An environmental control system includes a higher pressure tap to be associated with a higher compression location in a main compressor section associated with a gas turbine engine. A lower pressure tap is associated with a lower pressure location, which is at a lower pressure than the higher pressure location. The lower pressure tap communicates to a first passage leading to a downstream outlet and a second passage leading into a compressor section of a turbocompressor. The higher pressure tap leads into the turbine section of the turbocompressor such that air in the higher pressure tap drives the turbine section to in turn drive the compressor section of the turbocompressor. A combined outlet of the compressor section of the turbocompressor and the turbine section intermix and pass downstream to be delivered to an aircraft use.