Abstract: The invention is directed to a system and process operating on an air-standard cycle either to cool or heat a room. The system may be advantageously employed to cool or heat relatively small areas or rooms, particularly driver's cabins in locomotives and the like. In cooling operation, outside air is expanded in a turbine, cooled below ambient, and introducted into a heat exchanger. Air from the room to be cooled is introduced into the heat exchanger and heat is removed therefrom. Suitable valves are provided to change the operation of the heat exchanger to that of a regenerator and to direct the flow of air accordingly. Specifically, air heated by compression in the compressor is directly introduced into the room and air leaving the room is passed through the regenerator/heat exchanger and released into the atmosphere.