An environmental control system for an aircraft includes a higher pressure tap to be associated with a higher compression location in a main compressor section associated with an aircraft engine, and a lower pressure tap to be associated with a lower pressure location in the main compressor section associated with the aircraft engine. The lower pressure location being at a lower pressure than said higher pressure location. The lower pressure tap communicates to a first passage leading to a downstream outlet, and having a second passage leading into a compressor section of a turbocompressor. The higher pressure tap leads into a 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 turbine outlet receives airflow exhausted from the turbine section. A compressor outlet receives airflow exhausted from the compressor section. A combined outlet receives airflow from the turbine outlet and the compressor outlet intermixing airflow and passing the mixed airflow downstream to be delivered to an aircraft. A buffer air outlet communicates airflow to an engine buffer air system. The buffer air outlet receives airflow supplied to the turbocompressor. A gas turbine engine is also disclosed.