Air Conditioning Sys

[Guest lou ross]

After reading this section of the manual several times, I am a little confused. Is it correct that the desired, or auto set temperature is maintained by adding warm to to the coldest zone?thanks,

[Guest D17S]

That's the way I've understood it too. So, if any 2 packs fail, the remaining pack must be able to provide conditioned air to the entire airplane. If this is the case (and how could it not be?), then all the packs can provide air into all of the distribution manifolds.So far so good? (Sounds basically OK to me). If all the packs are basically blowing into the same manifold, then their output temperature is going to be basically averaged. One hot pack and one cold pack would output warm air. But since all the pack's airflows are being combined (more or less) in the airplane's distribution manifolds, all the different areas in the airplane would be getting the same temperature air (- - more or less). But some like it hot and some like it cold. What to do? We have lots of naturally occuring, pressurized hot air available (hey, from the engines!). We can use that to heat things up if we need to. So how about this as a strategy? Let's run all the packs at the temperature the coldest zone wants. That will get them cooled down with pressurized air. Then for those that want it a bit warmer, let's mix in hot engine bleed air (called "Trim Air") downstream from the main manifold right where the conditioned air is just about to blow into a particular zone. That will get it warm in there, for sure. That way we can get any temperature air to any zone. Well that's the way I'd design it anyway. (Although, I think Boeing beat me to it.)That's basic system ops, but now a question of my own. On the -400s . . . where are the temp controls? I want a knob to spin so I can control the temp for each zone individually. Are they still around, somewhere? In my old 747-1/200s there's a full square foot of dials and knobs for the ECS. I have all of the zone temp controls (i.e., the trim air valves) on the FE panel and I can watch the trim air valves move. Then I can see the zone duct 'feeds' vs the resulting compartment temps. I can look at mix valve positions and the resulting individual pack outlet temps. I can even look at the heat exchangers inlet and outlet door positions. Everything can be driven manually. It's paradise for a troubleshooter . . . and what kept that FE in a job for many years. Boy what a difference a couple of dash numbers make. The -400 the EICAS ECS screen shows virtually nothing. From what I can see, it looks like all the cabin zone temps select with that that single 'main' cabin temp control on the overhead. So, the entire airplane can only be controlled at one temp? Really? That's just hard to believe. The overhead has pack switches. That's OK, but like I was observing, there is only 1 temp control for the entire rest of the airplane (other than the cockpit 'zone'). What's up with that? Did they give zone control to the FAs? Do they have temp control panels down stairs? Gotta be. But if so, what

[Guest ColdBear]

Sam,The master temp for cabin and cockpit is on the overhead panel. By door 1L there is an individual zone control which gives the FA's about +/-2C.Martin

[Guest lou ross]

Thanks for the confirmation!

[Guest D17S]

Me too. Appreciate the feed back. (Thought there HAD to be something else going on.)We're on a roll. How about some more details. I see the master temp control on the over head has "Auto" at 12:00 and "Manual" at 6:00. I've never touched this particular knob, but it looks like a pretty standard control. Other similar controls use the top 8:00 to 4:00 rotation to set a higher or lower temp for whatever its controlling. The switch snaps over to a spring centered 6:00 position when the control is rotated beyond the 8:00 or 4:00 position. Then the pilot can hold the control up toward the 8:00 or 4:00 position to control a gizmo manually (valve position, pack temp, whatever). If you look at the model's graphic, the "Manual" nomenclature is at the control's 6:00 position. This suggests the kind of operation just previously described. It appears this is a pilot controllable way to directly control ACM outlet temps. Sounds great in theory, but is this actually how the system works on a 747-400? Just as a couple of 'for instances': On 747-1/200s, pack outlet temps can not be manually controlled. However pack outlet temps can be directly controlled (manual or auto) on those old ACM upgraded DC-8s. So it could go either way. Just curious because: The model does not allow these main temp controls to rotate to 6:00. Our discussion so far, the nomenclatures around the controls and this resulting "Ops theory" suggests that they should snap over to 6:00 and allow manual pack temp control. Really, this is purely a question though. I really don't know how they set up this ECS on these new fangled -400s. But let's find out!

[Guest ColdBear]

With the temp in auto the system automaticly compensate for temperature changes as cabin air humidity and passenger activity decrease during flight. The target temp slowly increases doing the ealy part of the flight. And vica verca doing decent.With the main temp controller in ALTN/MAN:

[Guest D17S]

Excellent, that makes perfect sense. Almost there: So, are we thinking that the temp control switches should snap over to 6:00 to get into the Alt/Manual mode (and then any switch rotation from the normal

[Qavion 19]

There seems to be a lot of confusion here....During normal AUTO ops the temperature is sensed in each cabin zone and the hottest zone temp is compared to the target temperature (i.e the target set on the overhead panel with the rotary switch). The hottest zone is the one which requires the most cooling. All packs will be commanded to provide cold air to get this zone down to the target temperature. Unfortunately, as a result, the other zones which are sensed to be colder will be getting air from the packs which is too cold for these zones. This means that heat will have to be added to these zones in various amounts (from the hot bleed air manifold).In ALTN (Cabin Temp) mode, at the 6 oclock position this system is bypassed. The Packs are simply made to output air which will produce an average zone temperature of 24degC (75F).Edit: Seems that the graphics are wrong on the overhead panel with regard to this function... I'll mention this to the PMDG team and see if this can be changed ;)In MAN (Cockpit Temp) mode, as you say, the 6 o'clock position is spring loaded... and the flight deck hot trim air valve can be opened and closed manually to add heat in various amounts to the cold air coming from the packs.During the flight, the humidity in the cabin will decrease dramatically. In cruise (only) the temperature in the cabin is slowly ramped upwards (only by a few degrees). This makes people perspire a little more than they usually do... I guess this provides people with their own micro-environment, humidification system. When either this system or the purser control system is active, you may see ECS Synoptic individual zone temperatures vary from the Master temperature setting. Hope this makes sense.Cheers.Q.