Ducted AC?- Crazy idea?

[Skatiero]

Awesome-- this kind of sytem intrigues me! Please let us know what you end up doing!!!

[Wingeezer]

One thing I would wonder about would be the suitability of teh fan to work into a duct system as opposed to more or less free discharge.

I don't have any experience in this directly but from an engineering background, I know that fans that are designed to work into virtually zero resistance such as found in a conventional roof/window air conditioner may not be so well-suited to feeding a duct system with its inherent resistance.

You may not move nearly as much air and overall effectiveness might suffer somewhat.

I guess the only practical way to know is to try it!

Brian.

[soldiermedic]

Uwe did a nice job running duct work from a residential unit to two different areas in his 63 Overlander.

[jm2]

Originally Posted by Skatiero

An Easy HVAC Retrofit for Old Houses - Old-House Online

YMMV-- no idea if it could be adapted for trailer use-- just thought I would put it out there!!!

Icocbw, but I think that the smallest airhandlers for Unico and Spacepak systems are 2 tons, or 24,000 Btuh vs. our TT units that commonly range from 11,000 to 13,500 to 15,000 Btuh.

oversizing AC equipment by 70 to 80% is usually not an effective solution....

ymmv.

[vswingfield]

Originally Posted by jm2

Icocbw, but I think that the smallest airhandlers for Unico and Spacepak systems are 2 tons, or 24,000 Btuh vs. our TT units that commonly range from 11,000 to 13,500 to 15,000 Btuh.

oversizing AC equipment by 70 to 80% is usually not an effective solution....

ymmv.

My guess would be that 24,000 Btu would probably be about right for my Excella. It might still even be a little small.

Sight unseen, I think Smokeless Joe's split unit is the most elegant solution. Running coolant takes much less room than moving chilled air. These designs are reputed to be very quiet, too. You would still need fans to move the air around inside, but an Endless Breeze or two should do just fine.

[TouringDan]

I am a home inspector, so I am familiar with split system heat pumps. They are used where you can not have duct work. Most have a single zone, but some have two or three zones. The advantages are no duct work, reasonably quiet with inside unit sound levels of 22-38 dba and very efficient with 18 Seer efficiency rating.

However one of my favorite sayings is new solutions have new problems. The system I found is made by Mitsubishi. It is 18,000 btu/hr, costs about $2,500 for materials and weighs about 175 lbs. Two inside zones each with dimensions of 30x11x8" (pretty large). Compressors require 240v not 120v. There will need to be 4 penetrations through the Airstream shell for the refrigerant lines.

For me right now, I will stick with my propane furnace, that works fine, and my Armstrong airconditioner, that also works fine, even though it is a little loud and vibrates more than I like- This motivates me to open the windows and turn on the Endless Breeze fans if it is not too hot, so I don't have to listen to the noisy air conditioner. My first option would be to go after a quiet efficient new air conditioner and just run it on low.

Dan

Dan

[Aerowood]

Check out this site as they carry a huge quantity of mobile air conditioning components.

Danhard Inc Mobile HVAC components and systems

[nvestysly]

Originally Posted by Aerowood

Check out this site as they carry a huge quantity of mobile air conditioning components.

Danhard Inc Mobile HVAC components and systems

A system with components like this may work well. Although I'm not sure if they solve the noise problem. There's nothing that says the condenser and evaporator has to be on the roof of the trailer. Leave the condenser up there if it makes sense and put two or three evaporators around the trailer where needed. I don't know exactly how to plumb this but I'm sure Danhard knows. They could design a system that will be much more effective and hopefully less noisy than a unit that drowns out everything while it's running. Are you listening Airstream?

Back to the ducted idea for a minute. I was thinking of the high velocity units when I chimed in above in support of ducted systems. I don't think simply running duct from an A/C unit to several output locations is the best solution. Yes, it is a solution but probably not the best solution.

I've seen the high velocity systems installed in homes and think they work well. I haven't studied the system to know how it works but the fan is obviously different than a traditional roof mounted unit. The system simply needs to be scaled down to accomodate an RV.

I'm sure the high velocity fan could be put in a cabinet or in the belly pan and make a fantastic improvement over the archaic roof mounted/roof blower system Airstream uses now. Yeah, I know the roof mounted system works but what happened to the thought Airstream espouses - we only make improvements, not changes. Guess Airstream doesn't think the A/C system needs to be improved.

Lucius

[Melody Ranch]

These are the folks I use for special applications.AAP - Providing Power, Comfort and Control Systems for Motorcoaches, Trucks, Specialty Vehicles, Trailers and Other Demanding Applications Worldwide

[crispyboy]

How does one run the furnace fan to circulate air?

[TouringDan]

Veggie

One of the problems with the mini split 18k btu system I discussed above was the 240v compressor. I don't know if there is a comparable 120v compressor. Also the inside evaporator is too large and takes up too much valuable space in the Airstream. A new evaporator would need to be designed that fit into the floor. I am not sure if enough Airstreams are made each year to justify the expense of designing and manufacturing such a specialized evaporator.

Crispyboy

If I set my furnace thermostat to call for heat and then not light the pilot light, the furnace fan will run. Your thermostat may have a fan only setting like in most homes with forced air heating and air conditioning systems.

Dan

[VeggieBullet]

hmmmm
after all it seems like the Amstrong wouldn't be able to handle the ducted system.
But it also seems to be doable with either a split system or the one designed for truckers.
We were always amazed about how well the units for the Sleeper's in the trucks works and that may be a way to go but not sure if that would cover the whole Trailer.
Does anyone knows where SmokelessJoe is?

[lcurrie]

Before I bought an AS, I was obsessed with building a Teardrop Trailer and did tons and tons of research and planning. Many of those guys ducted their ACs under their trailers. Can you just reverse that logic? If you've got a top mounted unit, just run the ducts on top. Of course, you'd probably need to insulate the ducts and to keep your AS looking great you'd probably want to build a sexy aluminum box/tube to hold the ducting, but that might be an easier challenge than either running through the ribs.

Lynn

[truckasaurus]

I like the SmokelessJoe split system but some of the split systems used on Semi trucks would seem to be a logical step. Last time I looked you can even buy the kit with pre-charged lines for a very easy installation. The only manufacturer option for an interior installed AC ducted unit I could find was a european model running 240V but it doesn't seem a great leap to figure out a 120V version.

[SmokelessJoe]

Veggie,

I’m still here and my LG split unit is working perfectly too.

Over the years there have been many threads discussing the unsuitability of typical North American RV cooling and heating systems. People object to the big, bulky profile ruining the classic Airstream lines and the noise, among other things.

You may have seen this thread. Details about my solution in post #41:

http://www.airforums.com/forums/f427...tem-60486.html

Dometic, the maker of one of the sleeper cab models is also the major supplier of rooftops to the American RV market. There are probably much better ways to do things but the incentive is missing. Why pioneer new methods when you have the market sewed up?

Detroit thought like this too before the Japanese and Koreans came along. And in technology the RIM Blackberries of the world regularly get taken out by the iPhones.

No such fear in the sleepy RV world, were much has not changed in 50 years or longer.

Just out of interest, this Australian company has a big piece of that market and offers both rooftops and their own version of a split unit, which may interest you.

RV, caravan, marine air conditioning and refrigeration products

In my opinion the truck cab solutions are not nearly as sophisticated as the modern commercial residential split A/C technology. And similar to the attempts here to adapt window type units, they share the same shortcoming: cold air collects along the floor because cool air falls, it doesn’t rise.


Sergei

[VeggieBullet]

Hi Sergei
Thanks for showing up and sharing.
Must to confess that your set up is so far the one that we like the most and the got the search option exhausted
We hope that you don't mind to share some feedback on your AC installation like:
a) Considering the size of your trailer and where the ac split is located how long does it normally takes to cool down the whole trailer when is really really hot?
b) Is the split located in top of the bed? doesn't freeze you guys up and the rest of the trailer is just warm?
c) Is it possible to use your system and also ducted around the AS?
d) is your system 120V or 240V?
We hope that you don't mind but is good to know that there is someone out there that is willing to take a different route and got it done!

[slowmover]

Go into an Airstream - supposedly a premium rig (at least it has a premium price) - and you can't even hold a conversation or listen to the radio or TV. What gives? Is Airstream listening?

Let's not throw out the baby with the bathwater. The current roof A/C units may lack aesthetic and are noisy but they are also simple to install, use and replace. There is no complexity of ducting, refrigerant lines and controls.

An A/S is "supposed" to be lighter weight as well as aerodynamic (however much A/S has gotten away from this), so a trailer most likely to be used in comfortable conditions -- where one wishes to be outside -- is not compatible with the higher principle. The real drawback isn't aesthetic but the worsening of trailer COG with that 90# on the roof (think lever length).

We can make the same argument about the heating system. Why are interior storm windows not standard, or walls not thicker with better insulating values? Cost, complexity, weight, size & reliability.

I'm no fan of these units in dispute (and I much appreciate the links above) but even high end motorhomes like the BLUEBIRD Wanderlodge right through the 1980's used multiple roof units as a highly popular option even though weight & complexity otherwise noted was no real concern. What was a concern was reliablity and service. The alternatives (basement mount) were authorized dealer only units for parts & service. So, even though the basement units (which did not take any relative storage away from a literal bus) were powerful, they weren't as popular as one might think. Or, were later removed and roof units added in their stead.

As I live even farther south than the OP (and in a sub-climate where one can make the argument that it is even hotter) I've no love for the "noise". I turned on my unit (a new 15k Coleman) at 1100 today (and for the past several weeks) and will run it until probably 2000. The temps won't even hit 80F outside, but full sun means A/C use in light of humidity, etc. A second unit is needed (and conversion to 50A service) once summer is underway. OTOH, this unit is powerful enough (fan) to leave no area without airflow. I use a fan to return air to the trailer center from the front lounge.

A friend in the refrigeration business (warehouse unit size) indicates that, IIRC, these 15k unit are about the equivalent of one-ton of A/C. Therefore I wouldn't even hesitate to "oversize" any cooling unit[s]. My concern would be the "amount" of electricity needed. This is where we go from the pretense of being mobile to being tied to utilities for A/C use (short of bigger & bigger generators). The trade-offs need to be considered over just aesthetic or relative sound level.

Great thread. Thanks for links, and look forward to more. Bookmarked.

.

[TouringDan]

Rednax makes some good points. We all would like to have an a/c system that was quiet with good distribution of cold air. It would be nice if it had an Seer of >18 and used propane too, but that is not going to happen. However it still needs to be light, inexpensive, easy to service and reliable. Maybe one partial solution is insulation for the windows, skylights and vents to cut down on the solar heat gain. I would also like to know what is the most efficient and quiet air conditioner in a smaller size. Selecting a smaller size would help in the noise level and also result in it using less energy. Maybe if we insulate the openings in the insulation envelope we can use an 11-13k btu unit instead of a 15k unit. Maybe this would also allow using one smaller generator than two small generators in parallel.

Dan

[VeggieBullet]

Well it seems like the quiet efficient and with a great cold air distribution all over the AS is an utopia....
So far seems like the Split system is the best choice and will probably give the option for the idea of ducting.
Still a lot of questions about the refrigeration for the AS and hope that other members can help as well as SmokelessJoe.

[SmokelessJoe]

Veggie,

Some of your questions might be answered in this post to my main thread; see #673:

http://www.airforums.com/forums/f227...-18448-49.html

I honestly don’t know how much time it takes to cool the trailer down. That would depend on the ambient temperature, of course, but it isn’t long.

The air temperature isn’t consistent all over the trailer. It is understandably colder near the blower head and less so the further you get from there. But the cabin is comfortable and the air movement is SILENT everywhere.

In my case, the AC is usually off for sleeping but if it needed to run all night I’d rather use a blanket than be kept up all night by noise.

I don’t live in a super hot area of the continent so I don’t know for sure how the split would perform there. I’m sure it will be superior to a roof mount.

I think that the biggest problem with air conditioning an Airstream is the trailer itself. They are largely still made the way they were 50 years ago, this despite all the advances in insulation and technology.

So if you are going to gut your trailer you should think about that issue first. If you want to go mini split-air you also need to think about where the outside unit will go.

In my case I was able to mount the compressor on the tongue because I have no LP tanks. I went diesel for heating and cooking.

Unless you are a boondocker you can achieve the same thing by going all-electric. I’ve always thought that an all-electric 12v/120v trailer is a perfectly reasonable solution if you are not boon docking.

You would want a generator for layovers and emergencies.

I don’t think you can modify a split unit to add ducting.

In any case, a ducted system would probably turn out to be even more involved than going split for no real benefit. What you really want in a small space like an Airstream is air movement, not restriction.

They also make mini-splits with dual heads. I’m guessing that something like that would condition your trailer as well as anything might.

Friedrich M24DYF Ductless Mini-Split System - Free Shipping | Sylvane


Finally, whenever you advance a non-traditional idea you will always have nay-sayers coming out to warn you about straying from the so-called path, even when that path leaves a lot to be desired.

Then it is good to remember a Steve Jobs saying: “ Don’t let the noise of others’ opinions drown out your own inner voice.”

Good luck,


Sergei