High Efficiency Air Conditioning Units for non-generator powered campers

[S2DM]

That's 600w at 110v, or 60A at 12v. (Grossly - allow some slop for inverter losses.) This is roughly what my Sharp AC consumes when the compressor is running. Typically you would have to size your inverter to allow for a starting surge of up to 5x. I use a 2800w inverter, might be able to go smaller with soft/hard start.

That part is easy. The fun comes in battery life. Assume a reasonable evening, so the compressor cycle is 50%. That gets you 30A consumed per hour. If lead acid batteries, then Peukert is going to increase that a bit. Sooooo, with a 600Ah lead acid battery bank, held to a 50% DOD, I get 300Ah/30 or about ten hours. Maybe better if I use the energy save setting, which I don't, because of noise and temperature swings.

Bottom line, this is right on the border line for overnight use, especially in warmer, more humid climes.

Solutions?

-- Bigger, lithium iron battery bank.
-- True 12v compressor.

All of the efficient mini splits actually use a dc compressor that is infinitely variable, which is where some of the efficiency come from (variable compressor speeds). Apparently they generally run on higher DC voltages though, so some inversion or step up would still be required.

Your math looks spot on.

Ours pulls ~450 watts. 37 amps per hour (our batteries float at mid 13s) so probably slightly lower on amps. 50% duty cycle, rounded up for inverter and transformer losses, 20amps/hr. 400 amp lithiums at 80% discharge = 320 useable amps = 16 hours at 50% or 8 always on.

Other factors to consider is how long your solar array takes to fully charge your batteries the next day if you take them down to their respective full discharge/if you are also running AC during the day. Ideally the system would be sized to fully charge from full discharge while still allowing enough solar to use Ac during the day and maintain other vital camper functions. LeishaShannons rig has 1200 watts fixed high efficiency LG panels and 400 watts of lower efficiency panels and they still occasionally have to run the truck.
Short answer is it takes a very efficient AC, a ton of Solar, and you'll still probably have to occasionally run the truck in the hottest climes.
Our interior space is fairly small and very well insulated, so I'm hoping my duty cycle will be closer to 25%, but I don't have any real world numbers on it yet.

 

[DiploStrat]

…
Your math looks spot on.

One hopes, as it was taken from two years of real world in our Tiger. Just haven had the courage/need to go to bed with the A/C running on batteries yet. ;-)

 

[S2DM]

One hopes, as it was taken from two years of real world in our Tiger. Just haven had the courage/need to go to bed with the A/C running on batteries yet. ;-)

In general, have you appreciated having it? At times I question my decision to include it in the build. I only use it a day or two a year at home, same with heat, and it's been a costly, time consuming effort to physically accommodate it in the design. But it was too tempting to resist including it in the camper. Just hope it wasn't hubris

 

[campo]

The first problem is that I do think that it is not possible to use these high efficient EER Mitsubishi, LG or other split units on expedition or off road vehicles. The vibrations are ,in that order that it's almost impossible to reinforce the interior components and the plastics. The deadly dangerous voltage 110/230V makes that any risk should be completely excluded, also water infiltration.
Another principal problem is that you win with high EER but lose some 15% with the conversion from 12 or 24V DC to 110 (US) or 230V (Europe)

The theoretical best solution is to build your own split AC system with only 12 or 24V DC components. I have a 24V DC split system that makes up to 1800 cooling Watt maximum for some 30A/24V at maximum speed. It works up to 12 hours on 440Ah/24V battery bank on half speed at 900 Watt cooling and 17Amps/24V . It's still too noisy. The better components could be found in the more modern boat 24V inverter based AC systems. But as it is … nothing cheap to build. And a hell of a job.
Campo

 

[LeishaShannon]

Another principal problem is that you win with high EER but lose some 15% with the conversion from 12 or 24V DC to 110 (US) or 230V (Europe)

The 15% (closer to 10% with a decent inverter) loss is tiny compared to the power the DC based units consume.

I have a 24V DC split system that makes up to 1800 cooling Watt maximum for some 30A/24V at maximum speed.

Thats 720W of consumption for 1800W of cooling whereas a Mitsubishi would use just 315W or 350W taking inverter losses into consideration.

Now you have to carry twice as much battery and solar for the same run time, which isn't really practical for most vehicles.

I get that domestic split systems may not be built to handle off road vibration, but when they cost less than 1/4 of a DC solution including the inverter you're able to replace them 4 times and still be ahead. They're also available and serviceable pretty much anywhere in the world, unlike specialist DC systems.

Not to mention the significant cost and weight saving of the additional solar and batteries.

I can't see any advantage in DC units except they -may- be built better, however if the roof top RV units available in Australia are anything to go by they most definitely aren't.

 

[Pntyrmvr]

Hi,

Traditional split systems use a pan to collect the condensation that drips off the evaporator while in use. The instructions for the unit stress level mounting so the drain tube can keep the drip pan flowing. Parking the rig level is SOP for us so no problem. I wonder what happens when one drives off the levelling blocks in the morning and the drain pan sloshes to one end, over the lip, and drops cold water on the bed. I also wonder about the beating the pressure fittings will take on a long washboard run. Nothing about a split system was meant to do what we want it to do where we want it to do it; in a 4x4 cabin.

How about taking a Danfoss compressor and controls meant for a custom marine fridge/freezer space and combining them with a generally easy to find rear a/c heater combo from a wrecking yard van like a late model Ford? Best of both worlds. Both ends of the system are meant for mobile, 12 volt use. One of our mathematically inclined members could easily read up on the marine unit and figure out the Btu capacity. I have no doubt the Ford evaporator specs could be found as well.

Regards,

Gavin


"Talk is cheap. Whiskey costs money."

 

[DiploStrat]

In general, have you appreciated having it? At times I question my decision to include it in the build. I only use it a day or two a year at home, same with heat, and it's been a costly, time consuming effort to physically accommodate it in the design. But it was too tempting to resist including it in the camper. Just hope it wasn't hubris

I didn't really have a choice - A/C is standard. I did consult/test the implementation.

Worth it? Absolutely; I live in the Eastern US; we do heat and humidity! More complex than a rooftop unit? Yes, condensate drains and booster fan for the compressor. But there was a height savings and the 6,000 BTU unit is quieter than rooftop units.

So, when we NEED A/C, we go to a campground and plug in. At other times, the ability to run for a few hours on battery is simply wonderful.

 

[adam88]

I think the true 12v models that run off danfoss compressors are worth a second look. The loss of efficiency to the inverter is worth noting. Specifically, the 12v "cube" air conditioner, which is a portable A/C unit: http://www.u-gofresco.com/en/

This is 3,250 BTU which is perfect for a small well insulated camper. It says it uses 36 amps MAX at 12 volts, but I believe it would be less in certain conditions. That is the max rating.

But let's look at the pros:
.
1) Portable. Remove it from your camper in winter and have extra storage space. Why haul an AC around 365 days of the year?
2) Self evaporation. No drain required.
3) Can vent through a window. No holes in the side of camper required
4) Built specifically for mobile use. Looks durable and able to easily withstand offroading
5) 12v. No inverter required. Safer and no inverter loss.
6) Can be used anywhere, other vehicles... your boat... your house... etc.
.
The cons would be:
.
1) Not as efficient as a mini split
2) Expensive. $1500 USD at least. Can buy a lot of $150 air conditioners for that and a nice inverter.
3) Parts. If it breaks who will fix it (although its not a critical unit).
4) Might not have enough power at 3250 btu for some people.
,
I think this unit is about as efficient as the model diplostrat is using on a btu to watt basis. I think Diplo, correct me if I am wrong, but you stated your ac can use around 60 amps when running?

 

[adam88]

I was hoping to build the system around 1400 watts of solar but the roof is only 7 Foot 6 by 14 foot and the most efficient panels that I found I can only get 1250 watts of solar to fit.

Look at Renogy Eclipse 100w solar panels. Just released. They are $219 each and they are much smaller than normal panels because they use high efficiency cells. If your roof is 7.5 feet by 14 feet you would be able to fit 16 panels on it easily. So that's 1600 watts.

 

[1aquaholic]

Thanks adam88.

Has anyone had experience with Microcell Carbon Foam batteries?

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[S2DM]

This is a little off topic, but it seems the AC interested folks are somewhat assembled here, so I have an ancillary question.

Please poke holes in this and convince me its a bad idea :ylsmoke:

My camper is a lifting roof design. One hurdle with a Mini split lifting roof install, all of the components need to be in the bottom box, I.E. my blower unit can be no higher than waist level. Because domestic AC splits utilize simi rigid lines and the top box (roof) lifts, having the condenser in the floor and the blower in the top didnt seem feasible. So, I designed it into my kitchen cabinets, under the countertop, and have it set to blow into our bed area. Alas, I miss having the drawer under the counter, there are some hurdles with having it there as well in terms of air intake that I have come up with an ok solution for, and the unit would be more effective up high.

I'm playing with the notion of either using one of the new stainless braided flexible line sets, or even going the automotive route, and using reinforced (internally braided) rubber line set. This would allow me to mount the AC over the kitchen counter. The line would have a pretty good amount of room to form a big raidus as the roof is going up and down. Yet to figure is drainage.

It seems conceptually possible, but I am sure there are hurdles I havent considered. Would love any input..

 

[Pntyrmvr]

I'd go stainless as the OE style rubber never seems to survive any type of motion. Your setup would have to allow hoses to be in motion (swaying) constantly. I believe the risk of a rubbing through would be lower with SS.


"Talk is cheap. Whiskey costs money."

 

[1aquaholic]

I'm just going to set this right here and slowly walk out of the room.

https://www.kickstarter.com/projects/kurt/noria-cool-redefined/description

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[OCD Overland]

I was looking at that one myself. It seems like a neat little unit - 5000btu, 4 amp, 10.4 seer. Doesn't say what the peak amps are. But it's only 30lbs and so easy to install/remove that you could leave it stowed while traveling and only snap it in place when needed. Leave it at home when you know you won't. Or if you have a need, use it at home and just take it with you when you leave.

 

[IdaSHO]

I see nothing particularly special about that unit, besides the connectivity features.

Does look nice, is light, and compact.

From the specs provided, it doesnt draw much less, if any, than a traditional 5k BTU unit.

Operating in a 12 Volt system it will still be drawing 40+ amps when running.