Semi radical AC idea-ductless mini split

October 02, 2012, 05:42:33 pm

Wyatt kind of brought it up, and thought I'd throw the idea out there. Here's an opportunity for some enterprising person to be endlessly busy retrofiting these.

I've been idly considering the possibility of using a ductless mini split system. There are several possible installation scenarios, but basically the small air cooled compressor units could install into the area where the coach muffler is/was before resonator. This would require an insulated box, probably of ductboard construction and coated with fireproof elastomeric paint. The existing access door would turn into a louvered door for air exhaust and an air intake provided also. This area is large enough to put two condensing units in.

There are several evaporator styles, the most common being about 36" wide, 12" tall, 11" deep. One of these could install in the cabinet over the bed. I expect one could be found to fit inside an upper cabinet in living area. There are also ceiling mount evaporator units which could simply replace the existing ac units, they are 9" tall, 24" square and do not hang down. There is also a slim line ceiling hugger model which is made to attach to a skinny duct system, much like exists in some Foretravels. All of them can utilize a small condensate pump and all of them use a prefabricated lineset which includes supply lines, electrical connections and condensate return. Basically, install, tighten compression fittings (no silver soldering), some use snap together fittings, vacuum the lines, release the precharge and run.

These are vairable speed inverter style units with a variable output from 3000 to 12000 btu, most are heat pumps also. Typically they use a wireless remote for control so there is no need to tie into thermostat. All are very, very quiet. SEER ratings in the 20 range (compared to the Dometic which I suspect has a SEER of around 6.

Some of the advantages I see to this would be:
Quiet. Like whisper quiet. Being deaf and in denial about hearing aids as per DW, this is a big deal to me.
Option to utilize numerous advanced filtration options.
Replacement parts are readily available from many sources and very easy to install.
No aggro with tying into thermostat system. Wireless remote with readout controls all options.
Most units have a sweep function which oscillates air flow.
High efficiency. It's possible to run these things at reduced output, as low as 3K BTU. I think a good battery bank would suport this in an application like keeping a closed bedroom cool for the night.
Reasonable cost for initial installation...more than new rooftop units...but replacement condensor unit swapout would be a 3-400.00 and 20 minute propositon with no need to climb on roof.
No more condensate running down the side of the coach, searching for an entry to the bulkheads.

Challenges:
Lineset routing. It almost seems like installing in a plastic duct on the roof would be a way to go if the ceiling mount units are used. If installed in upper cabinets routing through cabs might be possible.
Condensor unit installation. While there's plenty of room in the area mentioned for the compressors it will still require some fabrication and air flow considerations to make it work. Having noted pictures of toolboxes etc being fabricated for this unused area I don't think it is too much of a hill for a stepper.
BTU limitations. "If" 240 volt was available then it is possible to tie several evaporator units into a single condensing unit making a beautifully zoned system. However, for 120 volt the limit seems to be 12KBTU per unit.

All in all, considering the elaborate refrigerator conversions I've seen, I think it's doable by the average handy person and on the same order of difficulty. I've installed a few of these things in houses and the pre engineered aspects make it dead simple.

Here's a link to a Sanyo model showing several of the available options. There are many manufacturers, prices start around 600.00 for some complete systems. Google ductless mini split for more than you probably want to know.

ductless mini split air conditioners, from Ductless HVAC Supply, Inc.

I'd be interested in hearing your thoughts on this concept.

Chuck

Re: Semi radical AC idea-ductless mini split

Reply #1 – October 02, 2012, 06:04:45 pm

I checked out Mitsubishi ductless about 6 months ago but could not figure out how to install but looked like a good system, this unit cost more than the Sanyo but looks the same. jc

Re: Semi radical AC idea-ductless mini split

Reply #2 – October 02, 2012, 07:16:27 pm

Interesting, I have been meaning to look into using the space for a softener but this seems interesting. I don't care for the noise from the roof ac units and have seen/heard the split systems. So I look forward to you figuring it out so I can ride your coat tails! Thanks in advance!

Phil

Re: Semi radical AC idea-ductless mini split

Reply #3 – October 03, 2012, 07:49:50 am

What a super idea! I hate the noise of the AC units.

Sounds like a super idea for some enterprising entrepreneur (James Stallings?) to take on. I would think it would find a lot of customers if done well.

Re: Semi radical AC idea-ductless mini split

Reply #4 – October 03, 2012, 10:55:45 am

I have installed 8-10 of the split units in villas in Panama. They work great and are very quiet. One up to about 13,000 btu can be had in 120 volts.One of the MFGs has a indoor unit that is a picture frame. I think the ceiling mounted units would work well to replace the existing AC. Gam

Re: Semi radical AC idea-ductless mini split

Reply #5 – October 04, 2012, 05:42:35 pm

This is great information and ideas on Motorhome Air Conditioning. I may persue this at some time in the future, however, I have little need for motorhome A/C at this time.

There were two major factors which motivated my friend to remove the RV rooftop A/C unit and replace with basement A/C units, improved handling and reduced power needs.

I was sceptical about improving motorhome handling by reducing roof top weight. However, With my SOB P30 gas motohome, I removed the roof top A/C because I did not use it and wanted more light as well as fantastic fan ventilation. Added benefits were increased ceiling height and a noticeable reduction in side to side sway when driving, which I did not expect. I used to talk about this sometimes, however, after hearing much disbelief, ie "no way you could feel only 75 pounds on the roof", I stopped talking about it.

Reduced power needs are possible because manufacturers of home window A/C units build them to run on a 15 amp breaker so they can be plugged in anywhere and work.

Another factor was cost - it is hard to get A/C units less costly then home window units.

The noise factor with A/C units is to some extent not easily solvable. The A/C cold to room air temperature difference is much fewer degrees than the furnace hot to room air temperature difference. This means effective cooling requires a lot higher volume of air movement, than effective heating. Moving a lot of air makes a lot of noise. I am not sure how much noise is contributed to A/C by the roof top compressor.

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