Aircraft Air Conditioning Systems

Introduction

• Aircraft fly at high altitudes primarily for economic reasons, but humans can't survive in this environment without support systems.
• At 40,000 feet, temperatures are around -56°C, air pressure is low, and there's insufficient oxygen.
• Crew and passengers need protection from freezing and death.

Air Conditioning System

• The system maintains the correct cabin pressure to support life.
• It ventilates the cabin to keep a comfortable temperature range.
• Aircraft systems need cooling and heating to prevent overheating during hot days on the ground.

Air Conditioning Functions

• The system must regulate 5 key factors: freshness, cleanliness, temperature, humidity, and pressure.
• Regulations stipulate a minimum amount of fresh air per passenger (0.283 m³/min and 0.35kg/min at sea level).
• The air needs to be filtered and free of hazardous gases, which is achieved through ozone converters and air filters.
• Comfortable temperatures for passengers and crew range between 18°C and 30°C.
• Humidity levels must regulate to avoid condensation.

Pressurization and Zones

• Aircraft cabins have pressurized and unpressurized areas.
• Pressurized sections include the cockpit, passenger compartment, and some cargo compartments.
• Air conditioning systems regulate cabin pressure to match ground level conditions. This is necessary for passenger comfort and to safely operate the equipment.
• Unpressurized parts include landing gear bays, the radome, and the tail cone.
• Specific zones for different compartments on wide-body aircraft are defined (e.g. zones A-E and U/D on B747-400).
• The number of zones depends on the aircraft's size, for example, an A320 has 3.

System Layout

• Air conditioning systems draw air from the pneumatic system.
• Air is cooled using multiple, identical packs.
• The outflow valve regulates airplane cabin pressure.
• Hot air is mixed with cooled air for a desired temperature.
• Regulated air is distributed through compartments.

Exercises

• The air conditioning system begins at the pack valve.
• Normal cruising altitude for civil aircraft is regulated to a maximum of 14,000 feet.