Air conditioning
The air conditioning system keeps the air in the pressurized fuselage compartment at the correct pressure, temperature, freshness. In normal conditions, the pneumatic system supplies air to the air condition system from the main engine compressor, APU compressor, high pressure ground air supply unit and also can supply through a low pressure ground connection.
Then, air is regulated in temperature by the temperature regulation sub-system. Proper ventilation of the avionics equipment is ensured by the avionics ventilation sub-system. The pressurization sub-system ensures a cabin altitude compatible with crew and passenger comfort. The hot compressed air is cooled, conditioned and supplied to the fuselage compartments and then discharged overboard through the outflow valve.
The air conditioning system consists of the following sub-system:
Distribution
Distribution system delivers the conditioned air to the pressurized fuselage.
Pressurization control
The pressurization control system controls the pressure in the fuselage and it operates both automatically and manual backup. The pressure change rate is controlled to give satisfactory pressure value.
Air Cooling
The air cooling system decreases the temperature of the hot bleed air from the pneumatic system and also reduces the quantity of water in the hot bleed valve.
Temperature Control
The temperature control system controls the temperature of the air supplied to the cockpit and cabin.
Basic Principle:
Bleed air coming from the pneumatic system is controlled in flow before reaching two air conditioning packs which ensure basic temperature regulation. Air delivered by the packs is mixed with recirculated air from the cabin zones. A part of cabin air is recirculated to decrease air supply demand. Fine temperature adjustment of air distributed in the pressurized zones is obtained by controlling the amount of hot air added to the air coming from the mixer unit. Correct pressurization is obtained by controlling the conditioned air discharge through one outflow valve.
Pack Units
The air flow from the Air Bleed system is regulated by two pack flow control valves. Then two independent packs provide regulated temperature air to the mixer unit. Both packs provide air at the same temperature.
Mixer Unit
The mixer unit mixes regulated temperature air from the packs with part of the cabin air supplied by re-circulation fans. The mixer unit may also receive conditioned air from a low pressure ground connection or fresh outside air from the emergency Ram Air Inlet. The emergency Ram Air Inlet provides outside fresh air for ventilation of the aircraft in emergency conditions (loss of both packs and smoke removal).
Hot Air Pressure Regulating Valve
Hot air tapped upstream of the packs supplies the trim air valves through a hot air pressure regulating valve. This valve regulates the downstream pressure above the cabin pressure.
Hot Trim Air
A trim air valve associated with each zone optimizes the temperature by adding hot air, if necessary, to the cold air coming from the mixer unit.
Air distribution
The conditioned air is distributed to three main zones: cockpit, forward cabin and aft cabin.
Normally the mixer unit allows the cockpit to be supplied from pack 1 and, FWD and AFT cabins from pack 2.
Lavatory and galley ventilation
The lavatory and galley ventilation system uses air from the cabin zones. A fan extracts this air through an outflow valve. The LAV and GALLEY extract air is used to ventilate the cabin zone temperature sensors.