Air supply and cooling, thermal control and pressurization of the cabin i.e HVAC (heating, ventilation & air conditioning) are considered to be part and parcel of the aeroplane environmental systems.
Air in the aircraft is retrieved from the gas turbine jet engine at a point right before combustion.
The cold air unit i.e (CAU) has a major device that pumps air in the cooling system that is the air cycle machine i.e (ACM) cooling device which uses air as a refrigerant instead of freon or R 134A gas.
TYPES OF COOLING SYSTEMS
- Turbo compressor (boot strap)– uses two heat exchangers. It consists of a cold air unit and heat exchanger on the same shaft. one increases air pressure while the other increasing air temperature.increasing temperature is cooled by ram air hence reduced by heat exchanger. when this happens there arises a condition of water droplets which are later removed by a a water extractor. Air then expands across the turbine hence temperature drop below zero degrees. This is regulated by a cold air bypass line.
- Brake turbine
- Turbo fan
N.B – The above two uses the same principle of air from a gas turbine only on this case there is no boot strap.
Below are some gadgets used in the HVAC :-
- Coalescer – used to separate water from air and create large water droplets.
- humidifier/ humidistat – used to regulate relative humidity
- mass flow controller – makes available constant air in the air conditioning receiver
- water separator – is used at low altitudes while a humidifier at high altitudes.
- Gasper system – supplies cool air to individual seats.
- dump valve – is an air outlet used fro depressurization
- blow out panels – found beneath passenger and cargo to regularize pressure if door opens.
- ditching control – closses all outflow valves prior to landing on water in aquaplanning.
- HPSOV– high pressure shut off valve
- FAMV – fan air modulating valve.