I am MSC student of mechanical engineering and my project is about ACM machine. I have read something about various systems of air conditioning system in aircrafts;

  1. simple system
  2. boot strap
  3. reduced ambient temperature
  4. regenerative system
  5. boot strap with evaporator
  6. simple system with evaporator

I just know that reduced ambient temperature is for supersonic aircraft.I don't know other systems applications.For example, when is a regenerative system used and when boot strap is used?

Are all of the possible air conditioning systems exists in every aircraft and switch to another depending on flight condition?


1 Answer 1


Really not sure what you're asking, nor do I know what these terms you've found mean, so let's start with these drawings and see where we end up.

DC-9 Bleed air enters from the engine (or APU) at bottom left of this drawing and enters the primary heat exchanger. Then it enters the compressor in the ACM and then on to the secondary heat exchanger. From here it enters the turbine and this is the point that the heat loss occurs and cold air enters the water separator and then the cabin of the airplane.

Note the anti-ice screen and the pack anti-ice valve which adds a little heat if the air exiting the turbine is too cold and is causing ice.

The water separator is a cone-shaped cage with a heavy cotton bag over it. This collects condensation in the air and dumps it on to the face of the secondary heat exchanger to cool and improve it's efficiency.

Temperature in the cabin is controlled by the temperature control valve on the left side of the drawing.


737 This system is very similar to the DC-9 and really the main difference is that the pack anti-ice valve here is operated electrically, while on the DC-9 it is done mechanically with a pneumatically operated valve.


757/767 This is a much different system, many more electrical sensors and control. The pack cooling fan is an integral part of the ACM, where on the other two systems they are separate components. The water separators are much more advanced and don't require regular maintenance like on the other systems.


As you can see, these three systems are all basically the same with the only real difference being how they are controlled and some of the ancillary components.

  • $\begingroup$ thanks alot for ur answer.in this link there is different types of aircraft refrigeration system and its basic consepts my question was originated from this book. books.google.com/… $\endgroup$
    – ghlam
    Commented May 29, 2015 at 17:18
  • $\begingroup$ You're welcome. Thanks for the link. It seems then that these 3 systems are 'Bootstrap'. The text in the link says a bootstrap can't be used on the ground, however, each of these systems has a cooling fan in the ram ducting so that they can be used on the ground. The DC-9 and 727 use electric fans, the 737 has a pneumatic fan and the 757/767 has a fan driven by the ACM itself. $\endgroup$ Commented May 29, 2015 at 17:28
  • $\begingroup$ yes.im curious to know when regenerative cooling or simple system with evaporator is applicable? it is mentioned for supersonic flights ram air isnt usefull solely and there should be external turbine to cool the ram air for heat exchanger .my professor offer me to search about this topic(acm machines systems in aircrafts) and ask me to propose him detailed subject about it to work on it as my thesis .i generally know something but not in detaild. im wondering if you give me detailed subject to work on it as my thesis .thanks again $\endgroup$
    – ghlam
    Commented May 29, 2015 at 17:47
  • $\begingroup$ in this book there is more detailed information books.google.nl/… $\endgroup$
    – ghlam
    Commented May 29, 2015 at 17:51
  • 1
    $\begingroup$ Sorry ghlam, I don't know why you would choose one type of system over another. As for supoersonic maybe something at this site might help. heritageconcorde.com/#!concorde-air-conditioning-group-descript/… Reading over the description it all sounds pretty standard and not overly exotic. $\endgroup$ Commented Jun 1, 2015 at 16:01

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