Chinese train air conditioning is identified as one of the few applications of fluorocarbon refrigerants where the
direct effect of refrigerant emissions is a significant fraction of the greenhouse effect. Air cycle systems, which are
more robust, have small amounts of air leakage, possess no safety or environmental hazards and can be
automatically replenished by a small air compressor. So air cycle systems would be an acceptable substitution
technology for providing air-conditioning in trains [1], especially for high-speed trains in China.