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Old 07-04-2015, 19:20   #1
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A/C Refrigeration

We are now looking for a 38'-43' sail boat and have found a middle of the road boat that we both can agree on (the Admiral and myself) but it has as A/C refrig and freezer. I noticed lots of boats for sale have the engine driven compressors as well. I'm shocked that sailors have such units requiring the engine to be ran or the use of their genset. The boat in question here is a 43' Irwin. I fully understand the benefits as well as the drawbacks of the Irwin. I dont want to start a "Boat drama war". I had a friend who had a rather large refrig that was 12v and worked great. Thats what I'm looking for as well. We would like to do some long range island hopping without running the genset so many hours per day. The owner didnt know how many hours was needed to run the genset to keep food cold or frozen. It would be much better to have a solar/wind running a 12v cold plate. The unit in the Irwin is a Sea Frost and the doors to the refer are very thick (maybe 6"). I'm sure it works great in the marina though. So both units, refer and freezer are very large and work off the same compressor and water pump">RAW water pump (just like the cruise airs). How difficult and at what cost would I be planning for changing the systems to 12v? Thanks for the help.
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Old 07-04-2015, 19:42   #2
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Re: A/C refrigeration

Installing 12vdc hardware into your existing system would be fairly simple and not very expensive.


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Old 07-04-2015, 20:00   #3
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Re: A/C refrigeration

Inverters that change 12VDC to 120Vac or rather efficient. They are not expensive and many people use a dedicated inverter to run their refrigerator.
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Old 07-04-2015, 21:10   #4
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Re: A/C refrigeration

If you are planning on cruising in remote areas and spending most nights at anchor rather than in a marina - than a 120VAC Refrigerator/freezer system is definitely a "no-no." A lot of the Irwin and Gulfstars were designed as "marina boats" where they were primarily kept in marinas and used for partying on the weekends. Definitely not for cruising as a live-aboard.

If you plan on doing some serious full time cruising then I would suggest you research building a real "sailboat" refrigerator/freezer system that is based either around an engine driven compressor or 12vdc system that feeds a very well insulated chest type cold plate system.

My boat originally had what appeared to be ordinary household 120VAC "bar refrigerators" in it. They went "over the side" and I constructed a top loading chest type box that was located underneath the galley counter. It had a vacuum panel lid/hatch set into the galley counter and when opened revealed a 8 cu.ft. chest that had a divider in the middle. I installed two 12vdc cold plate systems, one in each end of the box and put a separator panel/wall in between them making two 4 cu.ft. chests.
One 12vdc system was designed as a freezer and the other 12vdc system was set for refrigerator.
The box was something like this one: s/v hello world: fridge box construction

So I had two independent cold plate 12vdc compressor systems set up so that if one failed I could remove the divider and convert the box into one large refrigerator.

The rectangular box was built to R-30 using Home Depot R-Max Plus panels. After constructing the box and insulation I installed kitchen laminate panels as the interior liner for the box. For a discussion of insulation for the box see: Kollmann Marine

There are numerous good references on how to build a refrigerator/freezer box in the galley and the whole thing was not difficult and has lasted 20 years so far. I have a very large "house battery bank" to allow the 12vdc system to run as they need each day. Then either I run the engine, genset, or wind generator to keep the batteries full.
Here's another link: Marine refrigeration and freezer on 22 AH per day
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Old 08-04-2015, 05:55   #5
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Re: A/C refrigeration

Quote:
Originally Posted by Magnawake View Post
We are now looking for a 38'-43' sail boat and have found a middle of the road boat that we both can agree on (the Admiral and myself) but it has as A/C refrig and freezer.

How difficult and at what cost would I be planning for changing the systems to 12v? Thanks for the help.

Might be useful to compare costs of your own conversion (time, materials, etc.) to the cost of simply buying new DC/AC units that might fit your slots. Shop NovaKool, Vitrifrigo, others...

And then also assess your battery situation to support...

-Chris
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Old 08-04-2015, 06:32   #6
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Re: A/C refrigeration

Having just done an icebox conversion to spill over I can tell you it's not inexpensive.

If you have a 120V fridge and it's working fine and not in need of replacement, I'd go the inverter route and beef up Solar and or battery bank if necessary.

Building your own will take a long time and cost I believe at least $3,000, but if done correctly will in fact be better than most anything you can buy at any price.
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Old 08-04-2015, 06:35   #7
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Re: A/C refrigeration

If you chose to replace your compressors with 12V ones, I'd definitely only consider an air to air condenser, not water cooled.
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Old 08-04-2015, 07:27   #8
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Re: A/C refrigeration

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Originally Posted by ranger42c View Post
Might be useful to compare costs of your own conversion (time, materials, etc.) to the cost of simply buying new DC/AC units that might fit your slots. Shop NovaKool, Vitrifrigo, others...
And then also assess your battery situation to support...
-Chris
I good friend and fellow cruiser who is now working their way "down-island" had a good idea that has worked very well to increase the freezer capacity of their boat.

They purchased an Engel multi-power source frig/freezer box. These units run on 120VAC or 12VDC or 24VDC. Although not inexpensive, they come ready to go with a well insulated box, lid and components. I have even heard of folks who built a shelf or enclosure in the galley and "built-in" one of these into the galley permanently (sort of). That skips a lot of the work building a well insulated "box" from scratch.
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Old 08-04-2015, 17:14   #9
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Re: A/C refrigeration

Thanks for the replies. I am looking for an A/C, D/C model but maybe just a DC one would work. I cant figure for the life of me why someone would want a A/C only on their boat. Heck the engine driven are bad enough. Lots of boats we are looking at have them too. Sailors never talk about that point. So who out there can tell me about how many hours per day I'll need to run the genset to keep food cold. I'm going to search DC cold plates.
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Old 08-04-2015, 17:33   #10
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Re: A/C refrigeration

Quote:
Originally Posted by Magnawake View Post
Thanks for the replies. I am looking for an A/C, D/C model but maybe just a DC one would work. I cant figure for the life of me why someone would want a A/C only on their boat. Heck the engine driven are bad enough. Lots of boats we are looking at have them too. Sailors never talk about that point. So who out there can tell me about how many hours per day I'll need to run the genset to keep food cold. I'm going to search DC cold plates.
Are you sure it doesn't have a cold plate already? We have an A/C only fridge/freezer made by Seafrost. It freezes the freezer block to about 0F pretty quick. I have to run it for about 20 minutes 2-3 times per day in warm weather and less than that in cold weather. The initial freeze up takes about 45 minutes to an hour but I do that at the dock. If I don't run it for 24-36 hours the stuff laying on the cold plate stays frozen hard as a rock. The fridge side warms up a bit though. After 48 hours the cold plate temperature starts to rise above freezing.

I like having the A/C fridge because it provides a good load for the generator when recharging batteries or running the air conditioner. When not using the freezer we heat water for a hot shower. It takes a ton of solar panels to make up for 6kWH of generator energy. Actually, not a ton but something like 600-700 watts of panels and a huge inverter.

Before you redesign the system try it and see how it really works. It may not be as dumb as you think.
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Old 08-04-2015, 20:48   #11
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Re: A/C refrigeration

The DC refrigeration versus AC powered refrigeration in my opinion has more to do with the availability of AC power than anything else. Of course, the higher AC voltage lessens the need for large battery banks - - but unless you can run a generator or plan to run a generator everyday for several hours the less efficient DC powered systems seem to make more sense as wind/solar/engine can refill your batteries.
I won't even talk about shore power as supposedly this is a forum for cruisers who go places in their boats and don't really just live-aboard permanently tied to a marina dock. And powering a massive inverter to convert DC to AC seems wasteful due to the significant conversion losses involved. Why convert DC to AC and lose energy in conversion when you can get refrigeration systems that run fine on DC power. Just more stuff that can fail and break down.
So the choice to me is about how much you want to be free to roam or cruise versus being static. DC powered systems to me may not be as technically efficient as AC systems but DC is more available to the cruiser who is cruising.
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Old 08-04-2015, 22:02   #12
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Re: A/C refrigeration

Unless you are just looking for projects, keep your A/C refrigeration. They are generally designed to run 1/2 to 1 hour per day, to keep your cold plates cold. Your genset probably sips 1/4 gallon an hour. You can buy a buttload of diesel for the cost to convert. And the A/C systems work pretty well.

Our boat was designed by the original owner to run the genset for 1/2 an hour to an hour a day. Runs up everything during that time run. Based on that, we hold nearly a years worth of diesel... We have a Grunert Passagemaker. Dometic product.
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Old 09-04-2015, 05:20   #13
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Re: A/C refrigeration

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Originally Posted by Magnawake View Post
So who out there can tell me about how many hours per day I'll need to run the genset to keep food cold. I'm going to search DC cold plates.

For our two NovaKool DC compressor units, and whatever other DC loads we run throughout the day and night, we run our genset approx. 1Ĺ hour twice per day... coinciding with cooking breakfast and dinner. That charges two main battery banks, 300 Ah each, one fridge on each bank.


Edit: FWIW, I don't actually know that I need to charge 2x/day just for the fridges... but I do know that our electronics suite is a power hog, so we also charge 2x/day so I can use some of that stuff throughout the day as necessary.

-Chris
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Old 09-04-2015, 05:26   #14
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Re: A/C refrigeration

I still think that there are some very efficient invertors out there now, maybe not the China Ebay ones, but what is the efficiency loss of a good invertor, less than 10%?
So with a good battery bank, maybe you don't have to run that genset more than a couple of times a week?

How long your food will stay cold is a function of how much mass there is in the cold plate, how much food mass there is and how efficient is the insulation, how large a box and of course how often you open the thing to get a beer out
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Old 09-04-2015, 09:58   #15
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Re: A/C refrigeration

Magnawake,
Your decision on 12 volt versus other types of refrigeration for your Hatteras 43 boat is simple math based on; box size, worst case cruising climate, desired temperatures inside box, and size, and type of boatís energy power grid. Amount of refrigeration box insulation required will also depend on the above combined answers. At least three inches of closed cell moisture free insulation is generally expectable although insulation with an R value of 30 is preferred.


If the refrigerator and freezer boxes are large or larger than four cubic feet each and you plan on cruising south of Latitude 27N adequate 12 volt power even with wind and solar would not be enough. To determine future energy requirement for a different type system calculate running time and wattage consumed daily by present refrigeration unit. Once you know present systemís daily watts consumed at an ambient air conditions where boat is now add 4% for each increase in air temperature of worst case 90 degree tropical weather. If your present compressor is Ĺ HP and runs a total of 7 hours per day to maintain a 33 to 38 degree refrigerator and a 5 to 15 degree freezer it is consuming around 7,250 watts per day if air and seawater is around 70 degrees. Moveing boat to 90 degree tropical island temperatures 20 degrees warmer the daily watts of power could be 1,350 watts. In this example other options available for pleasure boat refrigeration units are:
  • Two Danfoss BD50 compressor systems one for each box consuming in tropical conditions a combined total of 112 amp-hrs per day. Recommended DC power grid upgrade to 800 to 1000 amp-hr battery bank, a 100 amp 12 volt battery charger to be connected to present onboard generatorís output and at least a 100 amp-hr high output alternator with smart voltage regulator on main engine.
  • A large 12 volt belt driven or 12 volt shaft driven refrigeration system.. These large 12 volt units in warm climates require an alternator running when compressor is running.
  • An engine driven system is probably the best refrigeration system for large pleasure boat refrigeration but the need to run refrigeration every day is not expectable on boats that spend time connected to shore power.
  • Although expensive a Hybrid system that can operate on more than one compressor energy source is popular on 32 to 50 ft boats. These systems require there own evaporator coils in box or dual coil holding plates.
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