A compressing device includes a first turbine a second turbine and a compressor. The first turbine is configured to provide a first energy by expanding a first medium and the second turbine configured to provide a second energy by expanding a second medium. The compressor is configured to receive the first energy and the second energy during a first mode of the compressing device, receive the first energy during a second mode of the compressing device, and compress the second medium in accordance with the first mode or the second mode.