Mobile air conditioning with climate-friendly refrigerant CO2

Silver VW Touran in front of the UBA headquarters.Click to enlarge
The Federal Environment Agencies’ climate friendly official car (VW Touran)

R744 is the name for CO2 as a refrigerant. ‘R‘ stands for ’refrigerant‘

Source: Gabriele Hoffmann / UBA

An EU directive has banned the use of fluorinated greenhouse gases with global warming potential exceeding 150 in mobile air conditioning systems since January 2011. CO2 used as a refrigerant is an alternative. An UBA official car had used a CO2 mobile air conditioning system from 2009 to 2017. Since October 2016, first cars with CO2 air conditioning systems have been offered.

The refrigerant CO2

Using the refrigerant CO2 in mobile air conditioning systems is a climate-friendly alternative to the current refrigerant tetrafluoroethane (R134a for short) that must be replaced in all new passenger cars in Europe since 2017. The climate impact of CO2 is 1,430 times lower than that of R134a. CO2 has a high cooling capacity, is non-flammable, generates no decomposition products, and is available at low cost worldwide. Refrigeration branch designates the natural refrigerant CO2 as R744 (R stands for "refrigerant"). CO2 can also be used to operate heat pumps for efficient heating in winter, thus saving energy when using integrated cooling/heating systems.

UBA official car with CO2 mobile air conditioning

The German Environment Agency had operated an official car fitted with a CO2 air conditioning system from 2009 to 2017. Measurements taken on the prototype system for a research project by the Federal Ministry for Environment confirm the high performance of CO2 as a refrigerant for mobile air conditioning. The CO2 system cools the vehicle interior very fast and is energy-efficient. Under normal European summer weather conditions, the new mobile air conditioning system with CO2 uses even less energy than the serially produced system with R134a. Measurements taken by the German Automobile Club (ADAC) confirmed these findings.

After 165,000 kilometres vehicle mileage, the CO2 climate compressor – the heart of every air conditioning system – performed well and was still very tight. The prototype mobile air conditioning system in the UBA official car was retrofitted in summer 2015 with a new CO2 compressor. It was designed to meet the latest manufacturer requirements in terms of geometry and dimensions. At the time a heat exchanger was also replaced since the prototype part showed outside corrosion. The new CO2-compressor component proved its robustness in everyday operation till the end of the car operation in spring 2017.

Prospects for CO2 as a refrigerant

Although CO2 was already a real option for mobile air conditioning systems in the late 1990s, cars fitted with CO2 air conditioning systems are rare on the market. One reason for the delay is that the air conditioning system with CO2 required new development and testing of the pressure-resistant components for the refrigerant CO2. End of October 2016 first cars with CO2 mobile air conditioning became available. They are currently offered for luxury cars by a German car manufacturer and are announced for the future mass market. Meanwhile very tight electric driven CO2 compressors were developed, paving the way for CO2 mobile air conditioning in electric driven car models. First offers with heat pumps are now available for some car models of the German Volkswagen Group.

As alternative refrigerants for mobile air conditioning, hydrocarbons are also being considered. In 2023, an electric car with a thermal management system that cools and heats with propane, was presented as a concept vehicle.