Ducted Air

[switz]

In a home forced air system, the duct work starts large at the discharge of the air handler and gets smaller as one gets to the end of the line. It does the reverse on the return side. We then had adjustable registers at each outlet and an airflow gage to balance the airflow in each room. The returns were always wide open.

I am a little dusty on this, but one ton of air conditioning (12,000 BTU) needed about 400 cfm (cubic feet per minute) of air flow to keep the coil from frosting. Thus the analogy would be that the 13,500 BTU small AC in dual systems needs to move 450 cfm and the larger 15,000 BTU unit needs to move 500 cfm. Thus the noise associated with the fan moving that much air.

To save costs, I would imagine that Airstream does the same thing they do with the furnace and runs the same size duct all the way on the run. The best way to try and balance the air flow is with adjustable flow registers.

Our unit came with squashed crossed ducting (I photoed that defect on the assembly line when the kitchen cabinet was placed on top of the ducting during the assembly). The factory never must not have checked for airflow from all the registers. Our first trial trip there was no heat into the rear of the trailer. I showed the photo to the dealer and they were able to uncross the ducting without removing the cabinet . Amazing, there was air flow to the bedroom.

I would be concerned that early models might have issues with the duct installation....

[ghaynes755]

Last trip at the factory I talked with the duct installer. Ducts are very basic and what I saw match what is depicted in the drawing.

As I remember the long ducts are the same size in cross section. A guess would be about 2 inches high and 5 inches wide. Looking at the diagram it would make sense that the back would 'blow' harder than the front since there isn't much of the long ducts to the back of the AC unit to the end of the run as compared to the front one. At least in the drawing. May be different based on the various layouts of AC units and their placement on the different lengths of trailers.

[mefly2]

The metal ducts on our single AC unit are the same size front to rear - I would not expect otherwise on a less than 25' overall run; The actual heat pump is near the middle of the trailer. Furnace ducting is different as it incorporates variable sizes of flex ducting running under and near the floor.

You can see the upper ducts when you remove the louvers and they appear to be uniform front to back. The louver vanes may be bent slightly to impart directionality and best distribute the air...also may be installed with the vanes pointing 180 degrees from the original position; however, it is likely that bending / unbending would eventually damage the louvers. So, an external deflector (sold for under $5 at local hardware stores) attached with velcro or magnets might be a better solution. We have done just that with the rotating furnace louvers in the galley under the Eddie Bauer folding seats (magnets recessed into the wood allows for air flow control) but are quite happy with our current ducted air conditioning as engineered and delivered by AS.

[switz]

Too much of a rectangle which makes for a thin duct can cause air cavitation at the thin edges. The most efficient duct work design is round followed by square. I vaguely remember the ratio of 2 to 1 being the suggested profile.

The thin design could have too much resistance and the extreme ends farthest from the fan could have less flow.

Neat concept.

[LaBigDogs]

A couple of weeks ago my front unit (Zone 1 on my 2015 27fb) dropped out of service as it does not cool or heat the air any longer, therefore I leave it off until replacement. Last evening before I went to sleep I placed (Zone 2) on Auto and selected the interior temp of 65° as the low was forecast to be right at freezing by sunrise. I woke up this morning and moved the thermostat up to 71°. The outside air temp is 33.4° and the heat pump is still blowing very hot air, and it only took less than 10 mins to warm the cabin to 71° with the HP only. (Note Zone 2 has the option of Furnace, so when it gets very cold when AUTO selected the HP should drop out and the furnace take over.)

Non-Ducted, the contrast on my 2011 25fb with one only AC/HP I would select Auto on a cold night and the HP would run consistently trying to keep up, and never could, I could hear it going into defrost and then turn back on attempting to keep the cabin temperature at the selected temp but it never could. Then when the out side air temp would reach about 35°, when AUTO was selected the HP would drop out and the furnace would kick in and it would quickly raise the interior temp to the selected temp on the thermostat. On my new dual zone thermostat, it no longer has a button to get the exterior temp.

My question, does AUTO still switch over to furnace when the HP cannot extract any more heat from the air, or at 32°?

[KJRitchie]

Can anyone take a short video in their ducted AS with the AC off and then on so we can hopefully hear the difference?. Since its winter run the heat pump. It should be similar to AC operation.

Kelvin

[mefly2]

Originally Posted by KJRitchie

Can anyone take a short video in their ducted AS with the AC off and then on so we can hopefully hear the difference?. Since its winter run the heat pump. It should be similar to AC operation.

Kelvin

It is now below zero F outside; so no can do with regards to the HP at this time, but check my earlier posts in this thread; that "hearable difference" is exactly what I posted ... not sure of the post number - but a video with the same device recording from the same position in the same model - just that the first video and stats was a 2013 EB without ducted air and the second was a 2015 EB with ducted air.

Originally Posted by LaBigDogs

... Last evening before I went to sleep I placed (Zone 2) on Auto and selected the interior temp of 65° as the low was forecast to be right at freezing by sunrise. I woke up this morning and moved the thermostat up to 71°. The outside air temp is 33.4° and the heat pump is still blowing very hot air, and it only took less than 10 mins to warm the cabin to 71° with the HP only. ...

Be reminded -IIRC- that AS (and others) warn to not use the heat pump when the ambient temperatures are expected to be 40 F or below.

[graysailor]

Off subject a little but I could not find the refrigerator fan for my 2015 30' Cloud. The dealer said that the new models do not require a fan. I have not played with my trailer yet so have not had the opportunity to look around. Does anyone know if this is true???

[mefly2]

Suggest a more appropriate thread.
Meanwhile ... Read the Manual ... the fans vary from year to year and model and length but I would think that your dealer would be a good source of info for what you just purchased ... my wife enjoys reading the manual to me .... back to ducted air now.

[cory_can]

Someone posted this in another thread and I figured other ducted air owners would be interested in seeing it. They were shown in a new "2015" Classic Twin model video. Looks like a retrofit could be easy.



Directional vents that also allow you to close.

[ghaynes755]

Also it looks like they are mounted on some type of flex tube. In the video you can see the one he touches moving around and the rings on the one in the foreground.

[LaBigDogs]

After 4 trips - outside air temperature ranging from 85° to 32°. My Ducted Air system works flawless .... Directional vents are unnecessary. Air is distributed throughout the cabin in perfect harmony, the temperature is constant from the head to the tail. So if the temp is not right, I just adjust the thermostat. Anyway... this works for us.

[mefly2]

Originally Posted by LaBigDogs

After 4 trips - outside air temperature ranging from 85° to 32°. My Ducted Air system works flawless .... Directional vents are unnecessary. Air is distributed throughout the cabin in perfect harmony, the temperature is constant from the head to the tail. So if the temp is not right, I just adjust the thermostat. Anyway... this works for us.

Completely agree ... as I have advocated for the ducted air all along ......since last July ! It was the reason we traded in a 2013 EB to get the ducted on the 2015 EB - everything else is exactly the same ...

[SCOTTinNJ]

Originally Posted by ghaynes755

Moms does this drawing help?

Attachment 229388

I'm considering a 30' Bunk with the ducted air. Looking at the attachment, it seems that both AC units are connected to all of the ductwork in the trailer? So if one unit is on it blows throughout and if the second unit is fired up it only supplements?

Also, does anyone have a 30' bunk with the ducted air? I see two air ducts directly over the bunk. Is that problematic? Do they blow too much? I suppose they could be blocked off a bit but just wondering.

[ghaynes755]

The ducts, there are two long tubes from front to back on either side of the trailer, are one long run. So your comments about what happens is correct.

The latest Classic model now has outlets that can be shut off and swiveled for direction. Wonder if that will trickle down to the rest of the line or be something that could be retro fitted?

[2012FB]

Originally Posted by lewster

Just another example of Airstream 'paddling against the tide' from the rest of the RV industry! They use a single A/C gasket now when using the Dometic aux. drip kit when the specification from Dometic is for TWO gaskets! This raises the drip cups off the roof so the DON'T RATTLE and are not sandwiched between the roof and the base pan of the A/C unit.

Funny, how everyone else in the industry has no problems with the drains of their A/C units........except Airstream!

Lew,

I did notice that zone 2 has a pretty good rattle (low frequency noise) on HP startup and a decent vibration (higher frequency noise) when running. I actually started pressing up against the interior roof in various places and finally got the vibration noise to settle down audibly but you could still feel it.

Given the apparent tendency for the units to leak and rattle due to the new drain design (1 gasket, small drain cups), is this something I should complain about hoping that Airstream will remedy it or should I order the old style pan and gasket(s) and have them changed out as switz did? Is this a big deal and/or does it potentially open a can or worms if not done correctly by the dealer?

Or perhaps I should argue that it needs two gaskets per the manufacturer period, though in the past on similar "non-compliance with manufactures' specifications" it has never gotten me any where at all.

ANY OTHERS WITH LEAKS AND/OR RATTLES??

I have it scheduled for service Feb 2nd so maybe I should bring it back to the shop and see if I can get the startup rattle and running noise recorded on my iPhone and then send it off to Airstream and review with the dealer.

I did the RV550 swap out myself in order to insure it was done correctly but not sure about getting on the roof and man handling the AC units.

Follow up to other thread comments, the Dual AC ducted air is a significant improvement over the single AC non-ducted in my 2012 25FB. Overall it is significantly quieter, heats and cools better/quicker (even only running 1 zone), the heat/cool is more evenly distributed and the interior of the roof is cooler in direct sun. It was a significant factor in our trading up and is well worth the increase in cost.

Thanks!

[lewster]

Originally Posted by 2012FB

Lew,

I did notice that zone 2 has a pretty good rattle (low frequency noise) on HP startup and a decent vibration (higher frequency noise) when running. I actually started pressing up against the interior roof in various places and finally got the vibration noise to settle down audibly but you could still feel it.

Given the apparent tendency for the units to leak and rattle due to the new drain design (1 gasket, small drain cups), is this something I should complain about hoping that Airstream will remedy it or should I order the old style pan and gasket(s) and have them changed out as switz did? Is this a big deal and/or does it potentially open a can or worms if not done correctly by the dealer?

Or perhaps I should argue that it needs two gaskets per the manufacturer period, though in the past on similar "non-compliance with manufactures' specifications" it has never gotten me any where at all.

ANY OTHERS WITH LEAKS AND/OR RATTLES??

I have it scheduled for service Feb 2nd so maybe I should bring it back to the shop and see if I can get the startup rattle and running noise recorded on my iPhone and then send it off to Airstream and review with the dealer.

I did the RV550 swap out myself in order to insure it was done correctly but not sure about getting on the roof and man handling the AC units.

Follow up to other thread comments, the Dual AC ducted air is a significant improvement over the single AC non-ducted in my 2012 25FB. Overall it is significantly quieter, heats and cools better/quicker (even only running 1 zone), the heat/cool is more evenly distributed and the interior of the roof is cooler in direct sun. It was a significant factor in our trading up and is well worth the increase in cost.

Thanks!

Leaks and rattles caused by the use of a single A/C gasket will disappear when a second gasket is used AS DOMETIC SPECIFIES!!!!!!

Once the roof A/C gasket has been compressed from mounting, you will need to remove the original gasket and replace with a new gasket and then add the auxiliary drain kit with it's catch cups, included drain line, second gasket and additional solid foam blocking. The instructions are very specific and easy to use! Remember, that the recommended compression of the gaskets is 50% of original thickness.

To get a good seal at the outer edges of the A/C unit, you will need to actually exceed this at the center of the A/C unit, but it will work regardless, as I have never had a leak using this mounting method. Just finished replacing 2 roof units in an old Bluebird Wanderlodge that had more roof curvature than Airstream trailers have, and the water hose test after installation, along with the torrential downpour 3 days later showed not a drop of leakage to the interior of the bus.

I would not count on the factory doing this for you. It is fairly easy once you remove the unit from the roof and turn in on its top (use a heavy moving blanket as a cushion). This will give you perfect access to the bottom of the A/C unit to remove the old gasket, apply the new ones and then install the drain kit.

[2012FB]

Lew,

Thank you very much for the quick reply. So you would recommend sticking with the current plastic cup design reinstalled properly using the two gaskets over the older style pan and thicker gasket.

No issues with the plastic cups?

Would you have a link handy for the installation instructions?

[lewster]

Hi FB,

I don't, as I have done so many that it is almost a reflex action by now.

You might check on the Dometic USA web site to see if they are posted there.

Many other RV manufacturers have been using those drip cups for years with no issues.


Lew Farber
RVIA/RVDA Nationally Certified Master Tech
Master Tech Energy Systems, Inc.
AM Solar Certified Installation Center
Lifeline Batteries**Magnum Inverters
541-490-6357

[Endodoc]

Do the ducted air models have any inside access to the AC units for maintenance issues?