An environmental control system of an aircraft comprising: a ram air circuit including: a ram air shell having at least one heat exchanger (34, 36) positioned therein; a divider arranged within the ram air shell to separate the ram air shell into a first region and a second region, the at least one heat exchanger being arranged within both the first region and the second region, wherein the system is configured such that ram air flows through the first region and such that in a low altitude mode of operation a first medium and in a high altitude mode of operation a combination of the first medium and a third medium flows through the second region; a dehumidification system (52, 54) 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 and a turbine; wherein the system is configured such that the first medium or the combination of the first and third media that flow through the second region is exhausted from the turbine of the compression device; wherein the at least one heat exchanger (34, 36) includes a first portion arranged within the first region and a second portion arranged within the second region, the second portion of the at least one heat exchanger is integrally formed with the first portion; and wherein the system is configured such that the first medium or the combination of the first medium and the third medium that flow through the second region flows across the second portion of the at least one heat exchanger. a ram air circuit including: a ram air shell having at least one heat exchanger (34, 36) positioned therein; a divider arranged within the ram air shell to separate the ram air shell into a first region and a second region, the at least one heat exchanger being arranged within both the first region and the second region, wherein the system is configured such that ram air flows through the first region and such that in a low altitude mode of operation a first medium and in a high altitude mode of operation a combination of the first medium and a third medium flows through the second region; a ram air shell having at least one heat exchanger (34, 36) positioned therein; a divider arranged within the ram air shell to separate the ram air shell into a first region and a second region, the at least one heat exchanger being arranged within both the first region and the second region, wherein the system is configured such that ram air flows through the first region and such that in a low altitude mode of operation a first medium and in a high altitude mode of operation a combination of the first medium and a third medium flows through the second region; a dehumidification system (52, 54) 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 and a turbine; wherein the system is configured such that the first medium or the combination of the first and third media that flow through the second region is exhausted from the turbine of the compression device; wherein the at least one heat exchanger (34, 36) includes a first portion arranged within the first region and a second portion arranged within the second region, the second portion of the at least one heat exchanger is integrally formed with the first portion; and wherein the system is configured such that the first medium or the combination of the first medium and the third medium that flow through the second region flows across the second portion of the at least one heat exchanger.