Refrigeration: 110v (inverter) or 12v?

[mixman]

As my Gulfstar 36 refit project begins I've got some electrical decisions to make. The boat came with a rather nice 110v half-size freezer/refrigerator combination. I'm installing an inverter/charger combo that can more than handle the load (Pure Sine Wave 2000-watt continuous, 6000-watt peak I believe). The house bank isn't finalized yet but I'm most likely going with 400 to 600 amp hours. My current boat (30' power cat) has all 12v refrigeration and we can anchor for days with 235 watts of solar and just a few hours of generator usage. The Gulfstar will have 400 watts of solar plus a wind generator for the islands. With all that said what is your opinion of running 110v refrigeration off an inverter versus replacing it with a 12v system. Friends with experience I speak with give conflicting opinions (imagine that! .

Thanks!

 

[mbevins]

As my Gulfstar 36 refit project begins I've got some electrical decisions to make. The boat came with a rather nice 110v half-size freezer/refrigerator combination. I'm installing an inverter/charger combo that can more than handle the load (Pure Sine Wave 2000-watt continuous, 6000-watt peak I believe). The house bank isn't finalized yet but I'm most likely going with 400 to 600 amp hours. My current boat (30' power cat) has all 12v refrigeration and we can anchor for days with 235 watts of solar and just a few hours of generator usage. The Gulfstar will have 400 watts of solar plus a wind generator for the islands. With all that said what is your opinion of running 110v refrigeration off an inverter versus replacing it with a 12v system. Friends with experience I speak with give conflicting opinions (imagine that! .

Thanks!

Does the efficiency improve with the 12vdc unit? If not substantially then why waste the money changing it.
They're both drawing power from the same source at the end of the day.

 

[Ski in NC]

I went with a "bar sized" domestic fridge/freezer that runs on AC, easily powered by a 1000w inverter. It only draws about 1.5A AC while running, so under 200w. I went this route as fridge is inexpensive and a standard size. If it poops, I can replace it for under 200 bucks at any big box store.

Measure how many amps your fridge takes to run. Sounds like with your solar, wind and bank size you will be in good shape.

The marine specific DC/AC fridges have caused lots of folks trouble, and are expensive. I wanted to avoid that.

 

[mixman]

I think 12v units are more efficient (if nothing else, due to the inefficiency of inverters), but I've had my share of problems with 12v units. On my 30' power cat I run one of those $150 portable ice makers off inverter and it draws hardly anything.

You both make good points. Thanks.

 

[DavidM]

Well, I have some experience and some data. Even Energy Star 110V refrigerator/freezers use about double the WATTS of a 12V system. I am using watts as the basis of comparison because it is volts time amps and is the right way to compare the energy use of different appliances with different voltage requirements.

A 6 cu ft Nova Kool refrig/freezer for example is rated to use 5.2 amps at 12V DC running. It will probably run 50% of the time in the tropics so it will require about 60 amp hours daily. Your 400 watts of solar will produce about 150 AHs daily in the tropics. Since refrigeration is the single biggest load for a full time cruiser you should certainly be ok.

But the same size refrigerator designed for 110V will use 2-3 times the equivalent amp hours or up to 120 daily if it is a non Energy Star rated unit which is what I suspect that you already have. As Ski notes above his small bar size refrigerator uses about 200 watts running which is three times the wattage of the larger Nova Kool DC fridge. Your solar will barely keep up with that and whether you get meaningful wind power depends on where you anchor. But if you have a generator then you will probably be ok if you just run it for a few hours on cloudy days to recharge your batteries.

So I think you may want to upgrade to a DC system, particularly if you don't have a generator. The best for power consumption is a well insulated box with a keel cooled Frigoboat system. That will be particularly efficient in the tropics. But it does require building a box and insulating it yourself because AFAIK the Frigoboat is only available to install in an existing ice box. An air cooled system like the Nova Kool referenced above will use about 20-30% more power due to less insulation and air cooling but should still stay within your DC production capability.

David

 

[User915]

AC or DC

Hi !

My Grand Banks has 2 x 12 v fridges on board. Service battery bank is : 6 X 6 volts AGM batteries, 170 amp each. I can stay easily at the anchor 48 hours long without using my Onan generator, both fridges on, batteries still 45% of charge. I don't have solar or wind generator.

A friend of mine own a Trader 41 + 2 with 1 x 220 volts fridge (same size as 1 of mine), 2 x 12 volts service batteries, 200 amp each. His fridge is connected with a pure sine wave 2000 w inverter.


After 16 hours long at the anchor, his batteries died. So, be aware an inverter needs lot of power (as much as the fridge).

From my opinion only, I am very happy with my 12 volts DC fridge, I would never remplace them for any AC units.

Regards,

 

[Ski in NC]

It is true the DC units will be more efficient, or should be. He already has a AC unit, so there is a cost issue to consider. Also important to know if there is a gen on board. Nothing wrong with running it evey day or two to top up batts if solar and wind and main engine use can't keep batts up.

Also need to know running amps of fridge. Some older ones are truly power hogs.

 

[FlyWright]

I have a 12V/110V Norcold fridge/freezer and a 110V apartment size fridge/freezer. The Norcold switches to 110V when shore power or generator are on and runs at 12V the other times. The 110V runs on a small 1000W MSW inverter and is mounted securely on a countertop to ensure adequate air circulation along its heat-dissipating sides, a critical issue for this model.

My total load with LED lights, 2 fridges, various electronics and small chargers, fans and TV/stereo entertainment runs about 150-200AH per day. The greatest loads are in the summer with extra cooling needed for the fridges and fan operation.

If you have the solar and wind power to support the electrical needs of the 110V fridge, I'd go that route. If you find it's not sufficient to support the 110V fridge, you can always change it out later to a 12V model with better efficiency. It would be a simple matter to test this at the slip with shore power disconnected. A Kill-a-Watt meter will help you to quantify the electrical loads on your vessel.

Mixman, drop me a PM sometime. I've been thinking about Billy and was wondering how he's doing. Are you still in touch?

 

[stubones99]

I think 12v units are more efficient (if nothing else, due to the inefficiency of inverters), but I've had my share of problems with 12v units. On my 30' power cat I run one of those $150 portable ice makers off inverter and it draws hardly anything.

Conversion of energy requires energy which is lost as heat generated. That's the reason why your inverter has a fan, since during the power conversion, you lose some of the power you are converting in the form of heat. Plus some loss in the boost circuitry. If you had a bank of 10 batteries running into an inverter, your loss would be minimal, since all it would be doing is taking DC and forming the sine wave AC on the output.

It is always better to use power in the form it is currently in, especially DC.

 

[Bay Pelican]

Another viewpoint, it is not so much the 110v (220v) vs 12 volt, or the inverter inefficiency which makes a difference. What can make a difference is both the condenser and the insulation. Many/most 110v domestic units use fairly inefficient condensers and have little insulation. These are designed for the home market where electricity is plentiful and cheap and the condenser is a great place to reduce the price point of the unit. The same is true of the insulation.

A high end 12v marine unit has the very efficient Danfoss compressor, many accepting both 12 volt and 110v. The insulation is usually better. Some of the 12 volt units even have separate doors covering each shelf of the freezer.

When I switched from SubZero 110v units to Isotherm 110v/12v units my electricity usage was more than cut in half.

 

[User915]

Good view

Another viewpoint, it is not so much the 110v (220v) vs 12 volt, or the inverter inefficiency which makes a difference. What can make a difference is both the condenser and the insulation. Many/most 110v domestic units use fairly inefficient condensers and have little insulation. These are designed for the home market where electricity is plentiful and cheap and the condenser is a great place to reduce the price point of the unit. The same is true of the insulation.

A high end 12v marine unit has the very efficient Danfoss compressor, many accepting both 12 volt and 110v. The insulation is usually better. Some of the 12 volt units even have separate doors covering each shelf of the freezer.

When I switched from SubZero 110v units to Isotherm 110v/12v units my electricity usage was more than cut in half.

That's very true.

 

[Ted]

If you had a bank of 10 batteries running into an inverter, your loss would be minimal, since all it would be doing is taking DC and forming the sine wave AC on the output.

Everyone I ask for one of these "boxes" says no-can-do, no-such-thing'
I've already got the battery bank.

Ted

 

[mixman]

Thanks everyone. Many good points to consider. I do have a 4.4kw genset on the Gulfstar. There is no "box" to convert to DC refrigeration so that would have to be a custom project . My power cat has a box that I've put 3 different 12v systems in and out of over the years, so I'm quite familiar with Danfoss compressors and I always carry manifolds and R134a to keep them charged correctly (I've had to learn how to do that stuff the hard way).

Al, PM sent.

 

[CaptTom]

When I switched from SubZero 110v units to Isotherm 110v/12v units my electricity usage was more than cut in half.

Same experience here. I had an apartment-size home fridge the PO had installed. I replaced it with the same marine version that originally came with the boat (even the screw holes lined up.) I found it used a lot less electricity. I went from being able to go less than 12 hours on my house bank (before hitting 50%) to at least 24 hours.

Some might say it wasn't worth it. It cost a lot more than an apartment fridge. I still run the genset once or twice a day if I'm at anchor or on a mooring, so I technically didn't need the extra efficiency.

On the plus side: It looks great. When I want to, I can skip running the genset. If the genset fails, I'll be OK for much longer; just motoring a few hours will recharge everything. If I install solar I might never need the genset at all. Less stress worrying about where my next hundred Amp-Hours are coming from is a good thing.

Overall, I'm glad I went this route.

 

[ranger58sb]

The boat came with a rather nice 110v half-size freezer/refrigerator combination. I'm installing an inverter/charger combo that can more than handle the load (Pure Sine Wave 2000-watt continuous, 6000-watt peak I believe).

For a new install, I'd prefer the 12V/120V (DC/AC) versions like we have now (happen to be NovaKool).

In your case, sounds like you can do nothing (about the "rather nice" existing fridge) until it craps out.

I wonder if the frost-free feature in household AC fridges might account for some of their extra energy consumption. Wouldn't mind having that, too...

-Chris

 

[caltexflanc]

Some of the math here is off a bit, using watts. Compare the kw/hr ratings of like sized and featured fridge freezer combos, and it comes very close 12v vs 110. Then compare price. It will take a long time to make up the total cost of ownership difference.

 

[mixman]

Hi George!

This is interesting:

Norcold AC / DC Series - Model No. DE0061
Current Draw:
5.4 Amp @ 12 Volt DC
2.2 Amp @ 24 Volt DC
0.9 Amp @ 120 Volt AC

 

[FF]

"Does the efficiency improve with the 12vdc unit? "

Depends on the smarts of the DC unit.

A modern style like a Danfoss will run slower and use far less energy as the computer works out the load.

Also many will run full speed to a lower temp while it senses the engine is operating.

Higher voltage gives more (tho less efficient) cooling , drops back to most efficient when simply battery powered.

Beware of the amp ratings on house units as they do not include the heating elements required to defrost thin insulation .

Sunfrost is great , but does not fit too many boats.

1. Energy Efficient Refrigerators - SunFrost.com
   
   www.[B]sunfrost[/B].com/all_efficient_refrigerator_models.htmlCached
   
   Sun Frost refrigerators and freezers are so outstandingly energy-efficient, powering a home with solar power or other low output energy sources ...
   
   
   
   

 

[alormaria]

I voted for the cheap 110v unit and an inverter. It's been working for over 15 years and I'm not afraid if I have to replace it. It would be smaller, better and cheaper.

But that goes pretty much for the whole boat.

 

[caltexflanc]

Hi George!

This is interesting:

Norcold AC / DC Series - Model No. DE0061
Current Draw:
5.4 Amp @ 12 Volt DC
2.2 Amp @ 24 Volt DC
0.9 Amp @ 120 Volt AC

I could be wrong, but it looks from the manual that it is DC "native" and that it converts AC to DC, which would make AC less efficient. Looking at the price for that unit, vs what a straight 120 volt reefer of the same size costs, it would take a long time for that to pay back.

 

[LUVN LIFE]

Right, uses a rectifier when a/c applied to produce 12 volts dc if it is a dc comp and an inverter if it is a 110 ac comp.

 

[Cottontop]

Well, I have some experience and some data. Even Energy Star 110V refrigerator/freezers use about double the WATTS of a 12V system. I am using watts as the basis of comparison because it is volts time amps and is the right way to compare the energy use of different appliances with different voltage requirements.

A 6 cu ft Nova Kool refrig/freezer for example is rated to use 5.2 amps at 12V DC running. It will probably run 50% of the time in the tropics so it will require about 60 amp hours daily. Your 400 watts of solar will produce about 150 AHs daily in the tropics. Since refrigeration is the single biggest load for a full time cruiser you should certainly be ok.

But the same size refrigerator designed for 110V will use 2-3 times the equivalent amp hours or up to 120 daily if it is a non Energy Star rated unit which is what I suspect that you already have. As Ski notes above his small bar size refrigerator uses about 200 watts running which is three times the wattage of the larger Nova Kool DC fridge. Your solar will barely keep up with that and whether you get meaningful wind power depends on where you anchor. But if you have a generator then you will probably be ok if you just run it for a few hours on cloudy days to recharge your batteries.

So I think you may want to upgrade to a DC system, particularly if you don't have a generator. The best for power consumption is a well insulated box with a keel cooled Frigoboat system. That will be particularly efficient in the tropics. But it does require building a box and insulating it yourself because AFAIK the Frigoboat is only available to install in an existing ice box. An air cooled system like the Nova Kool referenced above will use about 20-30% more power due to less insulation and air cooling but should still stay within your DC production capability.

David

Many (most) full-size (>20 cu. ft.) household refrigerator/freezers with all the bells and whistles consume less than 1.5 kwh per day, nowadays, and plain-jane units get down to 1 kwh per day or even less. On an energy use per cu. ft. basis, this crushes the dc unit referenced above (700 wh per day for 6 cu. ft.).

I'm not sure "dc units, danfoss compressors, etc. are more efficient" is a given any more. I appreciate there are many variables (ambient temperature being a big one) that make precise comparison difficult.

But when you factor in purchase price, installation and repair costs, I'm starting to think household units may be the way to go, especially on cats where heeling is eliminated.

 

[Xsbank]

Aren't we forgetting the cost of an inverter? 2500 watts (I don't have an inverter) is about $2000, which is another thing to worry about when operating a big fridge. Also, losing an inverter (or have two, like many do) would take out all your 110 V appliances, single point of failure? Also, frost-free on a boat? I am skeptical that a frost-free would be prudent on a boat, the moisture under the fridge would be a problem in rough water - where would it go?

The Danfoss does not shut off, it runs constantly but at variable speed to avoid the high current draw required to start an electric motor. I just bought a new Nova Kool fridge.

 

[caltexflanc]

I don't think you would buy an inverter solely to run a refrigerator. I wouldn't. If you did, you'd buy a cheap one dedicated to that, not a $2000 model.

I highly recommend Calder's "Boat Owner's Mechanical and Electrical Manual", the first few chapters of which cover this whole subject in easy to read detail.

I always thought (rightly or wrongly) that a DC refrigerator has its highest and best use on boats that spend most of their time away from a dock and do not have or can practically use for long periods a gas or diesel generator, and cruise in such a way (ocean crossing for instance) that even running the main engine is to be avoided (sail boats).

 

[janice142]

One thing I might suggest is a fan to pull the heat away from your unit. My old cube was in a closed compartment so I added two fans. One blew at the compressor and the other pulled air out of the compartment.

These were the small computer fans, about 3x3x1" (or maybe 4")

The new unit is at the opposite end of the galley and is positioned by the aft bulkhead. It's got a lot more ventilation (natural) and the area NEVER gets hot. I've got the fans installed and have tested them a few times. The top gets warm now and then I turn on the fans.

It's never hot-hot like the cube. I did upgrade to a Haier 3.1 cubic foot model. That's the smallest unit with a separate freezer door.

Suggestion for whatever unit you do: Buy a weather station (Ambient would be the brand I'd recommend -- about $30 on Amazon) ... get one with an outdoor sensor and put that inside your refrigerator. Now you know at a glance how cool your unit is.

Easy and inexpensive -- my two favorite things.

Good luck.

And yes I opted for AC power with solar and batteries. An Engel would be lovely however I could have bought 4 solar panels for the price of an Engel... When my $120 (on sale from $150) unit bites the dust I'll give it a swimming lesson and get another. The totally inadequate cube was $70 in 2008 and I gave it away -- working. It spent at least three of those years running on a cheap inverter while at anchor.

Just in case you wondered. I'd use what you have until it croaks, AFTER adding some ventilation to the cabinet. If yours is in the galley just to the right of the steps up into the salon, you could poke a hole in the engine room and install a blower to pull air out of the reefer cabinet. That's what I'd do.

Good luck Kurt.

P.S. - The "swimming lesson" was me being facetious

 

[mixman]

So many good replies I'd spend hours replying to each. Here's the short reply:

I've already got a 2000-watt (6000-watt peak) pure sine wave inverter charger, so no extra expense there.

In my experience with units I've owned, if they're AC/DC combinations they're actually DC compressors with an AC transformer to convert AC to DC. I haven't really liked those units and converted the 34-quart AC/DC model on my cat to all DC. If I'm plugged in I'm charging the batteries anyway and if the compressor kicks on when I'm charging via generator there's no "hit" to the AC generator.

Janice, I keep a remote thermostat in my top-load refrigerator on my cat. It is easy, cheap insurance (for the freezer I keep some ice on top - if the ice is melted into a block, power was lost and the food must go!). I'm going to give the 110v refrigerator a try at first. I'll have the woodwork in the galley made to specs that will fit a 12v model just in case, but this is worth trying. I'll have around 600ah in the battery bank, 400-watts of solar, a wind generator and 4.4kw of diesel generator. We'll figure it out during a shake-down cruise.

Note: I forgot to get the model number of the 110v Frigidaire unit I've been talking about that's on the boat, but I seriously doubt it defrosts itself. But if it does I may really reconsider as that is going to use some juice!

 

[mixman]

Update: I comparing the height specifications of the two models that Frigidaire make in this range, it is this one and it is frost-free. I'm going to have to put that into consideration. A nice feature, but likely a power-hog. I'm also trying to figure out where to install/store the 34-quart portable Waeko-Dometic 12v freezer I have on my cat.

Frigidaire 4.5 Cu. Ft. Compact Refrigerator Silver Mist-FFPS4533QM

 

[RT Firefly]

Greetings,
Mr. m. We bought our 110V refrigerator from Home Depot. They have a unit similar to your listed Frigidaire for $229. Not frost free and with what seems a better warranty... Vissani 4.3 cu. ft. Mini Refrigerator in Stainless Look-HVDR430SE - The Home Depot
Just a thought...

 

[HiDHo]

A couple of years ago we replaced a wornout Norcold with a Summit FF 874 SS 8.1 cuft refrigerator freezer, 115 acv, 370 KWh/year, run amps 1.2, start amps 4.0. I thought a 900 watt inverter would run the unit but it doesn't, is there any way to calculate the size inverter I should use assuming that the 900 watt inverter can't start the unit because it was in a auto defrost mode ? Do I need a pure sine wave inverter ?
Sadly Summit discontinued this unit, it has proved to be quiet, and efficient and we love the convienience of the frost free feature.

 

[Mako]

As a comparison, a super-efficient LG or Samsung digital inverter fridge of 16cf uses about .85 kwhr per day or 320 kwhr per year. A Sunfrost will use about 260 kwhr per year. Admittedly, that's a nice difference.

Difference in cost…. $450 for the household versus $3500 for the Sunfrost.

That extra three grand buys a lot of solar panels, AGMs, inverters, cables, breaker panels, etc. Logically there is no way the Sunfrost can compete when it comes to long term dependability either. So for my money I'd go 110/220v versus 12v.