Keel Cooled Refrigeration in Freshwater Tanks?

[skipmac]

Originally Posted by TheNomadTrip

Well crap. I thought I had it figured out, decided on an air-cooled unit.

But, the unit I'm replacing is a Frigoboat water-cooled system. And what I wanted to replace it with was a Vitrifrigo air-cooled unit.

I've learned that they're not simply interchangable. So I'd have to replace the evaporator plate as well. I'm not sure if this is the right choice anymore.

The issue is that I'm using the factory-installed (Lagoon), front-loading box and I would prefer to leave that intact... I've been told it might be better to replace the box as well - but that's an undertaking I'm not totally comfortable with as the unit doesn't look like it'll be easy to take out. And I'm not that confident in my ability to make it aesthetically appealing, if I needed to replace the whole thing. It's in my galley, so a half-assed job would be noticeable and bug me every day.

So, I could just replace it with another Frigoboat system. But that runs a little over $1K for just the compressor. The Vitrigrigo unit can be had for less than $500.

Any thoughts on this?

A few thoughts and question or so.

- First, how old is the unit in the boat?
- What kind of shape is the evaporator in? \
- Why are you replacing it, did it leak out the Freon?
- can you get the compressor repaired by Frigoboat?


Comments
- make sure you match the size and capacity of the compressor and evaporator.
- if the system leaked down then you will have to find the leaks, repair, the flush and vacuum the system. If you do it yourself, the evaporator is in good condition AND not the source of the leak AND the system isn't too old AND all use the same type of refrigerant then it would probably make sense to replace just the compressor and keep the evaporator.
- What kind of compressor does the Vitrifrigo use? Danfoss same as the Frigoboat? Both BD50 or BD35?

[TheNomadTrip]

Originally Posted by skipmac

A few thoughts and question or so.

- First, how old is the unit in the boat?
- What kind of shape is the evaporator in? \
- Why are you replacing it, did it leak out the Freon?
- can you get the compressor repaired by Frigoboat?

- the unit in the boat is original. 15 years old. It's never worked since I've owned it (3 months) and before (no idea how long?)
- evaporator appears to be in good shape, but the compressor wont stay on long enough for me to test it. The previous owner said "it doesn't work" and rather than replace it, he installed an air-cooled holding plate under a bunk. This air-cooled holding plate works well as a freezer, but is less than desirable for fruits, etc.
- It doesn't work, and as old as it is (and corroded) - I'd rather replace the unit than to fight with it for weeks, sink money into it, and then only have a working 15 year old unit.
- Maybe, but it's not in the greatest shape (corrosion) and the boat is in Panama. Not ideal

Originally Posted by skipmac

Comments
- make sure you match the size and capacity of the compressor and evaporator.
- if the system leaked down then you will have to find the leaks, repair, the flush and vacuum the system. If you do it yourself, the evaporator is in good condition AND not the source of the leak AND the system isn't too old AND all use the same type of refrigerant then it would probably make sense to replace just the compressor and keep the evaporator.
- What kind of compressor does the Vitrifrigo use? Danfoss same as the Frigoboat? Both BD50 or BD35?

Vitrifrigo uses the Danfoss BD35 or 50. Current Frigoboat is the Danfoss BD35. Thinking about just going bigger (BD50) so I can use it as a deep-freeze, should the need/desire arise. Not sure of the logic there, open to suggestions.

It sounds like you're leaning towards replacing compressor and evaporator, yes? Any reason that would be a massive PITA?

[skipmac]

Originally Posted by TheNomadTrip

It sounds like you're leaning towards replacing compressor and evaporator, yes? Any reason that would be a massive PITA?

Replacing the whole unit, especially an air cooled is really a piece of cake (assuming you don't have the bad luck to get a new DOA unit). Everything comes with sealed connectors, precharged with the correct amount of refrigerant.

Bolt down all the parts, route the refrigerant lines, screw the connectors together, wire in a few little pieces like the thermostat and controller, add power, turn on. It's really that easy. After I glassed in a little shelf for the compressor unit I did the whole thing in an easy afternoon. I believe most if not all the new units are plug and play like this but not interchangeable as they use different types of connectors. The only glitch I had was very slightly low voltage on main 12V wires. Looked good on the meter and never saw a voltage drop but kept having intermittent problems on startup. I was skeptical since I was certain the wiring was good but on the advise of Mr Kollman put in new wires and I was golden.

I personally went with Frigoboat. I have read a number good reviews and owners reports on the Frigoboats but also a few major headaches with their older keel cooled versions. I think there are several good brands out there. Almost everyone uses the Danfoss compressors so the difference is going to be in the wiring, chassis, connectors and such.

You might even want to check with Rich Boren SV Third Day who has posted on this thread. He makes the Technautics Cool Blue system. Not only does he sell the systems I'm pretty sure you would get good tech support on the installation if you run into any problems.

PS
Hey Rich, Was not aware of your system when I bought my new unit a few years ago. If I had I would have given you a call.

[CarinaPDX]

A few comments:

First, while pumped seawater systems are thermally efficient they tend not to be the most reliable. I suffered through the evolution of the Isotherm versions and would never do that again. There is just so much to go wrong, and it does...

Second, I am underwhelmed with the designs of the commercially available keel cooler systems. (I do not claim to know all of them so maybe there is a good one available.) I cannot imagine trying to clean and anti-foul the cute Isotherm thru-hull with coils inside, but at least it should work and avoids a new hole in the hull. The sintered bronze (with internal tubing) Frigoboat (now Vitrifrigo?) doesn't have a good track record with corrosion (although this may be a result of electrolysis and bad boat wiring rather than a bad design of the cooler).

Third, It seems the OP is limiting himself to off-the shelf systems that he can install himself, in large measure due to cost. If we are only looking at the 2 commonly available systems then I would put the Vitrifrigo into the side of the water tank near the bottom if that is the approach taken. I would also try to isolate the bronze from the stainless (tricky) and carefully check the boat's electrical system (should do anyway). OTOH if the plate is in good thermal contact with the steel tank it might work with the tank empty, if not greatly so.

Fourth, the best way to get a great system is to have one made up custom. This requires a good pro and can get expensive. This is the way that I went, and I was lucky to encounter a competent company at reasonable prices in Marmaris, Turkey. I have a BD35 that outputs through a custom keel cooler (condenser). The cooler is fabricated from a bronze through-hull (IIRC 1") with a bronze plate installed flush to the outside flange. A cupro-nickel bronze tube (8 mm?) passes through 2 holes in this plate, bends 90 degrees on the outside and forms a loop about 18" long and 2" wide (very approx) with 2 mounting tabs brazed for attachment to hull. The thru-hull is filled with something, which may contribute to watertightness. This is mounted in the hollow of the port quarter almost to the prop aperture where it is very difficult to be hit. I primed it with epoxy primer then painted anti-foul over the top. I also put a second air-cooled condenser after this, which works well when hauled out, but makes it a bit tricky to charge. With or without the air condenser it is a good idea to install a fan to cool the compressor. Along with 4" of carefully installed insulation this system is very efficient (fridge and lighting at anchor supplied by 150W of solar, not optimally aligned). The box is small (approx 3.4 cu ft). In the tropics I doubt that it ever exceeded a 30% duty cycle on low speed (I rigged a switch for controlling compressor speed). In another life I would rig a timer to the fan power so I would know the duty cycle. This system has been working flawlessly for 8 years, other than the initial problems of some contamination blocking the capillary and getting the charge right.

I cannot imagine what a custom system would cost in the US, but I suspect that it would be ridiculously expensive. It would make a nice DIY project for someone with the skills or the time to learn them. OTOH there is nothing wrong with the packaged systems - just be certain that the couplers are immaculate before assembly, and don't buy one that has been sitting around long as the copper can lose the annealing (very difficult to bend without kinking). And unless you know what you are doing don't mix components (like using your old evaporator with a new compressor) as the backpressure caused by the valve or capillary must match the evaporator spec.

Good luck,

Greg

[Terra Nova]

Over the years I have built a number of refrigerator/freezers using all common types of refrigeration systems, holding plate, engine-driven, water-cooled, air-cooled, keel-cooled. The system that most impressed me, for efficiency and absolutely silent operation, was the Frigoboat keel-cooled unit.

On a Mapleleaf 50, two large side by side, top-loading boxes were installed. Either could be run as just a reefer or just a freezer. The owner reported 1 amp/hour/box in southern California summer temps.

So that is what I have purchased for Terra Nova.

I would never install an air-cooled unit for use in the tropics. And I would never use a keel-cooled unit to heat my fresh water supply (and my boat's interior).

[a64pilot]

If you use your freshwater tank as a heat sink, I think you'll be astonished at how much you heat up the water

[SV THIRD DAY]

Originally Posted by Terra Nova

The owner reported 1 amp/hour/box in southern California summer temps.

Sounds about right...our units do about 25AH/day for a 7CF box, but when the sea water temp warms up in the Sea of Cortez to 85-degs, our air cooled condensing unit won't lose efficiency like the keel-cooler.

Originally Posted by Terra Nova

I would never install an air-cooled unit for use in the tropics. .

Not sure why...we have successfully been sending our air cooled units to the Military with operational specs of 135-deg F ambient temp for portable desert food service use and that has been a great testing/proving ground for us. In addition we have thousands of cruising boats all around the world with our air cooled units. The trick is understanding that not air cooled units are the same and are desigend for the same ambient temperatrues.

[Terra Nova]

Originally Posted by SV THIRD DAY

...Not sure why...

Because I don't want to heat the inside of my boat in the tropics.

[belizesailor]

Originally Posted by DeepFrz

It seems to me that Richard Kollman is suggesting that air cooled, properly installed is the best type of refrigerator/freezer.

Air cooled in the tropics works just fine. I've run nothing but air cooled systems for over two decades. Last one (Danfoss BD35) did a fine efficient job for 14 years...outlived the box!).

OP...think this thru...the purpose of a keel cooler is to cool something. If you put it in a tank the water will be heated...reducing cooling potential...and thus defeating, or at least reducing efficiency, of the cooling process. Very different that sticking it in the big ass ocean. Could turn into a vicious feed back cycle depending on the details.

Would be interesting to verify the behavior with thermodynamics calculations. Maybe someone more versed in that than me could crunch a simplified example.

[onestepcsy37]

Being a keep it simple kind of guy I got rid of a troublesome water cooled fridge ten+ years ago and replaced it with a stock adler barbour cu200 which uses the bd50. It's air cooled but has facilities to add supplementary water cooling if desired. Sub tropical cruising florida and bahamas for the past ten years and its worked flawlessly using air cooling only; I've never felt the need to install the water cooling circuit.

[belizesailor]

Originally Posted by Terra Nova

Because I don't want to heat the inside of my boat in the tropics.

Good ventilation can eliminate that issue. My installation has an intake cowling just below compressor level in the cockpit and an exhaust cowling up higher. They are passive, and that has worked fine, but I've considered adding a fan to the upper cowling. A computer cooling fan switched in tandem with the compressor fan should work nicely.

[two fast]

Originally Posted by a64pilot

If you use your freshwater tank as a heat sink, I think you'll be astonished at how much you heat up the water

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

[CarinaPDX]

As I think about it I am perplexed by the claim that as one moves south the air cooled systems hold up better than the water cooled ones. I don't remember ever sailing in water over 85ºF, but I sure have spent time in air greater than 100ºF, so the water-cooled system will have the advantage as far as the temperature of the heat sinking flow. Water has a much higher thermal mass than air, which allows it to cool with a smaller contact area, but radiators make up for that with larger surfaces (all those aluminum plates). Of course if either heat exchanger has too high a thermal resistance then it will become a problem in higher temperatures, but that is not specific to water (or air). It is an issue of design, and specifically of the size of the heat exchanger. The (air) radiators are readily available in several sizes to cover a broad range of system requirements, and the system builder chooses the correct size. The water heat exchangers seem to be proprietary to each fridge conversion manufacturer so if they aren't adequate it is very much their fault.

In short the only way air is better than water in hot climates is if the manufacturer didn't get the design right; either will work just fine if properly specified. OTOH if a water system has a cooling fan on the compressor, and uses a keel cooler, there is no energy advantage other than the difference in temperature of the cooling medium, which may not be great in the tropics. It seems to me that the biggest difference is in where the heat is going, and for my installation it was much easier to use a keel cooler than try to vent that much air. As I said earlier I do not consider the pumped seawater systems to be worthy of consideration due to complexity/reliability issues, but also that pump requires precious additional power.

Any thoughts?

Greg

[Neptune's Gear]

Greg, you are right.
I too have an OZEfridge system, water cooled, and air cooled as well. It runs a really small ( about 1 ltr/min) pump, and uses fresh water. We have ice cream on the equator. It has required a fan replacement once ( PC type, cheap and available), and has Run continuously now for about 4 years. It runs about 30% of the time on the equator, and draws about 5 odd amps at 12v. Our freezer is 290 ltrs, and is always between - 15 and -21 deg C. I was very impressed with these units, so it is now one of the products I sell on my website.

Sent from my Nexus 7 using Cruisers Sailing Forum mobile app

[colemj]

Cooling can be too much, as well as too little. Both keel coolers and air condensers must strike a balance in how/where they are expected to be used. As long as that balance is met, the efficiency of the cooling medium is a moot point. However, keel coolers are fixed in size, while air coolers can be adjusted in the amount of cooling they provide (block part of condenser, add extra fan, bring cooler air in, etc).

I think Frigoboat recommends adding air cooling when the water is above some specific temperature (80F?). Likewise, AB recommends blocking part of the condenser when air temperatures are below a certain temperature.

By a vast amount, 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. After months of evacuating, vacuuming and refilling to no avail, all of them end up buying a new evaporator, installing a dryer/filter on the liquid line and evacuating and refilling the entire system. This seems to solve the problem, which suggests that the keel cooler itself is causing the problem.

Our air-cooled system has spent the past 6yrs in the tropics and runs efficiently. It is in an enclosed space, so we added a second fan on the shroud to push air into it from outside the space.

Mark