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Old 09-04-2015, 11:02   #16
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Re: A/C refrigeration

Richard,

All you have said is right except that watts per day is not a unit of energy consumption. Watt/hours per day is a valid unit of energy usage and maybe that is what you meant. I also don't understand why moving to tropical waters would drastically reduce the fridge energy consumption.
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Old 09-04-2015, 12:09   #17
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Re: A/C refrigeration

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Originally Posted by transmitterdan View Post
Richard,

All you have said is right except that watts per day is not a unit of energy consumption. Watt/hours per day is a valid unit of energy usage and maybe that is what you meant. I also don't understand why moving to tropical waters would drastically reduce the fridge energy consumption.
Actually I do believe he meant that there would be an additional power consumption of 1250 watt/hour. At least that's how I read between the lines
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Old 09-04-2015, 13:00   #18
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Re: A/C refrigeration

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Originally Posted by Richard Kollmann View Post
Magnawake,
. . . 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.. . .
There are a lot of people who know a lot more than me on this subject but all I know is that I built a divided box of 8 cu.ft. total with two 12VDC air-cooled Technautics Cool Blue cold plate units - one set for freezer and one set for refrigerator and sailed for a decade in the Caribbean all the way to South America and back. The systems worked wonderfully and used about 100 amphours to 150 amphours per day.

My box was made using Home Depot sourced R-Max Plus panels sandwiched together to give more than R-30 walls and floor. The hatch/lid was a prebuilt vacuum panel unit from Glacier Bay (horribly expensive).

One thing I did during the construction of the box was to install a thru-hull drain and hose from the bottom corner of the box to the outside face in the galley. This allows me to hook up a short piece of garden hose to the drain and use a water spray to defrost the whole box in 5 minutes or less.
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Old 09-04-2015, 13:23   #19
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Re: A/C refrigeration

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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.
Your compressor will be much more powerful than any 12v unit and so won't need to run too long. Try 45 mins every 12 hours and you should not need more than 1 hour in every 12.
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Old 09-04-2015, 13:40   #20
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Re: A/C refrigeration

This is all good news to me. I'm used to running a genset for 1.5 hrs x 2 times/day on our hatteras. I do notice a big difference while down in florida in run time for the refrigerator. The units on the irwin are seperate and huge. I guess it needs an AC compressor to haul the load. I will try it out and see if it works good before start changing things out.
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Old 09-04-2015, 13:43   #21
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Re: A/C refrigeration

If you decide to go with DC compressors you might have to invest in two of them.
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Old 09-04-2015, 14:32   #22
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Re: A/C refrigeration

" I cant figure for the life of me why someone would want a A/C only on their boat. "


MONEY.


Plain and simple, I can go to any thrift store and for $50-100 pick up a 15-20 cubic foot AC refrigerator. A clean modern one, too.


First rule on a boat, when you can figure out WTF the PO did or why they did it that way? MONEY.
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Old 09-04-2015, 14:49   #23
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Re: A/C refrigeration

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Your compressor will be much more powerful than any 12v unit and so won't need to run too long. Try 45 mins every 12 hours and you should not need more than 1 hour in every 12.
Very true - BUT - unless you are a motor trawler with unlimited power and a marina slip to bed down in most every night, the availability of AC power and the auxiliary equipment needed to generate it can be a major factor that makes DC power much more practical despite its comparative limitations.

To sailboat type cruisers running gensets, etc. every night is not a desirable activity when you spent all that money on sail and want to enjoy the experience with a minimum of machinery grinding away making smoke, fumes and noise.

Sources of DC power are more abundant to sailboats and their enviro-friendly mode of cruising. Heck, even wind generators are pushing it when peace and quiet is what you paid all that money for to enter the sailboat world. Running generators is, IMHO, a powerboat yachtsman thing.

So the discussion boils down to how you want to experience the cruising lifestyle. AC powered equipment requires generating equipment that can be both expensive to buy, expensive to run and noisy in that peaceful little anchorage you found. DC powered equipment/systems are better integrated into the sailboat operating world since we have wind, solar, and propulsion already able to provide the energy needed.
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Old 09-04-2015, 14:56   #24
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Re: A/C refrigeration

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Originally Posted by hellosailor View Post
" I cant figure for the life of me why someone would want a A/C only on their boat. "


MONEY.


Plain and simple, I can go to any thrift store and for $50-100 pick up a 15-20 cubic foot AC refrigerator. A clean modern one, too.


First rule on a boat, when you can figure out WTF the PO did or why they did it that way? MONEY.
Except in this case the system isn't a Home Depot fridge/freezer. It is a sea water cooled Seafrost system with a holding plate. It is not a cheap system. The reason the boat has that system is probably because they work. At the time the boat was built it was probably the only thing that would work. It is both fast and efficient requiring about 1 hour per day of generator run time. Even today it is not a dumb system. I see lots of people struggling to make one or two BD50's work and then find out their solar panels can't keep up.

There can be other reasons owners do things besides just low cost. They want a system that is simple and reliable. The Seafrost+generator is simple and reliable IMO when compared to solar+batteries+mains charger+alternator+MPPT+battery monitor+inverter+2X BD50+++.
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Old 09-04-2015, 14:58   #25
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Re: A/C refrigeration

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Originally Posted by Magnawake View Post
This is all good news to me. I'm used to running a genset for 1.5 hrs x 2 times/day on our hatteras. I do notice a big difference while down in florida in run time for the refrigerator. The units on the irwin are seperate and huge. I guess it needs an AC compressor to haul the load. I will try it out and see if it works good before start changing things out.
Before commissioning the system I recommend that you go through the user's manual and perform the recommended maintenance. It's likely the PO hasn't been doing that. For example, there are pencil zincs in a Seafrost system that have to be changed out once in a while. Other than the recommended maintenance the Seafrost systems I have seen run for 20-30 years without any other service.
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Old 09-04-2015, 17:44   #26
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Re: A/C refrigeration

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Before commissioning the system I recommend that you go through the user's manual and perform the recommended maintenance. It's likely the PO hasn't been doing that. For example, there are pencil zincs in a Seafrost system that have to be changed out once in a while. Other than the recommended maintenance the Seafrost systems I have seen run for 20-30 years without any other service.
The owner was living on that boat and i know it works great. The trouble with this system is that the refrig part is about 10 ft3, and the freezer is prolly 5 ft3. Much larger than a DC unit can support. I would need a very large bank with lots of solar panels as well as wind genny. If I could get by with 1 hr/ day run time I guess I would be happy with that. I dont need to tell those who cruise how great it would be to freeze fish that we catch as well as steaks. Everyone knows there is always a give and take thing. The system seems very well insulated so I guess it would last a long time without turning on the genset. The peace and quite thing is noble but not reality. Lots of people run their gensets in the morning and evening. It wasnt a problem in boot Key with hundreds of boats. However, there was this house boat at Cape Look out that ran a Generak (very loud) 24/7 for 4 days. That was crazy. I'm not going to spend thousands of dollars just to be quite and then have one of these guys pull in near me.
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Old 09-04-2015, 18:07   #27
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Re: A/C refrigeration

For whatever it's worth my factory icebox is 15 cu ft, I split it roughly in two with a spillover set up.
Rich at Cruise RO built me a custom dual cold plate system using twin cold plates and one BD80 compressor. Using the factory 27 yr old ice box it hold the freezer about 5 degrees below zero F and the fridge side right at 32F. I've not actually measured power required, but believe it to be about 80 to 100 amp hours max. My only problem so far is excessive condensation at the top due to inadequate insulation, with something other than 27 yr old standard insulation, I'm sure the amp hour draw would go way down, but it's a 12V system of course, so it's do-able.
But I still believe that for this application a 12V to 120V convertor is the way to go, that way you only run a gen set when the battery bank requires re-charging.


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Old 09-04-2015, 21:53   #28
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Re: A/C refrigeration

On our boat dad has a 3 cf freezer and 7 cf fridge front load just like at home keep the freezer at 15 f and the spill down fridge at 38f with a stock technautics system and use under 35 ah per day our 200 watts solar keeps up beautifully batteries are full charged before noon and the fridge afternoon run is fully supported by the solar
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Old 10-04-2015, 06:30   #29
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Re: A/C refrigeration

I didn't think to include our fridge sizes earlier. One is 7.5 cf, two door, about a third of that being freezer. The other is 2.6 cf, single door, with a tiny little freezer compartment near the top. IOW, not huge capacity.


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Old 10-04-2015, 07:03   #30
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Re: A/C refrigeration

Mine isn't usually the most popular advice on refrig., but I'll offer it anyways.

Once at temperature, there's going to be some regular heat loss due to finite insulation and occasional door openings. 12V systems will work just to keep up with that.

Holding plate systems take a lot of energy to get them to switch phase in the first place. A 12V system may take a *very* long time freeze the eutectic solution. For example, if fridge and freezer have 10kBTU worth of holding plates, ignoring losses due to insulation, etc., you'll have to put about 3kW*hr of energy in to make that happen. If you're getting 50-100W out of a BD50, that'll be *days* to reach temperature (assuming you ever reach it due to losses).

I find that when cruising we are running the genset or the motor anyways -- whether for propulsion, to make water, or to charge the batteries. Further charging the holding plates (removing heat) is easy, but requires a big enough compressor to do the work in 30 minutes, instead of taking hours.

We find that our 240W solar just barely keeps up with the refrigeration (not freezer) when left unattended for days -- and that is with a moderately powerful (600W?) 24V compressor.
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