Keel Cooled Refrigeration in Freshwater Tanks?

[Terra Nova]

Originally Posted by colemj

...the people we meet with compressor/evaporator problems have Frigoboat keel coolers. I mean, almost everyone we meet with a problem has this system, and we have met a lot of them. The problem is always the exact same one - blockage in the evaporator plate that cannot be cleared...
This...suggests that the keel cooler itself is causing the problem...

For the life of me I cannot see any logic in reaching this conclusion.

Evaporators are most often shaped by the installer to fit the box. If this is done carelessly, it might be possible to "block" some passages. Rough handling, in service or during installation, might also do that. But the type of heat exchanger can have nothing to do with it.

[a64pilot]

Originally Posted by two fast

Hi my water tank is 160l or around 35Gallons and it makes very little difference to the water temp


Sent from my iPad using Cruisers Sailing Forum

You are using your fresh water tank to cool your water cooled refrigerator?

[colemj]

Originally Posted by Terra Nova

For the life of me I cannot see any logic in reaching this conclusion.

Evaporators are most often shaped by the installer to fit the box. If this is done carelessly, it might be possible to "block" some passages. Rough handling, in service or during installation, might also do that. But the type of heat exchanger can have nothing to do with it.

It can if it is causing contamination. This isn't just my conclusion - Richard Kollman has also come to that conclusion, and Frigoboat itself has concluded that a filter/dryer is necessary on the liquid line to the evaporator of their keel-cooled systems. No one seems to be able to put a finger on how or why it is happening yet, but it is only happening on Frigoboat's keel cooler systems, and not their air-cooled ones.

It is unescapable that the keel cooler, or the design of it (including fittings) itself is a factor.

Please note that most of these evaporators with problems are not custom jobs or shaped in the field - they are bog-standard ones supplied by the manufacturer.

Mark

Mark

[Terra Nova]

Mark--thanks for mentioning the filter. On TN I have the box and evaporator installation completed, and the compressor mounted, but have not yet installed the keel cooler.

[two fast]

Originally Posted by a64pilot

You are using your fresh water tank to cool your water cooled refrigerator?

Hi Yes Ozefridge users both fresh water and air cooling I also have incoming ducted fresh air and a small exhaust fan to suck out the heat out of the cabin via a 100 mm or 4" duct.
This system works very well in hot weather and no extra holes in the hull.


Sent from my iPad using Cruisers Sailing Forum

[a64pilot]

So your air and water, I still think there is more heat being moved by your fridge than you might think and if you were water only cooled you'd end up having very warm drinking water. I think your air to air heat exchanger is doing more than you suspect
Doesn't warm water off gas chlorine faster, and is more likely to have biological growth? A double whammy? Plus I've read above about 85F that water cooled units loose efficiency and cooling?

[a64pilot]

I've got a Cold machine that has the water cooling option that I have disconnected after reading that the salt water eventually eats through and ruins the system, but now I'm curious and wondering if using a small tank and recirculating the water in it might not help? Say take a 5 gl tank, put a little antifreeze in it and use that as a cooling medium?

[DeepFrz]

Say take a 5 gl tank, put a little antifreeze in it and use that as a cooling medium?

Let us know how it turns out.

[Terra Nova]

How about just leaving a few inches of water in your bilge and recirculating that?

[a64pilot]

If I give this a try, I'm not sure how valid a test it will be, based on mine is both air and water cooled, so how much of each? I'd like to increase the efficiency of my fridge as I'm sure we all would, and as has been noted water ability to absorb heat is tremendous.
The water in my bilge is brackish as I still don't have that dripless seal yet and I'd rather not circulate salt water through the condensor, plus if I have a known mass of water and measure it's temp rise I can determine how much heat is being transferred to the water.

[two fast]

Originally Posted by a64pilot

So your air and water, I still think there is more heat being moved by your fridge than you might think and if you were water only cooled you'd end up having very warm drinking water. I think your air to air heat exchanger is doing more than you suspect
Doesn't warm water off gas chlorine faster, and is more likely to have biological growth? A double whammy? Plus I've read above about 85F that water cooled units loose efficiency and cooling?

Hi 64 pilot 85 F or over 29 C is pretty hot I don't think mine would get that hot,also most of my water is rain or desal water it also goes though a carbon filler for drinking. Either way works for me.


Sent from my iPad using Cruisers Sailing Forum

[Neptune's Gear]

Two Fast, sounds like we have the same setup, although the specific model/sizes might be different. I don't have a water maker though, so the cooling water for the fridge/freezer is just one of my freshwater tanks.

The tank I use is fibreglass, and built into the hull, (GRP, Coremat core), and about 150 ltr (40 US gal). Of course, sometimes it’s not full. It works very well, and barely raises the temp of the water at all. (When full, and it is 35 deg C outside (95F)) the tank goes up about 1 Deg C. That’s it.

Now I guess that most of that heat is dissipated through the hull to the ocean, as there is no noticeable heat given from the water tank, although it's unlikely that you would notice such a small increase anyway. Both our fridge and freezer are cooled by the same unit, 290 Ltr fridge and same size freezer.

It is my understanding on the OZEFridge systems, that, when the water cooling is switched on, the air cooling is only used to cool the electric circuitry, so the unit is effectively water cooled, not really both. It is very noticeable that the fan exit Air is significantly cooler using the water cooling system. If you turn that off (and you do have that option), the expelled air is very much warmer...

One of the reasons for the short runtimes is that water is a far better heat sink than air. Therefore, (given the same size heat exchanger), water will remove the heat from the system much faster. Less runtime is saved power.... I have seen multiple air cooled systems that draw more than twice as much power as these, and run 100 % of the time! YES I KNOW this is an installation/design problem, but there are many of them out there.

You are all free to decide what you think is best of course. This system has worked fantastically for me, and my Admiral thinks it is the best single upgrade we have ever done to the boat. For me, the logic of the extra heat sink availability of water, and the desire not to heat the interior of the boat any more than absolutely necessary, plus the technical ability of the OZEFridge support in answering my questions, made it an easy choice.

I will not get into an argument with anyone about the pros and cons of what system will be best. What I can say, is that everyone I’ve met with the freshwater cooled OZEfridge has been really happy – not so many, or even most of the other cruisers with electric fridges/freezers. Many simply don’t use them because they are too power hungry in tropical conditions.

[colemj]

Originally Posted by Neptune's Gear

One of the reasons for the short runtimes is that water is a far better heat sink than air. Therefore, (given the same size heat exchanger), water will remove the heat from the system much faster. Less runtime is saved power.... I have seen multiple air cooled systems that draw more than twice as much power as these, and run 100 % of the time! YES I KNOW this is an installation/design problem, but there are many of them out there.(

That is not how refrigeration works. The refrigerant needs to be cooled to a certain range, and as long as the medium can provide this cooling, it is the same as any other medium. There is no "getting it colder" or "getting it colder faster".

Run time is not a determinant of efficiency. A good evaporator plate system will shoot for about a 50% run time using slower compressor speeds and less energy than a poorly designed system running shorter times using higher speeds and more energy.

Of course, box design and implementation is the other variable on run time. If a compressor is running 100% of the time, I guarantee you it is not because it is using air cooling instead of water.

Mark

[Neptune's Gear]

I mostly agree with that, and I'm not saying that it cannot be done with Air.
IMO, Using the same refrigerant flow rate (same compressor) you just need more air, or a larger/better heat exchanger, to move a certain amount of heat energy from one place to another, in a set time, than you do the same amount of heat energy with water as the cooling medium, in the same time. The medium the heat is transferred to is totally irrelevant as long as the efficiency of the heat exchanger is the same. Air, Water, whatever...

To say it cannot be done faster is not accurate unless the heat exchanger can cool the heated refrigerant to the desired level in one pass through. If the system requires more than one pass of the heat exchanger to cool (normal) to the desired level, then of course that can be improved. (for example, if Liquid nitrogen replaced air or water as the cooling medium of the heat exchanger) more heat would be removed on each pass, therefore more efficient, therefore shorter runs effectively drawing less power.
It is a well known fact that water is a far more efficient heat sink than air, especially when the Air is over, sometimes well over, 30 deg C. That was not the primary point. Like me, most cruisers in the tropics are looking to cool the interior of their boats, not let the fridge/freezer heat it up. THAT is my real point.
The power use, and cycle time related to the heat exchanger, and how much heat energy that it can transfer in a set period. The more the better. The one that OZEfridge use is good, there MAY be air ones that are better, but unless ducted outside, they WILL heat your boat. If they are the same, given the same flow, you'll have the same cycle time, for the same heat energy transferred.

I know some people will try to disagree with this, and I'm not going to enter into an endless, circular debate about it. This is my final post on the matter in this thread. As I said, people are completely free to make their own choices....

[crazyoldboatguy]

I had thought there was a more current thread on this subject but couldn't find it. So many folks indicate that placing a refrigeration keel cooler in a fresh water storage tank would be improper.

What about placing the keel cooler in the diesel fuel tank?