrigerants from the hydrofluorocarbon group (Zanchi, Boban, and Soldo 2019). Commercially available  “natural refrigerants” include: ammonia (R-717), with a GWP of near zero; hydrocarbons (HC )(e.g., propane [R-290] and isobutene [R-600a]), with GWPs of less than 4; and CO2 (R-744)  (with a GWP of 1). The use of hydrocarbons (e.g., iso-butane and propane ammonia and carbon dioxide).

Commercially available fluorinated substances include O2, the low-GWP HFCs, also known as hydrofluoro-olefins (HFOs), some with GWPs of less than 1, according to the IPCC. Other alternatives include, HFC-32, with a GWP of 677, and HFC-152a, with a GWP of 138, according to the IPCC. There are also “not-in-kind” alternatives that do not involve refrigerants, such as district cooling


[1] Such as Chlorofluorocarbons (CFCs) like R-11, R-12, and R-502; Hydrochlorofluorocarbons (HCFCs) like R-22; Hydrofluorocarbons (HFCs) such as R404A, R134a, and R 407; and natural refrigerants like CO2 and NH3.

[2] The total quantity of refrigerant gases in existing equipment.

[3] For more on the Total Addressable Market for the Materials Sector, click the Sector Summary: Materials link below.

[4] For more on Project Drawdown’s three growth scenarios, click the Scenarios link below. For information on Materials Sector-specific scenarios, click the Sector Summary: Materials link.