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Old 09-22-2021, 01:58 PM   #1
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Mini Split v. Roof Mount

I am trying to make the final decision on a mini-split heat pump on our '74 Broken Arrow (currently gutted). My daughter is planning on living in this trailer for an extended period and using it for an AirBNB, so consistent temps are at the top of the comfort list.

The trailer is 28' interior with (soon to be) closed cell insulation - actually measures 206sq ft of floor space, with 673 sq ft of wall / ceiling area (that includes 81sq ft of window and door openings). There are 3 standard openings in the roof (14x14) front / center / back. The center one had an old Coleman roof mount in it. I plan to have at least 2 MAXXFAN 4500k installed in the open vents.

Concerns with a roof mount Heat Pump is the noise level and lack of consistent temp in the bedroom/bath - there is a sliding door between front of house and bedroom, and between bed and bath. This trailer originally had a forced air furnace with ducting down the middle of the floor from front to back so there was heat delivery to the full trailer. That ductwork is still in the floor, but the furnace is gone.

I have been looking at a mini-split that would have the condenser on the hitch, with the interior being a concealed slimline ducted unit that would make use of the existing ducting, and would be installed below the built-in front bench seating area. Return air would be handled thru the ends of the seating benches. Would love to have return air from the bedroom, but not sure if there is a way to get the ducting up the wall and over to the bedroom.

The distance from exterior unit to interior unit would be less than 3', and I would have a flexible line set made to offset the vibration concerns of a solid copper line set. The elec for the mini-split has to be 220v because of the ductless interior unit. I had thought that adding a 115v AC only unit in the back vent opening above the bathroom might be an option so if she is at a location without 220 service, she would at least have AC for the bedroom and bath.

Last but not least - we luckily have a professional AC guy in the family and he will be doing the actual install. I just need real world feedback of how mini-splits are working in an RV, and recommendations on the brands that last.

Mini Split is something like this (not necessarily this brand):[URL="https://www.amazon.com/Cooper-Hunter-Pre-Charged-Installation-Thermostat/dp/B08ZHXYV2D?ref_=ast_sto_dp&th=1&psc=1"].
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Old 09-23-2021, 12:26 AM   #2
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Nice project. It seems efficiency is not an issue for you (power will not be battery). That helps a lot. The ducted mini that you plan will be much less efficient than a wall mount, but is fine if there's power available.

Roof mounts are terrible in all respects. Certainly not something a tenant would enjoy. Mini splits are a huge improvement.

My son has a Gree 9K unit wall mount on his 34' motor home. It runs mostly on solar and battery. His wall mount is in the front living area so the bedroom tends to be warm. He also does time in Utah in the summer where it's very very warm .... probably much warmer than Oklahoma ever sees. He may install a second unit serving the bedroom. Units down to 6K are available (Mitsubishi). His runs 220 from his 120V inverter via an autotransformer. This is off-topic for you.

I have a 9K 120V C&H waiting to go into my 30 foot fifth wheel. It will run only on battery/solar. It's in the living area but I will duct some cooler floor level air up into the bedroom when needed.

Some questions that I can think of .....

How well insulated is the duct down the length of the trailer?

Where will the trailer be in the summer when A/C is needed?

It's easy to check statistically representative weather at specific locations. I could envision 9K being enough in some regions but 12K being not enough in the Southwest.

I've done Model J type calcs for my and my son's RVs assuming walls are R6 (assumes some help from cabinets and sofa and drapes) and 9K is on the low side but a mini split running full out is not very intrusive. A ceiling unit running full out would be unbearable.

I'm fading from a long day, so might think of something more to offer tomorrow.
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Old 09-23-2021, 06:45 PM   #3
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Mini Split Wall or Ducted

Thanks for your time and advice.

After cussing and discussing this with my heathen child, she said she could live with a split system with a wall mount unit after experiencing one this last weekend at a friend's cabin. Keeping the electric service at 115v will give her the option for solar in the future if she chooses. We are investing in closed cell foam insulation, 3 inches in the ceiling and 2 inches in the walls. The floor ducts are straight sheet metal that lays directly on top of the belly pan, so HIGHLY inefficient. That realization makes the wall mounted system even more practical. Now I am thinking about how to get insulation into the existing duct so that it is not just a cold air holding chamber going the full length of the floor.

I did come across a mini split load calculator at that was easy to use. It calculates 6000 BTU/hr, so the 12,000 unit should be fine. I don't see her going to the desert SW in the summer months, and at this point in time the locations that she plans on parking at (long term) are all shaded.

I have been looking at the C&H, but reviews can be pretty brutal on the customer service side. Our family AC guy has had great experience with the Senville systems - but that is on apartments not RVs. On Amazon you can purchase an extra 4yr protection plan for $96 - think that is a good gamble on any system that you would purchase, just in case any of the mfg's were derelict in their customer service dept.

I will let you know what we settle on, and once again, thank you for your advice - especially the question on the duct insulation.
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Old 09-23-2021, 08:19 PM   #4
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Good thinking. While a "multi-split" would be ideal with indoor units at either end of the RV, finding wall space for two indoor units likely rules that out. But, in your floor plan, the bed is not at the extreme far end from the living area so if you can mount the indoor unit mid-ship, you could use the left/right vanes in the indoor unit to throw cooled/warmed air toward the living end during the day and the bed area at night.

The insulation you plan is going to help a lot.

Yes, C&H is probably not the best service wise, but in my case the total cost of the unit was about $1100 for the recently released SEER 25 / EER 15.5 120V unit. It's likely that neither indoor or outdoor unit will ever be serviced. It will simply be replaced if there's a failure (that I can't fix). Often indoor and outdoor units are a matched set and a few years after install, it's likely neither is available alone, so a new (and likely more efficent) set would be swapped in for a fast and reliable fix.

As you've observed, the indoor wall-mounts are very quiet, and relatively quiet (compared to a roof mount) even when at max output. And, it's surprising how good 80F feels when you come in from 85F outside. Part of that is the moving air effect. I.e., you don't necessarily need to hold low 70's on a hot day to make A/C feel good.

My son's 9K Gree looks to be a 12K unit with some tweaks to fill out the product line at minimum cost. It behaves more like a 12K but is wholly tolerable noise wise. His outdoor unit sits up front where the generator once was in his motor home so isn't far from the living area. It's audible from inside, but just barely.

My 5er roof mount only got used twice before I removed it, but the air it produced wasn't very cold by the time it got out through the ceiling ducts to the various registers. I abandoned those ducts in short order and let the cold air pour straight down. Much more effective cooling, but noisy and annoying and rarely needed so the unit was removed.

My space heater had mylar ducts that mostly got crushed or torn by the tanks so wasted about half of my heat. I soon bypassed all of those with short ducts to the nearest wall. That reduced the morning warm-up time by 2/3 and hugely reduced propane usage.

My point re the next two above paragraphs is that the wall mount mini split will be far more effective/efficent than any other alternative. I'd go 9K, but 12K makes sense if the RV will see cold winters or hot summers.
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Old 09-24-2021, 12:55 PM   #5
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I have a place near me that manufactures "tiny houses" and I noticed they all have mini splits. I've wondered how appropriate they be on campers.
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Old 09-24-2021, 01:53 PM   #6
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They have been used on campers even truck campers. The hardest part is having room for the condenser/compressor unit with plenty of air flow and getting the condensate line out.
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Old 09-24-2021, 03:27 PM   #7
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Most mini splits are 208/230 vac so it would need at least a 50 amp service and most likely at 20-30 amp breaker
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Old 09-24-2021, 03:30 PM   #8
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Location of Mini Split Condensor

We had planned on having the condenser on a platform with the propane tanks mounted on the hitch. The wall mounted unit would be just inside the front wall above the windows, connected to the condenser with high pressure automotive AC hoses (that's the plan). But the condenser owners manual specifically states that the condenser is to be nowhere near pressurized gas tanks - I assume for fear of a fan blade flying off, or a condenser seizing up and throwing a rod that punctures a propane tank and causes an explosion (not sure that is a real concern as opposed to a liability concern for the mfg).

The front of the trailer slopes inward, so there is good airflow space for the condenser. We have a gas stove and gas tankless hot water heater, so propane is necessary. The front view photo is pretty close to scale, the condenser is 31.5 inches wide by 22 inches tall. The propane tanks are right at 22 inches tall.

The hitch is short, especially for any tight corners, so extending it is a definite option. Extending it 12-15 inches would give us room to have the condenser set to the driver side, and tanks on the passenger side of the platform. We could have a divider between the condenser and the tanks for a little security blanket. I do have sway bars for this trailer, I think any change in balance with the longer hitch could be offset with the sway bars.
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Old 09-24-2021, 03:33 PM   #9
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Senville 12,000 115v

The Senville 12,000 is 115v for both condenser and wall unit - keeps the electrical service simpler.
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Old 09-25-2021, 01:13 AM   #10
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Quote:
Originally Posted by ACJC View Post
Most mini splits are 208/230 vac so it would need at least a 50 amp service and most likely at 20-30 amp breaker
Yes, "most," but there are now quite a few 120V mini splits. I've seen 12K units at 120V. I'm not sure whether there are larger ones. I have a 120V C&H in my garage waiting to be installed. All of these, including IIRC the 12K ones, require only a 15 amp circuit breaker. My son has a 9K Gree that is 230V and fed by an autotransformer from his 120V inverter. If shore power is available, he plugs that autotransformer into the post 120V duplex receptacle (everything else in his RV remains on the battery). Normally his Gree runs from his LiFePO4 battery and solar. My C&H will only run from LiFePO4 and solar (I have no way to use shore power beyond an old converter that I can use as a charger).
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Old 09-25-2021, 01:25 AM   #11
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Quote:
Originally Posted by 74BrokenArrow View Post
We had planned on having the condenser on a platform with the propane tanks mounted on the hitch. The wall mounted unit would be just inside the front wall above the windows, connected to the condenser with high pressure automotive AC hoses (that's the plan). But the condenser owners manual specifically states that the condenser is to be nowhere near pressurized gas tanks - I assume for fear of a fan blade flying off, or a condenser seizing up and throwing a rod that punctures a propane tank and causes an explosion (not sure that is a real concern as opposed to a liability concern for the mfg).

The front of the trailer slopes inward, so there is good airflow space for the condenser. We have a gas stove and gas tankless hot water heater, so propane is necessary. The front view photo is pretty close to scale, the condenser is 31.5 inches wide by 22 inches tall. The propane tanks are right at 22 inches tall.

The hitch is short, especially for any tight corners, so extending it is a definite option. Extending it 12-15 inches would give us room to have the condenser set to the driver side, and tanks on the passenger side of the platform. We could have a divider between the condenser and the tanks for a little security blanket. I do have sway bars for this trailer, I think any change in balance with the longer hitch could be offset with the sway bars.
Definitely a plan! Since you only plan on running the mini split from shore power, your layout is perfect. As you know, mini split condensers need only 4--6 inches to the wall behind and a clear path to the front, just as you plan. If you were going to run the unit from solar, having it blow air into a head wind would not work so well.

You mention the flexible lines. My son's installation, and maybe mine, will use the standard 1/4 and 1/2 soft copper lines with only a couple of feet of flexible line right at the condenser. This allows for shaking of the condenser during travel. My own condenser will have a top brace to limit shaking so I'm not sure I'm going to use the flexible pieces. https://smile.amazon.com/Protech-667...2551066&sr=8-5
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Old 09-25-2021, 01:30 AM   #12
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Originally Posted by CedarCreekWoody View Post
I have a place near me that manufactures "tiny houses" and I noticed they all have mini splits. I've wondered how appropriate they be on campers.
Search for "mini split on an RV" on Youtube. Lots of installations are documented there. There are some issues to consider such as condenser shake, but otherwise they work well. I would want one even if I only ever ran it on shore power. Hugely quieter and more efficient (no duct losses).
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Old 09-25-2021, 10:32 AM   #13
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Quote:
Originally Posted by 74BrokenArrow View Post
We had planned on having the condenser on a platform with the propane tanks mounted on the hitch. The wall mounted unit would be just inside the front wall above the windows, connected to the condenser with high pressure automotive AC hoses (that's the plan). But the condenser owners manual specifically states that the condenser is to be nowhere near pressurized gas tanks - I assume for fear of a fan blade flying off, or a condenser seizing up and throwing a rod that punctures a propane tank and causes an explosion (not sure that is a real concern as opposed to a liability concern for the mfg).

The front of the trailer slopes inward, so there is good airflow space for the condenser. We have a gas stove and gas tankless hot water heater, so propane is necessary. The front view photo is pretty close to scale, the condenser is 31.5 inches wide by 22 inches tall. The propane tanks are right at 22 inches tall.

The hitch is short, especially for any tight corners, so extending it is a definite option. Extending it 12-15 inches would give us room to have the condenser set to the driver side, and tanks on the passenger side of the platform. We could have a divider between the condenser and the tanks for a little security blanket. I do have sway bars for this trailer, I think any change in balance with the longer hitch could be offset with the sway bars.
Having installed several mini split systems the first I see in your picture is how much clearance does the manufacturer call for behind the condenser? Something to to verify.
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