Do Aeroplanes need air conditioning at an altitude of 10 KM ?

 

Aeroplanes generally fly at 10KM above the earth's surface and temperatures at that altitude are less than -50 °C. But still, it requires air conditioning because of the following reasons:

• At 10KM above earth's surface pressure is at 0.1 atm. At such low pressures, respiration isn't easy for our lungs. So pressurization of air is required through conditioning
• Air is rammed into the jet through small openings near wings from a 1000km/hr moving aeroplane. This ramming of air causes a lot of temperature rise around 30 °C.
• There is a lot of solar radiation at that altitude and the heat gain due to solar need to be taken care of.
• Usually, in a domestic plane, there would be 150 flyers on an average. If we consider 100 watts per person as heat dissipation then the total heat load is around 5 TR
• Apart from all the above loads, aeroplane involves a lot of electronic control circuitry that dissipates a reasonably high amount of heat, which will add up to the heat load

In order to take care of all heat loads or heat gains and pressure regulation, an aeroplane requires the air conditioning system. Conditioning of air isn't only cooling instead it covers pressurization, filtration, acoustic correction etc.

Generally, air refrigeration systems are used in air crafts because of many advantages like:

• Low cost as air is free and cheap
• Air is inert and safe
• Operating pressures are low
• Easier to operate
• No secondary heat transfer medium as air itself can be directly circulated 
• No need of specialized compression systems as the turbo compressor in the gas engine of aircraft can do the required job.

The same aircraft refrigeration system cannot be used in domestic applications as the COP of these systems is very low. The benefits mentioned above are outweighing the COP problem in aircraft but not for other applications.