Water-cooled or air-cooled fridge in tropical waters?

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Rhapsode

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I have to replace the compressor on my fridge which uses a sea-water cooled condenser.

I am getting conflicting advice as to the best approach in tropical waters - to replace with another water-cooled unit or to go for an air-cooled unit?

Locally (Brazil) they say go for air-cooled. So I can't help wondering that they must know what's best for their waters.

On the other hand I am told by a major UK supplier that the water cooled is the best option and that it uses less amps than the air-cooled option.This is disputed by the Brazilians who say the exact opposite.

The sea water temperature is 27 C at the moment and the ambient temperature inside the boat gets close to 40C most afternoons, especially rainy afternoons when I can't open the hatches fully.

So what I am after from the distinguished members of this forum are first hand experiences of what actually worked for them when in tropical waters.

Many thanks.
 
Sea water cooled fridge

Sea water cooled must be much more efficient than air cooled.
So if you already have sea water cooled it should be retained.
The replacement of the compressor should not be different in either type of system.
Of course the compressor itself will get hot so it will always be partially air cooled.
Is it a battery powered fridge or engine driven.
An airconditioner compressor off a car should be cheap and very powerful such that a short engine run would cool a fridge quickly. Of course it would not be so convenient when moored with shore power. This certainly would need to be water cooled. good luck olewill
 
Maybe not relevant to you but by coincidence yesterday I thought the compressor on my fridge had gone. Checked with a voltmeter that power was going in, reading 12v+ so that seemed ok. Checked the thermostat that seemed to be ok. So thought it must be the compressor. By coincidence a friend on another Bavaria 38, was next to me and he said he had the same problem last year. He bought a compressor and problem still persisted. After investigation found that one of the connecting terminals at the back of the switch panel was the worse for wear. Cleaned it up and fridge started working. Exactly the same thing I found in mine. It would appear when not under load the terminal would draw the 12 volts but was not sufficient to overcome the resistance when load was being drawn through the terminal.
As I say may not be relevant to you as you have a different boat but may be worth checking?
 
I would go for air cooled so that it will work when lifted out AND add an extra water cooled unit to help reduce the heat and therefore reduce the power consumption. Try asking Penguin Refrigeration.
 
When I discussed this with Waeco (who offered both air and water cooled) a few years back they said the advantages of water cooling were often lost by problems caused by the extra parts and the power to run the pump and especially if the system, notably filters, was not maintained regularly. The point made was that if the unit drew or could be made to draw air from the bilges, the difference in temperature between air there and the water outside was smaller than you would expect, therefore by the time the extra power used by the water pump was factored in the difference in overall efficiency was tiny.
 
Yes, but the temperature of the heat exchange medium is not the only factor by a long shot. The specific heat of air is only about 1.005kJ/kg.K at a density of only 1.205kg/m3 (at 20C to boot), compared to 4.184 for water at a density of 1000kg/m3, or more than 800x (!) that of water. Air, in fact, is an excellent heat insulator, and most heat insulating materials work by entrapping air.

Water, on the contrary, has the highest specific heat of any common material. It is about 3200x more efficient by volume than air. That is to say, one litre of water weighing one kg can absorb and hold 3,200 times more heat than one litre of air. Or to put it yet another way: In order to get rid of the same amount of heat which can be dealt with with one litre of water, you need 3200 litres or 3.2 cubic metres of air, which weighs more than 4 kilogrammes. Pushing around 4 kg of air will require more energy than 1 kg of water, and the surface area of your heat exchanger will have to be much larger to get that heat into the air in the first place. Bah!

In order to avoid the complication and inefficiencies of pumps and sea water circulation, one can use a keel-cooled type system like SeaFrost or one of the clever self-pumping systems like Isotherm (the condensor coils are contained within a special skin fitting which is used for a sink drain or deck drain, and sea water self-pumps through it from the natural motion of the boat). No pumps, no fans, no extra sea water running around inside the boat, no filters, no electrical consumption other than the compressor itself. It is much simpler, more compact, quieter, and more elegant than any air-cooled system.

Besides the inherent inefficiency of air cooling compared to sea water, you have the problem of getting rid of the hot air. In the tropics, especially, it is very unpleasant to have the hot air from an air-cooled fridge condensor pouring out into your cabin space, or even into a locker space. This problem is wholly absent in sea water cooled systems, as the heat is simply dumped into the sea.

I would never consider an air-cooled fridge myself. Other than being usable on the hard, I can't think of a single advantage of it.

I spent more than 10 years cruising the tropical waters of SW Florida. I don't believe I ever saw anyone using an air-cooled fridge there. We used a conventional pumped sea-water cooled system which worked perfectly the entire time without the slightest problem. We now have an Isotherm system (actually two of them -- one for fridge and one for the separate freezer). The power consumption of the two Isotherms is less than the single Waeco we had before, although the difference in water temperature (UK versus SW Florida) probably plays a large role in that.
 
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We went for water cooled as the surveys of the ARC and World rally yachts came down pretty well unanimously in favour of water cooled systems. In response to Robins comment on the pumps breaking down, we have gone with a water cooled system that doesn't have a separate water pump, having heard the same argument about complexity and reliability from a number of sources.

Penguin do a system that has the condenser in an underwater fitting and no extra pump. Last year was its first year in use, and we have to turn the thing down because it is so darned efficient. Probably helps that I put LOTS of insulation round the new s/s liner.
 
I have a water cooled unit in a standard Waeco fridge, built by my son. It is pumped by a Jabsco Par Max 1 pump via a 12 - 6 volt converter to reduce flow rate. It consumes 0.6 A against the fridge's 3 - 4 A, depending on the cooling stage. The fridge cycles on for about 30 - 40% of the time but no doubt the insulation of the fridge could be better. This is in summer temperatures in Greece. When hauled out I cycle water from a bucket through the fridge and it will run like this indefinitely without overheating.

My thinking in fitting this type was that air circulation in my boat is very poor. If the boat had a good, uninterrupted flow of air along the bilge and out to the exterior of the boat it would be worth considering air cooled but if air leaving the heat exchanger enters the boat, where it will have a significant heating effect, I would go for water cooling.
 
TQA said:
Most people I know that have a watercooled fridge seem to be changing the pump pretty often something like every year to 18 months.
Click to expand...

The original, secondhand Shurflo pump that I used was still working OK after about six years in service. I changed it because I thought I could save power by going to a small pump but this proved not to be the case. I fitted an ammeter at the same time and found both pumps to consume the same. I spoke to Jabsco before buying the Par Max 1 and their advice was that if running it on 6 volts and without pressure it would last indefinitely. It has been in for two seasons now, no problems. My fridge runs continuously May to October.

The suction strainer needs cleaning of general flotsam and fouling every three weeks or so. A bonus on fitting the Jabsco has been that it has so far not needed to be cleaned at all, whereas the valves on the Shurflo needed to be cleaned about twice per season.

April020.jpg


One way around the fouling is to circulate the fresh water supply through it. This works well and I would have done it except that it is very difficult to arrange on my boat.
 
TQA said:
I have an air cooled fridge out here in the Windward / Leeward chain and can make two trays of ice a day as well as keeping a large box pretty cold.

Most people I know that have a watercooled fridge seem to be changing the pump pretty often something like every year to 18 months.
Click to expand...
We have a water cooled fridge - but NO PUMP - the condenser is mounted in a bronze fitting that bolts onto the hull. I can't see it as being any less reliable than a normal compressor. In fact the compressor IS a normal compressor - its just plugged into the full cooling condenser instead of an air cooled condenser...
 
Thanks

Thanks everyone - I think I will go with the water-cooled version but am also investigating whether I can retrofit the keel-cooled version when I next get the boat out of the water sometime next year (probably Trinidad) and keeping the same new compressor (Danfoss BD35F).

The Customs in Brazil can be a nightmare despite going through the boat temporary importation scheme. One of the boats here has been waiting or six months for a part held up in Customs. Three months is the norm but some items never make it through the system.

So I will bring the compressor out in my suitcase. I have been liaising with Ian Gorringe of Penguinfrigo who has been very helpful indeed. He will discharge the gas in the compressor for me so that I don't get into trouble with the airlines or airport officials anywhere along the route.

Happy sailing.
 
Rhapsode said:
Thanks everyone - I think I will go with the water-cooled version but am also investigating whether I can retrofit the keel-cooled version when I next get the boat out of the water sometime next year (probably Trinidad) and keeping the same new compressor (Danfoss BD35F).

The Customs in Brazil can be a nightmare despite going through the boat temporary importation scheme. One of the boats here has been waiting or six months for a part held up in Customs. Three months is the norm but some items never make it through the system.

So I will bring the compressor out in my suitcase. I have been liaising with Ian Gorringe of Penguinfrigo who has been very helpful indeed. He will discharge the gas in the compressor for me so that I don't get into trouble with the airlines or airport officials anywhere along the route.

Happy sailing.
Click to expand...
When I was on a boat in Brazil, we had to use a local agent to help us collect some items from customs. I seem to remember having to come up with some cash for some special sort of import duty that they discovered was payable.... I went to the airport customs house with the agent and the cash, and the parts magically appeared a few minutes later.
 
john_morris_uk said:
We have a water cooled fridge - but NO PUMP - the condenser is mounted in a bronze fitting that bolts onto the hull. I can't see it as being any less reliable than a normal compressor. In fact the compressor IS a normal compressor - its just plugged into the full cooling condenser instead of an air cooled condenser...
Click to expand...

Yes, agree, same set up as mine
 
From Penguinfrigo...

Quote

The keel cooler http://www.penguinfrigo.co.uk/shop/#E50361Z is shown in the link it can be mounted within 1.5 m of the compressor and in any part of the hull under water. The lower the keel cooler in the water the better but on my own boat which dries out it is 30 cm from the waterline and works very well.

A water cooled system can be converted to keel cooled at a later date as well as an air cooled system. The self-sealing couplings mean the condenser (keel cooler) is just installed between the evaporator and compressor.

Unquote
 
Rhapsode said:
From Penguinfrigo...

Quote

The keel cooler http://www.penguinfrigo.co.uk/shop/#E50361Z is shown in the link it can be mounted within 1.5 m of the compressor and in any part of the hull under water. The lower the keel cooler in the water the better but on my own boat which dries out it is 30 cm from the waterline and works very well.

A water cooled system can be converted to keel cooled at a later date as well as an air cooled system. The self-sealing couplings mean the condenser (keel cooler) is just installed between the evaporator and compressor.

Unquote
Click to expand...

£300.09 exc. VAT! Don't know whether that includes the couplings. It's a hell of a lot more than my little Par pump was.
 
hot air cooled !

Having an aircooled fridge in a hot climate , I find that the cockpit air temp is so warm around the fridge that it runs almost continuosly . This is a new fridge too . I am thinking it needs a cooler air supply , so as its a cat I wondered about making a , say , 50mm hole in the bridgedeck , which is well out of the water , to feed cool air directly under the fridge .
A water deflector would need to be fitted to stop any splashing water and then , perhaps a solar vent in the coachroof to expel the hot air ?
Is this a bit desperate, or may it work ? ?
 
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