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Old 16-10-2014, 18:07   #61
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Re: What's the best modern freezer unit?

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Originally Posted by crazyoldboatguy View Post
I have read so many posts on the subject and have slowly come around to the air cooled concept. Kollman and others have provided ample evidence from small to mammoth installations that air cooled is as efficient, easier to install and - most importantly - less stuff to break. The extra heat pushed into the cabin is minimal altho you must make sure there is adequate space around the compressor unit.

If you are seeking to make the current box a "freezer" the recommended insulation is 6". If your unit is the original built in unit, it is quite likely the 3" insulation you believe is there......isn't. You may have to remove the entire unit and re-insulate. While your power supply may be sufficient to handle the load with the insufficient insulation, condensation will form as a consequence of the insufficient insulation and drip down onto other surfaces of the boat. If any of them are wood - mildew and rot will likely occur. Also, the condensation will likely saturate the existing insulation causing it to be less efficient, leading to cascading problems of more condensation and less efficiency.

I am also learning much about this stuff and watch these streams closely. I have learned a lot and will learn more. Good luck with your refit!
You sum up the situation well.
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Old 16-10-2014, 18:49   #62
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Re: What's the best modern freezer unit?

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Originally Posted by Terra Nova View Post
This is precisely the result you set out to prove--and you proved it! To yourself.
I set out to prove nothing. I set out to, very informally, take a couple of measurements to see if my subjective opinion was right or wrong.
I am an engineer and engineering lives and dies by the numbers; opinions and assumptions are as likely to wrong as right.

Regardless, if it gets too hot I have air conditioning on the boat so it really doesn't matter to me if the fridge makes the cabin hot as the hinges. Get's too hot for whatever reason I turn on the cool.

Now I have said several times this was no formal, scientific test, but even so, I'm pretty sure that if the compressor was putting a serious amount of heat into a small, enclosed, completely unventilated space covered and insulated with a carpet I would have seen a significant temperature increase. 3 days and the temp is still only 2-3 degrees F warmer than the main cabin.

On the other hand, would I be wrong in supposing you have some version of water cooling on your fridge and just might feel the need to justify the extra money you spent?

So if my little test is so wrong then tell me exactly what is wrong with the conditions of my test that would dramatically skew the results and I'll modify the test. Or do your own test and report back what you find.
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Old 16-10-2014, 19:22   #63
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Re: What's the best modern freezer unit?

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Originally Posted by a64pilot View Post
My compressor and condensor are in my lazarette which is about the twice the size of a full size couch, I can tell there is some heating once it has been closed up for days, but it's not much.
Of course there is heat, you can't make cold, all you can do is move heat around, so of course the compressor moves the heat from inside of the box to the outside, it amounts to the amount of heat that you can get from 5 amps or so of DC current times the number of hours the compressor runs in a 24 hour period, the heat amount is roughly equalivent to 5 regular incandescent 12W lights being on inside of the cabin when the compressor is running.


Exactly. The numbers don't lie. The highest consumption I've measured was 66 amp hours over one day. This by the way, was before I finished the lid so the top was closed only with a couple of sheets of 3/4" foam and a piece of plastic so was not at max efficiency.

66 amp hours is an average draw of 2.75 amps. At 12V that's 33 Watts so less heat generated than running a 40 Watt light bulb for 24 hours.

So no experimental variables, no chance of invalid data or the heat from the compressor being absorbed by an alien spaceship. This much power used, period. If I really cared that much I would go dig out my old thermodynamics book and calculate how many calories of heat that would produce and how much that would heat X cubit feet of air, but I won't.
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Old 16-10-2014, 19:28   #64
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Re: What's the best modern freezer unit?

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For those who want to pick the nits let me be clear, this was not in any way a rigorous, exact, scientific test. I had no control for comparison, no previous baseline data, it was a single 48 hour test, I used a test sample of one boat one time so the results will be statistically invalid.

However based on this very casual test AND my subjective impressions from working on the boat with the fridge on and off, I see no significant heating of the cabin from a Danfos BD50m air cooled compressor.

Anyone that wants to do a more exact test to refute my impression feel free. I would be extremely interested in seeing the results and totally open to changing my opinion.

Skipmac, I totally agree with you! We have 2 air cooled Seafrost systems under the galley floor, drawing air from our hallway and notice NO extra heating in the main cabin from the units. We have an 8 cubic ft freezer and 9 cubic ft fridge. Both have been flawless in the tropics for 8 yrs.


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Old 16-10-2014, 19:37   #65
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Re: What's the best modern freezer unit?

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Originally Posted by skipmac View Post
...if it gets too hot I have air conditioning...
On the other hand, would I be wrong in supposing you have some version of water cooling on your fridge and just might feel the need to justify the extra money you spent?...
As long as you don't mind running a generator to run your air conditioning, you're OK. But, as engineers, we must be able to see that the heat you put inside your boat raises your interior temperature. Simple as that.

No, I didn't spend extra for water cooling that I didn't want. The Frigoboat unit is very affordable; comes with keel cooler. And won't heat the inside of my boat.
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Old 16-10-2014, 19:52   #66
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Re: What's the best modern freezer unit?

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Originally Posted by Terra Nova View Post
As long as you don't mind running a generator to run your air conditioning, you're OK. But, as engineers, we must be able to see that the heat you put inside your boat raises your interior temperature. Simple as that.



No, I didn't spend extra for water cooling that I didn't want. The Frigoboat unit is very affordable; comes with keel cooler. And won't heat the inside of my boat.

We have NO a/c and notice NO heat from the fridge and freezer compressors in the tropics! Keep it simple!


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Old 16-10-2014, 20:06   #67
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Re: What's the best modern freezer unit?

Quote:
Originally Posted by Terra Nova View Post
As long as you don't mind running a generator to run your air conditioning, you're OK. But, as engineers, we must be able to see that the heat you put inside your boat raises your interior temperature. Simple as that.

No, I didn't spend extra for water cooling that I didn't want. The Frigoboat unit is very affordable; comes with keel cooler. And won't heat the inside of my boat.
OK, how many times do I have to say it. Yes, yes, yes. The heat removed from the refrigerator must go into where the compressor is mounted AND in addition the compressor and motor, due to inefficiencies will generate additional heat that will also go into the cabin That is the law of conservation of energy and for anything else to happen would violate basic laws of physics.

What I am saying is the heat that we all agree is removed from the fridge and goes into the cabin is not significant. Look at my previous post. If a fridge at 12V used 80 amp hours in a day (a very high power draw and not realistic for most boat systems) that would be the equivalent of a single 40 watt light bulb. So are you saying that a single 40 watt light bulb would make your cabin noticeably hotter?

I bought a Frigoboat too and the water cooling cost more than my air cooled system that works great, has very low power draw and doesn't heat my cabin to any noticeable degree.
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Old 17-10-2014, 05:14   #68
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Re: What's the best modern freezer unit?

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Originally Posted by Terra Nova View Post
As long as you don't mind running a generator to run your air conditioning, you're OK. But, as engineers, we must be able to see that the heat you put inside your boat raises your interior temperature. Simple as that.

No, I didn't spend extra for water cooling that I didn't want. The Frigoboat unit is very affordable; comes with keel cooler. And won't heat the inside of my boat.
That's great that you're happy with your system. but Skipmac accomplished exactly the same thing with his air cooling refrig/freezer. He's stated pretty clearly for even a non engineer to understand how much heat is being generated by using the comparison to a small/medium lightbulb left on all day. Yes, of course it generates some heat, but not so you'd really notice much, even in the tropics. Plus, with his compressor generating its heat under his floorboards in a confined space below the waterline, he essentially has the equivalent of a keel cooler too. Most of the surface area that heated air comes in contact with is part of a huge heat sink, his hull. Of course that's immersed in an even larger heat sink, the ocean!

I have a Seafrost system that I like a lot that has selectable air or water cooling for both frig and freezer compressors located under the aft bunk. There are 3" air ducts for both air intake and exhaust. When it's running and I put my hand over the outlet, the air feels barely warm. Of course in the tropics there would be greater losses through the frig and freezer walls so it would run more and I might want to use the water cooled option. But an even better option might be to simply run the exhaust air duct under the floorboards to avoid heating my cabin even a little bit without having to constantly be pumping salt water into and out of the boat.

I suspect the mindset that water cooling was necessary came from the early cold plate units that had large plates and much larger compressors than are now commonly used. I had one of those on my last boat and when that compressor ran, it generated some serious noise and heat. It only needed to be run once a day for about an hour to refreeze those big plates, but during that time period, something more than air cooling was definitely necessary! While my current system generates just as much heat, the heat is generated over a much longer period of time and spread all throughout the day, so is pretty easily dissipated by simple air cooling. If my boat didn't already have the water cooling option installed, I wouldn't bother doing it. Extra complication, extra expense, and another hole in my boat below the waterline...
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Old 17-10-2014, 05:56   #69
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Re: What's the best modern freezer unit?

I still think the missing data point is that as soon as its considered to be even a little bit warm, almost all of us open the hatches, and that 5 amps worth of heat, is gone.
You know pretty much all energy is dissipated as heat, even using your stereo creates heat, it's just so little that its not noticeable is all.
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Old 17-10-2014, 06:33   #70
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Re: What's the best modern freezer unit?

I have a Dometic portable unit that supplements my main fridge/freezer and gives me a good backup. Several of the Dometics have an optional insulated soft case, which has vents in the appropriate places and a zippered flap where the box opens. I have that case, bought for the extra insulation, but it also keeps the box from sliding around and protects it, in general. I am happy with it. It runs on AC or DC. I turn the main fridge (DC only) off when I'm away from the boat, and leave the portable on when at the dock, filled with the beer and cold drinks. My main fridge had a brain board crap out a couple of months ago, and I just used the little one until we could install a new brain.


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Old 17-10-2014, 07:23   #71
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Re: What's the best modern freezer unit?

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I still think the missing data point is that as soon as its considered to be even a little bit warm, almost all of us open the hatches, and that 5 amps worth of heat, is gone.
And since heat rises opening a hatch can be pretty effective.
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Old 17-10-2014, 10:30   #72
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Re: What's the best modern freezer unit?

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Originally Posted by jtsailjt View Post
...Skipmac accomplished exactly the same thing with his air cooling refrig/freezer. He's stated pretty clearly for even a non engineer to understand how much heat is being generated by using the comparison to a small/medium lightbulb left on all day. Yes, of course it generates some heat, but not so you'd really notice much, even in the tropics. Plus, with his compressor generating its heat under his floorboards in a confined space below the waterline, he essentially has the equivalent of a keel cooler too. Most of the surface area that heated air comes in contact with is part of a huge heat sink, his hull. Of course that's immersed in an even larger heat sink, the ocean! ...
There are 3" air ducts for both air intake and exhaust...
But an even better option might be to simply run the exhaust air duct under the floorboards to avoid heating my cabin even a little bit without having to constantly be pumping salt water into and out of the boat...
While my current system generates just as much heat, the heat is generated over a much longer period of time and spread all throughout the day, so is pretty easily dissipated by simple air cooling...
Same as a small light bulb?

Skip's boat is on the hard. So it is an air to air heat exchanger,

And forcing your cooling air through 3" ducts will severely choke the efficiency out of your reefer. No wonder it has to run all day.

Running 3" ducts will severely restrict an air cooled unit's efficiency.

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...as soon as its considered to be even a little bit warm, almost all of us open the hatches, and that 5 amps worth of heat, is gone...
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And since heat rises opening a hatch can be pretty effective.
When you're sitting in the tropics with all your hatches and windows wide open, and you're gasping to catch even a breath of air, what will you do? Open the hatch wider? I know skip will run his a/c.
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Old 17-10-2014, 11:07   #73
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Re: What's the best modern freezer unit?

=== When you're sitting in the tropics with all your hatches and windows wide open, and you're gasping to catch even a breath of air, what will you do? Open the hatch wider? I know skip will run his a/c ===

I have reviewed information from an acknowledged expert in this area - Kollmann Marine. We all know the physics involved. Heat is removed, it has to go somewhere. Frankly, if Kollmann indicates air cooling is sufficient, and provides ample evidence that it works well, is efficient, and the heat produced is not noticed to any great extent, I will accept that.

It is clear you don't. So be it. Nothing else to see here, really.
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Old 17-10-2014, 12:16   #74
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Re: What's the best modern freezer unit?

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Same as a small light bulb?
Max power use I have recorded was an average of 2.75 amps. At 12V 2.75 amps is 33 Watts. A 33 Watt light bulb is small to me.


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Skip's boat is on the hard. So it is an air to air heat exchanger,
Not a whole lot of heat exchanging from my bilge and since the temp differential between my bilge and the main cabin is only a couple of degrees then the heat gain or loss of the interior from outside would be about the same in both areas so would not have a significant impact on the temperature difference between the bilge and cabin.



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When you're sitting in the tropics with all your hatches and windows wide open, and you're gasping to catch even a breath of air, what will you do? Open the hatch wider? I know skip will run his a/c.
But Skip spent several years as a liveaboard in the Caribbean without a/c and only really wanted it a few times and then more because of the mosquitoes and noseeums than the heat.
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Old 17-10-2014, 12:46   #75
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Re: What's the best modern freezer unit?

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Same as a small light bulb?
Do you understand what a watt is? Yes, I would call a 30 or 40 watt lightbulb small.

Skip's boat is on the hard. So it is an air to air heat exchanger,

And forcing your cooling air through 3" ducts will severely choke the efficiency out of your reefer. No wonder it has to run all day. Not if the duct has air being drawn through it by a small fan. The reefer doesn't run all day because of lack of air cooling. It runs just about the same amount as when I have the water cooling selected and in use. It runs more frequently than my old system because the compressor is smaller/quieter and so are the cold plates, so they warm up quicker and must be cooled off more frequently. I thought I had made that clear in my last post but hopefully this will help you understand.

Running 3" ducts will severely restrict an air cooled unit's efficiency. Again, not if a fan is blowing air through that 3" duct.





When you're sitting in the tropics with all your hatches and windows wide open, and you're gasping to catch even a breath of air, what will you do? Open the hatch wider? I know skip will run his a/c. Do you really not understand the amount of BTU's provided by tropical sunshine that your boat is exposed to in a day is larger by a factor of thousands compared to the BTU's provided by that tiny compressor under his floorboards, adjacent to a surface that will always be within a degree or two of the outside ocean temperature, no matter how much he runs his compressor?
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