2 or 4 window ac units out the back?

[basil]

I have a big bus with lots of windows I really want to keep, and i need an AC solution.  I have been seriously thinking about putting 2 or even 4 big window units through the back cap as an alternative to roof airs.  I used 28,000 btu Frigidaire units in my apartment, they seem to work well, and at $500 each it doesn't really matter if one fails after a few years.  They slide out of their sleeves, so I am thinking about constructing a steel framework to hold the sleeves in a 2x2 grid and then inserting the ACs.  3 or 4 inches separation top and sides should leave enough room for air flow to the chassis vents.  They would stick about 18 inches out the back.  The cold air output is horizontal on the top front of the unit, so I might duct the top two along the ceiling with a wide thin duct to get closer to the center of the bus.  The bottom two I might duct to the side for a foot or two to get around an eventual back closet.  I'd cool the front of the bus with a beefed up driver's air system.  (I'm even thinking about two through-the-wall LG units mounted crosswise in the front cap venting out the side of the bus, instead of normal driver's air.)

My rooftop alternative is probably 5 or 6 roof airs.  I was able to mount two low profile roof airs nicely side by side on another Eagle, and they don't look bad that way, so I could do 3 rows of 2.  However, they are noisy and don't seem to cool at their rated level, adding credence to the opinion of some board members that for realistic operating conditions they are conspiratorially over rated by the industry.

Does this sound like a crazy idea?  It seems to me for the same work to cut and reinforce 5 or 6 roof holes and get 6 tons, more realistically 4 tons of noisy roof ac I can have over 9 tons out back for half the cost and equal or less work.

I appreciate your thoughts.

[tekebird]

IMHO it would work but likely look like  hillbilly.

if you buy good roof airs two will keep your bus plently cool threee if your really worried about it on a 40 footer

[makemineatwostroke]

2 roof airs will not keep a 40ft bus cool  ( maybe Canada )with the factory windows I have 4 15,000 BTU penguins on a 45 footer and a hot day in AZ or Nev it takes 3 running and they work hard and my bus is spray foamed even under the floors and I have 8 dual pane in motion windows

[Ednj]

Lets stur things up 
Guess he is still at it 
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5. What is Walker A/C? ( Patent Pending, No images at this time )
The Walker Air Conditioning system is a very simple 3 zone, 3 120 V 18,000 BTU A/C systems. These units are mounted on a shelf inside the back of the bedroom area inside the rear fiberglass cap. Nothing is protruding through the roof or the rear of the coach. Units mounted in this fashion give you almost 5 tons of air conditioning, yet can be zone controlled for each area. However, this type of system mainly works with a raised roof coach. The duct work would be running through the ceiling.

[HighTechRedneck]

Basil, that is basically what I described I am thinking of doing on my RTS in another thread.  On the RTS it has a louvered rear cap and a roof top inlet vent because that is where the huge original AC condenser is mounted.  So mine wouldn't even show through.  You might consider adding something like that and keeping them inside it.  I am planning to stick with 15K units because they are 120v and the total power needs fit within a 50 amp shore hookup and still leaves power for the rest of the house needs.

In terms of capacity, my RTS came with a 10 ton AC capacity.  That was designed to keep it cool inside with 47 people, minimal insualtion, and the doors opening frequently.  Now my bus is well insulated, typically only has 2 people in it and the door opens only when needed.  3 15K units will give 4.5 tons and be very adequate under these conditions.

[HighTechRedneck]

Lets stur things up 
Guess he is still at it 
>
>
5. What is Walker A/C? ( Patent Pending, No images at this time )
The Walker Air Conditioning system is a very simple 3 zone, 3 120 V 18,000 BTU A/C systems. These units are mounted on a shelf inside the back of the bedroom area inside the rear fiberglass cap. Nothing is protruding through the roof or the rear of the coach. Units mounted in this fashion give you almost 5 tons of air conditioning, yet can be zone controlled for each area. However, this type of system mainly works with a raised roof coach. The duct work would be running through the ceiling.

Ok, the Walker system won't work as shown.  Anybody want to guess why?

[Lin]

I suppose you could do the out-the-back system and cover the units that are sticking out with a facade or a grill.  You could also run your ducting on the roof and cosmetically cover that also.  In that case, it could be some sort of sheet metal or fiberglass solution and not be near the effort of raising the roof.

[DMoedave]

our bus had a house unit sticking out the back bedroom but inside the rear cap into the radiator compartment. It worked but the condensation drips have to be addressed,

[tekebird]

my 04 had2 30 year old roof airs that kept it cool in S Cal and it hadd ALL it's original bus windows single pane.

Can't immagine that another 200or so Cu Ft would add to much cooling difficulty espacially if you had efficient glass

[TomC]

The three units shown are too close to each other, plus 15,000btu is really the high end extent of 120vac cooling.
If you want to do that kind of cooling, you should get a through the wall unit where most of the unit is inside and the outside grill is flush with the outside wall.  I don't like this idea though of having two or three units in the back of the bus with all the associated noise when you're trying to sleep.
I have 2.25" of sprayed insulation, Peninsula single pane lightly tinted glass and I cool my bus with 2-13,500btu (Colemans) up to 100 degrees, and kick in the third over 100.
Doing some research there are 15,000btu basement units for RV use where the condenser air is intaked through the side of the bus then blown out the bottom of the floor, for $900 each. Personally would use these over any window unit since they are designed for basement use.  If I were to do anything, there are some of the roof tops that can be converted to basement units-like the Duotherm Penquin since it has a squirrel cage blower for the condenser; the low profile Carrier and low profile Colemans since they have top mounted exhaust fans for the condenser that can be ducted.  Use the roof tops that are designed for ducting since they have stronger fans, and remote mounted thermostats.  Good Luck, TomC

[basil]

Wow, thanks for all of the comments....a few details

- bay space is mostly committed so basement air will be tough for me
- at 45' with raised roof and all the original windows even the 9 ton otr seems to have a tough time keeping up when it is hot on the road....replacing all the windows or foaming the interior seems to work out to being way more expensive and time consuming than just overprovisioning AC to solve the problem
- bathroom is in the rear, then bedroom next forward, so I am thinking that my bathroom and the 6 foot roof duct to the bedroom will kill some of the noise
- I was thinking about some sort of nice decoration around the rear ACs that would make the four units look - more like one single 'backpack' type of device, maybe even make the whole thing look like some sort of rocket exhaust, or at least less hillbilly.  I hear you about possibly putting them fully inside the rear cap with some venting, but it seems like the decorating effort to make the external part look nice is worth not losing at least two feet of space inside.
- I expect 220v generator power or 50a 220v campground power so feel comfortable going out of the 120v envelope.  I would never be able to come close to cooling it on 120v anyway, i'd need half a dozen circuits from different campground spots or neighbors houses.

Some followup questions for the board....

- I'll research the Walker system.  Any idea of cost?

- Does anyone know of any other packaged unit or more commercial AC system that might hang nicely off of a rear cap?

- Also, if you have a link for the $900 basement units I'd like to take a closer look at the size.

- I see the condensation drip issue if the bus is not level.  I wonder how much outward tilt would allow them to still operate but maximize the likelihood of condensate not coming into the bus?  I suppose I could also put a bunch of holes in the bottom of the removable chassis.

- The external ducting idea I had not thought of.  Are you familiar with any insulated, flat wide ducting product that could be used?

- My remaining question is whether there might be a high failure rate on the residential units bouncing around on the road?  I would expect only 5000 miles or so per year, so it is not heavy use.

[HighTechRedneck]

- I expect 220v generator power or 50a 220v campground power so feel comfortable going out of the 120v envelope.  I would never be able to come close to cooling it on 120v anyway, i'd need half a dozen circuits from different campground spots or neighbors houses.

Be sure to check into the amp rating of the units you are looking at.  Looking at Home Depot's online specs, a 24000btu unit draws 13.2 amps (240v).  Four of those would exceed the capacity of 50amp shore power.  3 combined with other household usage may exceed it even.  A 14KW genertor could handle 4 of them as long as they were controlled not to all start at the same time, but at quite a cost for fuel.  Two 28000btu units would be almost equal to 4 15K roof units.  Rarely do you see more than 4 roof units on a bus.

- at 45' with raised roof and all the original windows even the 9 ton otr seems to have a tough time keeping up when it is hot on the road ...

If a 9 ton OTR AC designed to keep 53+ passengers cool, with all the windows, is struggling without the body heat load (about 28000btu of heat), then I suspect it is low on refrigerant or otherwise failing.

[JohnEd]

Teke,

I am with you.   My old roof unit kept my S&S 30 footer chilled with 95 ambient.  Had two roof units but never turned both on at the same time.  Stock glass but the roof has 4 inches of "extra" polyiso board added to it plus FG stuffed in all the cracks and spray foam all around.   That is 6 inches of foam in the center and that tapers to 4 at the edge.   But, the AC worked really well when I had only two inches in the roof before it sagged and I had to build another roof on top of the roof.   I wouldn't contradict anybody but 4 AC units and they struggle?   That would frost my butt.

John