How is the Environmental Control System (ECS) designed?

ECS provides cabin pressurization, air conditioning, and ventilation. Design requirements: Pressurization - Maintain cabin altitude below 8000 ft at cruise, differential pressure limits (8-9 psi typical), and emergency descent capability. Temperature - Maintain 65-80F throughout cabin, zone temperature control, and ground cooling in hot conditions. Ventilation - 10-20 CFM per person of fresh air, air quality, and smoke removal. Architecture: Conventional - Engine bleed air, air cycle machines (bootstrap cycle), packs; Bleedless (787) - Electric compressors for cabin air, improved engine efficiency. Sizing: Pack flow for cooling load, pressurization rate, and fresh air requirements. Components: Packs (ACM, heat exchangers), outflow valve, recirculation system, and temperature control valves. Analysis: Thermal load calculation (passengers, solar, equipment), pressure schedule design, and failure mode effects. Bleed extraction affects engine performance; ECS design optimizes aircraft-level efficiency.