Water Cooled Refrigeration

[admiralslater]

we are very happy with our frigaboat keel cooler. Quiet ,small and and gets the freezer to 12 degrees f .(an experiment). The idea of a switchable system to allow for on the hard use is an interesting idea

[redsky49]

We have ten years experience with the (self-installed) Frigoboat keel cooler system. Our cruising has taken us along the east coast, from the Chesapeake to Florida and the Bahamas, and during all seasons, so we have have at least a good personal experience with this system.

During this period I have monitored duty cycle (typically 20-40% depending on outdoor and interior temperatures), as well as operating speed, and have recorded typical daily amp consumption from as low 18 AH in cool or cold conditions, up to a maximum of about 40 AH in hot air and water conditions (as in Florida in July).

Repeated door openings, or adding warm items to the fridge, naturally increases the compressor operating times.

By the way, my refrigerator is not particularly well insulated.

I am sure that there are other systems that operate just as well. I went with this type of arrangement to avoid dumping the heat of rejection into the occupied space (something that would be viewed as absurd in residential applications), as well as omitting the fan noise and energy consumption.

I should add that I also utilize a small magnetic-bearing muffin fan (consuming about 1/2 watt) to remove the heat of compression from the locker where the compressor is located. This is a highly recommended fan - 100,000 hour to failure, six year warranty, etc. :
Noctua NF-A8 FLX. Runs very quietly. You can wire this to operate only when the compressor is cycling, but I just let it run whenever the refrigerator is energized. Energy use is so small I am challenged to even measure it.

We do not operate the refrigerator when on the hard, though I am aware of people who have, some using a garden hose to trickle on the keel cooler.

[a64pilot]

I have never seen a residential refrigerator that did not have the condenser mounted on the back of the fridge, therefore of course it dumps the heat into the living space.

Look at it this way, the human body at rest depending on your source radiates between 100 and 120 watts of heat, continuously.
If your fridge draws 5 amps at say 13 volts, then it draws 65 watts, if it runs continuously and never shuts off and loses 100% of its power to heat, then it adds as much heat as 1/2 a person, if it runs less than continuously, then of course less heat is added.
I'd be more concerned with the noise a fan can make, mine is mounted in the lazarette which of course is small in comparison to the salon, when it's closed up for a week, the heat gain is barely noticeable. At first I thought I may have to leave the lazarette open to help the unit cool, but seeing as there is no noticeable heat gain, I don't bother.


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[redsky49]

Originally Posted by a64pilot

I have never seen a residential refrigerator that did not have the condenser mounted on the back of the fridge, therefore of course it dumps the heat into the living space.

Look at it this way, the human body at rest depending on your source radiates between 100 and 120 watts of heat, continuously.
If your fridge draws 5 amps at say 13 volts, then it draws 65 watts, if it runs continuously and never shuts off and loses 100% of its power to heat, then it adds as much heat as 1/2 a person, if it runs less than continuously, then of course less heat is added.
I'd be more concerned with the noise a fan can make, mine is mounted in the lazarette which of course is small in comparison to the salon, when it's closed up for a week, the heat gain is barely noticeable. At first I thought I may have to leave the lazarette open to help the unit cool, but seeing as there is no noticeable heat gain, I don't bother.


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I was waiting for someone to make this exact comparison

In the case of refrigerators, there is no practical alternative until you get into restaurant or other commercial applications.

A resting person (average adult) generates 120-150 btuh of sensible heat (or at least that is how it is calculated here in the US) for the sake of estimating heat gain in a space. The actual amount of heat rejected to the atmosphere with an air-cooled refrigeration system is a bit of a fuzzy calculation. Not all energy consumed results in heat being vented to the boat interior. Your best bet would be if manufacturers provided this information.

My approach is to eliminate or reduce any heat gain to the space. A 60W incandescent bulb for example, will generate about 80-85% of its energy consumption into heat, not light. So I use LEDs, which are up to ten times more efficient - less heat generated.

To your assertion about 65 watts, and all energy being converted into heat - if this did indeed occur (and you haven't exhausted your battery bank with such a system), you would end up with 222 btuh being generated [3.42 btu per watt]. Not a huge figure, but just as in back packers watching the ounces, big things occur when you don't ignore the little things.

I agree, the fan noise may be the biggest concern, as well as ensuring that the exhausted hot air is not redrawn into the unit - well separated intakes and exhausts.

SailorChic make take minor exception to my generalizations, but she and I can argue the finer engineering points off line.

Glad you are happy with your system, A64Pilot. Hope the OP finds what he needs too.

[contrail]

Sea Frost makes an excellent unit, their Bait Freezer, which can also be used for a a freezer or refrigerator. It can be air or water cooled, or both. After a year and a half in the Caribbean, I have yet to install the water pump. Probably do it this year, since I have already installed the thru-hull. I will put a switch on the pump and turn it off in dirty harbor water.

[bytownboy]

My refrigeration uses a BD 50 compressor which is sea water cooled. I have two freshwater tanks with a total of 250 gallons. Is there any reason I cannot plumb into one of the tanks and use the water in it to cool the compressor, eliminating the need to use the two thruhulls.

[cruisersfarm]

Originally Posted by bytownboy

My refrigeration uses a BD 50 compressor which is sea water cooled. I have two freshwater tanks with a total of 250 gallons. Is there any reason I cannot plumb into one of the tanks and use the water in it to cool the compressor, eliminating the need to use the two thruhulls.

One reason...

Check into the toxicity of cupro-nickel heat exchangers. That's what you currently have to deal with salt water.

Either that's fine and you don't have to worry, or you'll need a heat exchanger that's sa
fe for potable water.

[bstreep]

Water is 24 times more efficient than air at the same temperature, for heat transfer. Pretty simple math.


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[rwidman]

Water cooled is going to be more efficient than air cooled. I would hope everybody would understand that.

The question to be answered is; Is it worth the extra expense and complexity? The answer varies depending on the size of the boat and how you use it. The best advice will come from those who have been using it.

[stevec195]

I like our little isotherm. As mentioned earlier it requires no active circulation pump for the condenser coil which is co-located with our galley sink drain. I would say that this would not be the choice for you if operated in the slip all the time, as without an influx of "new water" the efficiency does go down a bit. At anchor or under way-no problem.


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[bytownboy]

This thread has me seriously considering switching my refrigeration to fresh water cooling. I can use my smaller freshwater tank dedicated to this, it is about 90 gallons I think. That will still leave me about 130 gallons of fresh water in the other tank. As we carry bottled water for drinking and rarely are away from the dock for more than 3 weeks I think that will be sufficient.

Using the freshwater tank will mean two less seacocks to open, close and maintain, the elimination of a sea strainer, and the ability to run the refrigeration when away from the boat without worrying about thru hulls failing. I should also expect the pump to last longer as it will only pump fresh water.

Those and probably a few more are the upside, what would be the downside?

Your collective wisdom is always greatly appreciated.

[SV THIRD DAY]

What a lot of people get hung up on is the concept of taking two equally sized condensing units placing one in air and one in cold water....sure the water (depending on the temp of course) will take away more heat. But that isn't how the game works. A properly designed air condensing unit will be larger with more surface area that can just as easily dissipate the heat, even in the tropics.

The units we sell for the US Military for example, are air cooled only and rated to 135-degs F ambient temp. No water cooling...no fuss...no loss of condensing efficiency just good old air at 135-degs F.
It ain't magic folks...it's engineering.

So as with most things in the mechanical world, it's all about engineering. But it's just a myth to make a general statement like water cooled is more efficient than air cooled.

Then with water cooling...lets throw on the maintenance, amp draw if there is a water pump, and then the loss of having the ability to run the unit out of the water.

Lets not even talk about the zincs, electrolosis risk from either a poor installation or equipment malfunction, or your boat neighbor in the slip pumping enough amps into the marina to light up a small community.

We all remember the Frigoboat horror story thread...that risk doesn't exist...gone...nada...with an air cooled unit.
http://www.cruisersforum.com/forums/...ry-117397.html





Below are images of a properly designed air condensing unit and compare that to the dinky little air condensing units on critical charge/orifice systems. Critical charge/orifice systems say in their manuals to add water cooling when the air temp gets above above 90-degs F. They recommend water cooling not because water is better than air...but because of the design limitations of a critical charge/orifice system where they can not install a larger air condensing unit due to the refrigerant balance issues. In condensing units...Size Does Matter.





[[[Disclosure...as the owner of Technautics refrigeration I know a little something about air cooled refrigeration units. Sea water is evil keep it out of your boat.]]]

[a64pilot]

I think several people have plumbed their water cooled systems into their freshwater tanks to prevent the issue with sea water cooling.
At first I was skeptical due to heat gain, but several have done it and measured pretty much zero heat gains, seems the water tanks radiate the heat about as fast as it's added so net gain is close to nothing. I think if your tanks make contact with the hull or are metal tanks, it makes a difference, none that I know of are insulated.


My example of a continuous 5 amp draw, with 100% of it being converted to heat was worst possible case, it's neither of course, but even at worst case, heat gain in your living space is pretty negligible.

[SV THIRD DAY]

Originally Posted by a64pilot

I think several people have plumbed their water cooled systems into their freshwater tanks to prevent the issue with sea water cooling.
At first I was skeptical due to heat gain, but several have done it and measured pretty much zero heat gains, seems the water tanks radiate the heat about as fast as it's added so net gain is close to nothing. I think if your tanks make contact with the hull or are metal tanks, it makes a difference, none that I know of are insulated.


My example of a continuous 5 amp draw, with 100% of it being converted to heat was worst possible case, it's neither of course, but even at worst case, heat gain in your living space is pretty negligible.

It was a pretty common thing I saw while cruising down in Mexico's Sea of Cortez. It solves the evils of sea water problem and if I had a water circulation cooled unit that is what I would do as well. Just be sure to never run that water tank dry or....gulp...you could overheat your unit and break out another Boat Buck.

[a64pilot]

I love to get into conversations with people who think the automobiles they drive are water cooled, cause they aren't