Powering Three 24 volt battery driven roof mounted rv air conditioners

[apcorob]

I am considering replacing my three 120 volt dometic 15k btu air conditioners (approx 1500 watts requiring the generator) with these 24 volt dc units which have a maximum draw of a little less than 1400 watts each (half that once the temperature is stabilized). The pdf with the specs is:

I am not worried at all about firing up the generator (8.5kw 120volt ) anytime it is necessary (I am never in a place I have to be quiet). I am putting these lower profile units on the roof so I can mount a "flat top" "shady" "aircraft carrier" solar panel array of eight 450 watt panels (total 3600) above the air conditioners. With that said I would like to be able to go 14 hours through the night without the generator with only one of the air conditioners working and little else.

I will probably get a Victron Easysolar inverter charger 3000 kva which will be lightly used for musical instruments, the refrig, computers and light use of the microwave.... Our 12 volt draw is small, few led's phones laptops etc.

I am completely unsure how to connect these three heavy power users to the batteries knowing that the could be fired up at the same time. Might even get a 800 watt dc microwave.

I am also unsure, even after reading many posts here, how large a 24 volt Lifepo battery bank I need to make this work comfortably. Please help me with seasoned advice. No need to overkill as the generator is always (24/7) an option.

My absolute number one concern is reliable service. I have no repair facilities within 500 miles of where the bus will spend its time; and, finally, sun is not the problem. I live on the equator in the middle of the rainforest where 98 degrees and 99 percent humidity is the norm.

Please help me with advice on the battery bank and how to wire this. I will hire a pro; but, want to have a good understanding also.

THANK YOU ALL IN ADVANCE FOR YOUR HELP AND ADVICE.

Rob

 

[curiouscarbon]

dear @apcorob, welcome and thank you for posting

pdf say 55A 24V rating = 1,320 W i guess peak since it says total.

4000 thermal Watt cooling for 1,320 electrical Watt = Coefficient of Performance 3

1,320 W * 14 hours = 18,480 Wh or ~19kWh to run a single unit at full blast for fourteen hours. but the temperature will probably stabilize a little if there’s some insulation, so maybe only 50-75% of that? maybe less?

with 98F 99%RH and those units mounted up above you, sounds like you should put a mini hydroelectric turbine on the condensate tubes!

hope this helps with scoping a bit. approximately max 19kWh per 14 hour period.

 

[apcorob]

This was hugely helpful.
Thank you....

Guys, is it safe to say that the high SEER mini splits will always deliver more cooling than roof mounted DC air conditioners for the same amount of energy at this time? I maybe should abandon my quest for the perfect dc unit and make a mini split work.

 

[chrisski]

maybe should abandon my quest for the perfect dc unit and make a mini split work.

IMO AC is a better choice for any high wattage appliance than DC. There are efficiency losses, but AC air conditioners have been around longer and are produced way more. You may find yourself with a 20% bigger battery pack and panels, but if reliability is a real factor, than you may not want to be blazing new trails with high wattage DC.

I think there is a reason that when over 100 years ago DC power systems and AC power systems competed against each other that AC won. I'm finding that a 12 volt and 24 volt build is easy to find components, but bigger than that they start to get expensive. Arcing is a concern with DC much more than AC and to get to the 120 volts these high wattage appliances need for power balanced against voltage loss and wire size, AC power needs to be used for safety.

AC power won not because Tesla was a better marketer than Edison, but it was actually better.

 

[curiouscarbon]

dear @apcorob
i have not done a full analysis of mini split vs 24 roof mounted, cannot say confidently categorically.

using ac will involve conversion losses 5-15%, right?

whether 24v type wins maybe consider Coefficient of Performance for each unit alongside AC Conversion Loss for a combined merit value.

a hypothetical 24VDC 10,000 thermal Watt cooler with CoP 8.0 would need 1,250 electrical Watt to act. very efficient.

a hypothetical 120VAC 10,000 thermal Watt cooler with CoP 8.0 would need the same 1,250 electrical Watts plus conversion loss of 15% (+187W) for total 1,437W.

changing out the numbers for CoP and AC Conversion Loss and evaluating for every device you consider and the clear answer should emerge! ??

 

[curiouscarbon]

also agree that 120v type mini split will probably be easier to engineer with more off the shelf parts to select and also have the 10-15% tax of conversion power.

i’m really interested in chasing the efficiency of 24V cooling with variable cooling power. personally if you can find a 120V mini split with Coefficient of Performance 5-6 then i would say get it and don’t worry about the conversion losses, because it will make wiring easier maybe. but does create high voltage source, with moist air maybe 24V is nice to not exceed? just rambling and thinking out loud at this point, cheers and good luck!

 

[curiouscarbon]

 

[HRTKD]

Rewiring for DC could be challenging. In my RV trailer I would not look forward to replacing the 120Vac wires with larger DC wires.