An environment-friendly vortex air cooling unit has been investigated experimentally. The unit uses only compressed air as the working fluid. The low efficiency of a simple vortex tube has so far prevented the wide application of the technology for air conditioning. This study investigates a 2-stage vortex tube which uses hot air from the first stage to drive the second stage in order to improve efficiency. Commercial vortex tubes could be adapted to operate in this way, so the technique would be easy to apply. A range of operating conditions including inlet air pressures and cold air fractions were tested and analysed in this study. The minimum compressed air pressure required for the operation of the unit was identified, and the benefit of using a heat pipe heat exchanger to cool the hot air from the first stage for use in the second stage of the system was investigated. It was found that the cooling power of the system could be increased by up to 11 percent.