Current systems use a synthetic hydrofluorocarbon known as R134a. Developed as an ozone-safe replacement for the chlorofluorocarbon R12, this refrigerant may prove inadequate for future vehicles. Automakers have encountered a fork in the road. Eventually, however, energy-efficient automobile engines may not generate enough waste heat to warm passenger compartments during cold weather. A heat pump, which operates like an air conditioner in reverse, may be required.
Carbon dioxide is much better suited for heat-pump applications.
So, if the path of improving the R134a system ultimately dead ends, it makes sense to consider alternative technologies now. To compare the two systems, the researchers constructed identical environmental test chambers. A variable-speed wind tunnel simulated the range of operating conditions encountered in normal applications. As a basis for comparison, the two heat exchangers had nearly equal volumes and the same pressure drop on the air side. The two compressors were also of similar sizes.