12 volt or mains power fridge?

[Strolls]

Originally Posted by roland stockham

Front opening fridges are much less efficient than top opening one as you let out all the cold air when you open the door.

and:

Originally Posted by Sternwake

So in my opinion cold air spilling out, is not the reason they are more efficient. They are more efficient as there is no door seal at the bottom, where it is coldest, and can more effective insulation there.

Sorry, pet peeve of mine - air spilling out makes no difference, as it's literally 1/1000 the weight of (for example) water.

Let's say you open the door to your fridge and 10 litres of cold air spills out - when you close the door you now have to waste electricity cooling the warm air back down to the same level as the other contents of the fridge.

That air weighs 12.5g, or about 1/25 of the weight of a can of soda. I.e. it takes the same energy to cool all the air in a fridge of that size as it would to cool 2.5 teaspoonfuls of cold water. For most of us this is negligible.

(This comment assumes that it takes the same energy to cool 1kg of air as it takes to cool 1kg of water - this is not true, but it's close enough for a simple explanation.)

This PDF is excellent: http://www.swingcat.co.uk/what/fridg...lculations.pdf

[Dsanduril]

I agree with your pet peeve, and air is convenient for calculations. It weighs 1 kg/m3 or 1g/l. It takes 1 J/l/C to cool. => cooling 100l of air by 30C (so from tropical temperatures to 4C fridge temp) takes ~3000J. That's less than 1Wh. Even if you decide your fridge is only 25% efficient at removing heat that still not very much energy.

Freezers are a bit more difficult because you have to account for the freezing of any water vapor in the air. 30C air can hold up to 30g/m3 of water. For a 100l freezer that means you could get 3g water exchange per door opening (assuming the freezer is empty and you get 100% exchange). That adds, conveniently, 1000J to the equation. And cooling the air to -18 from +4 adds another 2000J, in the end each door opening on the freezer takes 2Wh.

[wingssail]

Originally Posted by Dsanduril

Here are the tech specs for the newest units:

Liebherr GP 1486 freezer - rated for climate class SN-T (T=tropical, up to 43C/109F). Standardized testing rated at 273 Wh/day (23Ah/day).

The Liebherr TP 1720 and 1760 fridges are rated SN-ST (subtropical, only 38C/100F max ambient temperature) and 169/173 Wh/day (14.5Ah/day).

There's been a fair amount of argument around here about those energy ratings, I can only report one data point, ours, and we find them to be pretty close in the tropics, and up here in the chilly water we use significantly less. For both units that's 40Ah/day, add another 15Ah/day for inverter idle losses and inefficiency (tech specs Victron Phoenix) and you're still at only 55Ah/day for all your cooling.

Too bad you're not selling these things. Since the AH numbers quoted are about 20% of the typical marine units I have been exposed to, and are 1.6 times more volume. That's like 1/8 the power required for a similar sized box. And with 1/2 the insulation, and are front loading! And cost a LOT less.

My god, once the word gets out people will be flocking to buy them. Miracles!

What did my daddy say about something that sounds too good to be true?

[Dsanduril]

It is too good to be true. And I only stumbled there by accident. I've been running (and repairing) boat refrigeration systems for going on 30 years (before that we just didn't have refrigeration). When we bought this boat the PO, a prudent Swiss-German engineer fellow who didn't know a whole lot about boats set out to put aboard the most efficient refrigeration he could find. And he did. And now I am a convert. I can't express how much simpler, cleaner, easier, and better having these units is than any built-in marine system I have ever encountered. Of course they only come in specific shapes and sizes, and standard shapes and sizes aren't the strong point of any boat, but if you can make a match, well, in my experience/opinion you'll get a far better system for far less money. YMMV.

[Simi 60]

Originally Posted by Strolls

and:



Sorry, pet peeve of mine - air spilling out makes no difference, as it's literally 1/1000 the weight of (for example) water.

Agreed
Real life demonstration is a thermometer outside with probe inside.
Open our big door fridge and close it, temp dropped slightly but within minutes, less even is back at temp.

[Thumbs Up]

Front opening frosts up a lot more.

[Macsea]

Thanks all,
I will add that I operated the now dead fridge entirely from a single 300watt solar panel and deep cycle battery, the existing unit is a 10 year old Dometic 12/220v one.
I am not on a marina so I cant "plug in" I keep it separate from the house and starter banks to avoid flat batteries.

[chrisr]

there is a lot of 12v fridges intended for caravans which are perfectly acceptable for boats, and much cheaper

ok, maybe they only last half as long...but if 1/3 the price, you're in front...

cheers,

(ps : before anyone asks, we have a large front opening fridge + 2 large top opening freezers...all marine, all 12v)

[Michael Cobbe]

We had a 240v fridge and water maker the reason is they are commercial products that last longer than marine products.

[Jef & Marin, Netherlands]

See

https://www.cruisersforum.com/forums...an-205650.html

[Leighpilot]

Depends how much money and battery capacity you have. I love my ARB 12v Portable freezer. Runs off 100w panel. Not cheap but works well with very little draw.

[davenrino]

Originally Posted by Dsanduril

It is too good to be true. And I only stumbled there by accident. I've been running (and repairing) boat refrigeration systems for going on 30 years (before that we just didn't have refrigeration). When we bought this boat the PO, a prudent Swiss-German engineer fellow who didn't know a whole lot about boats set out to put aboard the most efficient refrigeration he could find. And he did. And now I am a convert. I can't express how much simpler, cleaner, easier, and better having these units is than any built-in marine system I have ever encountered. Of course they only come in specific shapes and sizes, and standard shapes and sizes aren't the strong point of any boat, but if you can make a match, well, in my experience/opinion you'll get a far better system for far less money. YMMV.

Do you know anyone that runs similar units in a monohull?

[RobTryon]

One year ago today, we came home from a long road trip to find a dead fridge. It was a 12-v Norcold that was about 3 cubic feet and its freezer fit a six-cube ice tray and that was about it. It also frosted up so fast you could barely get a single batchof ice before the tray was fully consumed. Hoping for a direct replacement, we went to Norcold's site and discovered the closest match would run $2500. �� We started researching alternatives.
I found a thread by sailorchic34 detailing how she installed a dorm fridge and inverter on her boat, and how well it was working. Considering we could try this for a tenth of what a much smaller "marine" fridge would cost to install, we thought it was worth a shot.
I deliberately haven't posted about it because I wasn't entirely convinced our experiment would be successful. I mean, the user manual very clearly forbids:
* powering with an inverter
* mounting in an enclosed cabinet
* using on a boat or RV
I won't say this fridge has been life-changing, but it's not a far stretch. It's got about double the space of the marine fridge AND freezer. We've only had to defrost it once in a year AND it's big enough for ICE CREAM! What a luxury! Plus, with accessories and install, we're all in a whopping $400. Not saying this is the solution for everyone, but it's worked great for us -- and that includes several trips to the Channel Islands, a bumpy ride up the coast to the Bay, and running 24/7. Thanks Beni for the inspiration,
Our old unit drew 4 amps, but cycled often. The new combo draws 6.5 amps but cycles much less. I think we are even on power used but have a much bigger fridge.

[Old fella]

Originally Posted by Macsea

Hi cruisers, I need to replace my fridge, (aprox 100 litre capacity)
"Marine" 12 volt units are expensive and there are few brands to choose from, compact mains power units are made in lots of different brands and are cheap (by comparison) so, would it be worthwhile to use a mains power fridge with an inverter as opposed to a dedicated 12volt unit ?? I am not overly concerned by corrosion, what other things should I consider?

Hi macsea, I had 2 x 100 Ltr fridges and 1 x 100 Ltr chest freezer, all 12v, and 7 x 250 w solar panels with 1200 amps of batteries, and struggled to keep up. There power use claims are BS, they would suck about amp hours each per day, so I threw them out and put in a 350 Ltr house hold inverter fridge freezer and knocked my battery bank back to 540 amps. This was the best thing I’ve done, I would go to bed at night and the volt meter would read 12.6v, and when I got up before day break the volt meter would still reading 12.6v or at worst 12.5v. If you can fit a LG inverter fridge ( I don’t know how small they go ) you will be laughing all the way to the bank ( battery bank ) oh, and they keep food better and longer because there temperature doesn’t vary like others. I can’t fit one on the boat I have now ( to small ) but I don’t live aboard anymore, best of luck, Brian.

[Icarus]

Originally Posted by Macsea

Hi cruisers, I need to replace my fridge, (aprox 100 litre capacity)
"Marine" 12 volt units are expensive and there are few brands to choose from, compact mains power units are made in lots of different brands and are cheap (by comparison) so, would it be worthwhile to use a mains power fridge with an inverter as opposed to a dedicated 12volt unit ?? I am not overly concerned by corrosion, what other things should I consider?

Inverters will drain your batteries very quickly.
IMHO get 12V unit, some like Isotherm have a 'smart' regulated compressor, which does save power depending on the charging state of the battery.
When in port your shore charging system will keep your beer cold and the batteries full.
When sailing I turn my fridge down a bit but despite 2x 80W solar panels I still have to run the engine every two days for a few hours.