Controlling Dual A/C Packs

[tfhastie]

The company I work for is developing a cargo conversion kit for an existing twin turbo-prop commuter aircraft. I’m working on the air conditioning modifications that we’ll need to perform to provide ventilation control to the Class E cargo compartment, and conditioned fresh air to the cockpit.

The existing aircraft has dual air conditioning packs with the right pack delivering air to the passenger cabin, and the left pack providing air to the cockpit. The existing aircraft also has a temperature sensor in the cabin area and a second one in the cockpit. A separate temperature controller is provided for each pack. In automatic mode the temperature controller compares the current temperature from the applicable temperature sensor with the commanded temperature on the temperature control knob, and operates the air conditioning pack Temperature Control Valve as required to reach the selected temperature.

In the new system we want to use both packs to provide air to the cockpit with a small secondary duct to deliver a small amount of air to the cargo area. My question is regarding the automatic temperature control of the two packs in our new cargo aircraft. Both packs will now be feeding into the relatively small cockpit area. I would simply relocate the cabin temperature sensor to the cockpit, except I want to ensure that the packs don’t ‘fight’ each other during automatic control mode. (i.e. one pack goes full hot while the other pack goes full cold). Does anyone know if there is a standard way of controlling two air conditioning packs to a single small area? I have access to the maintenance manuals for quite a few different aircraft here at work. Does anyone know of any existing aircraft that use this type of system that I could adapt? Am I worried about something that isn't even going to be a factor?

Any help would be appreciated.

Regards,

Tom

 

[Sparweb]

Is one A/C pack sufficient to cool the flight deck? If so, do away with the second entirely. Save weight, save maintenance!

Taking the heating system out of a Twin Otter when it flies in the tropics saves 40 pounds!


STF

 

[davidjh]

See 737 Combi manuals?

 

[Icey]

Why don't you use the standard method of pack control by using trim air valves to mix hot air into the air conditioning pack flow outlet to the flight deck. With this system which are usually present on large aircrafts, you have a pack setting which is standard and the trim air valves which provide hot air would be regulated to allow for temperature variations.

 

[graemew]

Do not use 2 packs to feed the cockpit if the cabin pack recirc air inlet draws air from down the back. In the event of a fire you will be feeding smoke into the cockpit.
I like the notion of taking one out.
If you want the redundancy that using 2 units will confer, then use only one temp control in the cockpit to drive both units. This will prevent unacceptable feedback causing problems. You may need to check the rating of the single control to ensure that it can operate both and you will need sensors located to detect which unit is not operating optimally so that it can be deselected as required. Watch your valving so that you do not get back-flow into the inoperative unit (it should be inherant in the unit, but check its operation anyway ).
You will need to supply cargo compt air from both units to create a balanced load on the units I believe, otherwise one will always be working harder than the other. This will be a lot easier than trying to balance airloads to 2 different sources by other means.
Regards