An environmental control system for an aircraft configurable to operate in at least a low pressure mode and a high pressure mode, the environmental control system comprising: a first inlet for providing a bleed air from an engine or an auxiliary power unit of the aircraft; a air cycle machine in communication with the first inlet, wherein the air cycle machine comprises: a compressor configured to receive the bleed air, a turbine downstream of the compressor , and an electric motor configured to drive the compressor ; and at least one heat exchanger , comprising a plurality of passes by which the bleed air flows, wherein each pass of the plurality of passes comprises an entry and an exit by the bleed air, and the plurality of passes comprising at least a first pass and a second pass; wherein an outlet of the at least one heat exchanger is in fluid communication with an inlet of the compressor and an inlet of the turbine ; and wherein in the low pressure mode, the bleed air is mixed with a recirculation cabin air at a first mixing point located downstream of the compressor of the air cycle machine downstream of the first pass of the at least one heat exchanger and upstream of the second pass of the at least one heat exchanger; and in the high pressure mode, the bleed air is mixed with the recirculation cabin air at a second mixing point located downstream of the turbine of the air cycle machine . a first inlet for providing a bleed air from an engine or an auxiliary power unit of the aircraft; a air cycle machine in communication with the first inlet, wherein the air cycle machine comprises: a compressor configured to receive the bleed air, a turbine downstream of the compressor , and an electric motor configured to drive the compressor ; and at least one heat exchanger , comprising a plurality of passes by which the bleed air flows, wherein each pass of the plurality of passes comprises an entry and an exit by the bleed air, and the plurality of passes comprising at least a first pass and a second pass; wherein an outlet of the at least one heat exchanger is in fluid communication with an inlet of the compressor and an inlet of the turbine ; and wherein in the low pressure mode, the bleed air is mixed with a recirculation cabin air at a first mixing point located downstream of the compressor of the air cycle machine downstream of the first pass of the at least one heat exchanger and upstream of the second pass of the at least one heat exchanger; and in the high pressure mode, the bleed air is mixed with the recirculation cabin air at a second mixing point located downstream of the turbine of the air cycle machine . a compressor configured to receive the bleed air, a turbine downstream of the compressor , and an electric motor configured to drive the compressor ; and at least one heat exchanger , comprising a plurality of passes by which the bleed air flows, wherein each pass of the plurality of passes comprises an entry and an exit by the bleed air, and the plurality of passes comprising at least a first pass and a second pass; wherein an outlet of the at least one heat exchanger is in fluid communication with an inlet of the compressor and an inlet of the turbine ; and wherein in the low pressure mode, the bleed air is mixed with a recirculation cabin air at a first mixing point located downstream of the compressor of the air cycle machine downstream of the first pass of the at least one heat exchanger and upstream of the second pass of the at least one heat exchanger; and in the high pressure mode, the bleed air is mixed with the recirculation cabin air at a second mixing point located downstream of the turbine of the air cycle machine . <EOS>