A method of operating an environmental control system of an aircraft includes providing a first medium to the environmental control system including a compressor and a turbine. The first medium is provided to the compressor and the turbine sequentially. A second medium is provided to the environmental control system. In a first mode of operation, the first medium and the second medium mix within the turbine and in a second mode of operation the second medium bypasses the turbine such that the first medium and the second medium mix downstream from the turbine.