Airbus A320 Airconditioning System

ATA 21 Airconditioning

ZC (Zone Controller) ×1

Main Functions:

-Optimized Temperature Control

-Basic Temperature Regulation Elaboration

-Flow Control Optimization

• If Primary control computer fails “ALTN” message on ECAM + with alternate mode operation, 24 °C will be maintain in the cabin, No trim valve control.
• If both ZC's fails Pack controller will controls in basic regulation, flight deck will be maintain at 20 °C & cabin will set to 10 °C, trim & hot air valve close 

PC (Pack Controllers) ×2

Main Functions:

-Basic Temperature Control

-Flow Control

• If primary control computer faulty, secondary computer takes over for reduced level of operation by remaining at previous setting.
• If both fail 15 °C temp. will maintain by anti-ice valve.

Pack flow control valve

• Pneumatically regulates air flow according to the demand by controller command
• Closes pneumatically by
  • Compressor OVHT
  • Lack of air pressure
• Electrically close
  
  • During Engine start, after 30 sec. open again (to avoid supplementary pack closer cycle at 2nd engine start)
  • Engine Fire P/B OUT
  • Ditching P/B set to ON
  • Pack valve P/B manually select OFF 

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Enhanced vs Classic:

On the Enhanced aircraft, the ZC and PCs are replaced by the Air Conditioning System Controllers (ACSC) ×2

ACSC does:

    -Temperature regulation.

    -Flow control and Monitoring.

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Air-Conditioning Cycle:

FCV - PRIM EXCHGR - COMPRESSOR - MAIN EXCHGR - REHEATER - CONDENSER  - WATER EXTRACTOR - REHEATER -TURBINE - CONDENSER - MIXER UNIT

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Keep in mind

- In case PC fails > Outlet temperature is fixed at 15 C by Anti-ice valve

- In case ZC fails > Outlet temperature is fixed at 20 C by the Packs

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PRESSURIZATION CONTROL                                                                                                                                             

CPCs (Cabin Pressure Controllers) × 2

• System consist 2 identical controllers, only 1 operates at a time other STBY
• If both systems failed manual mode to be selected
• Out flow valve can be controlled by manually by control panel 

-Each CPC controls one electric motor on the outflow valve assembly Automatically .                    

-A third motor is installed for manual operation of the outflow valve in case both automatic systems fail.

Cabin Pressure and Altitude

• Cabin altitude limited to 8000 ft
• Differential pressure limited to 8.06 psi at 39000 ft
• If cabin altitude = 9550 ft M/W comes ON
• At altitude 11300ft passenger signals activated
• At 15000ft safety device activates to close valve 

Safety Valves: 

 Located on the rear pressure bulkhead to protect the fuselage against excessive cabin differential pressure, also protect against negative differential pressure. 

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AVEC (Avionics Equipment Ventilation Computer)

• AEVC controls and monitoring of Avionics ventilation system automatically provided Blower and Extract P/Bs pressed IN

• If both Blower and Extract P/B released out (OVRD)

• Blower fan stops
• Skin exchanger outlet bypass valve and Skin exchanger inlet bypass valve close (all valves close).
• Air condition inlet valve opens to supply air.
• Skin air outlet valve partially opens.

    AEVC failure:

• System as same as smoke configuration except Skin exchange isolation valve open.
• Inlet and skin exchange inlet bypass valves remain in the position before the failure occurred.
• Extract fan keep on running

    AEVC power failed:

• Both blower and extractor fan P/B set to OVRD
  • Blower fan stops
  • Air condition inlet valve opens
  • Skin air outlet valve partially opens
  • Other valves stay at its last controlled position

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Aft Cargo compartment ventilation and heating system

• Cargo ventilation controlled via controlling isolation valves and extract fan
• Cargo ventilation controller controls and monitor isolation valves and extraction fan of the cargo ventilation system.

    Heating controller

• Cargo heating controlled by information received from 2 temp. sensors and control trim air valve to add hot
  air if required.

   If failed
- Hot air valve close + E/W message 

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EMERGENCY RAM AIR INLET FLAP OPERATION

If both packs failed, an emergency ram air inlet flap can be opened for A/C ventilation or smoke removal. 

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Main Definitions/Functions

AIV(Anti-Ice Valve):
Prevents ice build up in the condenser of the ACM turbine,
Controls pack discharge temp In case of failure via the pack outlet Pneumatic Sensor

By Pass Valve:
Controls ACM by pass for pack outlet modulation

Bleed Temp Sensor:
Provides supplementary info to pack & zone controller

Compressor Temperature Sensor:
Provides Compressor outlet temp to pack controller primary channel for overheat detection.

Compressor Overheat Sensor:
Provides compressor outlet Temp to pack controller Secondary channel for overheat detection & ECAM

Condenser:
Cools airflow in water extraction loop below its dew point

Compressor Pneumatic Overheat Sensor:
Protects against pack overheat by gradually closing FCV When comp discharge temp ^ 230 C

FCV (Flow Control Valve):
Controls the flow of bleed air entering the pack and trim air system

Main Heat Exchanger:
Uses ram air to cool air leaving the ACM compressor

Primary Heat Exchanger:
Uses ram air to cool the air entering the ACM compressor

Pack outlet Temperature Sensor:
Provides pack outlet temp info to pack controller for ECAM & overheat detection

Plenum Chamber:
Ensures ACM fan airflow thru ram air circuit on ground

Pack outlet Pneumatic Sensor:
Modulates AIV to control pack outlet temp in case of failure

Ram Air Inlet and Outlet Actuator:
Regulate ram air flow for minimal drag

Reheater:
Optimise ACM turbine efficiency
Stops presence of water at turbine inlet

Water Extractor:
Removes moist from the air leaving the condenser by Centrifugal Force.

Water Ext Temp Sensor:
Provides info for pack temp modulation

Water Injector:
Increases the cooling efficiency of the heat exchanger 

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MEL/DEACTIVATION

Note:
The following deactivation procedures are only for training purposes and should not be used on actual aircraft.

PACK FLOW CONTROL VALVE

A/C may be dispatched per MEL with FCV secured in the CLOSED position;

Single pack operations are limited to specified altitude depending on aircraft/engine combination.

Deactivation procedure:

- Pneumatic OFF

- Pack Switches OFF, 


- Deactivate the FCV by removing the special screw (this allows the valve to continually vent, spring tension closes the valve),


- With the valve in the CLOSED position, use the special screw to secure the valve CLOSED. 

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MEL/DEACTIVATION

AVIONICS VENTILATION SKIN AIR OUTLET VALVE

May be deactivated in the PARTIAL-OPEN position for dispatch per the MEL. This will allow for smoke removal in case of avionics smoke in flight.

When the outlet valve is deactivated PARTIAL-OPEN, the Skin Exchanger Isolation Valve is deactivated OPEN.

Deactivation Procedure:

- Push latch to release the handle from the valve,


- Pull the handle to engage the splines,


- Set the Deactivation switch to OFF,


- Turn the handle clockwise until the main flap is closed and the auxiliary flap is OPEN,

- Stow and latch the handle,

- Move the Skin Exchanger Isolation Valve to the OPEN position and remove the connector to deactivate,

- Perform AEVC BITE. 

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MEL/DEACTIVATION

AVIONICS VENTILATION SKIN AIR INLET VALVE

May be deactivated in the CLOSED position for dispatch per the MEL.

When the inlet valve is deactivated CLOSED, the Conditioned Air Inlet valve is deactivated OPEN. This allows supplemental cooling from the cockpit air conditioning supply for the avionics equipment.

Deactivation procedure:

- Push latch to release the handle from the valve,


- Pull the handle to engage the splines,


- Set the Deactivation switch to OFF,


- Turn the handle counter-clockwise until the flap is closed,

- Stow and latch the handle,

- Move the Conditioned Air Inlet Valve to the OPEN position and remove the connector to deactivate,


- Perform AEVC BITE.

AVIONICS VENTILATION CONDITIONED AIR INLET VALVE

In addition to the Skin Air Inlet Valve deactivation, other ventilation system deactivation tasks also include deactivation of the Conditioned Air Inlet Valve in the OPEN position. These affected components are:

- The blower fan,

- The extract fan,


- The ventilation filter. 

Credit :    Rakesh Singh

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