13.11.2 Air Conditioning

Question 1

Air conditioning

Answer 1

Supply cold air to aircraft cabin and flight deck and mixed with hot air to make pax comfort better

Question 2

Vapour cycle cooling
Small to medium size aircraft

Answer 2

Refrigeration system or freon system
Fitted on older piston aircraft or small jets

Question 3

Vapour cooling

Answer 3

Continuously repeating loops or cycles that use the flow of a sealed refrigerant that converts back and forth from liquid to gas to transport heat from lower temps to higher temps

Process known as a vapour cycle

Question 4

Vapour cooling components

Answer 4

Compressor - pulls the low px refrigerant from the evaporator & compresses it which means pressure and temp increases

Condenser - condenses hot regorgèrent gas coming from the compressor it takes the hot air from the cabin and dumps it overboard which takes the refrigerant and condenses it from gas to a liquid

Receiver/dryer - acts as a reservoir for the refrigerant it contains a desiccant that absorbs the moisture in the system

Thermal expansion valve - regulates the amount of liquid refrigerant flowing in the evaporator setter mined by temp and px

The evaporator- absorbs heat of the aircraft cabin into the refrigerant as the heat is absorbed the refrigerant is turned to gas

Refrigerant - low vapour pressure & low boiling point

Question 5

Common refrigerant

Answer 5

R134a

Question 6

Vapour cycle operation

Answer 6

Compressor draws the refrigerant vapour from the evaporator, then compressed it increasing pressure and temp, high pressure high temp vapour is drawn through the condenser, heat is transferred to ram air which then cools the refrigerant back to a liquid, then leaves the condenser via the filter dryer to the thermal expansion valve. Drop in pressure through the expansion valve allows the refrigerant to cool and change into a low pressure cold liquid then goes back to the evaporator to start the cycle again.

Question 7

Vapour cycle compressor

Answer 7

Piston compressor - small aircraft
Radial compressor - large aircraft

Uses a belt driven compressor from a drive source

Question 8

Air cycle cooling large commercial aircraft (boot strap system)

Answer 8

Flow control valve

Air cycle machine

Heat exchanger

Turbine bypass valve water separator

Ram air inlet & outlet

Anti ice valve

Sensors

Question 9

Air cycle machine

Answer 9

Cooling unit with a expansion turbine and compressor on a common shaft & drives a cooling fan

Compressor increases px and temp of the air to increase efficiency of the heat exchanger

Turbine performs the second stage of the air cooling cycle

Compressed air partially cooled by the heat exchanger expands in the turbine gives up heat energy to drive the compressor & cooling fan.

The temp decrease causes the turbine outlet temp to go below ambient ram air temp which can decrease below freezing

Question 10

TBV

Answer 10

Used to control the pack outlet temp if the valve is closed more air flows over the ACM and the pack outlet temp drops

Question 11

Water separator

Answer 11

Due to the reduced temp it causes moisture

Separator removed moisture and injects it into the ram air to increase efficiency

Has a bypass valve incase if clogging

Question 12

Compressor bypass check valve

Answer 12

Opens and let’s air bypass the compressor during acm start or low cooling demand if the acm runs slow

Question 13

Ozone converter

Answer 13

Coverts ozone to oxygen to improve the air quality in the cabin

Usually fitted upstream of the pack just before the pack valve

Question 14

Temp control

Answer 14

Automatic or manual control
Auto controlled by the temp controller
Manual control the trim air valves

Question 15

Equipment cooling

Answer 15

To control and maintain equipment temps
Can have a skin air heat exchanger
Inboard normal cooling

Overboard usually smoke clearance
Can use cabin air supply