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Old 07-12-2022, 09:40 PM   #1
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Mini Split A/C Upgrade

I'm the owner of a Thor Windsport 34J and it has two A/Cs - a 15k btu and a 13.5 btu. In the Texas summer, it won't keep the coach cool enough ... I can keep it around 87 or so during the day and that's just not cool enough.

I've added an RV Air Flow system to both A/Cs. I've added insulation board into all the windows. I've added a ShadePro in the front windshields. It's not enough.

I've considered a third A/C, but my generator won't run all three (5500w) and we spend quite a bit of time at softball parks where we're on the generator.

I thought about replacing the two Coleman roof a/cs with a mini split AC system which is significantly more energy efficient. I like the idea of a 36k btu system with three ceiling cassettes.

My challenge - where is the best place to install the outdoor condenser? Here's one I'm looking at

I've thought about a hitch setup, but was wondering if anyone has done anything like this in a storage compartment? I'm completely new to this and will need quite a bit of guidance.

Thanks in Advance!
Daniel

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Old 07-12-2022, 10:31 PM   #2
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Yes, its been hot here.


Your plan will run into many problems, starting with large mini splits won’t run on 120 VAC which is what your generator makes. 3 Tons is hardly “mini”.

I suspect you may have existing A/C issues that should be fixed first. I’d start by testing cooling capacity of each A/C first.

I’m not certain an Onan 5,500 won’t power three (3) efficient 13,500 A/C. I’d research that if you don’t find cooling issues with existing A/C and or motorhome.
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Old 07-12-2022, 11:29 PM   #3
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Yes, the LG referenced needs 240V AC so it won't work on your existing generator. For 120V you will probably need two outdoor units, one probably at 24,000 btu/hr that will service two indoor units and another 12-16,000 btu/hr unit for the third.

You can't put the outdoor unit in a storage compartment. It needs to be open to the air. Maybe mount them on an extended (and reinforced) bumper.

David
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Old 07-13-2022, 12:19 AM   #4
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If you wnat to install a third 13.5K BTU A/C and then add a SoftStart Kit to each one, I think your generator could handle the load. The SoftStart will allow two 13.5K units to run on 30A. However, you probably could not run anything else or at least just minimal load like phone or laptop charging.

I think a third A/C plus SoftStart isnyour best option.
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Old 07-13-2022, 01:22 AM   #5
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You should only need Soft-start on third A/C to start compressor.

I’d run existing two first (already possible), set thermostat cold enough so that they stay on without cycling, and “then” start a Coleman high efficiency 13,500 with built-in Softstart

With nothing else on, Onan 5500 is about the same per unit as Honda 2200/1800 Watt which people power one 13,500 A/C. Considering cost and relative ease, I’d try that first but only after confirming two existing units are working at 100% of cooling rating.

Even if required, 3 new 13,500 efficient roof-top units should cost less than adapting 2 or 3 mini-split. Roof-top may not be as efficient over time, but cost of energy is almost a non-issue when only used occasionally like most motorhomes.

Other option is add 3rd air conditioner and power with a portable generator when off grid. Mounting a generator on hitch is extremely easy compared to mini splits.
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Old 07-15-2022, 06:04 PM   #6
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We have a similar sized (38') coach with two of the same units on the roof and recently stayed on the Texas coast and didn't really have as much trouble cooling as we assumed we might considering the heat and humidity down there. Even here in DFW area it stays reasonably cool during the 100+ days.
The units never really shut off the whole trip but it wasn't above 78 degrees inside at any time. I would certainly have yours checked before anything else and make sure they're doing all they can.

I have always wondered why some form of mini split wouldn't be ideal in an RV? It seems like anything would be more efficient than those rooftop units, easily quieter as well.

I had a friend build out a school bus to take to races and used something like one of these to cool the sleeping area. It runs directly off of 12 volts and according to him it was great.
Not the best to look at though.
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Old 07-15-2022, 07:31 PM   #7
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Originally Posted by howzball View Post

.....cut....

I had a friend build out a school bus to take to races and used something like one of these to cool the sleeping area. It runs directly off of 12 volts and according to him it was great.
Not the best to look at though.

That particular unit you linked (which may be different than your friend’s) has horrendous performance numbers listed. Data below from ad shows a cooling capacity of +/- 7,900 BTU/hr and requires +/- 900 Watts of power. The EER is less than 9.

There is nothing INHERENTLY more efficient about separating the compressor and condenser from the evaporator. It is a packaging benefit that doesn’t make A/C more efficient. The same results can be achieved with other arrangements as long as the same level of technology is utilized.

Chinese companies have a bad reputation for overstating air conditioner performance, and in this case the price is so low compared to equivalent European truck parking coolers that I would be hesitant even if stated performance was much better. Also, the warranty is a joke.

When inverter technology is applied to window air conditioners, as an example, 8,000 BTU/hour A/C from major manufacturers have CEER of over 15. That’s the direction we need in technology whether packaged to mount on roof or elsewhere. And best of all cost is becoming much more affordable due to mass production volumes; suggesting components are cheaper too.
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Old 07-15-2022, 08:31 PM   #8
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That particular unit you linked (which may be different than your friend’s) has horrendous performance numbers listed. Data below from ad shows a cooling capacity of +/- 7,900 BTU/hr and requires +/- 900 Watts of power. The EER is less than 9.
........

Yeah, I'm not even sure what his exact set up was, all I knew was he wanted to cool the sleeping area he built out in the bus and, since he had one of those redneck patio's on top of the bus he couldn't use a normal RV roof unit.
He had no shore power voltage in the thing either.

The unit in my link I'm not sure I would go through the trouble of installing even if if they'd given it to me.
I think one of the main draws to these split system is just they're less noisy, with a pair of these RV units roaring at full song you need headphones if you ever plan to watch TV in the thing.
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Old 07-21-2022, 03:06 PM   #9
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the two existing units provides 30k Btu, your thinking of a multi split of 36k Btu it will in theory give you 6k Btu more . if you think that 6k will bring down the coach temp to your liking, I wish you good luck. the original design is meant for brining down the temp to a differential of 15F outdoor to indoor so if your are in an environment of over 100F and your indoor temp at 87F is pretty close to the units capacities.
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Old 07-21-2022, 03:23 PM   #10
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Installing any type of unit made to operate in a static situation and then taking that unit driving down our pothole filled, broken concrete, and rut filled HI ways should certainly prove interesting.
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Old 07-21-2022, 03:48 PM   #11
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Installing any type of unit made to operate in a static situation and then taking that unit driving down our pothole filled, broken concrete, and rut filled HI ways should certainly prove interesting.
Yeah, if the piping to/from the condenser/evaporator units is copper it can cycle only so many times before ductile failure will occur. If it is synthetic, hopefully it will last many more cycles.
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Old 07-21-2022, 03:58 PM   #12
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Only thing I could suggest is.. AFTER You check to see that the ducting is connected correctly with no blockages. I'd be swapping out the 13 and replace with another 15, and adding the Soft Start to both, because You will be at the ragged edge of the generator's capacities
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Old 07-21-2022, 04:30 PM   #13
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For reference, that 15 F design number for inside versus outside we keep seeing is probably in the right ball park for many RVs by “coincidence”, or by choices RV engineers make at factory, but it has very little to do with how cold an RV can be in any ambient condition.

For example, RV air conditioners are indeed capacity rated at 95 F ambient and 80 F inside temperature. That is 15 F but only means a 15,000 BTU/hr air conditioner will cool at 15,000 BTU/hr at those temperatures (and at 50% RH inside if I recall correctly). That rating does not preclude that same A/C from operating at other conditions, though cooling rate could (and probably will be) much different.

Also, many RV air conditioners have air flow rate designed so that air going in and out of evaporator cools down by at least 15 F (sometimes 20 F or more). Again, this selected A/C design air flow does not directly prevent air conditioner from cooling inside of RV to a much lower temperature than 15 F below outside ambient temperature.

Inside versus outside temperature that can be achieved is mostly limited by air conditioner capacity versus total heat load on RV. Increasing A/C capacity (2 units versus 1 as example) or reducing load on RV (park in shade, cover and or have dual pane windows as examples) can result in inside temperature being much lower than 15 F below ambient.

My son’s not-too-large Class B+ came with 2 X 15,000 BTU/hr units, and with its fairly good thermal design, can easily stay cool parked in 100 F Texas sun. A differential of 30 F is possible, though it is overkill in other ways — unless one was planning to camp in desert regularly, two smaller A/C would have been preferable.
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