In response to a number of policy measures, such as the G20 committing to progressively phase down HFCs and the European Union effectively banning R134a under the MAC Directive, the industry is developing new mobile air conditioning (MAC) systems designed to use low-GWP (global warming potential) refrigerants.
Johanna Gloël of GIZ Proklima presented research findings that demonstrate that under a wide range of Chinese climate conditions, environmentally friendly MAC systems using natural refrigerants, particularly R744, proved more energy efficient than synthetic refrigerant alternatives. With the implementation of natural refrigerants in MAC systems, GHG emissions could be reduced by 30% in China.
China will overtake US and EU MAC unit stocks by 2030
Not only does the use of MAC systems containing HFCs contribute a significant percentage to total vehicle greenhouse gas emissions, refrigerant leakage rates in MAC systems are also disproportionately high compared to other air conditioning systems. What is more, air conditioning systems are now standard equipment in passenger cars, and their number will only continue to grow as car availability and affordability increases around the world.
China is expected to become the biggest market for passenger vehicles in the near future. The country’s share of global MAC systems increased from 3% in 2000 to 11% in 2014 and is expected to reach nearly 25% in 2030. Sales of cars in the EU and US are relatively stable, indicating that the market is saturated and new sales mainly replace old cars. Sales in China on the other hand, indicate that the market is growing. As a result, it is predicted that the stock of MAC units will surpass that of the US before 2020, and will overtake the stock of all 28 EU countries by 2030.
Potential refrigerant replacements
Gloël noted that in the past, the global MAC industry has adopted a single air conditioning solution for use worldwide, so it can be expected that EU MAC regulation and its impact of refrigerant selection, will also have an influence on the MAC industry in other countries. In addition, since the US and the EU comprise nearly 50% of global MAC systems, regulations in these countries are more likely to influence the global market. A number of refrigerants are being considered as replacements for R134a, which was the standard MAC refrigerant, but which is now being phased out due to its high GWP. These include natural refrigerants hydrocarbons and R744, and fluorinated refrigerants R152a and R1234yf. These refrigerants have the following properties:
- Hydrocarbons have a higher safety class due to higher flammability, but have a GWP of <3.
- R744 is currently the only non-flammable refrigerant under consideration, and it is chemically inert and and low toxicity. German car manufacturer Daimler has committed to developing CO2 MAC systems.
- R152a falls into the A2 safety class and has a GWP of 124.
- R1234yf has a lower flammability than hydrocarbons, but when burning, it releases hazardous chemical hydrogen Fluoride HF. Its GWP is 4.
How do alternative MAC refrigerants measure up?
In order to compare the performance of the different MAC refrigerant replacements, the coefficient of performance (COP) of a standard refrigeration cycle comprised of a closed single stream refrigeration cycle with inner heat exchanger was calculated. The COP was determined for the ambient temperatures 25, 30 and 35°C and corresponding cabin outlet temperatures of 16, 18 and 20°C. The results indicate:
- The COP of an R744 MAC is the highest for ambient temperatures below 30°C, but the lowest for higher temperatures.
- The COP of a MAC using R1234yf is only slightly better than R134a at 25°C, but worse for higher temperatures.
- Hydrocarbons (R290 and R1270) performed better than R134a under all temperature conditions.
In addition, a TEWI (total equivalent warming impact) evaluation was conducted, combing the climate impact of both direct refrigerant emissions and indirect emissions due to energy use. In all four cities in China for which the TEWI emissions were calculated (Shanghai, Hanghzou/ Hong Kong, Beijing and Chengdu), the lowest emissions are reached with natural refrigerants R290 and R744.
Global GHG emissions due to MAC expected to double by 2030
Using stock and sales figures, current and future CO2 emissions were calculated using a bottom-up stock model considering additional parameters such as initial charge, cooling capacity and emission factors.
Under a business as usual scenario, global GHG emissions due to MAC use are expected to double to 1,150 Mt CO2eq p.a. in 2030. However, if energy efficient MAC systems and natural refrigerants are introduced, 30% of total emissions in 2030 could be avoided.
The emission reduction potential in China is around 30%, about 70% of which stems from the reduction of direct emissions through the introduction of natural refrigerants. In the EU and US, it would even be possible to reach an absolute reduction compared to the emissions in 2014.