water cooled peltier cool box conversion

I tested my standard cheap Peltier box. With it pretty full of liquid it gets down to -12C ambient I can then switch it on and off on an hourly cycle and it only warms up one degree then cools down again.
Could be improved with better insulation ( simply dropping the existing chest into an insulated carton)
I decided that this was still not cool enough for me in Spain and a fair amount of heat generated if we used it in the saloon.
This water cooling possibility has got me thinking again though, The trial with the Kelco cooler indicated that much lower temps can be achieved. MY idea was to use my 100 gallon fresh water tank ( which has a large surface area on the underwater hull) as the heat sink ( no holes in hull). I will appreciate comments on using the fresh water tank.
 
Tomi Pasanen said:
Guys, please read https://www.practical-sailor.com/issues/25_2/features/4227-1.html
Click to expand...

As the article says, it is a CONTINUOUS drain of an amp or so. I can understand why - to simplify, a Peltier effect device pumps heat from the cold box via a highly heat conductive path to a hotter environment. As soon as the current goes off, that highly effective conductive path simply allows heat to travel back from the hotter environment to the cold box.

Another point is that it achieves that low a current usage by taking over 12 hours to cool the box. It also requires a through hull to get good thermal connection to the water.

Finally, I note that the product doesn't seem to be available anywhere, and isn't on Origo's web-site.
 
As your passage progresses...

Freshwater drops making it less effective?
Amount of liquid in the coolbox reduces (you ate / drank it) which actually makes it harder to maintain temp ?

Did you load the fridge with cold goods or room temp goods that it needed to cool?
 
AntarcticPilot said:
As the article says, it is a CONTINUOUS drain of an amp or so. I can understand why - to simplify, a Peltier effect device pumps heat from the cold box via a highly heat conductive path to a hotter environment. As soon as the current goes off, that highly effective conductive path simply allows heat to travel back from the hotter environment to the cold box.....
Click to expand...
From what I recall of peltier characteristics, a device which was pumping 20 degrees at 1A only needed about 100mA or thereabouts to maintain the 20 degrees with no backflow of heat.
But I think I'd rather have a compressor fridge I can run when there's solar power and switch completely off when there isn't.
£79 table top freezer. 150kWh per year? that's around 1.5A 'average'.
Dire warnings about using such things in 'outbuildings', I expect our boat is too much of a shed?
I assume that's all about the compressor needing a minimum temperature to function?
Power when it's running about 130W?
 
Last edited:
Tomi Pasanen said:
Thanks, I'll mail them.

Tomi
Click to expand...

I got answer from there:
"Hi,

I am afraid that we stopped selling MarineCool/OZcooler many years ago and the access of spare parts is very limited. If the copper plate has corroded and badly damaged then I would unfortunately recommend that you look for another solution.

If you are a very handy man then I still have peltier elements in stock. The error with the corroded copper plate is in 90 times of 100 caused by a corroded peltier element. "

Actually there is one system without the copper plate for sale (!)
https://www.lespucesnautiques.com/v...esseur-fonctionnel-pour-frigo-origo-4495.html
 
pcatterall said:
I tested my standard cheap Peltier box. With it pretty full of liquid it gets down to -12C ambient I can then switch it on and off on an hourly cycle and it only warms up one degree then cools down again.
Could be improved with better insulation ( simply dropping the existing chest into an insulated carton)
I decided that this was still not cool enough for me in Spain and a fair amount of heat generated if we used it in the saloon.
This water cooling possibility has got me thinking again though, The trial with the Kelco cooler indicated that much lower temps can be achieved. MY idea was to use my 100 gallon fresh water tank ( which has a large surface area on the underwater hull) as the heat sink ( no holes in hull). I will appreciate comments on using the fresh water tank.
Click to expand...

I would love to know the volume of the box and liquid what temperature it started at and finally got down to, how long it took and how much power it used.
 
Fr J Hackett said:
I would love to know the volume of the box and liquid what temperature it started at and finally got down to, how long it took and how much power it used.[/QUOTE

And I would love to remember!! I did record everything but can't find the records now. It was just a small chest say 18x15x12 inches, the unit worked at 2 amps and it was at least half full of water.
I recollect that I left it overnight to get down to the lowest temperature but did not really measure this as my main concern was to see if I could reduce the power requirements while maintaining a reasonable temperature. I believe that I demonstrated that it was not essential to run the unit continuously once optimum temperature was achieved. Possibly a thermostat with a 1 degree on to off range would be of benefit. regarding actual temperatures achieved i'm afraid I cannot recall, it would have been somewhere around the Peltier's potential.
Perhaps I will try/play with a water cooled mock up system and do another test. It was the air cooled systems inability to get down to the temps required that put me off going further.
Click to expand...
 
Looking at some peltier datasheets, it looks like you can get a COP of 2 for a 20degC delta T, if you run a peltier at about 1/4 of its maximum current.
Given that the peltier elements are pretty cheap on ebay, 10 off 60W units for £19, it might be worth looking into.
20degC delta T is enough for ice, using seawater as a heat sink.
Making ice is a) nice for drinks, b) a 'store of cold' due to the latent heat.
The specs above are at some 85degC hot side, I'm not sure how that would change at 20degC?
A fridge which had a lot of peltiers in it to run efficiently at low power could be run in turbo mode when the engine was running.
Kingspan insulation board is .022w/m/k so 10cm thick 1sqm area would be 4.4W at a 20 degC delta T.
Cool beer here come?
To cool a litre of beer by 20 degC is 20x4200 J = 84kJ or 23Whrs. Assuming beer behaves like water...
Latent heat of ice, 334J/g, so 100g of ice cubes is 33.4kJ or 9.3Whr.

You can get one-way or 'diode' heat pipes BTW.


I acquired one of those novelty peltier dehumidifiers, grossly inefficient, but the power it uses helps keep some instruments dry....
A better solid-state dehumidifier might be an idea.
 
pcatterall said:
Fr J Hackett said:
I would love to know the volume of the box and liquid what temperature it started at and finally got down to, how long it took and how much power it used.[/QUOTE

And I would love to remember!! I did record everything but can't find the records now. It was just a small chest say 18x15x12 inches, the unit worked at 2 amps and it was at least half full of water.
I recollect that I left it overnight to get down to the lowest temperature but did not really measure this as my main concern was to see if I could reduce the power requirements while maintaining a reasonable temperature. I believe that I demonstrated that it was not essential to run the unit continuously once optimum temperature was achieved. Possibly a thermostat with a 1 degree on to off range would be of benefit. regarding actual temperatures achieved i'm afraid I cannot recall, it would have been somewhere around the Peltier's potential.
Perhaps I will try/play with a water cooled mock up system and do another test. It was the air cooled systems inability to get down to the temps required that put me off going further.
Click to expand...

I was reading your post as saying that the box got down to MINUS 12°C (-12C) I was assuming the ambient bit meant from some ambient temperature which could have been anything.

I would normally be polite and say I think you might be mistaken in that a Peltier element could cool 25L of water from ambient to -12°C so I think I will leave it there.
Click to expand...
 
Fr J Hackett said:
pcatterall said:
I was reading your post as saying that the box got down to MINUS 12°C (-12C) I was assuming the ambient bit meant from some ambient temperature which could have been anything.

I would normally be polite and say I think you might be mistaken in that a Peltier element could cool 25L of water from ambient to -12°C so I think I will leave it there.
Click to expand...

That's entirely possible, but the COP will be rather less than one, so it's going to take a long time....
Click to expand...
 
I think different people have different requirements for a fridge.

Some people want to turn up on Friday night. Put their warm beer in the fridge and set off on a two week anchoring only cruise. Topping up the fridge as they use more

Others are turning up with cold food, an ice pack, a bottle of water prefrozen. They are sailing for 3 days and want to keep their chicken breast cold ready for a feast on the final night.

And yet others will be cruising for a few hours, need the champers to be cold each night when they pull into the marina so they can sip the first glass while plugging in to the mains electricity...

It's the middle group - who potentially need a really good cool box rather than a fridge - that the Peltier might be helpful...
 
lw395 said:
Cast Iron has a thermal conductivity 1/5 of copper, it will be moderately poor at spreading the heat within the keel.
Click to expand...

But is it better than cabin air?

Does that mean you just need 5 times as big a surface area on the keel.?

Fibreglass is a rubbish conductor. But only ?5mm thick... Would it be better to just epoxy the heat sink to the glass where the hull will be wet on the other side?
 
Fr J Hackett said:
pcatterall said:
I was reading your post as saying that the box got down to MINUS 12°C (-12C) I was assuming the ambient bit meant from some ambient temperature which could have been anything.

I would normally be polite and say I think you might be mistaken in that a Peltier element could cool 25L of water from ambient to -12°C so I think I will leave it there.
Click to expand...

No. I meant 12 C below ambient temperature
Click to expand...
 
For what it's worth I cobbled together a Peltier device, a computer heat sink, a miniature USB aquarium pump, a 5 litre container and lots of spray foam insulation. It is powered by the surplus solar panel power when the battery has had it's requirements met. The heatsink is in the cold side and the pump circulates warm water in a loop around the bilge area. It's not perfect by any means but it does stop the butter melting so I haven't turned right yet!
 
Alan S said:
For what it's worth I cobbled together a Peltier device, a computer heat sink, a miniature USB aquarium pump, a 5 litre container and lots of spray foam insulation. It is powered by the surplus solar panel power when the battery has had it's requirements met. The heatsink is in the cold side and the pump circulates warm water in a loop around the bilge area. It's not perfect by any means but it does stop the butter melting so I haven't turned right yet!
Click to expand...

Sounds reasonable. How have you worked the solar bit...

You measured temps?
 
I've got a home made solar reg using a PIC micro controller which diverts the solar power away from the battery to the "fridge" when the battery voltage reaches an adjustable present level. On a sunny day with no demand from the battery I have seen 6° C with ambient in the mid twenties. It's only a 5 litre box so not even enough space for a couple of beers
 
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