Water cooled or air cooled

oxman

oxman

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Looking to fit a fridge in our Cat before we head off on a circumnavigation next year - so my question is - Water cooled or air cooled?


I have read arguements on this forum in the past on this issue but the answer was as clear as mud!
 
I have posted on this a couple of times having just installed a new fridge unit for the same purpose.

In the end we went for air cooled but with a Isotherm ASU holding plate. I'm sure you've heard of these (they basically freeze a solid block in the fridge when there is enough power to do so and then this keeps the fridge cool - when it melts it reverts to working like a normal fridge) - so far very impressed (UK waters only though so far).

If you go air cooled you need to make sure you have lots of air to cool it - preferrably from the bilge as this is the coolest place (and consider 12v computer fans to assist - although this increases the power consumption). If you go water cooled you have to choose between the Isotherm and Frigoboat systems (seacock or plate design respectively).

The main feeling seems to be water cooled will be more efficient than air cooled as the water is cooler than the air in the tropics. That said, we were informed that an air cooled ASU unit was more efficient than a water cooled evaporator plate. Depending how much you can afford you can of course always go for a water cooled ASU - but this was way beyond our budget!

Sorry I can't be more help - I can only pass on what we found and let you know what we went with. Let me know if you need any more info on the ASU etc

Jonny
 
We have a Frigoboat Keel Cooler and are very pleased with it. It is economical and has a large enough freezing compartment to hold about three weeks (flat) food. We can't really get to the fridge to heavily insulate it and we use about 20amps overnight. Our friends, who have a cat and a really well insulated fridge use only 20amps a day for the whole boat including their keel cooler. Water cooled fridges make irritating noise for both you and anyone near you, most boats with water pumped fridges anchor with fenders over the side for the water to run down to try to stop the noise. Keel coolers are silent.
 
>water cooled will be more efficient than air cooled as the water is cooler than the air in the tropics.

Depends on time of year but often the water temperature is only couple of degrees C less than the air. Having said that we have a Grunert 240v fridge that is water cooled and is fine.
 
As long as heat extracted is not pumped out in cabin - same.

But probably easier with water cooled to have warm water leaving boat though hull than hot air leaving boat on deck.

But DO NOT have hot air being pumped out in cabin!

John
 
Water cooled is more efficient than air cooled because the specific heat (heat capacity) of water is much higher than that of air. Water cooled by a keel cooler is more efficient than water cooled by a pump because no pump is needed: the only power demand is to run the compressor, which circulates the refrigerant through the keel cooler. Beware of "keel coolers" made of brass fitted to an existing through-hull, e.g. sink drain. Instead get a Frigiboat which has a bronze plate outside the hull, with cupronickel tubing inside. It requires another hole through the hull, which is totally sealed during installation. Corrosion risk is virtually nil. Ours works fine.
 
Talk to Penguin Refrigeration Good people to deal with.

FWIW I fitted an electric keel cooled system with a holdover plate. Not too grim on power and kept my beer frosty cold when the Florida ICW water temperature reached 32 C.

Though my current boat has a fan assisted system I'll be changing it for a keel cooled one before we head south.
 
If you are going all the way around your going to be in some hot weather. The keel cooler type will use less power and keep the cabin cooler than an air cooled type when the weather is hot. If the rest of your electrics are set up so you dont need to run your engine regularly for charging then the holding plate type means you will be running your engine. We have a keel cooler type from Frigoboat. With 100mm insulation on a 100litre fridge we use 1 amp per hour on fridge mode with a 3 litre ice box. Convert one third to freezer and we run at 2 amps per hour. In high ambient cabin temperatures the air cooled variety simply cannot compete on power consumption. Expect at least twice as much current draw. Hope this helps
 
Hi Wanderlust. I must cofess, I cannot beleive a claim of 1 Amp per hour on a 100 ltr fridge.. I think you are mistaken.

As for air cooled. the modern units are very, very efficient, and there is no need to place the heat exchanger in the cabin area (Depending of course on layout and pipe run.

There are two excellent books on marine refrigeration from http://www.kollmann-marine.com - the comparison of water v air cooled on modern units including the keel cooler is both objective and enlightening.

It is worth obtaining the books for anyone contempalting such a decision.

In a well designed unit using modern materials the cost performance benefits are in the favour of air cooled.

Joe.
 
[ QUOTE ]
If the rest of your electrics are set up so you dont need to run your engine regularly for charging then the holding plate type means you will be running your engine.

[/ QUOTE ]

This is the case with the Frigoboat holding plate, but the Isotherm holding plate (ASU) system works without the engine and is designed to work with solar panels / wind genny. We have found that it works very well and during the day with solar and wind pushing the battery voltage up the ASU will use the spare power to freeze the holding plate and then at night with no solar and the nav lights on etc the reduced power means the holding plate runs normally once it has thawed.

We found it very interesting that Frigoboat only recommend the evaporator unless you have an engine driven compressor, yet Isotherm highly rate their ASU (a 12v holding plate system). Isotherm don't sell an engine driven holding plate, and Frigoboat don't sell a 12v holding plate.

I know this is deviating away from air vs water cooling, but interesting none the less as the choice of plate has a substantial impact on power consumption. The Isotherm website has some interesting graphs of power consumption - when I spoke to them they suggested a holding plate (ASU) air cooled would be more efficient than an evaporator plate water cooled, but a water cooled ASU would be the most efficient (at a price).

Jonny
 
Good link - the forum of the website looks like an excellent source of info on this topic:

http://www.kollmann-marine.com/phpBB/index.php

Hopefully this should answer most people's questions in this area (wish we had found this some months ago - it may have prevented the 'clear as mud' scenario the discussion on this forum seems to have provided the Oxman with!)

Jonny
 
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