AIR CONDITIONING SYSTEM A/C

 AIR SUPPLY

AIR SUPPLIES

        Typical air supplies for air conditioning systems used on commercial aircraft are usually from one or more of the following sources:

       1       Gas Turbine Compressors

       2       Engine Driven Blowers

       3       Auxiliary Power Unit (APU) Compressor

       4       Ambient Ram Air Inlets

AIR CONDITIONING ON THE GROUND

        A ground conditioning unit may be connected into the system to supply conditioned air to the aircraft cabin while the aircraft is on the ground.

 

GROUND SUPPLIED AIR CONDITIONING

TYPICAL AIR CONDITIONING SYSTEM USING GAS TURBINE ENGINE COMPRESSOR BLEED AIR

        This is a typical method used in turbojet aircraft. The hot air, readily available from the main engine compressors, is tapped off and supplied to the cabin. In a typical system the aircraft pneumatic manifold supplies hot air to two separate and independent cooling packs located in the fuselage under the centre wing section. 

Some of the typical major components of Gas Turbine Bleed Air Conditioning Systems are:

       1       Air Selector valves from Engine / APU

       2       Isolation and Non-return Valves

       3       Air Conditioning Packs

       4       Mixer Chambers

       5       Distribution Systems

       6       Recirculation Fans

 

 A/C SYSTEM LAYOUT

DESCRIPTION AND FUNCTION OF THE SYSTEM COMPONENTS

        The cooling packs are controlled by electro-pneumatic pack valves. The pack valves are opened initially or closed by switches on the pilot’s overhead panel.  After opening they modulate (open and close) to maintain a constant flow of air into the cooling packs. Each cooling pack supplies cold air to the main distribution manifold. Before entering the main distribution manifold, the hot and cold air is mixed together. The ratio of hot to cold air is determined by the temperature control system. From the main distribution manifold, the conditioned air goes to the main cabin area. The conditioned air is ducted from the right end of the main distribution manifold into a series of risers.  These carry the air up within the forward sidewall to a large overhead distribution duct. A slot in the lower face of the duct distributes the airflow evenly throughout the passenger cabin. The flight compartment receives conditioned air from a smaller duct at the left end of the main distribution manifold.Cold air is ducted through the gasper system to individual outlets throughout the passenger and control cabins. These outlets can be adjusted for personal comfort. Floor level louvres in the sidewalls allow an outward flow of the air from the cabin into the area under the floor. It passes behind the cargo compartment wall linings and heats these compartments before it is discharged overboard through a pressurisation system outflow/discharge valve.The air conditioning pack valves control the flow of air into the air conditioning system. They act as the shut off valve for the air flowing into the air conditioning pack. They also meter the airflow to the pack.  When the APU is supplying the air, the flow rate is increased. The valves are pneumatically operated and electrically controlled.When the engine low pressure stage cannot supply the required amount of air the pneumatic system will automatically open the engine high pressure stage to satisfy the needs of the air conditioning system.

 EXAMPLE AIR EXHAUSTS