Mobile air conditioning (MAC) systems are a significant source of greenhouse gas (GHG) emissions from vehicles. This study, conducted by the ICCT in partnership with the Institute for Governance & Sustainable Development (IGSD), examines the GHG benefits and costs of switching to improved refrigerants and more efficient AC systems. This research is intended to support implementation of the Kigali Amendment to the Montreal Protocol on Substances that Deplete the Ozone Layer, which requires the phase-down of HFC refrigerants and also targets improvements in energy efficiency.
The MAC system is responsible for an estimated 3%–7% of by global light-duty fuel consumption, up to 20% of fuel use in congested and hot, humid climates. 81%–88% of GHG emissions are associated with the energy required to run the AC system, while the rest are associated with leakage of the refrigerant (R134a, the leading refrigerant globally, has a global warming potential [GWP] 1300 times higher than CO2). In this paper, we examined the GHG benefits and costs of R134a and the three leading MAC alternatives—R744 (CO2) and R1234yf, both with GWP of 1, and R152a, with a GWP of 138—employing improved efficiency and low leak systems, load reduction and powertrain optimization strategies.
A simple change to a refrigerant can almost eliminate 12%-19% of MAC emissions. Enhanced MAC systems, already prevalent in many markets reduce overall emissions by 40%, with additional load reduction technologies and system optimization offering another 15%–19% in reductions. All these strategies together can offer approximately a 70% reduction in GHG emissions and $1,000 to $3000 in lifetime savings, compared to non-improved systems.
In temperate climates, R744 offers the greatest GHG benefits. In hot climates, where MAC emissions are almost three times higher, R1234yf or R152a offer the best and roughly equivalent emissions benefits. While each of the alternatives offers important benefits, there are tradeoffs: R744 is much less effective in high temperature conditions, R1234yf systems can be illicitly recharged with cheaper R134a all but eliminating the benefits, and R152a requires a bigger system change and does not achieve the extremely low GWP of the other alternatives.
MAC use is considered to be an important factor in the growing gap between CO2 regulations and real-world emissions. In order to overcome the market barriers—improved MAC systems add costs for vehicle manufacturers while offering value to consumers—better policy is required. Substantial policy improvements are possible in every market, but recent changes supported by the current U.S. administration stand out as an especially egregious example of poor MAC policy.