Newbie wants to run 24,000 BTU AC

[sdold]

Your plan is underpowered for what you’re trying to do. A 24,000 BTU split usually averages ...

Where are you located? Do you have a solar-related business?

[J.P.M.]

Your plan is underpowered for what you’re trying to do. A 24,000 BTU split usually averages around 1.2 to 2 kW while running, so over six hours you’re realistically looking at 7 to 10 kWh of consumption, not 6 kWh. Your battery sounds large at 1,800 Ah, but at 12 volts and with real usable depth of discharge plus inverter losses, you’re closer to about 10 to 11 kWh usable, which leaves very little margin for daily cycling. The 3 kW inverter is also likely undersized because these units can have higher peak demands, so a 5 kW class inverter would be safer. With only 1.2 kW of solar, you will not reliably replenish what the AC uses each day, so the system may run the load but will steadily drain the battery and struggle to sustain that schedule long term.

You are responding to an almost 3 year old post.

[J.P.M.]

Assuming we work with the latent heat of fusion and ignore sensible heat, its 144 btus per pound of ice so that is 153 pounds of ice to cover one hour of operation of the AC. The volume of the ice is about 57 cubic pounds per cubic foot or 2.68 cubic feet of ice per hour.

Every time I looked at ICE storage for inlet air cooling on gas turbines, the numbers just would not pencil out. Even on facilities unless the capital cost was offset with grants, they didnt pencil out.

There was an individual I believe in upper New York State that built an ice chest in the basement surrounded on five sides with water with a very well insulated front door. He installed a coil in the tank run to an outdoor coil filled with refrigerant making sure all the lines were sloped properly.. In the early winter, the freon vapor would rise to the outdoor coil, cool down and condense into liquid and run back down to the basement tank which would gradually freeze solid. The ice storage was sized to last the entire summer. It was in the early days of the internet and I have lost track of the link, it was on a Bild it Solar type site.

I too recall something like that in Mother Earth News from the late '60's - early '70's or so but the past is getting fuzzier as time goes by.

I piddled around with seasonal storage (but mostly for HVAC heating wet dreams for cold climate applications) and came to the conclusion that it was more hassle, and as a practical matter less likely to work as well as very difficult to accomplish in a cost effective way than other ways of skinning the alternate energy cat.

If I was looking to cool a space now and wanted to exercise my eccentricity, after I reduced the heat transfer at the boundaries of the conditioned space as much as might be cost effectively possible, and if I had a freezer and a swamp cooler, I'd dump the ice from the freezer into the swamp cooler and let it sublime to vapor and maybe some left over latent heat of evaporation for the remaining melt. Although that melt evaporation probable wouldn't work very effectively in what are probably high dew point Carribean conditions, that will most likely be offset by the idea that the sublimation process of H2O takes place below 0 deg. C under the described conditions.

[peakbagger]

Assuming we work with the latent heat of fusion and ignore sensible heat, its 144 btus per pound of ice so that is 153 pounds of ice to cover one hour of operation of the AC. The volume of the ice is about 57 cubic pounds per cubic foot or 2.68 cubic feet of ice per hour.

Every time I looked at ICE storage for inlet air cooling on gas turbines, the numbers just would not pencil out. Even on facilities unless the capital cost was offset with grants, they didnt pencil out.

There was an individual I believe in upper New York State that built an ice chest in the basement surrounded on five sides with water with a very well insulated front door. He installed a coil in the tank run to an outdoor coil filled with refrigerant making sure all the lines were sloped properly.. In the early winter, the freon vapor would rise to the outdoor coil, cool down and condense into liquid and run back down to the basement tank which would gradually freeze solid. The ice storage was sized to last the entire summer. It was in the early days of the internet and I have lost track of the link, it was on a Bild it Solar type site.

[J.P.M.]

I think we need to come up with a home brew ice plant so the PV freezes the water into ice and then cooling come from ice melting

Depending on the application and load, that might not be as impractical as it might sound.

[peakbagger]

I think we need to come up with a home brew ice plant so the PV freezes the water into ice and then cooling come from ice melting

[bcroe]

The direct PV panel powered heat pumps are another option. They
are generally a big advance in reducing energy consumption and CO2
emissions, with far quieter operation. This without troublesome batteries.

But they still suffer from the problem of renewable energy production
not lining up with consumption. Your situation may usually have good
sun coincide well with the need for AC. Or, it may not, and what about
operation for heating? Batteries may not be a practical fix for energy use
on this scale overnight, and never between seasons.

The PV option HVAC will certainly reduce energy use any time the sun shines,
but never eliminates consumption when used with grid connected backup. If
the sun shines but no cooling is needed, the energy available from those
panels is lost. There is the issue, that once connected to HVAC, the PV panels
cannot be connected to anything else. This is a matter not discussed, and
under some scrutiny here as a partial solution if my net metering ended. Also
not discussed, is the use of dual arrays favoring early or late parts of the day.
to increase total time of capacity operation.

So the best solution depends on each individual situation. Here the favorable
Net Metering program with 1:1 energy exchange allows maximum efficiency
of my facilities, which might not work for many others. It goes like this:

Mini split heat pumps are selected which cover the temp range here, which
can drop well below 0F, and for highest SEER. There is resistance heat
backup heat available, but never used. Instead more mini units are used
which may drop to the same COP of 1 in really extreme cold, but that
condition is uncommon. They all operate on 240VAC, which requires space
for a lot of double circuit breakers, but saves a lot on wiring.

Benefits of these Mini Splits include highest effiency and very quiet operation.
HVAC is decentralized, so no one failure can cause complete system shutdown.
The old duct air system blower is still cycled regularly to help even out temp
and humidity, and to let the electronic air filter remove dust and pollen. They
lend themselves to far cheaper DIY installation, mounted under a large roof
overhang and several feet above the ground (on a brick wall) to stay clear of
snow.

The PV solar system operates independently, with Net Metering giving full
credit for summer KWh, to be used when most needed in winter. The PV
system may be as large as needed, to generate enough energy for 24/7/365
use as needed. No potential PV output is lost. Energy surges are handled
by the PoCo. Of course all electrical, as well as HVAC needs, are covered,
ongoing energy charges for electrical and HVAC are zero. Maintenance is
very low, mostly checking energy flow and reserve from time to time.

Bruce Roe

Mini51.JPG

[MangoCat]

...seeing how there's mini-splits that are basically shipped to a customer turn-key, I would emplore OP to take a look at those systems as they will do the job and are proven setups.

Otherwise, going the route of a diy solar energy system will help that existing system run off of solar--you'll just need to overbuild it since you're using less conventional (and efficient) parts.

Yeah, I'm on the fence, myself. My workshop is in the planning phase, so I _could_ go with the turn-key solar A/C, but then that would leave me building a parallel system to charge the tools, etc. I do agree, the existing standard A/C compressor is going to need a lot of overbuild / overcapacity to work, and OP may end up with more spare capacity than he knows what to do with by the time he's got the 24,000 BTU conventional A/C running from solar+battery. Also worth mentioning, batteries are rated in charge/discharge cycles - not really years - so if your A/C setup is charging / discharging your batteries 6 to 8 times a day, that 3000 cycle battery will last closer to 2 years than the manufacturer's advertised 10 years.

[SamirD]

Thank you so much for the links!! What a rabbit hole! There's a lot of development in this area.

After looking at the various options out there and seeing how there's mini-splits that are basically shipped to a customer turn-key, I would emplore OP to take a look at those systems as they will do the job and are proven setups.

Otherwise, going the route of a diy solar energy system will help that existing system run off of solar--you'll just need to overbuild it since you're using less conventional (and efficient) parts.

[littleharbor2]

Hopefully my previous post will be approved. It simply listed the solar powered mini split ac units I found on the internet. I have no affiliation to any of them. If not, the OP just needs to google "solar powered mini split"

[littleharbor2]

EG4 Hybrid Solar Mini-Split Air Conditioner Heat Pump AC/DC | 12000 BTU | SEER2 22 | Plug-N-Cool Do-It-Yourself Installation (PRE-ORDER) - Signature Solar

Airspool MS12: Solar-powered mini split air conditioner (12,000 BTU/1-

DC Solar Air Conditioner Heat Pump | Solar Air Conditioning | Solar Heating | Manufacturers (hotspotenergy.com)

ACDC12C Solar Air Conditioner Heat Pump - Practical Preppers

Solar Powered Air Conditioners: A Comprehensive Guide (cielowigle.com)

[SamirD]

I think your best shot would be to
use a mini split or other unit designed to run directly from solar panels.

I had no idea units designed to work directly from solar existed. You have a link to one? I'll research more from there.

[MangoCat]

Just to emphasize an earlier poster: many new mini-split AC units have "inverter technology" which in their world means that they can run the compressor at fractional power, just what you need not the full 24,000 BTU or 0. This makes them MUCH friendlier loads under normal circumstances, drawing a more continuous current and in connection with a solar system: needing less battery or wasting less PV capacity when the compressor is cycled off. I have a similar "inverter tech" 12000 BTU marine A/C on our sailboat and it runs happily off of "shore power" at the marina, through a 15A breaker and a 75' 14 gauge extension cord carrying 110V, typical loads run around 4 or 5 amps while it is cooling (though on a blasting hot day it will crank up to around 12A to keep cool...) In theory it would also run through the 12V->110AC inverter we have on the boat, but I've never tried stressing out our alternator or lead-acid house batteries that way.

[Jommy747]

Ok thank you

[Ampster]

.... I don’t understand Pb. The truck battery is here local. No shipping. I know lithium is the way to go but $$$$$$

Pb is short for Lead. I understand shipping costs can change the economics and I don't know anything about the logistics to your island.