Air Conditioning Flashcards
How many packs are there and how do they function?
2 packs, supplied by pre cooled air from bleed system.
• It enters the pack and goes through a primary heat exchanger where it is dried and cooled.
• It then enters the pack compressor where it is compressed and heated and goes through a main heat exchanger where it is cooled.
• Finally passes through a turbine where it is cooled even further.
• From there it goes to a mixer unit to be mixed with recirculated cabin air and ducted to 3 zones to be mixed with hot air
How is a/c temperature regulated?
The air leaving the packs enters the mixer unit at the lowest selected zone temp. It’s mixed with recirculated cabin air and then ducted to 3 different zones. Each zone adds hot air via a trim air valve
What do the trim air valves do?
Trim air valves add hot air to the cool air from the packs to optimise cabin air temperatures
How many Air Conditioning Controllers are there and what do they control?
2 Air conditioning Controllers
Controller 1 controls pack 1
Controller 2 controls pack 2
They control pack control valve, trim air valves and pack outlet temperature by adjusting the pack turbine bypass valve
What is the purpose of the ram air inlet and when will it open if pressed?
Ram air inlet provides ram air to mixer unit to supply fresh air in event of smoke or loss of both packs.
When ram air pb is pushed, ram air inlet will open and if below 1psi, a check valve will allow the air through to the mixer unit. The outflow valve will open to 50%. The aircraft will be depressurised so not to be used above 10000ft
Where are the 3 zonal temperatures measured?
Cockpit: behind the FO seat
Cabin: Lav extraction system and the galleys
What happens if Air Conditioning Controller suffers single or dual channel failure?
Controller will still function with single failure
Controller is lost if dual failure
Can a pack still function with loss of the Air Cycle Machine?
Yes. Air still passes through primary heat exchanger and then bypass valve. Temp is regulated by position of ram air inlet and bypass valve
Consequences of hot air valve failure?
Fails in open position, no effect
Fails in closed position, cabin zone optimisation is lost
