Refrigerator: AC vs. DC

[ranger58sb]

Originally Posted by a64pilot

Chris, I think you have the gist of it, I think.
However what I do not understand, is what is the advantage of a fridge that runs off of both AC and DC ?
When I am plugged into shorepower, my battery charger is on, and power essentially passes though the bank, the battery bank is not depleted and then recharged, power just passes thru. I see no advantage of the additional complication of a fridge that is voltage flexible, unless it a portable, then of course you could take it into a building and plug in.

I suspect any advantage depends on the specific situation.

For example, without an inverter (a situation), we would have had to fire up the genset to power an AC-only fridge while underway or at anchor. Whereas with an AC/DC model, we could flip a few breakers, fridges run while underway and at anchor, nose wet. Lots of folks don't have an inverter.

I can't really speak to potential "efficiencies" attained from either type and in either (AC or DC) mode. Intuitively, I'd suspect that there's some loss during any of the conversion processes, but whether it would be significant... got me.

Even then, in one situation one might really depend on those "efficiencies" whereas they might not matter all that much in another situation.

-Chris

[a64pilot]

I was actually thinking of a pure DC fridge as opposed to an AC / DC one.
I understand the desire for a DC one, just not a voltage switchable one as the battery charger serves that function, and I assume we all have chargers.

Although if a stand up house type of fridge were an option for me, I have to think that I would find the most efficient house one I could find, run it off of an inverter and pocket the considerable savings

[darylat8750]

"For example, without an inverter (a situation), we would have had to fire up the genset to power an AC-only fridge while underway or at anchor. Whereas with an AC/DC model, we could flip a few breakers, fridges run while underway and at anchor, nose wet. Lots of folks don't have an inverter."

Chris, I would suggest that if you need to replace your current fridge that when shopping you consider the cost of a domestic (apartment sized?) unit and the cost of a suitable inverter. I think that the savings will amaze you and the power draw will be a very small increase over the current unit. In fact depending on the age of your current unit you may even see a slight decrease in electrical consumption. Also still no need to run the genset under way. I did this and even though I had to do a little cabinet work to make the new unit fit (I now have at least 30 percent more refrigerator space and 50% more freezer space) five years later I am still very happy with the results.

I also have a power boat and with an 800 amp battery bank and with the original (small) alternaters if I powered at least 8 hours a day I didn't need to run the genset at all. A couple of years ago I put a 170 amp school bus alternator with battery voltage sensor on one engine and now given 4 hours of main engine a day I don't need to run the genset. I should also point out that we are power hogs and the TV and DVR get used several hours most days.

[rom]

Originally Posted by makobuilders

rom you've got the right idea. I have two suggestions though: hardwire a dedicated tiny pure sine wave inverter to your refrig since inverters work at max efficiency at about max load (your 3kw inverter might be running at 50-60% at low load); and try to find an A+++ digital inverter refrig which avoids the huge "locked rotor" draws.

at last ! thank you makobuilders for your comment !

I will check the victron manual, 50-60% efficiency at low loads sounds extremely low and I would have expected much better !

As for the "digital inverter refrig" I don't know what your talking about ... BLDC motor maybe ? Well, I suppose this is how the latest generation a+++ works ?

[rom]

Originally Posted by a64pilot

I was actually thinking of a pure DC fridge as opposed to an AC / DC one.
I understand the desire for a DC one, just not a voltage switchable one as the battery charger serves that function, and I assume we all have chargers.

Although if a stand up house type of fridge were an option for me, I have to think that I would find the most efficient house one I could find, run it off of an inverter and pocket the considerable savings

Thank you a64pilot for validating one of my argument in favor of the house appliance !

Yes, fridges (as many other items) dedicated to the marine environment are way overpriced !

[mako]

rom, first of all I have done dozens of calculations on various refrigerators installed and used over here (230v 50hz) and these A+++ European frig/freezers are so efficient they even blow away the typical 12v marine Danfoss. The only system more efficient is the 12v Sunfrost but those cost thousands of dollars!

Here in the Middle East, India and SE Asia the digital inverter appliances (frigs, washing machines, split unit Aircons) are extremely popular. Probably in Europe too. Just go to LG or Samsung websites and you'll see them.

Where are you located?

[rom]

Originally Posted by makobuilders

rom, first of all I have done dozens of calculations on various refrigerators installed and used over here (230v 50hz) and these A+++ European frig/freezers are so efficient they even blow away the typical 12v marine Danfoss. The only system more efficient is the 12v Sunfrost but those cost thousands of dollars!

Here in the Middle East, India and SE Asia the digital inverter appliances (frigs, washing machines, split unit Aircons) are extremely popular. Probably in Europe too. Just go to LG or Samsung websites and you'll see them.

Where are you located?

Currently in Martinique, floating between the med (mostly France) and the caribbean. I was thinking about doing the update when I am back in France where we can easily find all those latest generation appliances. I am not yet settled on which brand I will buy, the example I gave is for an AEG 140L rated at 64 kWh a year.

[mako]

Originally Posted by rom

Currently in Martinique, floating between the med (mostly France) and the caribbean. I was thinking about doing the update when I am back in France where we can easily find all those latest generation appliances. I am not yet settled on which brand I will buy, the example I gave is for an AEG 140L rated at 64 kWh a year.

Not sure how much room you have, but there are 300 liter and even 400 liter units that burn about 170 kWh/year. A single 300w solar panel could easily power that.

[Typhoon]

Originally Posted by rom

Currently in Martinique, floating between the med (mostly France) and the caribbean. I was thinking about doing the update when I am back in France where we can easily find all those latest generation appliances. I am not yet settled on which brand I will buy, the example I gave is for an AEG 140L rated at 64 kWh a year.

The model you quote shows 168 kWh . Could you post the link showing your data ?

Regards John

[rom]

Originally Posted by ColdEh Marine

The model you quote shows 168 kWh . Could you post the link showing your data ?

Regards John

I could not find it on the UK website so that will be in french:

SKS98800C0 Refrigerators | AEG

click on "Etiquette energie" to see the European Union energy label showing 64 kWh.

[a64pilot]

One thing I'm thinking is with a Lagoon 440, you can fit a nearly insane amount of Solar and can accept less than the most efficient option. There reaches a point with anything that it takes twice the money to get a 10% improvement. I try to buy a couple of steps down from the best available in most anything as there is a point of diminishing returns.
If you have to have the best, your going to pay for it.

[Typhoon]

Originally Posted by rom

I could not find it on the UK website so that will be in french:

SKS98800C0 Refrigerators | AEG

click on "Etiquette energie" to see the European Union energy label showing 64 kWh.

Ok I got the link , thanks .

Just to clear a few things up , this fridge is not that much more efficient then a Danfoss BD35. Actually in real world usage I would give it to a BD35 hands down in real world usage.

First of all they don't show how they got the data, fridge full or empty ? if it is ever opened ? what the ambient temperatures were during the test? So with out this information the data is really of not much use.

As an example. My on board refrigerator has R30 insulation with R20 top doors of 2 square feet . I collected my data over weeks of logging the amp hrs used, the ambient temperatures and keep the fridge half full . The fridge on average was opened 20 times a day . With this real world use data I can calculate the Kwh used per year as I did in post 2 . Now if I take into account the difference of size and recalculate the values, I get 71.24 Kwh per year with a box like mine, scaled down to 140 Liters of volume. Remember, I got this data as I was using the fridge during the summer months up here , and it was a hot one. If I never opened it, and the ambient temperature were like the inside of a house at 72 degrees , (thats probably how they tested theres , or at 70 degrees) this data would be vastly different, in the favor of the Danfoss by a long shot .

All I am trying to say is that in real world usage with that little fridge you may be disappointed in its power usage, but this is only an educated guess . Remember it is a front loader , thats a energy killer right there . Did they take that into account when they did there tests , who knows ? Also a final note , these home fridges are designed to be used in a home were it is always 72 degrees , they don't like high ambient temperatures and are not designed for it and will suffer in performance and also , heeling ? They really don't like that ? The BD series of compressors are designed for mobile applications and will tolerate a 30 degree heel with no ill effects .

Sorry for my rant but I see far to many people using home fridges on there sailboats and then being unhappy with the result.

Regards John.

[Brewgyver]

Originally Posted by rom

I could not find it on the UK website so that will be in french:

SKS98800C0 Refrigerators | AEG

click on "Etiquette energie" to see the European Union energy label showing 64 kWh.

I'm not able to do so now, but when I get on my computer I'm going to have to research how the EU energy consumption ratings are derived. 64 kWh per year breaks down to 7.3 watts per hour. Sounds like a lab setting, with room temp ambient, and virtually never opening the fridge door. I don't think that's remotely achievable in the real world.
In actual use, ALL refrigeration circuits have to work harder with increased loads. The same fridge running in 95 F ambient works a lot harder than when it's in 70 F ambient. Higher current draw and longer, more frequent run cycles.

[sailorchic34]

[QUOTE=ColdEh Marine;2348075
All I am trying to say is that in real world usage with that little fridge you may be disappointed in its power usage, but this is only an educated guess . Remember it is a front loader , thats a energy killer right there . Did they take that into account when they did there tests , who knows ? Also a final note , these home fridges are designed to be used in a home were it is always 72 degrees , they don't like high ambient temperatures and are not designed for it and will suffer in performance and also , heeling ? They really don't like that ? The BD series of compressors are designed for mobile applications and will tolerate a 30 degree heel with no ill effects .

Sorry for my rant but I see far to many people using home fridges on there sailboats and then being unhappy with the result.

Regards John.[/QUOTE]

As someone who has had a 120V fridge for over 10 years. It's not that bad. My old fridge was a pig and used roughly 60 ah a day in 90+ degree heat. For a outlay of under $200 for the fridge and inverter, a cheap $40 msw inverter. It used about 2.5 ah on average running 10 minutes every hour.

The new 120V fridge uses about 26 watts an hour in 74 degree cabin temp and runs about 20 minutes every hour or so. Of course I got fancy and have a PSW inverter for the new fridge. Overall I save about 20ah a day, give or take over the old fridge. The biggy is of course the price. I spent $420 for my new fridge and inverter that uses about the same power or less then an equal 12V unit by norcold that costs $800 more and does not have a separate freezer compartment, which is an energy hog as it tends to over cool the fridge and cause partial thawing in the evap freezer bin.

A good 12V marine system should be a bit more efficient but it costs at least $1000-$1500 more. This has more to due with box insulation though then compressor efficiency.

As to the vertical door being an energy hog, that is again overstated. Yes some air will fall out of the door, but that may only amount to a pound or two of air a day (~10 cf, based on 5 openings) which would take roughly 100 btu's's (a day) to cool or an added 20 minutes run time, for less then 2 ah a day. It's a small loss. A large fridge would be more but for a 3-4 cf fridge its pretty much a non issue. With the money saved on refrigeration I can have a bottom job on the boat. Score....

BTW I am very happy with my 120V fridge (at anchor now)

[rom]

ColdEh Marine, thank you for sharing your interest in the subject, but I really think you should gather some actual specification before making so many assumptions.

But most importantly I think you are missing an important point on the consumption matter. One fridge is rated by the EU label to be among the best, the other does not have the EU label (though it is Italian) and by spec consumes 3 times more.

Which one would you choose ? It seems to me the answer is pretty straightforward.

Brewgyver, you might search how the label works, it would certainly be interesting but I fear this thread will end up like the other one "solar panel ouput verse rating" Really, if you want that information to be useful then we also need to know the testing procedure of Vitrifrigo (or any other marine fridge maker) and I bet they don't publish it.