Sizing an off-grid Air Conditioning (AC) and fan system

[ReluctantTraveler]

After researching a bunch of options, I think I've landing on the Mabru rooftop AC for the expedition vehicle I'm planning out (a flatbed cab-over camper on an F-550/5500 platform).

Where I'm maybe a bit stuck is on whether I can get away with 1 unit, or if I need 2.

Our build will be about 150 sq ft, with rear bunk and cabover sleep areas. Both the bunks and cabover will have light block curtains for privacy.

The Mabru is not a ducted system. Do you think one centrally located unit (12,000 btu) will sufficiently cool the space, or should we have two units: one for the main area with the bunks and another for the cabover?

Similarly, would a centrally located MaxAir fan (or similar) work for the whole camper, or should I be looking at two?

In case anyone's curious about electrical draw, 500ah of LiFePo4 gets you about 8-10 hours of continuous use. I'm planning for 800ah, plus 1k watts of solar and a DC-to-DC charger from the truck alternator, which should get us close to continuous use off-grid unless it's stormy.

 

[carleton]

12,000 BTU should be enough for the space.

The issue you are may have are hot spots due to poor insulation or windows.
The cab over, for example, in my Tiger is the hottest part of the vehicle. Heat rises, lots of windows, less quality insulation.
You only have so much real estate on a roof, though, so most folks will do 1 a/c, and 1 MaxAir.

 

[Peter_n_Margaret]

AVANTI® | Split Systems | Mitsubishi Heavy Industries Air-Conditioners (mhiaa.com.au)
These are the common choice in Oz. Inverter compressors. Nothing on the roof.
Cheers,
Peter
OKA196 motorhome

 

[ReluctantTraveler]

AVANTI® | Split Systems | Mitsubishi Heavy Industries Air-Conditioners (mhiaa.com.au)
These are the common choice in Oz. Inverter compressors. Nothing on the roof.
Cheers,
Peter
OKA196 motorhome

As much as I'd love to keep the roof without a 6" device sticking out of it, I don't have the wall space to sacrifice for the mini-split interior control unit. I also need more control over where the air goes than they generally allow. The Mabru has a handful of ports that let you send air in various directions.

If I could find a mini-split with multiple ducts instead of the big wall panel, I'd jump on it.

 

[carleton]

As much as I'd love to keep the roof without a 6" device sticking out of it, I don't have the wall space to sacrifice for the mini-split interior control unit. I also need more control over where the air goes than they generally allow. The Mabru has a handful of ports that let you send air in various directions.

If I could find a mini-split with multiple ducts instead of the big wall panel, I'd jump on it.

Cruise N Comfort?

12/24/48 Volt DC Air Conditioners..Battery Powered..Solar Powered..Hand Made In Arizona Since 2010<br/> — Battery Powered Air Conditioners 12/24/48 Volts DC

We manufacture DC powered air conditioners in various voltages for various applications..... Off grid living, solar powered, energy efficient...... Made in Arizona.... Custom applications welcome.

www.cruisencomfortusa.com

More money, though.

 

[ReluctantTraveler]

Cruise N Comfort?

12/24/48 Volt DC Air Conditioners..Battery Powered..Solar Powered..Hand Made In Arizona Since 2010<br/> — Battery Powered Air Conditioners 12/24/48 Volts DC

We manufacture DC powered air conditioners in various voltages for various applications..... Off grid living, solar powered, energy efficient...... Made in Arizona.... Custom applications welcome.

www.cruisencomfortusa.com

More money, though.

A lot more money, doesn’t seem like a ducted solution or multi directional at least, and for whatever reason, they don’t make it easy to find electrical draw specifications on their site.

 

[carleton]

A lot more money, doesn’t seem like a ducted solution or multi directional at least, and for whatever reason, they don’t make it easy to find electrical draw specifications on their site.

It is ducted, but they really don't explain it well.
Not really made for the DIYers, I guess

Looks like they use some heater hose to get the output to blow where you want it to, similar to an Espar or a Webasto.
The advantage is that you can duct the output well away from the input, so you can then get some air movement.

The roof top units have the input right next to the output......so some of the cold air is sucked directly back into the unit.

 

[ReluctantTraveler]

It is ducted, but they really don't explain it well.
Not really made for the DIYers, I guess

Looks like they use some heater hose to get the output to blow where you want it to, similar to an Espar or a Webasto.
The advantage is that you can duct the output well away from the input, so you can then get some air movement.

The roof top units have the input right next to the output......so some of the cold air is sucked directly back into the unit.

i’ll have to see if I can find some install videos on YouTube or some thing, in that case.

my ideal system needs to be able to run pretty much continuously. I know a lot of the systems like the one for earthcruiser, and such are only specced for 4-5 hours of daily use.

 

[DiploStrat]

Scholars differ, but having 12v A/C scars, I will offer some comments you may wish to consider or ignore.

-- For a 12v unit, you gotta run some big wires a long way, otherwise you will have performance loss. Not a problem, but just a cost.

-- Most important of all, for me at least, having had one, is that a roof air conditioner that is not either ducted or fitted with a horizontal diffuser is a non-starter. One as shown in the picture will simply dump air in one spot and not cool the whole camper. You can improve things with fans, but the only real answer is a unit that projects below the roof with horizontal, not vertical, vents.

-- Keep your two roof fans if you can.

-- If the air conditioner is over the bed, consider a curtain or door.

-- Running a 12v air conditioner when plugged into shore power will work, but your charger will generate a lot of heat and is probably not properly vented to dissipate 150F+. (I moved mine out of the camper and attached to an aluminum box.

No matter what they claim, the compressor will draw some 50A+ when running. You can guesstimate 5A per 100w of solar panel. (Some newer ones may be better, but don't bet on it.) As Jason of Everlanders has demonstrated, the "magic" point is abut 1500w for unlimited A/C in sunny weather. (I have a bit over 500w )

The problem is less running the air conditioner and more getting enough power to recharge the batteries.

Offered with best wishes, YMMV.

 

[ReluctantTraveler]

Scholars differ, but having 12v A/C scars, I will offer some comments you may wish to consider or ignore.

-- For a 12v unit, you gotta run some big wires a long way, otherwise you will have performance loss. Not a problem, but just a cost.

-- Most important of all, for me at least, having had one, is that a roof air conditioner that is not either ducted or fitted with a horizontal diffuser is a non-starter. One as shown in the picture will simply dump air in one spot and not cool the whole camper. You can improve things with fans, but the only real answer is a unit that projects below the roof with horizontal, not vertical, vents.

-- Keep your two roof fans if you can.

-- If the air conditioner is over the bed, consider a curtain or door.

-- Running a 12v air conditioner when plugged into shore power will work, but your charger will generate a lot of heat and is probably not properly vented to dissipate 150F+. (I moved mine out of the camper and attached to an aluminum box.

No matter what they claim, the compressor will draw some 50A+ when running. You can guesstimate 5A per 100w of solar panel. (Some newer ones may be better, but don't bet on it.) As Jason of Everlanders has demonstrated, the "magic" point is abut 1500w for unlimited A/C in sunny weather. (I have a bit over 500w )

The problem is less running the air conditioner and more getting enough power to recharge the batteries.

Offered with best wishes, YMMV.

Thanks for all of this! What brand/model of 12v do you have experience with?

Our current travel trailer (104 sq ft) uses a traditional Mach 3 that seems almost overpowered for the size of our rig. I'm realizing as I type this that it's vents point out the sides.

The Mabru's vents point down but let you angle them, and I hadn't really considered that that might result in a different airflow pattern.

I'm assuming this is the Everlanders video you were referring to? Watching now.
All of the big vendors (Tiger, EarthCruiser, EarthRoamer) seem to use residential mini-splits, but also seem to assume only 4-5 hours of use per day, which I don't think will realistically work for my family and how/where we travel.

 

[DiploStrat]

That is the video. Watch/read closely - Jason is not idiot. In future life, I would build slide out solar panels, both for the amperage and, perhaps more importantly, as a double roof and shade for the sides. FWIW, Jason has never bothered to charge from his alternator. But then he shot that video in Oaxaca, Mexico, with just about the best solar conditions on earth.

Used a Kalori unit - not recommended. Now have a BeCool unit in the cab. Has the same downward vents, but the cab is so small. Those "adjustable" vents don't. (Adjust, that is. Don't ask me, or our cat, how we know this,) And did I mention that it was loud and leaked rain water. I think they designed these for sale in the Gulf.)

Most residential splits are WAY more efficient than any 12v unit. The best solution that I know is a 6k BTU window unit, which I had on our Tiger. Dirt cheap and the best air distribution, bar none, because of the powerful fan. We had to raise the temperature and still had to sleep the other way around in the cab over. The trick is that they require careful mounting to keep condensation out of the camper and to assure adequate fresh air for the compressor/condenser. Not impossible, but nobody does it right.

We are now using a Houghton rooftop unit. Solved the air distribution problem, but we have only tested on heat pump setting as it is winter. Claims a built in "soft start" facility, but still wants at least a 3kW inverter. We are using a 2kW inverter, but we added a soft start. Pulls about 100A when the compressor is running, but run time is limited as it is powerful and the air distribution is excellent. This is the unit that Advanced RV uses and they on my short list of people I really respect. And it is dead quiet - not small split unit quiet, but normal conversation and sleep all night quiet.

My logic goes like this. If it is really that hot (over 95F), then you are going to a commercial campground, and most won't give you a discount for not taking their power. In this case, you are running on 110V and sparing your batteries.

At more reasonable temps, you are looking for 6PM to 6AM - round down to 10 hours @ minimum 50A the hour, or, hopefully about 500Ah. With 800Ah, this is not a problem. The problem is that it it hard to get 100A of charge for eight hours, in the real world.

This is what I used. You can save money with the high profile or the 9k units.

Will give you a long term report after the summer.

Lots of folks got lots of opinions on this, so, as always, YMMV.

RV Air Conditioner Low Profile 13.5K Quiet AC Unit with Heat Pump, Remote, Non-Ducted

Are you tired of sweating in your RV during hot summer days? Say goodbye to discomfort and hello to the RecPro RV Air Conditioner! Our product is here to keep you cool and comfortable.

www.recpro.com

 

[ReluctantTraveler]

That is the video. Watch/read closely - Jason is not idiot. In future life, I would build slide out solar panels, both for the amperage and, perhaps more importantly, as a double roof and shade for the sides. FWIW, Jason has never bothered to charge from his alternator. But then he shot that video in Oaxaca, Mexico, with just about the best solar conditions on earth.

Used a Kalori unit - not recommended. Now have a BeCool unit in the cab. Has the same downward vents, but the cab is so small. Those "adjustable" vents don't. (Adjust, that is. Don't ask me, or our cat, how we know this,) And did I mention that it was loud and leaked rain water. I think they designed these for sale in the Gulf.)

Most residential splits are WAY more efficient than any 12v unit. The best solution that I know is a 6k BTU window unit, which I had on our Tiger. Dirt cheap and the best air distribution, bar none, because of the powerful fan. We had to raise the temperature and still had to sleep the other way around in the cab over. The trick is that they require careful mounting to keep condensation out of the camper and to assure adequate fresh air for the compressor/condenser. Not impossible, but nobody does it right.

We are now using a Houghton rooftop unit. Solved the air distribution problem, but we have only tested on heat pump setting as it is winter. Claims a built in "soft start" facility, but still wants at least a 3kW inverter. We are using a 2kW inverter, but we added a soft start. Pulls about 100A when the compressor is running, but run time is limited as it is powerful and the air distribution is excellent. This is the unit that Advanced RV uses and they on my short list of people I really respect. And it is dead quiet - not small split unit quiet, but normal conversation and sleep all night quiet.

My logic goes like this. If it is really that hot (over 95F), then you are going to a commercial campground, and most won't give you a discount for not taking their power. In this case, you are running on 110V and sparing your batteries.

At more reasonable temps, you are looking for 6PM to 6AM - round down to 10 hours @ minimum 50A the hour, or, hopefully about 500Ah. With 800Ah, this is not a problem. The problem is that it it hard to get 100A of charge for eight hours, in the real world.

This is what I used. You can save money with the high profile or the 9k units.

Will give you a long term report after the summer.

Lots of folks got lots of opinions on this, so, as always, YMMV.

RV Air Conditioner Low Profile 13.5K Quiet AC Unit with Heat Pump, Remote, Non-Ducted

Are you tired of sweating in your RV during hot summer days? Say goodbye to discomfort and hello to the RecPro RV Air Conditioner! Our product is here to keep you cool and comfortable.

www.recpro.com

What I think just doesn't quite work for mini-splits for us is that we'll have beds at both the cabover and rear (bunks over the dinette).

If we mount the inside unit at the rear, the air will be much cooler near the rear bunks that the cabover (or vice-versa if we mount at the front). Mounting in the middle would mean blowing air towards the door or back wall, and eating up a bunch of cabinet space.

 

[DiploStrat]

A roof top unit has lots to recommend it. As I say, I am really happy with the Houghton, but that is based on limited testing so far - been too cold for a real stress test. This year may not be a great test as we will be back in the US in July for the hottest months. But, with no access to 110v, I will get to geek out battery recharge issues!

I REALLY like two vents. With only one, we love our skylight and we have four internal fans to blow things around.

Have you published your proposed floor plan? With sleeping areas fore and aft, do pay some attention to the placement of your unit. Ours is in the rear, on what had been a roof vent. Great with a rear bed and may allow really long battery life at night, but not as good for our primary sitting area, forward.

Lots of compromises.

 

[ReluctantTraveler]

Have you published your proposed floor plan? With sleeping areas fore and aft, do pay some attention to the placement of your unit. Ours is in the rear, on what had been a roof vent. Great with a rear bed and may allow really long battery life at night, but not as good for our primary sitting area, forward.

Lots of compromises.

I'm not sure my sketches are good enough to make sense to anyone without me walking through it just yet.

The plan for the rear bunks is to have them above the dinette benches. They're going to fold up against the wall when not in use, for more head room while sitting and eating.

What you described is why I've been hoping to have something either ducted, or ductless mounted mid-rig for even distribution in both directions (like we have in our current travel trailer).

I know many 4-sleeper expedition rigs put all of the sleeping spaces together (ex. a convertible dinette in front of the main bed). We take extended trips in ours, and having some separation of sleeping space for additional privacy is a major goal with this build.

As you noted, comprises!

So many little decisions and tradeoffs you need to make as part of the process. To be honest, it's a lot of fun, though challenging at times!

 

[DiploStrat]

Are you building your own box? If so, have you thought of simply building your own ducts, perhaps with booster fans?

You might dump the cold air into a plenum and then use something like a bilge fan (with a speed control to reduce noise) to force air into your two sleeping areas. Ideally, you want a big fan with low volume for low noise. There are some ideas here: https://www.amazon.com/s?k=6+inch+b...x=6+inch+bilge+fan+12v,aps,517&ref=nb_sb_noss