An environmental air conditioning system is described for conditioning compressed air for supply as conditioned air. The system includes an airflow path to which the compressed air for ultimate distribution as conditioned air (i.e., airflow path compressed air) is supplied. Then airflow path has various components of an air cycle system, and also includes a power turbine outside of the air cycle that receives compressed air and discharges it as exhaust. The power turbine transfers power to a compressor in the air cycle system.