Propane AC could help avoid global temperature rises

A report published at the Proceedings of the National Academy of Sciences (PNAS) has highlighted the emissions that could be avoided by switching to propane as a refrigerant in split-system air conditioners. The research team estimates that such a transition could avoid a 0.09°C increase in global temperature by the end of the century.

Global opportunity

The report notes that split ACs are currently the most used appliance for space cooling worldwide, and that in 2016, space cooling accounted for around 10 per cent of global electricity demand. Based on current trends, demand from air conditioners is expected to triple by 2050 and the stock of ACs would increase from about 0.9 billion in 2017 to over 3.7 billion in 2050.

Most of these units carry HFCs, which are being phased down globally.

“The phase-down of refrigerants with high global warming potential (GWP) prescribed by the Kigali Amendment to the Montreal Protocol has triggered a major effort to find less harmful alternative refrigerants,” says Pallav Purohit, lead researcher on the project and senior research scholar in the Pollution Management Research Group of the IIASA Energy, Climate, and Environment Program.

“R32 is currently the most common refrigerant to replace R410A in split ACs,” says Purohit. “The GWP of R32 is about one third that of R410A, but still considerably higher than that of a growing number of non-fluorinated alternatives like propane with a GWP of <1, which have recently become commercially available for split ACs.

“While analysing the consistency of Kigali ambitions with the 1.5°C Paris Agreement goal, we have realised that propane-based residential air conditioners (ACs) are being manufactured in India and in China with cooling capacities up to 7kW. In 2020, the actual globally installed base was over one million units, mainly in India and China.

“Therefore, in this study, we show that a switch to propane as an energy-efficient and commercially available low-GWP alternative in split ACs, could avoid 0.09°C (0.06–0.12°C) increase in global temperature by the end of the century. This is significantly more than the 0.03°C (0.02–0.05°C) avoided warming from a complete switch to R32 in split ACs.”

Focus on direct emissions

The study focussed on the environmental impact of direct emissions (refrigerant leakage).

But Purohit says that in terms of indirect emissions (energy use), split ACs using propane perform similarly to those using R32, and are more efficient than currently widespread appliances using R410A and R22.

He points to another study by an International Energy Agency (IEA)-sponsored program that found domestic unitary air conditioners using propane refrigerant have a lower life-cycle climate performance (LCCP) than comparable units running with R410A, R32, and other alternatives in 11 cities around the world.

The research team has previously published a study that takes into account both direct and indirect emissions. This indicated that if technical energy efficiency improvements are fully implemented, the resulting electricity savings could exceed 20 per cent of future global electricity consumption.

“The combined effect of HFC phase-down, energy efficiency improvement of the stationary cooling technologies, and future changes in the electricity generation fuel mix would prevent 411–631Gt CO₂ of GHG emissions between 2018 and 2100, thereby making a significant contribution towards keeping the global temperature rise below 2°C,” says Purohit.

Barriers to uptake

Although there have now been many calls for greater uptake of hydrocarbons in split systems, the major manufacturers are yet to show signs of moving. Purohit believes this is largely due to safety standards regarding the use of flammable refrigerants.

“Therefore, countries are encouraged to support the adaptation according to technological improvements of these safety standards to allow larger charge sizes while including guidance on safe application,” he says.

He highlights the recent decision by the International Electrotechnical Commission (IEC) to approve an international standard on safety requirements for electric heat pumps, air conditioners and dehumidifiers for domestic use.

“This new standard allows for higher charge limits for hydrocarbons such as propane (R290) and other flammable refrigerants in domestic technology,” says Purohit, “which in turn means potentially massive reductions in the emission of climate-damaging refrigerant gases.”

The study considers the capacity of split ACs (<7kW) that will require less than the higher load of flammable refrigerants allowed by the IEC.

To read the report, click here.