Real world mini-split advice needed

[Bpike]

Ok, first the purpose:
Weekend warrior camper
Shore power 50A when avail, 30A if I have to (so efficiency isn’t high on the list)
No solar panels

Now the setup:
30’ flat front bluebird
Floor was recovered with 1/2” plywood, no insulation (fighting for every 1/2”)
Ceiling is removed, plan to foam board and then tongue and groove.
Roughly 50% of the bus windows will be removed and a delete panel added.
What remains without glass in it will also be foam boarded (walls).

Now the plan and the question:
Planning on (1) 12k BTU mini split (120v, probably 15-20A)
And (1) 18k BTU mini split (240v, probably 15A)

This would allow me to run just the 12k unit when on 30A service. When I am on 50A service, I should be able to kick them both on for 30k BTU of cooling.

So looking for real world answers to these questions. By real world, I mean you have a mini split in your bus and can speak to it’s service life and reliability. If you have ever used the words “floor”, “penny”, and “galvanic corrosion” in a sentence, then I respect your knowledge (I am a Mechanical engineer), but not the kind of advice I am looking for. This thing isn’t a space shuttle, and nobody is gonna die if the floor corrodes over a period of 10 years. I digress, on to the questions:
Have you experienced any failures of the mini split you would attribute to it’s unconventional installation, or road life?
I plan to mount the outside units under the skirt with that portion of the skirt being replaced by expanded metal, any advice or unique problems you ran into if you did similar?
I really think 30k btu of cooling should be plenty, but would listen if you have real world experience in a similar setup. I should add that my wife thinks she is an Eskimo, and likes 65F in the summer. My area in the summer is no stranger to 100F and humid. We seek shade for parking when available, and avoid spots with glass facing South or West.

Any reason on the electrical side I couldn’t just flip the breaker for the 18k unit to the off position when on 30A service?

[FAC]

My setup is 40’ front nose flat engine, insulated to about r-10 just trying to average the r value over the floor ceiling etc with a 12k running 110v it pulls a max of 15 amps. It has been in service for 9 months about 3000miles

It can only do 25* delta when in direct sun but if the bus is shaded it can hold any temp just fine

I mounted the condenser on a frame under the skirt and used some Louvered sheet metal to make a grill area. I have had zero problems with it. And wouldnt change anything about my install.

I have seen breakers fail eventually by tripping randomly when used as a switch continuously but I doubt you would have problems just because it should take years and years to finally fail

[DeMac]

Both single pole and two pole "light" switches are often used as a means of disconnect, especially common on well pumps, air handlers, and motors. Ought to be a disconnect means (fuse, switch, breaker) accessible & near the compressor on all high voltage applications. A second inside is fine too. A switch costs a dollar. Go all out, get a fancy $8 illuminated switch. Just make sure its Amp rated for your application.

[Ronnie]

I installed a 30,000 btu unit in a railroad passenger car last spring . Pulls 7amps on each leg , so 14amps total. So far no trouble at all with it ,nothing has shaken loose or been damaged . The car is in regular service and is not stationary.


I have rooftop a/c units in my bus and the only comment that is of value to you is that one unit at 13,500btu will cool our 34 ft bus nicely. Stock 2" fiberglass ceiling insulation. The drivers area we have a curtain across, and curtains on the windows. Keeping direct sun out really helps, and of course letting the sun in on a cold day help heating.


I would say the 18,000btu would keep you cool, even in the worst of heat, and will not draw enough power to warrant 50 amp service.

[somewhereinusa]

I have 2 12,000 btu units. Forty foot Bluebird. RV windows, walls and floor extra insulation, roof factory. Stays quite comfortable in 100 degrees, no shade. No problems after initial installation 7 years ago.

[Bpike]

Thanks for the input

"I would say the 18,000btu would keep you cool, even in the worst of heat, and will not draw enough power to warrant 50 amp service."

The 18,000btu is a 240v unit, I would have to have a 50A service connection to get 240v, right? I was under the impression that 30A was 120v (3.6kw), and that 50A is 240v (12kw). Am I incorrect, and could somehow get the 18,000btu unit to run on a 30A connection at the pole?

In any case thanks for the real world input.

[somewhereinusa]

Just some additional thoughts. Some RV parks cheat and their 50A pedestal isn't really. They aren't split phase, just two 120V lines on the same leg. If you avoid anything 240V it isn't really a problem. I can and do quite often run both 12's on a 30A circuit and have even run both on a 15.

[Ronnie]

Originally Posted by Bpike

Thanks for the input

"I would say the 18,000btu would keep you cool, even in the worst of heat, and will not draw enough power to warrant 50 amp service."

The 18,000btu is a 240v unit, I would have to have a 50A service connection to get 240v, right? I was under the impression that 30A was 120v (3.6kw), and that 50A is 240v (12kw). Am I incorrect, and could somehow get the 18,000btu unit to run on a 30A connection at the pole?

In any case thanks for the real world input.

For a campground you are correct generally that the 30 amp is 120 volts, and the 50amp is 240.


Most of the time one 12,000 unit will do just fine, but one 18,000 btu should do good for even the most extreme heat, and still be under 30 amps. I see you said the 18,000 is 240.... hmmm this is where home and campground electric use different standards. My suggestion would be to have one 12,000 btu unit and then a smaller one (9,000btu? or two 9,000?) at the other end of the bus so that both at the same time are under 30 amps 120 volts.



I am running 208 three phase where my mini split is and using just two legs.

[peterbylt]

We installed a 12,000 BTU Pioneer Minisplit, with the Condenser in the front drivers side Luggage Bay and the evaporator over the windshield.

I have been extremely pleased with the result, given enough time the single unit will cool the 40 foot MCI bus nicely.

We use a box fan to get the cool air to the bedroom in the back.

The problems come when you want to cool the bus down quickly, living in Florida we also have issue when the temps start to get into the upper 90’s.

Neither the Wife nor I really wanted to put an air Conditioner on the roof, After much thought and debate, We decided we would rather be cool, and the decision was made to install a Coleman 15,000 BTU Mach 15 roof top AC in the rear Escape hatch.

So far we are very happy with the result, the best of both worlds, We can run both roof top and mini split and cool the bus down instantly, once the bus is cool we shut off the Coleman and maintain with the mini split.

With minimal power we can run the Mini Split only, We can also run both Roof top and Mini Split under full load at approx. 20 Amp, Need almost 30 amps to run both AC’s, refrigerator, Hot water heater, TV and house battery charger, need to shut off the Roof Top to run the Microwave at 30 amp.

Everything runs at 50 amp.

I wanted to keep everything at 120 volt.

I have also wired the Minisplit with a 120 plug in the circuit, we have on occasion run into the issue were the supposed 30 amp circuit would not support 20 amps, the power boxes at most campgrounds that have 30 amp plugs usually also have a 20 amp plug as well and I can plug the Minisplit in separately or on one occasion run an extension cord over to the power box on the next site.

Peter

[Michael_Grumbach]

you mounted it under the bus?
I wanted to mount mine under the bus, under the drivers seat, but my wife is concerned about lack of over head ventilation, but there is pleanty of ventilation coming into and leaving the coil.
How many years did you have it there and any issues?

[cadillackid]

I would only install a minisplit that close to the front if the bus is a rear engine.. on a front engione you will have lots of engine heat if you try and use the mini while driving or fopr several hours after you park lots of heat will be under the bus in a front engine.



generally the top requirement is for servicing the unit.. any service performed requires taking the top off.. otherwise you can mount it close to the floor.. (id leave some space so the unit doesnt heat the bus floor when you bounce over large road divets.. )


-Christopher

[Inner Love]

I don't want to create another thread, so here is my question:

For those that have mini-splits with heat pump ratings below 32F / 0C (how cold it can be outside before there's not enough heat for the unit to extract), at what outside temperature did your mini-split stop heating your space? Forget efficiency for a moment, I want to know how low you could go.

The leading mini-splits advertise heating down to -20F. I know efficiency drops off the closer you get to that. Regardless, having a machine that pumps the majority of your heat from cold outdoor air is awesome.

[Ronnie]

Originally Posted by Fastlane

I don't want to create another thread, so here is my question:

For those that have mini-splits with heat pump ratings below 32F / 0C (how cold it can be outside before there's not enough heat for the unit to extract), at what outside temperature did your mini-split stop heating your space? Forget efficiency for a moment, I want to know how low you could go.

The leading mini-splits advertise heating down to -20F. I know efficiency drops off the closer you get to that. Regardless, having a machine that pumps the majority of your heat from cold outdoor air is awesome.

-20? That would be nice. So far mine stops being useful below freezing.

[cadillackid]

I have 3 units in my house.. I have run them at -10f before. however they just run at maxx speed constantly. and the efifciency is next to nill.. the air was somewhat warm but the power usage was high.. they went into defrost quite often too..



the only reason I ran them that cold was because a gas main break down the street rendered my 95% efficienct gas furnace inoperable..



reading the book for them and with my own experience the highest C.O.P. is achieved at temperatures above 35f outside.. they will blow nice hot air down to about 10-15f outside but they do go into defrost fairly often and the energy usage goes up..



the Defrost cycle shuts off the indoor and outdoor fans, then sets the reverse valve to cooling mode. and runs the compressor up to its absolute maximum speed.. it runs this way until the outdoor coil inlet and outlet sensors are above freezing or 10 minutes, whichever comes first.. then it cycles back into heat mode again.. where it turns the outdoor fan on high speed quickly to sling the water off of the coil, then it sets the reverse valve back to heat, ramps up until the indoor coil gets warm then restores the indoor fan.. I cant imagine being able to heat even an insulated bus at -10f with one of these.



they kept me from freezing to death in my house during the gas outage but it definitedly wasnt able to get it anywhere close to the 75 I had the thermostats set..



as an emergency heat source if you run out of firewood or propane or diesel fuel they would surely help in tempoeratures that cold.. and of course for milder conditions they are an excellent source of heat.. other than the fact they blow the heat out high where the units are mounted so your feet are cold but face is hot..

[Deb&John]

Do you drive with your mini splits running? If so, do they keep you cool enough?
We have a 40 ft RE with full spray foam and RV windows. I absolutely cannot decide how much is too much when upsizing to drive.

[HamSkoolie]

Originally Posted by Deb&John

Do you drive with your mini splits running? If so, do they keep you cool enough?
We have a 40 ft RE with full spray foam and RV windows. I absolutely cannot decide how much is too much when upsizing to drive.

We're not on the road yet but we have a 40' RE that will be spray foamed and has RV windows. We're putting a 9k BTU mini in the front over the windshiled and another in the bedroom.
Worst case when driving is that we'll have to put up a curtain behind the driver and passenger to contain the air from the mini but we doubt that will be necessary. And my gal says "it will have 24/7/365 AC or else".


Conventional wisdom (for houses) is that you need 20BTU per SqFt of space to cool. However, if you figure that's an 8' ceiling and few if any of our buses have an 8' ceiling, we should go with CuFt.


So a 400 SqFt house (8' ceilings) needs 8000 BTU to cool it's 3,200 CuFt.
8000 BTU divided by 3200 CuFt is about 2.5 BTU per CuFt.


Lets take the example of our 40' RE. The back 5 feet will be closed off from the living area as a "garage area" with access from outside. It will be an insulated wall. So we have approx 35 linear feet. Wall to wall inside our bus will be 7.5". and vertical clearance at teh center is about 6'3" with the sides substantially lower so we will use a 6.2 conservative figure for the average height.
This gives us 35x7.5x6.1 feet or 1601.25 CuFt. 2.5 times that is 4003.125 BTU
A single 9000 BTU mini, provided the bus is well sealed and insulated, should be more than twice the need. However, buses are long and so for both consistency throughout the rig and redundancy in the event of a failure, two 9000 BTU rigs was our choice. Overkill to keep mama happy and redundancy.
That's how we came up with our choices.

[Jolly Roger bus 223]

you can go on manufacturers websites and look at specific units and they should tell you the sqaure footage capability that each unit was designed around.
choose wisely.
not in a mobile application but in commercial construction i have seen a few systems even after balanced over engineered especially in lab/computer/classrooms that over pressurized the well sealed areas and actually slowed the fans down because it couldnt move the air.
it was balanced with windows open or no doors installed yet but once everything was complete the balance dropped and nothing passed inspection for airflow?
so over sizing could be just as bad as oversizing.
or pic a brand and call the manufacturer tech support.
dont say mobile or bus? maybe RV but dont mention running while driving cause all they hear is oil sloshing in the compressor because its bouncing around but has been proven to not be a problem on here.
the cheapest brands i know of are pioneer and lenox.
i went to work on a pioneer brand unit today that whoever installed it had no clue?
a 3 ton multi split unit feeding 1 one ton head and both were in a connexe box and the were giving the outdoor unit no airflow once it came on.
long story short?
size for what you need. a little oversize maybe? alot of overkill not so good?
it not like you are gonna add space to a bus? unless you plan a slide out?

[cadillackid]

I think the consensus is from a couple members experiences that 2 running in a well insulated bus in hot summer sun keeps the occupants OK but not cold.. thats with one over the windshield .. and my guess is starting oiut wit ha cool bus.. they wouldnt stand a chance if you got into a 100 degree bus and tried to cool it down while driving...

[HamSkoolie]

Originally Posted by cadillackid

I think the consensus is from a couple members experiences that 2 running in a well insulated bus in hot summer sun keeps the occupants OK but not cold.. thats with one over the windshield .. and my guess is starting oiut wit ha cool bus.. they wouldnt stand a chance if you got into a 100 degree bus and tried to cool it down while driving...

Why the concern over driving performance? Isn't that more a function of how well a bus is closed up or how poorly it contains the cooled air?
Our rig will have very little (almost no) air leakage. There isn't much I can do to remove the flow from the drivers side outside electrical panel which, while the door is sealed, the interior isn't sealed at all has some openings to the cabin. There's also the nose doors. Other than that and the cat box vent (24/7) out bus will be sealed up quite well.
The entry door is to be rebuilt into a single unit that opens outward and seals water and wind proof when closed. The windows are standard bus windows, they're transit style that seal quite well and are sealed with polyurethane PL 3X and spray foamed around the frames.
I suppose in a bus with the notoriously air exchanging OEM doors, windows, vents, etc. it could be a problem on a hot day. With a well but not perfectly sealed cabin and more than double the cooling capacity I just don't see an issue. But when it's built and tested in the real world I'll be sure to Blog about it as well as post here.

[Rucker]

Originally Posted by Bpike

<snip>
Any reason on the electrical side I couldn’t just flip the breaker for the 18k unit to the off position when on 30A service?

Short answer is 'not really'.

If you plan on a 240 VAC subpanel you might be able to use an autotransfer switch that senses power on the second hot leg ('red wire') and energizes when present. That would prevent circuit popping if you forget to flip the breaker off when hooking up to a 30A service.