Keel Cooled Refrigeration in Freshwater Tanks?

[SV THIRD DAY]

Originally Posted by 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?

Really....the Diesel tank?

[crazyoldboatguy]

Originally Posted by SV THIRD DAY

Really....the Diesel tank?

Well, now, that's helpful.

[SV THIRD DAY]

I was trying not to say...that is a crazy idea of placing a heat exchanger circulating a pressurised, flamable gas/oil through a diesel fuel tank. But there I said it....

[crazyoldboatguy]

You don't sell a system with a keel cooler, do you?

Coolant is non-reactive. Compressor oil is flammable, yes, but how much is actually in the system? A few ounces, by my understanding. How much volume/pressure is in these small systems? Where is the ignition source?

Why would the keel cooler fail, anyway? There is no corrosive substance, like saltwater, present. I am just brainstorming. Been doing it all my life. Get some of my best ideas that way. Not sure this is one of them.

Would you recommend a keel cooler be placed in a water tank">fresh water tank? Oh, wait, you don't sell a system with a keel cooler.

While I am being snarky, I appreciate you taking the time to respond. But, I think there is a bit of bias involved.

[SV THIRD DAY]

Originally Posted by crazyoldboatguy

You don't sell a system with a keel cooler, do you?

Coolant is non-reactive. Compressor oil is flammable, yes, but how much is actually in the system? A few ounces, by my understanding. How much volume/pressure is in these small systems? Where is the ignition source?

Why would the keel cooler fail, anyway? There is no corrosive substance, like saltwater, present. I am just brainstorming. Been doing it all my life. Get some of my best ideas that way. Not sure this is one of them.

Would you recommend a keel cooler be placed in a fresh water tank? Oh, wait, you don't sell a system with a keel cooler.

While I am being snarky, I appreciate you taking the time to respond. But, I think there is a bit of bias involved.

No bias.. not at all...I would recommend a keel cooler be placed in your fresh water tank rather than in sea water...no problem...have friends with it and it's a good set-up. But that is not what you asked, nor what I was commenting on. Just because I call a keel cooler in a diesel tank crazy doesn't mean I call a keel cooler crazy...apples and oranges.

Now for some technical details to save you from yourself and more importantly from the others that would read that crazy idea and then think that is is some how safe...this is now chat room rumors start.

There is a continual scream of flammable compressor oil/refrigerant mixture that flows through the refrigeration loop. Have you seen the blow torch of refrigerant propelled combustible oil? I have...it ain't pretty...not pretty at all. But I'm a self described cruising Bozo remember, so go ask the makers of a refrigeration Keel Cooler if they would recommend putting it in a diesel fuel tank. Then go ask a marine surveyor if he would endorse that set-up.

Maybe I should have stuck with my original "really question" but you didn't take the hint and I can play in the snark tank...it's happens to be my specialty.

[crazyoldboatguy]

Those same makers of keel coolers decidedly are against placing the unit in a fresh water storage tank. I've read the streams.

Trading snark for snark - won't get us anywhere. I don't need you to save me from myself. I engage in due diligence all the time. Looking for information is what I do.

Peace.

[jwcolby54]

Originally Posted by colemj

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".

Compressor based refrigeration uses a mechanical pump to compress the refrigerant. That compression is what causes the heat. The heat has to be dissipated. So there absolutely is "colder faster", though possibly not "colder".

It is a simple fact that if you take a heat exchanger and blow air over it, the exchange of heat between the heat exchanger coil and the air blown over it is less efficient than pumping water past it. Computers use water cooling all of the time for this exact reason, you can design a tiny little heat exchanger that takes water through the little thing that is an order of magnitude more efficient than a huge block of metal with fins and air blown past.

It is also a fact that there is no free lunch. The heat pushed into the water has to go somewhere or it builds up. In computers the answer is to use an air / metal heat exchanger, which truly simply moves the air exchange part of the cycle to a different location. Of course that works just fine for that purpose since getting the heat out of the computer case is the precise objective.

Or, as in the case of a nuclear power plant, the water is pulled out of a body of water that moves water by, and the hot water goes back into that same body of water down stream.

Those who say the water is not heating up may be finding that the tank shares a wall with the ocean, and thus that wall acts as a heat exchanger, pumping the accumulating heat into the ocean through that shared wall. Or they may be using the water and replacing it somehow, with a water maker etc.

The heat is going somewhere.

[a64pilot]

We have been here before, it's been determined that an average air cooled system dumps an equal amount of heat as one person does, so heat added is the same as if you had a guest.
It IS heat, just maybe not as much as you may have thought.
Water has a very good ability to absorb heat, that is why we use it as coolant in our automobiles, right?
But if you think about it, all that heat the coolant picks up is removed in the radiator with air.

Sized correctly an air cooled unit can be very efficient, think of our heat pumps in our houses, water cooled units were all the rage for awhile, but have gone away. Reason is air cooled can be just as efficient, with fewer service issues.


Sent from my iPad using Cruisers Sailing Forum

[Pelagic]

I think if you study the Ozefridge System
http://www.ozefridge.com.au/
You will note that the Fresh water "additional" heat exchange cooling is an option that you can switch on or off at control panel.
In other words, it is designed as a stand alone Air Cooled system with additional compressor cooling if desired.

Presently installing 2 units in my boat.....will let you know if I am as happy as the other customers who have been using them for years in the tropics

[sailorchic34]

Rich / Third Day raises a fair point. Some of the newer refrigerants are using propane, well fluoropropane (R211 to R290 ish or so) as refrigerant. Really low flash point too. Flame on. Why? Because it's cheapish and zero ozone depleating and not bad from a greenhouse gas standpoint. So a leak in the high pressure side near a flame could get exciting, rather quickly.

Myself from a will it work standpoint, well in a 100 gallon water tank that's half full there is still enough water to reject lots O heat into it. A fuel tank will be low sometimes and that would make Mr. compressor and the frozen foods less then happy. A small AB50 compressor would raise 50 gallons of water about 1 degree per hour. Really about 0.73 ish degree and hour give or take. 1 degree is a good ballpark number. But then once the box is cold, hopefully the compressor only has a 40% duty factor, is it might only be 1/2 degree per hour per 50 gallons.

Of course the tank will radiate heat to cooler outer casing, so in many cases it would work just fine. Until the cooler leaked and fouled the drinking water

Myself, I think a air cooled condenser is perfectly fine for a small AB50 system. It works and is not complicated. Simple is good in engineering.

[Terra Nova]

One of the most troubling side effects of transferring your reefer/freezer's heat into your fuel or water tanks is that, in warm weather, your crew has to suffer from higher ambient temps inside the boat. Whereas, when you exchange the heat into the sea, the heat is completely removed from your boat.

[Pelagic]

Let's take Diesel tanks out of this discussion as it is not practical for a number of reasons.

If you have a steel hull with integral fresh water tank, you know that its temperature is the same as sea water even after motoring for hours with the interior closed up and becoming very hot.

That support the idea that hull radiation is very effective


Pumping and returning FW thru a small heat exchanger via a potable rated plastic hose will have an imperceptible affect on Fresh water temp, if your tank is kept reasonably full.

[jwcolby54]

Originally Posted by a64pilot

We have been here before, it's been determined that an average air cooled system dumps an equal amount of heat as one person does, so heat added is the same as if you had a guest.
It IS heat, just maybe not as much as you may have thought.
Water has a very good ability to absorb heat, that is why we use it as coolant in our automobiles, right?
But if you think about it, all that heat the coolant picks up is removed in the radiator with air.

Sized correctly an air cooled unit can be very efficient, think of our heat pumps in our houses, water cooled units were all the rage for awhile, but have gone away. Reason is air cooled can be just as efficient, with fewer service issues.


Sent from my iPad using Cruisers Sailing Forum

Water cooled units are still all the rage in very hot places, like the southwest. When you are trying to dump heat into 115 degree air it is NOT very efficient. Don't much care how you try to sell it, it isn't very efficient. My sister in Phoenix has a system that dumps the heat into a ground based coolant system. VERY VERY efficient.

Sized correctly an air based system can FUNCTION, which is very different from EFFICIENT. Efficient discusses the delta between two sides and the COSTS to transfer heat. The lower the delta, the higher the efficiency. The higher the thermal mass of the heat sink, the higher the efficiency. With water you can get a very high ability to absorb heat (thermal mass).

According to this:

The Advantages of Liquid Cooling | Data Center Knowledge

Water is 3,400 times more efficient than air in removing heat.

In addition to that built in advantage, the water will tend to be much lower temperature to start with, so the DELTA between the heat source and heat destination is much lower.

If an air based system is so efficient, why is coolant circulated through your engine? The old VW had air cooling, but it was NOT efficient, and they overheated like crazy in Yuma AZ in the summer time. Ask me how I know.

If air cooling is so efficient why does every data center in the world use water based cooling? The answer is simple, it is very reliable, very simple, and very efficient to use a liquid to absorb heat and move it somewhere.

Water simply has an enormous thermal mass and so the cost of the heat transfer is vastly lower.

This in no way discusses ANYTHING other than efficiency. You MAY be right (though I have my doubts) that a fan based system is simpler and more reliable than a water pump.

[jwcolby54]

Originally Posted by sailorchic34

Rich / Third Day raises a fair point. Some of the newer refrigerants are using propane, well fluoropropane (R211 to R290 ish or so) as refrigerant. Really low flash point too. Flame on. Why? Because it's cheapish and zero ozone depleating and not bad from a greenhouse gas standpoint. So a leak in the high pressure side near a flame could get exciting, rather quickly.

Myself from a will it work standpoint, well in a 100 gallon water tank that's half full there is still enough water to reject lots O heat into it. A fuel tank will be low sometimes and that would make Mr. compressor and the frozen foods less then happy. A small AB50 compressor would raise 50 gallons of water about 1 degree per hour. Really about 0.73 ish degree and hour give or take. 1 degree is a good ballpark number. But then once the box is cold, hopefully the compressor only has a 40% duty factor, is it might only be 1/2 degree per hour per 50 gallons.

Of course the tank will radiate heat to cooler outer casing, so in many cases it would work just fine. Until the cooler leaked and fouled the drinking water

Myself, I think a air cooled condenser is perfectly fine for a small AB50 system. It works and is not complicated. Simple is good in engineering.

Done correctly you would never pump the refrigerant through the water tank. You would pump it through a heat exchanger and pump water through the other side of the heat exchanger.

[jwcolby54]

Originally Posted by a64pilot

Water has a very good ability to absorb heat, that is why we use it as coolant in our automobiles, right?
But if you think about it, all that heat the coolant picks up is removed in the radiator with air.

Yes, but the air movement is free (mostly). Just drive the car and air flows past.

But if you have ever lived where it is very hot (the southwest for example) seeing people alongside the road with their hoods up and steam pouring out is not an uncommon sight. You are pumping an enormous amount of heat into the water, and then trying to pump the heat from the water into very hot air.

In a refrigerator you are trying to pump heat from the inside (very low temperature) into potentially very warm air (very high delta).

Have you ever used one of those Peltier plate ice boxes. They very plainly state that there is a heat delta which cannot be overcome, the higher the outside temp, the higher the inside temp.

Delta ALWAYS matters, even in our electric compressor refrigerators. The higher the delta, the higher the heat load that has to be dissipated in the radiator, the longer the compressor and fan have to run, and therefore the higher the electricity requirements for running the fan and compressor.

Water cooling is incontestably more efficient at pumping heat, by a lot. All you can really argue is that the complexity doesn't warrant the efficiency gain. But it absolutely does if you have a limited electricity supply.