Non Marine Fridge - 11 Watt

[myocean]

Hi Together!

We are refitting our catamaran and I am thinking about fridges. It would be great to get your thoughts about the following:

There are probably reasons why normal 'civil' fridges are not used on monohulls or catamarans. What are the most important ones?
- would not work with heeling angles (what about cats?) or movements in general?
- prone to corrosion
- needs AC power supply
- not reasonable to operate in tropic climates??

Looking at the highly modern fridges which are meanwhile available here in Europe it would be so great to have such a nice (and cheap) thing on the boat: A modern 130 liter fridge (4.6 cubic feet) consumes 100 kWh per year (at normal room temperature). This is a mean power consumption of 11 Watts only.

Ulf

[Tellie]

100kwh is 100,000 watts. Where does the 11Watt figure come from?

[foggysail]

I don't know about 11 watts but I do know that hte Summit 8.3cu ft I purchased to replace an old Norcold 7.+ works just fine. And it even has an interior light and self defrost. I power it from dock/generator power when available with an automatic switch over system or a 1KW watt true sine wave inverter. And it is soooooo quite!

[sailorchic34]

Well its not quite 11 watts when it running. I've been using a 3.5 CF 120V fridge with a cheap modified sine wave inverter for over 5 years now here in the US.

Running it pulls 14-15 amps on 12V (1.3 amps at 110V). What makes it feasible is duty factor. It only runs for about 2.5 minutes every 14 minutes so about 2.5 amps used on average per hour (in the 90+ degree Cali Delta heat). So figure 60 to 70 amps a day. Which is in the ballpark of 12V systems...

I just bolted it down, added L brackets at the top rear to the cabin side and a latch to keep the door closed. For less then $200 its works fine.

Even healed over 25 degrees for hours at a time. Though really with the waves the boat bounces about a little so oil starvation of the compressor is not a problem.

[Tellie]

He still needs to figure out what he means by an unrealistic 11 watts, it might be a typo. First you need to find out what his power abilities are and what voltages he plans to use. There's a big difference in electrical capabilities on a 36' boat and an Outremer 50'.

[sailorchic34]

Oh the 11 watts came from dividing the 100,000 watts by 365 and 24. They must have some great fridges in the EU. Mine burns about 31 watts an hour.

Oh I figure if he's in EU he's running 24V and 220v/50hz. But the principle still works

He did mention a 4.5 CF fridge. So think my little bit o nothing sort of applied...

[Tellie]

24 volts at 11 watts would be about .4-.5 amps per hour.
220 volts at 11 watts would be about .05 amps per hour. I gotta get a EU fridge. Maybe two or three.

[foggysail]

If European fridges are that efficient, it might just be at the expense of available cubic feet of interior volume for refrigeration in any given box size. They follow the same rules of thermodynamics as the rest of us.

[ughmo2000]

You might look at the "Engle" portable fridge/freezer,s or they're equally good but half the price "Edgestar" units. Sizes up to 84 quart, they're quiet, sip power, and will freeze to -8 degrees. I'm amazed more boats don't have them aboard.

[Cheechako]

Yeah, but thery're not $120 like an apartment 120v fridge!

[senormechanico]

24/7/365 = 8760 hours.
Divide it up and you get 11.4155 watts on a continuous basis.
At 12 volts that is 22.831 aH give or take.

[Fuss]

Originally Posted by Tellie

He still needs to figure out what he means by an unrealistic 11 watts, it might be a typo. First you need to find out what his power abilities are and what voltages he plans to use. There's a big difference in electrical capabilities on a 36' boat and an Outremer 50'.

100000w / 365 / 24 hrs = 11 watt hrs

Originally Posted by foggysail

If European fridges are that efficient, it might just be at the expense of available cubic feet of interior volume for refrigeration in any given box size. They follow the same rules of thermodynamics as the rest of us.

Modern A+++ energy star fridge freezers have about 40mm 1.5 inches of insulation.

Turned off, they keep the food frozen for more than 35 hours

the domestic fridge industry has more funds for r and d than the marine fridge industry therefore they are well ahead.

I have suggested to some of the magazines that they do a head to head test with a water cooled marine fridge against a modern energy star A+++ fridge freezer. I suggested that this would make a great magazine article to YBW in the UK but they and others seem reluctant to make this test.

[myocean]

Hi together!
Thank you for your contributions to the discussion. Yes, the 11 Watts are calculated as described above and adre the MEAN consumption. Certainly there is a duty cycle with on/off operation.
The reason for the low consumption in Europe is similar to the low consumption of european cars: Higher enegry prices, stricter rules and consumers with different priorities than in the US. As a result the companies put more money into research an development for better isolation and more efficient cooling systems.
See here a result: http://www.google.com/url?sa=t&rct=j...jRJrCEbtL6nF9g
One of the fridges mentioned is the "KIL18A75". Price in Germany 400 Euro.

However - which technical problems have to be expected over time?

So yes, a systematic head to head test with a good marine refrigerator such as a water cooled IsoTherm (costs about 2000 Euro?) would be very interesting...

[Tellie]

Originally Posted by senormechanico

24/7/365 = 8760 hours.
Divide it up and you get 11.4155 watts on a continuous basis.
At 12 volts that is 22.831 aH give or take.

Guys, I get the easy division answer of 11 Watts an hour. That math is not the question. It's the 11 Watts per hour usage. Maybe I'm missing the obvious. But unless I=P/V has changed, 22.831 at 12 volts is still 273.9 Watts, and 11 Watts per hour at 12 volts is still .9 Amps.
Even Engels top loading 84 quart or 2.8 cubic feet uses .7-3.6 amps at 12Volts or 8.4 to 43.2 Watts and the OP is talking practically twice the size at 4.6 cubic foot fridge or 137.6 quarts and it's probably a front loader he's looking at and my guess is on a 50 Cat that door will open a lot. Maybe myOcean will chime back in with the make and model of this fridge.

But it's early here in Vienna and German beer is better than American beer so missing a step would not be hard.

[myocean]

Hi Tellie!
The point is here the difference between power and energy.
Watts are a power (P) - same as horse powers. So you don't calculate them "per hour".
Power multiplied by time is Energy (W*h)
The 22 which has been calculated above are Ampere hours. So Ampere multiplied by hours. I this case 24 hours which gives the Ah needed per day.

This is even the reason why the calculation from above (100000w / 365 / 24 hrs = 11 watt hrs) is misleading because the units are wrong.
Correctly it has to be 100000 Watt*hrs / (365 * 24 hrs) = 11 Watt. (which is the mean power consumption)
To check the units you can easily calculate "Wh/h" which equals to W. This is why writing units correctly helps a lot.