Cooling on the Move

Air conditioners in passenger cars, vans, buses and freight trucks – collectively known as mobile air conditioning (MAC) – consume almost 2 million barrels of oil equivalent per day (Mboe/d).

Greenhouse gas (GHG) emissions from MAC stand at around 420 million tonnes of CO₂ equivalent (MtCO₂-eq), more than 1% of global energy-related CO₂ emissions. Energy consumption is responsible for around 70% of these emissions, while GHG emissions from refrigerant leakage account for 30%.

The proportion of annual vehicle fuel consumption used by MAC varies by country, ranging between 3% in colder climates and 20% in hotter climates. Though over shorter timescales, MAC can peak at over 40% in warm climates and congested traffic. For electric vehicles, MAC can reduce driving range by up to 50% on hot and humid days.

Without further policy intervention, MAC energy consumption may rise to over 5.7 Mboe/d by 2050. This near tripling of consumption is driven by an increase in the number of passenger cars on the road, from around 1 billion today to over 2 billion, with a greater proportion of the increase in warmer climates. The overall expected increase in global ambient temperatures will drive further air conditioning demand. Without further policy intervention, GHG emissions resulting from energy use and refrigerant leakage in 2050 could triple to 1 300 MtCO₂-eq.

In an Efficient Cooling Scenario, improvements in energy efficiency could limit energy consumption to 2.8 Mboe/d. With low-global warming potential (GWP) refrigerants included in this scenario and partial electrification of the vehicle fleet, GHG emissions by 2050 would be 20% lower than today at 320 MtCO₂-eq.

Policy will play a critical role in limiting growth in emissions from MAC. MAC energy consumption could be included in existing fuel economy standards, expanded vehicle testing methods and/or minimum performance standards for specific air-conditioning components.

Air conditioners in passenger cars, vans, buses and freight trucks – collectively known as mobile air conditioning (MAC) – currently consume over 1.8 million barrels of oil equivalent per day (Mboe/d). This represents more than 1.5% of current global oil consumption.

Estimates from the literature reveal that around 6% of the annual global energy consumed by cars is used for MAC, varying by country between about 3% and 20% depending on climate, driving patterns and traffic congestion. It can peak at over 40% in warm climates and congested traffic. This equates to around 1.2 Mboe/d consumed by MAC units in cars alone, with other road vehicles adding another 0.6 Mboe/d. For electric vehicles, MAC can reduce driving range by up to 50% on hot and humid days.

In 2015 total carbon emissions from MAC amounted to approximately 420 million tonnes of carbon dioxide equivalent (MtCO₂-eq). Of this, around 70% was due to fuel use, whilst greenhouse gas (GHG) emissions from refrigerant leakage were responsible for the other 30%.

This study adopts two scenarios to explore different futures of MAC energy consumption and emissions to 2050. The Baseline Scenario assumes no further policy intervention. In this scenario, the average global energy efficiency improves slowly – the only improvements are made by the switch to electric vehicles and in those countries with MAC policies in place. No changes in refrigerant use are included beyond those already mandated. It foresees energy consumption almost tripling to 5.7 Mboe/d by 2050. This is driven by the large increase in activity: there will be more than 2 billion cars and another 450 million other road vehicles globally, nearly all of which will have MAC installed. The uptake of vehicles with MAC will be greater in countries with warmer climates such as Indonesia and India, while at the same time the expected increase in global ambient temperatures will drive further MAC demand in more moderate climates.

Potential efficiency gains for cooling in vehicles can be achieved through better MAC technology, improving other components of the vehicle, such as thermal insulation, reflective windows and body paint that reduce heat load, and optimising power trains. If applied in combination, best-in-class technologies could reduce MAC energy demand by up to 67%, halving energy-related MAC emissions. In the Efficient Cooling Scenario the efficiency potential of MAC is fully realised, limiting energy consumption to 2.8 Mboe/d – less than half of the Baseline Scenario in 2050.

Alternative refrigerants already available on the market would eliminate most direct emissions from MAC. Historically CFC-12 was the most common refrigerant used in MAC, a chlorofluorocarbon ozone-depleting substance (ODS) with a global warming (GWP) 10 200 times that of CO₂, and high ozone depleting potential (ODP). Since the adoption of the Montreal Protocol, this has shifted globally to the hydrofluorocarbon HFC-134a, with no ODP but still a high and unsustainable GWP 1 300 times that of CO₂. Alternatives with no ODP and low GWP now exist.

Improving the energy efficiency of MAC and transitioning to refrigerants with a GWP of less than 1 would avoid more than 950 MtCO₂-eq in overall MAC-related GHG emissions, or the equivalent of almost 1% of global energy-related CO₂ emissions. Further emission reductions could come from decarbonising vehicle fuel supply and through greater electrification of the vehicle stock, especially if coupled with low-carbon electricity.

Significant GHG emission reductions are therefore available from the use of more efficient MAC and switching to low-GWP refrigerants. Governments have an essential role in ensuring GHG emissions from MAC are limited.

No country currently has a policy of directly regulating the energy efficiency of MAC. However, several countries award efficiency bonus credits to manufacturers for the inclusion of energy-efficient MAC technologies, which can be used towards meeting their efficiency or fuel-related carbon emissions targets.  

The use of this approach could be extended; though ideally, the energy consumption and energy efficiency of MAC systems within vehicles would be identified through the use of a low-cost, reliable and reproducible standard testing procedure, either as part of the overall vehicle energy test or for the MAC component alone. This would open up multiple policy opportunities to influence the efficiency of MAC. Further research and international collaboration are needed to develop such testing standards for vehicles.

For limiting refrigerant emissions, the European Union, Japan and Canada have introduced restrictions on the maximum GWP of the refrigerants used in MAC, while the United States encourages the same low-GWP technology with credits toward carbon emission reductions. The wider use of limits on the allowable GWP of refrigerants in MAC would dramatically reduce the direct GHG emissions from refrigerants globally.

Further research is needed to provide more robust estimates of GHG emissions from MAC equipment, and extended to go beyond road vehicles.