water cooled peltier cool box conversion

[stu9000]

Cool box conversions have been discussed on ybw before.
I know peltier cool box conversion kits are less energy efficient that compressor based systems but I can't afford the latter.
Ice blocks and frozen stew will do the job for a while but I was wondering what you thought of a water cooled peltier system.

connecting one of these to a water block

What I like about this system is that the heat on one side of the peltier device is well away from the coolbox so wont leak residual heat back into the box.
I can connect a pc heat sync and fan to the hot side of the peltier to dissipate.
The water block goes on the cold side and cooling water is pumped through tubing on a closed look running around the inside walls of my cool box.

I might need more than one peltier device to get the cool box down to temperature but I could have a system for when the engine was running and run two or three or four peltier devices. I read somewhere that peltiers will only drop 40F below ambient temps but my mini fridge at work has ice build up on the metal panel at the back so it must have the (admittedly weak) potential to get the water loop down to a good temp.

I need to think about whether it would be better to run peltier water blocks in series which would require just the one pump, or have a "boost" water loop with its own pump. When the engine is off I could run a single peltier device, ideally with some kind of 5 mins on 10 mins on/off timer switch.
But I have not googled that yet.

I think the peltier devices draw about 3amps.
I have not yet worked out what the water pump and pc heat sync fan would draw and am not an expert on amp hours and the like.

What do you think?
Am I mad?

You've got to admit, it looks fun though!

 

[Lon nan Gruagach]

I only once looked at peltier cooling and quickly dismmised them as being pathetic, only useful for that extra last mile on top of more conventional systems. However you are right, it does look fun.

 

[William_H]

As an experimental project it may have merit. certainly the peltier device should be improved in efficiency with the water cooling.
Your 2nd 3rd line are very confusing. The computer fan and heat sink should go on the inside of the cool box while water block would go on the outside of the cool box.
If you have decent water flow then water temp rise won't be much so water blocks in series or in parallel OK.
However ultimately with the peltier elements, heatsinks, fans, the water blocks and pump I thyink you will end up spending something similat in price to a small Waeco compressor box. For less current and better freezing. good luck olewill

 

[stu9000]

As an experimental project it may have merit. certainly the peltier device should be improved in efficiency with the water cooling.
Your 2nd 3rd line are very confusing. The computer fan and heat sink should go on the inside of the cool box while water block would go on the outside of the cool box.
If you have decent water flow then water temp rise won't be much so water blocks in series or in parallel OK.
However ultimately with the peltier elements, heatsinks, fans, the water blocks and pump I thyink you will end up spending something similat in price to a small Waeco compressor box. For less current and better freezing. good luck olewill

From what you write it would seem the water tubes should be used to disperse heat and the fan and PC heat sinc and fan should be used inside the fridge. I imagined it the other way round.

I'm also interested in the waeco compressor box you mention. I would expect to pay under £50 for my peltier project but would stretch to £100 ish for a compressor system. The ones ive seen seem to come in around £500.
Thanks

 

[stu9000]

As an experimental project it may have merit. certainly the peltier device should be improved in efficiency with the water cooling.
Your 2nd 3rd line are very confusing. The computer fan and heat sink should go on the inside of the cool box while water block would go on the outside of the cool box.
If you have decent water flow then water temp rise won't be much so water blocks in series or in parallel OK.
However ultimately with the peltier elements, heatsinks, fans, the water blocks and pump I thyink you will end up spending something similat in price to a small Waeco compressor box. For less current and better freezing. good luck olewill

I had another hunt round for compressors . the best (cheapest) I could find was this one from mailspeedmarine.

http://www.mailspeedmarine.com/waeco-coldmachine-series-80-fridge-kits.html
That is £100 and I think the plate and other bits and bobs would maybe double it..?

 

[BabaYaga]

I have a water cooled peltier cool box system, manufactured in Sweden during the 90's, under the name MarinCool. It was sold under the Electrolux brand for a few years, IIRC. Mine still works fine. Power draw is perhaps marginally greater than than would be the case with a compressor based system, but there are other benefits. Completely silent, for instance.
The design is very different from what you are proposing, though. The heat is transferred through a very thick copper braid leading to a large copper plate which is bolted to the hull below the WL. No moving parts at all.

 

[jimmcgee]

I have a water cooled peltier cool box system, manufactured in Sweden during the 90's, under the name MarinCool. It was sold under the Electrolux brand for a few years, IIRC. Mine still works fine. Power draw is perhaps marginally greater than than would be the case with a compressor based system, but there are other benefits. Completely silent, for instance.
The design is very different from what you are proposing, though. The heat is transferred through a very thick copper braid leading to a large copper plate which is bolted to the hull below the WL. No moving parts at all.

http://www.fe83.org/docs/sisusta/fridge/

 

[Tomi Pasanen]

I have a water cooled peltier cool box system, manufactured in Sweden during the 90's, under the name MarinCool. It was sold under the Electrolux brand for a few years, IIRC. Mine still works fine. Power draw is perhaps marginally greater than than would be the case with a compressor based system, but there are other benefits. Completely silent, for instance.
The design is very different from what you are proposing, though. The heat is transferred through a very thick copper braid leading to a large copper plate which is bolted to the hull below the WL. No moving parts at all.

Hi BabaYaga, I have Marincool too but now my copper plate (heat sink) is quite corroded. Do you have any idea if it is possible to replace?

Thanks
Tomi

 

[Ana]

Check http://www.aten.it/KECO_Eng.html Sailing Uma has installed one https://www.youtube.com/watch?v=twW36wFmm9U

 

[BabaYaga]

Hi BabaYaga, I have Marincool too but now my copper plate (heat sink) is quite corroded. Do you have any idea if it is possible to replace?

Thanks
Tomi

Hi Tomi,
the Marincool concept was later marketed as, IIRC, the OzEcoCooler, by a company called Oz Marine. This might have lasted until around 2005 or so. The company refocused on marine electric propulsion and operates today as GreenStar Marine. Possibly they might be able to help or direct you further:
http://greenstarmarine.se/en/kontakt/
If you are successful in sorting your problem, I'm sure other Marincool users would be interested to know.

 

[lw395]

The other cheap route is to buy a normal domestic fridge and run it via an inverter.
A variation on that is to dismantle the frdige and put the working parts in a different, better insulated enclosure, without breaking the circuit.
If you can find someone who is junking a fridge that still works but e.g. the door seals and plastics have gone, it might be done quite cheaply.

 

[Tomi Pasanen]

Hi Tomi,
the Marincool concept was later marketed as, IIRC, the OzEcoCooler, by a company called Oz Marine. This might have lasted until around 2005 or so. The company refocused on marine electric propulsion and operates today as GreenStar Marine. Possibly they might be able to help or direct you further:
http://greenstarmarine.se/en/kontakt/
If you are successful in sorting your problem, I'm sure other Marincool users would be interested to know.

Thanks, I'll mail them.

Tomi

 

[pcatterall]

I have been considering installing a built in unit to augment our waeco compressor cool box.
If they can really reduce tempts by 25 degrees below sea water temp then they should work ok in Spain where 28 degrees is as hot as the sea gets.
We have a large shallow fresh water tank (100 gallons) with a lot of its external surface in contact with the submerged hull.
I wonder if we could plumb into the fresh water which in turn is cooled by the outside sea water?

 

[DownWest]

Most of the these units in cool boxes use 5amps continuously. So can your supply cope with that?

 

[ShinyShoe]

Most of the these units in cool boxes use 5amps continuously. So can your supply cope with that?

But WHY! I've never understood why they do that. Why are they not thermostatically controlled and so able to shut themselves off when desired temp is reached and then the cool box part keep it cool for a period before it switches back on? They are fairly instant at cooling so you'd get some effect quickly... the only reason I can think is they are mostly designed for cars where when you park up the power goes off. If your thermostat is holding it between 0-5C and you park up with it reaching 4.9C its not switching on... you'll complain the box is useless?

I quite like the idea of using sea water (bilge, keel, external) on the hot side. They drop 15-20C below the 'ambient' temp normally. You can stack them on top of each other so 2 can drop probably 35C below ambient if needed. Can't figure out if the cold side is better just being a big piece of metal in the cold box, or a water system (with antifreeze?)

 

[Daverw]

They are just not that efficient, that’s why they are not used in the real world, as said they need to run all the time as they have no thermal mass, the reported design figures are always very over stated, compression refrigeration is minimum 1 watt in, 4 watts of cooling and the system has a high thermal mass and just works

 

[Tomi Pasanen]

Guys, please read https://www.practical-sailor.com/issues/25_2/features/4227-1.html

 

[ShinyShoe]

They are just not that efficient, that’s why they are not used in the real world, as said they need to run all the time as they have no thermal mass, the reported design figures are always very over stated, compression refrigeration is minimum 1 watt in, 4 watts of cooling and the system has a high thermal mass and just works

I get they they are incredibly inefficient. BUT I can buy a coolbox "off the shelf" that I can put goods in at 2C and 12 hours later they will be 8C. All I then need is the Peltier to switch on, cool it back to 2C and switch off. In fact I can but units that can stay cold for 3 days (apparently).

The practical sailor article is good - its main concern is installing the braid. I think you could get round that - albeiet by having to add some extra parts...
(~£5)
With 2 or 3 peltier's on it (~£5)
With a suitable metal plate on the other side (inside the exceptionally well insulated cool box). Personally I'd put a small 12V fan across that to 'share the cold'

A < £10 digital thermostat

A magnetic relay on the door to switch the fan off when fridge door open

Silicone tube to pump the liquid away from the heat sink and then perhaps a similar block on the keel somewhere else it can exchange lots of heat.

A tiny 12V pump circulating the liquid around the hot side.

Unlike the Practical Sailor article you aren't limited by the length of the braid - because you use the silicone tubing with the hot liquid, rather than cold braid (or as OP suggested cold liquid). There could be advantages of using cold liquid that I haven't thought about though... if you plug in to the mains lots and could cool that liquid on the mains with ?3 peltiers and then reduce to 1 peltier while at sea if there was sufficient liquid already cooled your effect would last longer... so add a insulated sump into the cold side?

If you are in hot climes - you may need two peltiers stacked above each other.

Peltiers are dirt cheap. Its running them that isn't, and I can't help but feel the answer is thermostats and insulation - same as it is for inefficient compressor fridges! £25 would buy the bits above!

 

[lw395]

I've used peltiers in an industrial design.
To move 5W of heat about 18degC took about 18W of DC.
You wouldn't want to b moving the power used to drive a fan.
These days, you'd use heat pipes instead of any 'braid' surely?
Such things are found in moderately upscale PCs and laptops.

For a boat fridge, I think it's only a solution if you have a lot of DC available and your fridge needs are very modest.
For our coastal cruising, we are generally OK buying ice or frozen food and having a well insulated cool box.

 

[Tomi Pasanen]

I wonder could the ballast keel be used as heat sink? In my boat that is iron and 1330kg