CO2 in car air conditioning systems

Within the scope of the long-discussed measures for reducing direct refrigerant emissions, and the ban on the use of R134a in MAC systems within the EU, the development of CO2 systems has been pursued intensively for several years.

At first glance, efficiency and therefore indirect emissions of CO2 systems under typical ambient conditions appear to be unfavourable. But it must be considered that previous R134a systems are less efficient than stationary plants of the same capacity, because of specific installation conditions and high pressure losses in pipework and heat exchangers. With CO2, pressure losses have significantly less influence. Moreover, system efficiency is further improved by the high heat transfer coefficients in the heat exchangers.

This is why optimized CO2 air conditioning systems are able to achieve efficiencies comparable to those of R134a. Regarding the usual leakage rates of such systems, a more favourable balance is obtained in terms of TEWI.

From today's viewpoint, it is not yet possible to make a prediction as to whether CO2 can in the long run prevail in this application.
It certainly also depends on the experience with "low GWP" refrigerants that have meanwhile been introduced by the automotive industry (R1234yf). Among others, operating safety, costs, and global logistics will play an important role.