An environmental control system includes a pair of parallel operating environmental air compressors (EACs) that receive a first outside air, wherein each EAC includes a respective EAC compressor and EAC turbine. A first regenerative heat exchanger is downstream of the EAC compressors and upstream of the EAC turbines, wherein the first regenerative heat exchanger receives environmental air from an enclosure for occupants. A primary heat exchanger is downstream of the first regenerative heat exchanger, wherein the primary heat exchanger receives a second outside air. An air cycle machine (ACM) is downstream of the primary heat exchanger. A condenser is downstream of the ACM, wherein a conditioned air exits the condenser and into the enclosure. A water extractor is downstream of the condenser. A reheater is downstream of the water extractor and upstream of the ACM. A secondary heat exchanger is downstream of the ACM, wherein the secondary heat exchanger receives the second outside air. An actuated door that controls an amount of second outside air to the primary heat exchanger and to the secondary heat exchanger, wherein, in a second outside air flow, the primary heat exchanger is downstream of the secondary heat exchanger.