AC Electrical Expense?

[Blue Crab]

Curious about cost of running the AC 24/7 on a 39' Prowler Power Cat Cub.

The boat owner is paying $45 a month flat fee. I suspect that is far too little.

Anyone have a ballpark number for the monthly elec bill?

Thanks

[Sailmonkey]

We racked up a $50 bill just running a dehudifier on high for a month (following a hosing and bleach scrubbing of the interior)

[StuM]

As a rough estimate:
A 24000 BTU aircon (appropriate for a 40-45ft boat) runs at around 2.5KW.
That works out to about 1800 KWh per month if run continuously.

So multiple your local KWh rate by 1800. i.e. If it's 10c per unit, that's $180 per month.

[Blue Crab]

Perfect Stu. Thx. That's what I needed to know. This big ugly thing is near me (too near ... I hate marinas) and the owner told the marina it was 29' long and nobody questioned that or apparently even thought about it for an entire YEAR (while moving it by hand twice) til old troublesome Blue Crab came along with my critical eyestalk for detail.

You big boat guys, consider this: This giant 39' cat which must be a 1/4 mile wide and 100' high, is paying $6 US a foot as a non-liveaboard ... $172/ month plus a flat $45 US for elec service with AC running 24/7 ... $217 per month ... because he's here with a bunch of retired redneck rubes in their gated community.

He pays less than I do! That's what got my attention ... unfortunately for him.

[valhalla360]

It's a bit more complicated.

Is it really running 24/7?
Also, what size AC unit does he actually have?

If they have an undersized unit and it's only on a 50% duty cycle, it could easily be in the $50/month range. When we are on metered electric, that's pretty close to what our 12,000btu unit runs uses in hot humid weather.

Are you managing the marina? I would be wary of the law of unintended consequences. Even for a 29' boat, that is a bargain. Does someone decide they need to raise all the rates and hit everyone skirting the rules up for extra cash?

[motion30]

Running one 12000 and one 16000 btu. Units. Electric is $150 over my normal bill. Which is around $50

[Blue Crab]

Originally Posted by valhalla360

It's a bit more complicated.

Is it really running 24/7? Only 30 days a month on average.
Also, what size AC unit does he actually have? ????????

If they have an undersized unit and it's only on a 50% duty cycle, it could easily be in the $50/month range. When we are on metered electric, that's pretty close to what our 12,000btu unit runs uses in hot humid weather.

See Stu's comments above.

Are you managing the marina? I would be wary of the law of unintended consequences. Even for a 29' boat, that is a bargain. Does someone decide they need to raise all the rates and hit everyone skirting the rules up for extra cash?

I hear you. I was here last hurricane season on metered electric and portable ac : $57 a month. Moving back to metered electric tomorrow to make a point. I'm not seeking the job but I may get an offer, as I'm the only one here who can tie a bowline or even knows what it is.

Based on Stu #s above, with the elect here at 9.98 cents in the summer, the cost is at least $180 a month. I passed this story on to my old dive shop where this boat used to be slipped, and the owner thought the Ac would be $250-350 a month.

At some point it starts to be criminal behavior in my view.

[piloto]

So, a work in progress. A friend of mine who occasionally works for DOE and NREL in renewable energy, and has a phd in nuclear physics calls me and tells about an energy efficient 6,000 btu AC unit that uses 500W made by Frigidair in the 52nd state (of china) costs $179 @ Home despot. Cools 250sf of room. I bought one. Taking it down to the boat, throwing on 550Watts of solar panels and running it through a Xantrex 2kW sine wave inverter and turning it on. Cost for running after installation? $0

[StuM]

Originally Posted by piloto

So, a work in progress. A friend of mine who occasionally works for DOE and NREL in renewable energy, and has a phd in nuclear physics calls me and tells about an energy efficient 6,000 btu AC unit that uses 500W made by Frigidair in the 52nd state (of china) costs $179 @ Home despot. Cools 250sf of room. I bought one. Taking it down to the boat, throwing on 550Watts of solar panels and running it through a Xantrex 2kW sine wave inverter and turning it on. Cost for running after installation? $0

Good luck with that. Depending on where you are, I'd guestimate that 550W will give you 200-250 Ah per day at most. That will keep your aircon running for maybe 4 - 5 hours.

What sized boat? That 250 sqf is a maximum for 6000 btu. Common guidelines are anything from 100-180 to 150-250 sqf for a room in temperate climates (where are you based?). And that's for a decently insulated room inside a house. It won't cool nearly as large a volume in a boat sitting in the sun.

[colemj]

Originally Posted by piloto

So, a work in progress. A friend of mine who occasionally works for DOE and NREL in renewable energy, and has a phd in nuclear physics calls me and tells about an energy efficient 6,000 btu AC unit that uses 500W made by Frigidair in the 52nd state (of china) costs $179 @ Home despot. Cools 250sf of room. I bought one. Taking it down to the boat, throwing on 550Watts of solar panels and running it through a Xantrex 2kW sine wave inverter and turning it on. Cost for running after installation? $0

That 500W is the draw at 120V AC. This will be about a 50A DC draw on the batteries from the inverter. Your 550W of solar will only provide ~30A of that DC draw for a couple of hours/day, and less than that during the rest of daylight. You will end each day with lower batteries, and this will spiral down quickly unless you charge them with other sources. Depending on the size of your battery bank, I suspect you will have dead batteries within 3 days.

Mark

[Blue Crab]

AC and solar .....$ 1,000
PhD in Physics ...$ 150,000
Dead battery in 3 days ..... Bummer

[piloto]

Sorry to differ Mark, but 500W is 500W on either side. It ampacity that would differ in calculation. As to the 5 or 6 hrs. a day of run time, that's fine. If I'm sitting inside a boat for that long, I need to get outside! There is the issue of conversion efficiency of 10% to 15%, depending on where you are on the power curve of the inverter. As to running the batteries down, the 550 is dedicated to that particular item as the initial set aside. Another 550 goes to the house batteries bank and starter battery. I may just run the AC unit off of a single separate battery and separate smaller inverter, thereby sidestepping the whole run down on the house and start batteries. As I said, it's a work in progress and the worst thing that can happen is I find out I'm only half right, or half wrong? Anyway, my friend has already done this with a separate battery and small inverter, so no interaction with other parts of the system. The idea is just to keep up with the coincidental load and supply of this one device.

[piloto]

Blue crab, luckily it's not my post hole digging degree and I don't know the he spent that much getting his, but.... a) not a bummer if it works, b) only risk is the AC unit ($179) and small inverter ($100 to $200). The battery can be repurposed at any time (put a meter and data logger on it) and so can the panels (back to the main bank). Again, work in progress. If I've learned anything, besides premature admission of defeat, not a bummer just a little cooler for awhile longer. Then I could see about fitting a unit to a standard hatch and selling a boatload of the systems to the weak & hot. But maybe you're right, I should give up and resign myself to the advanced stages of dementia, write my memoirs before I forget everything. This is your brain, this is your brain being fried on the boat while trying to write... Anyway, worth a try and I'll let you know how it goes.

[Blue Crab]

I hear you sir. I like the post-hole comment. And I am reading this in air-conditioned comfort, coffee close at hand. On the hook tho, I make do with 12 volt fans and cold beer.

[DotDun]

Originally Posted by piloto

Sorry to differ Mark, but 500W is 500W on either side. It ampacity that would differ in calculation. As to the 5 or 6 hrs. a day of run time, that's fine. If I'm sitting inside a boat for that long, I need to get outside! There is the issue of conversion efficiency of 10% to 15%, depending on where you are on the power curve of the inverter. As to running the batteries down, the 550 is dedicated to that particular item as the initial set aside. Another 550 goes to the house batteries bank and starter battery. I may just run the AC unit off of a single separate battery and separate smaller inverter, thereby sidestepping the whole run down on the house and start batteries. As I said, it's a work in progress and the worst thing that can happen is I find out I'm only half right, or half wrong? Anyway, my friend has already done this with a separate battery and small inverter, so no interaction with other parts of the system. The idea is just to keep up with the coincidental load and supply of this one device.

Yes, 500W is 500W, but I think you are severely underestimating the efficiency/loss of the inverter/solar/charger/batteries combined. A guess would be 10% less from the solar panels, then another 10% on the charger, battery efficiency(??), and 15% from the inverter. Guessing you would be lucky to run the AC 3-3.5 hours/day.

Do report back on the actual numbers you experience.