Towards sustainable aviation: A state-of-the-art review of energy-efficient aircraft environmental control systems (ECSs)

The transition towards more-electric aircraft (MEA) has intensified the need for energy-efficient environmental control systems (ECSs) that can maintain cabin pressurization, thermal comfort, air quality, and avionics cooling while reducing fuel consumption and emissions. This paper critically reviews studies on bleed and bleedless air cycle systems (ACSs), vapor compression refrigeration systems (VCRSs), low global warming potential (GWP) refrigerants, thermodynamic modelling, and optimization strategies for aircraft ECSs. The reviewed studies indicate that ACS performance is strongly influenced by wheel configuration, operating conditions, and component parameters. Genetic algorithm (GA) based optimization reported in the literature has proven effective in improving ECS performance while reducing experimental effort during system design. In addition, VCRSs using low-GWP refrigerants, such as R1234yf, demonstrate potential as viable alternatives to conventional ACS-based ECSs. VCRS studies have primarily emphasized component validation and ground-based testing, while ACS remains the dominant technology in operational service. Future research should prioritize integrated system-level models that combine ACS and VCRS architectures with advanced control strategies to reduce electric-compressor power consumption. These findings provide guidance for researchers and manufacturers developing next-generation energy-efficient ECS technologies.