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Old 10-27-2016, 04:26 PM   #1
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Ducted Roof RV AC

I'm starting the planning of the AC system, Plan is 2 possibly 3 roof mounted ducted AC units, Question I have is do I actually install sheetmetal ducts or do I build up the stringers with furring material to keep a lower profile? How do factory RV's do their ducted systems ?
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Old 10-27-2016, 05:55 PM   #2
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To me a ducted unit is made to push/force air through several dust runs within a structure so a single ducted style unit on the roof that is sleeved straight through to the bus interior to a 4-way throw style of register will way out perform its intended design and last year's longer.
It was designed to push air through many restrictions of twist and turns that go into ductwork that slows down the airflow and creates resistance on the fan motor and blade. So a unit designed to run with a restriction will over perform without one. Maybe to the point that you need to add a speed controller to slow it down?
Maybe you only need one? or two if you have built seperate zones /walls that seperate spaces?
Sorry I do commercial HVAC and ducted to me has a different perspective and I have know clue what an RV ducted unit does?
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Old 10-27-2016, 06:53 PM   #3
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my TT has ducted, works well to get cold air into the bedroom. I don't know, not having taken it apart, how it works or is built.

ON my home HVAC which I participated in the design there's a lot of 'science' to make it work well - and a whole lot of guess work. I don't see anything remotely that complex in a camper - but they're not usually 4 season like a house, efficiency isn't remotely as important (anyone compare utility costs/efficiency on a camper a/c or heater or fridge or anything? ). Since most campers don't pay for electricity what does it matter?

I"m tempted to consider a very different option...as part of the solution to the new furnace in my house the addition, with no way to get ductwork to it, got an LG minisplit as they call them. It's a heat pump, runs on a 10 amp 120v cirtuit - so no 220 needed. and freon is included, just connect the lines and open the valve.

it's wonderful..cheap to run and will pull heat from subzero outside temps.
Something like this - MANY models to choose from.
Of course you'll have to mount the outside unit somplace..roof would work I'd think.

https://www.acwholesalers.com/LG-Air...RYQxoCBI_w_wcB
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Old 10-27-2016, 08:00 PM   #4
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Quote:
Originally Posted by Jolly Roger View Post
To me a ducted unit is made to push/force air through several dust runs within a structure so a single ducted style unit on the roof that is sleeved straight through to the bus interior to a 4-way throw style of register will way out perform its intended design and last year's longer.
It was designed to push air through many restrictions of twist and turns that go into ductwork that slows down the airflow and creates resistance on the fan motor and blade. So a unit designed to run with a restriction will over perform without one. Maybe to the point that you need to add a speed controller to slow it down?
Maybe you only need one? or two if you have built seperate zones /walls that seperate spaces?
Sorry I do commercial HVAC and ducted to me has a different perspective and I have know clue what an RV ducted unit does?
you pretty much have it right... a ducted RV unit uses smaller flatter ducts that require a higher statuc pressure and velocity to the air..

the iones Ive seen, the ceiling level as a whole is slightly lowered as the thin but wide ducts are mounted below the insulation layer.. there are rooftop units made for this type of installation...

of course there is basement / central air.. where the ducts are in te floor or are run partially up the interior walls (as to not worry about insulation compromise on outside walls...

ducted rooftop units are fairly rare from what ive seen... even the really large coaches end up with multiple roof-top units and simply run the ones they want in the rooms they are.. I suppose the best case for a ducted unit ive seen would be a duct to the bedroom so the door can be closed.. (a whole unit for a bedroom would be over-kill in most skoolies).. and a duct to the bathroom just because the bathroom is cramped when showering it helps with moisture..

otherwise I dont see a good case to use ducting..

you definitely want it below tour ceiling insulation layer or you will have condensation and heat gain issues...
ive never torn the ciling ducts open in a camper to know what the OEM's use for duct..

I also dont know what the velocity and pressure of the various rooftop units are capable of...
-Christopher
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Old 10-27-2016, 09:11 PM   #5
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My thinking is
1. I don't have dash Ac, driver area is going to be walled off with door into the cabin, run 1 unit off alternater / inverter while traveling close registers in back & pump it to the front.

2. While sleeping run 1 unit up front so I don't have to listen to unit running over my head while trying to sleep.

3. Run aft unit while up front in living area for same reason as #2.

4.Everyone I 've talked to who only installed 1 unit is sorry they didn't go 2.
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Old 10-27-2016, 09:19 PM   #6
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sounds like a lowered ceiling and a maze of ducts in the ceiling....

are the newer units really that loud still like the old ones?

put one far enough forward that its in the driver compartment so when the door is closed it cools that area mainly... when the door is open it would cool the front area without being too noisy... a quiet little in-wall fan could even be run to circulate the air..

then your rear unit you locate outside of the betterroom and only ducting you need is to duct it into the bedroom where the door is closed and the noise is isolated away.

-Christopher
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