Researchers have found a CO2-based heat pump to be the most efficient of four options studied for mobile air conditioning.
Guangzhou Dinghan Railway Transportation Equipment Co. also debuts direct power supply system and an intelligent control system.
Carbon dioxide is the coolant of the first all-electric Citaro bus, which will soon enter series production.
The French company presented a system using the refrigerant CO2 for bus cooling and heating at the European event.
At ATMOsphere Europe 2017, rail giant Deutsche Bahn called on manufacturers to help it achieves its goal of using natural refrigerants for air conditioning in new trains by 2020.