Energy Analysis of the Aircraft Environment Control System Using Air with and without Humidity

This paper presents a thermophysical study approach for a pure environmental control system (ECS), incorporating the geometric dimensions of heat exchangers, ram air duct, and air cycle machine (ACM) blades of the Sabreliner’s environmental control system. Real flight scenarios are simulated by considering flight input variables such as altitude, aircraft speed, compression ratio of the air cycle machine, and the mass flow rate of bleed air. The study evaluates the coefficient of performance (COP) of the environmental control system, the heat exchanger efficiencies, and the work distribution of the air cycle machine based on five flight scenarios, with a particular focus on considering the effects of humidity on environmental control system performance. The results demonstrate that at cruising altitude (11,000 m), air humidity conditions allow an increase in the COP of around 9.28% compared to dry conditions. Conversely, on land, humidity conditions reduce the performance by 4.26% compared to dry conditions. It was also found that the effects of humidity at high aircraft speeds become negligible. In general terms, the humidity conditions in the air proved to have positive effects on the environmental control system’s performance but negative effects on the heat exchanger efficiencies, reducing them by 0.22%. Additionally, land conditions reflect significant improvements in performance when the compression ratio of the air cycle machine is varied. Furthermore, in the work distribution of the air cycle machine, humidity conditions were demonstrated to consume 2.91% less work from the turbine compared to dry conditions.