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Old 19-07-2016, 09:47   #1
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Bare with me here - Reefer as A/C

Okay so I know this is a dumb idea but the more I think of it, the more potential it has.

Here is the background:
I have a 1979 Pearson 365 Sloop. Great Vessel. I have a standard Ocean Breeze A/C which does great when running from the dock. On the hook, I know if I were to try to run it off a Honda 2K generator it would be just a bit more than the genset could handle (probably have to have a 3k which is just too big and also $1900) , plus the whole noise, gas on a diesel boat issue, and other issues.

I live / sail mainly in Florida. 4 months of the year it is HOT. Like 90+ heat index in the evening! A little breeze (with LOTS of humidity) brings down actual temps to low 80's but the Heat Index stays up about 90 at night in the boat.

So recently I replaced the original AB Fridge system. I mean at 36 years old, I couldn't complain about the service life. Got a good price ($850) for an Isotherm 2501 - installation was easy - cools GREAT! Draws 1-5 amps depending on how much I open the cold box.

Proposed Idea:
SO that is what got me thinking. What if I bought another Iso 2501, installed in the bottom of my starboard locker in the forward compartment, built a water proof box on the next shelf up for the evaporator, added a blower to blow over the evaporator and out into the forward v berth, and only ran it right before I went to bed, until the humidity and temp dropped a bit. Maybe pulling 7 amps for 5 hours of cooling in that fwd compartment only. Say 35 amps for the evening of relaxing sleep in the v berth. As this is an air cooled unit - Hot Air cold be directed into head which has roof hatch. Many little issues to be thought out but I think you get my drift.

Assumption is 250AH House Bank (4 6v T105's in 12v config)
Recharge via 2 x 250W solar panels on mppt controller
Total average battery usage on hook or underway is 85 amp per day
so on the days we used this hybrid a/c kludge we would use 135 amps per day.

So Much Better than a gas generator and all the accompanying issues.

So how bout it friends? Is this a ridiculous idea?

Look forward to your thoughts, ideas, etc
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Old 19-07-2016, 09:56   #2
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Re: Bare with me here - Reefer as A/C

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Originally Posted by Jhowell5558 View Post
So how bout it friends? Is this a ridiculous idea?
I have been sailing for over 40 years now and have never heard someone use a refrigerator for Air Conditioning...

Using a refrigerator would not be effective on Florida's humidity and it would be inefficient as a cooler, even if you used multiple fans and ducting.

So the answer to you question is.... In my opinion this is a ridiculous idea!

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Old 19-07-2016, 13:24   #3
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Re: Bare with me here - Reefer as A/C

A fridge usually pulls about 5 amps max at 12 VDC or so, that about 60 watts
An efficient 16K AC pulls about 11 amps at 120 VAC, or about 1320 watts, Using a fridge as an Airconditioner will work of course and provide about 1/22 as much cooling as a 16K Airconditioner. 1320 divided by 60 = 22


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Old 19-07-2016, 14:05   #4
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Re: Bare with me here - Reefer as A/C

40 plus years in HVAC here. .. No my dear... tis not going to work.

A boat in Fla that size would need TONS! of AC.

a "ton" of ac is 12000 btu

the little, and I mean little refrigeration units are only about 300 - 600 btu. not even close AC cooling requirements.

They will cool a space! about the size of the box they are cooling now.... not, much larger.

refrigeration horsepower by old school figuring was 12000 btu also.

you would need 2-3 tons or 2-3 hp of ac to cool the whole boat.

by comparison a walk in box about 8X8 X 7 high only needs about 1/3-1/2 HP to keep it 38 degrees.

electrically the little refrigeration units will not stop running.. just like leaving the door open on the home fridge eventually they will go off on high amp draw and maybe never restart. Air conditioning compressors and refrigeration are designed/built for different duty factors. "Low temp" and " high temp" as called in the trade.

There are many more reasons, but that should cover it. And no.. you are not the only one that's thought of how to cool a boat in hot places without large electrical requirements.
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Old 19-07-2016, 14:40   #5
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Re: Bare with me here - Reefer as A/C

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A fridge usually pulls about 5 amps max at 12 VDC or so, that about 60 watts
An efficient 16K AC pulls about 11 amps at 120 VAC, or about 1320 watts, Using a fridge as an Airconditioner will work of course and provide about 1/22 as much cooling as a 16K Airconditioner. 1320 divided by 60 = 22


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The figures are much worse than that because fridges are much less efficient at cooling than aircon. The Coefficient of Power (COP) of a fridge is about 1.6, whearas a decent aircon will be over 4x, so more than twice as bad as your figures show.

I actually have a fridge freezer aircon so to speak and it does nothing much. I have a very small cabin with a keel cooled fridge in it, which runs non stop when on, so all the heat that can be is sucked out of that cabin and dumped by the keel cooler into the sea. A 1 deg C or max 2 deg temp drop maybe compared to the rest of the boat. It's a 35w unit.
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Old 19-07-2016, 15:35   #6
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Re: Bare with me here - Reefer as A/C

I run my 16,000 BTU WEBASCO from my little Honda 2000. I added a hard start capacitor to the AC unit. I also can feed my generator from my 3 gallon outboard motor tank. The longest I ever ran it was more than 15 hours between gas refills!
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Old 20-07-2016, 08:58   #7
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Re: Bare with me here - Reefer as A/C

Sorry Jhowel but the short answer to your question is YES. Both AC's and freezers are designed to meet specific needs. As others have pointed out the power demands for an AC are very much larger then even a very large freezer. Why not get a diesel generator like my Westerbeke 4.0? It runs my Cruisair stowaway turbo with no problems despite the Florida heat. Like you, I would reject the idea of gasoline aboard except for the small can that lives in the dinghy.
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Old 20-07-2016, 09:10   #8
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Re: Bare with me here - Reefer as A/C

we would use window units for wine cellars. There are refrigeration units that do "high temp" But unlike AC they are just a tad colder and maintain in the 40-65 degree range.
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Old 20-07-2016, 09:15   #9
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Re: Bare with me here - Reefer as A/C

If you have the 2000 and are willing to jury rig something silly looking, I would suggest a 5000btu window unit with a box built to fit it into a hatch.


That should do a pretty good job if you can close off the berth.
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Old 20-07-2016, 09:41   #10
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Re: Bare with me here - Reefer as A/C

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If you have the 2000 and are willing to jury rig something silly looking, I would suggest a 5000btu window unit with a box built to fit it into a hatch.


That should do a pretty good job if you can close off the berth.
Why reinvent the wheel? The Cruiseair Carry On doesn't need a box built and there are plenty available for $200-$300 second hand. Mine was used, still blowing ice cold 3 summers later. They seem very well built. Bacons in Annapolis Maryland has several used ones on consignment.

https://youtu.be/-bd-HODgZCk
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Old 20-07-2016, 09:48   #11
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Re: Bare with me here - Reefer as A/C

For portables, the Cruseairs are hard to beat, I didn't know about the used option.
I have seen many window units in the companionway, course then you get to climb over them each time.
5,000 BTU isn't much, beats nothing by a wide margin, but as a comparison point I have 21,000 BTU and on a hot day I could use more, but I do not have any kind of shade tent and I know that would help a lot if I did.
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Old 20-07-2016, 09:50   #12
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Re: Bare with me here - Reefer as A/C

Refrigeration is only heat transfer how do you plan on evacuating condenser heat? It sounds as though you want to make cool at a reduced efficiency and then add the heat back into your cabin?
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Old 20-07-2016, 10:23   #13
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Re: Bare with me here - Reefer as A/C

If you insulated a coffin sized box it might work
You get the picture ?
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Old 21-07-2016, 21:22   #14
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Re: Bare with me here - Reefer as A/C

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Why reinvent the wheel? The Cruiseair Carry On doesn't need a box built and there are plenty available for $200-$300 second hand. Mine was used, still blowing ice cold 3 summers later. They seem very well built. Bacons in Annapolis Maryland has several used ones on consignment.

https://youtu.be/-bd-HODgZCk
We had one on a previous boat. Better than nothing and no need to fabricate a mount but wouldn't trust it to stay in place in a rocky anchorage and was looking for the ability to use it away from dock.

Of course if you are talking used, a $50 window unit and some scrap lumber is even cheaper and you could build it braced so it would handle most lumpy anchorages.
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Old 21-07-2016, 21:53   #15
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Re: Bare with me here - Reefer as A/C

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If you insulated a coffin sized box it might work
You get the picture ?
Or just run a cold air duct into your sleeping bag.

I originally wrote this as sort of a joke but now that I think about it, it sounds great.

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