An environmental control system of an aircraft comprising: a ram air circuit including a ram air shell having a primary heat exchanger and a secondary heat exchanger positioned therein; a dehumidification system arranged in fluid communication with the ram air circuit; and a compression device arranged in fluid communication with the ram air circuit and the dehumidification system , the compression device including a compressor , a turbine , and a fan coupled by a shaft , wherein the fan is operable to move ram air through the ram air circuit and the turbine includes a first inlet for receiving a first flow of medium and a second inlet for receiving a second flow of medium, wherein the second flow of medium is a fresh air; wherein the compressor has an inlet for receiving the second flow of medium and an outlet; wherein the secondary heat exchanger is positioned downstream of the compressor to receive the second flow of medium; wherein an outflow heat exchanger is provided downstream of the secondary heat exchanger to receive the second flow of medium from the secondary heat exchanger , wherein the dehumidification system is provided downstream of the outflow heat exchanger to receive the second flow of medium discharged from the outflow heat exchanger ; and wherein the second flow of medium exiting the dehumidification system is provided to the turbine ; further comprising a valve (V6) configured, when opened, to direct a portion of the second flow of medium output from the compressor to an inlet of the fan of the compression device to rotate the fan and drive movement of ram air through the ram air circuit . a ram air circuit including a ram air shell having a primary heat exchanger and a secondary heat exchanger positioned therein; a dehumidification system arranged in fluid communication with the ram air circuit; and a compression device arranged in fluid communication with the ram air circuit and the dehumidification system , the compression device including a compressor , a turbine , and a fan coupled by a shaft , wherein the fan is operable to move ram air through the ram air circuit and the turbine includes a first inlet for receiving a first flow of medium and a second inlet for receiving a second flow of medium, wherein the second flow of medium is a fresh air; wherein the compressor has an inlet for receiving the second flow of medium and an outlet; wherein the secondary heat exchanger is positioned downstream of the compressor to receive the second flow of medium; wherein an outflow heat exchanger is provided downstream of the secondary heat exchanger to receive the second flow of medium from the secondary heat exchanger , wherein the dehumidification system is provided downstream of the outflow heat exchanger to receive the second flow of medium discharged from the outflow heat exchanger ; and wherein the second flow of medium exiting the dehumidification system is provided to the turbine ; further comprising a valve (V6) configured, when opened, to direct a portion of the second flow of medium output from the compressor to an inlet of the fan of the compression device to rotate the fan and drive movement of ram air through the ram air circuit . <EOS>