Keel Cooled Refrigeration in Freshwater Tanks?

[SV THIRD DAY]

And so the water cooling myth continues, as if you would use the same surface area size condensing unit in an air vs water medium....hello Mcfly. I guess people don't understand that there is a thing called designing the condensing unit of sufficient size to handle the heat dissipation in an ambient temp target. Well at least it works efficiently on the air cooled moble food service units we sell to the US Military rated for a 135-deg ambient temperature and on literally thousands of Cruising boats around the world...who knew this engineering thingymajig.

[Pelagic]

I don't see it as an either/or decision Rich.

If the same air cooled designed evaporator for heat dissipation offered the added option of fresh water cooling so as to help reduce interior ambient air temp in the galley.... That is a real consideration.

[jwcolby54]

Originally Posted by SV THIRD DAY

And so the water cooling myth continues, as if you would use the same surface area size condensing unit in an air vs water medium....hello Mcfly. I guess people don't understand that there is a thing called designing the condensing unit of sufficient size to handle the heat dissipation in an ambient temp target. Well at least it works efficiently on the air cooled moble food service units we sell to the US Military rated for a 135-deg ambient temperature and on literally thousands of Cruising boats around the world...who knew this engineering thingymajig.

LOL. You confuse efficiency with possibility. I can cool into 1000 degrees if necessary, with water or air. That has absolutely NOTHING to do with EFFICIENCY.

Efficiency is calories moved per watt of electricity used. Efficiency is not measured in thousands of units sold. Hello McFly!

It absolutely is POSSIBLE to do it. So what?

Water cooling is NOT a myth. It is the ONLY thing used in a data center. Why do you think that is? Because they must remove so much heat that the cost to do it with air would be enormous. They COULD do it, but they don't.

No MYTH at all.

And the fact that there are thousands of boats using air cooled refri is absolutely irrelevant. There are also about a million Texans that think that their guns make them safer. Hello mcfly your own damned self.

You obviously sell air cooled and so you have a hand in the game. I don't sell either, I don't own either, but I know the simple fact is that water pumps heat better than air. You say so when you discuss having to make a bigger heat exchanger. Hello McFly!

[Terra Nova]

Originally Posted by jwcolby54

...The lower the delta, the higher the efficiency...

You were doing well until this.

The greater the delta T, the higher the efficiency.

and this:

Originally Posted by jwcolby54

...There are also about a million Texans that think that their guns make them safer...

[exkma367]

I hope this doesn't cause anybodys head to explode, but I had a BD35 compressor laying around that ran but did not build pressure. I gave it a labotomy, cutting the top off with a grinder. I found the tube from the compressor to the liquid line had failed. I brazed the line, cleaned it up and brazed the top back on. I used the evaporator and condenser from an old dorm refrigerator. The evap went into the old icebox. I bent the condensor into a U shape and mounted it in a box behind and above the icebox. I put holes in each side of the box and wired a 12 volt computer fan to provide air flow through the box when the compressor came on. I splurged on on Johnson Controls thermostat. I charged her up and ran it for two years. It was still running when I sold the boat.

Back when I did domestic refrigeration, I replaced a couple hundred refrigerator evaporators and cap tubes that became fouled by a flaw from the factory after running for a year. I think it was a reaction between the winding insulation, oil and refrigerant. Stuff happens.

If the refer added any extra heat to the cabin, we never noticed. To busy having fun cruising..

PS: The lid for the fridge is behind the sink.

[skipmac]

Originally Posted by Pelagic

I don't see it as an either/or decision Rich.

If the same air cooled designed evaporator for heat dissipation offered the added option of fresh water cooling so as to help reduce interior ambient air temp in the galley.... That is a real consideration.

I have seen this point mentioned a few times so conducted an experiment to see how much warmer it would actually get from an air cooled compressor.

I have a Frigoboat system with am air cooled BD50 compressor in a box total 9-10 cu ft which includes about 1.5 cut ft freezer section.

My compressor is under the floors in a high section of the bilge. Very odd shaped so hard to calculate the exact size of the space but something like 60-80 cu ft. Certainly way, way smaller than even the smallest main cabin in a boat. Further, I had the cabin sole covered with a heavy carpet while I was working in that part of the boat so covered most of the holes where the hot air would normally rise out and also added some additional insulation so the heat was pretty well contained in the compressor area. Again, out of the water so not much heat dissipating through the hull to the outside.

During the first 24 hours cool down when the compressor was running at a higher duty cycle I measured just 2-3F higher temp under the floor compared to the air in the main cabin. This was during the heat of the day. Earlier in the day when outside air temps were 75-80 the difference was over 10F but that of course was due to holding the warm air enclosed in the compressor space. After three days the difference was 3-4F at midday.

I could detect no difference in temps in the main cabin over the compressor vs the aft cabin behind the cockpit or the forepeak. If I had removed the carpet and allowed all the heat into the main cabin which is at least 10-15 times the volume of the under floor area AND well ventilated I don't think the heat would have been detectable.

I completely agree that the heat has to go somewhere. It doesn't magically disappear into the ether from the compressor cooling system but in my simple testing in a real world situation it didn't add enough heat the cabin to notice.

In Florida last August daily highs running 90-95F (32-35C) after initial cool down I was using under 50 amp hours per day. This is out of the water so no cooling of the interior from water around the hull. This degree of efficiency in 90F+ temps to me is quite good enough that I see no reason to add the extra cost and complexity of a water cooled system. It might make sense if the ambient temps were much higher but I think even areas further south if you're in the water will not get warmer than this.

[a64pilot]

Reference the automotive thing, all automotive applications are in reality air cooled, from Bulldozers, Locomotives to small cars, water is used as a transfer medium as it's much easier to both control temps with a thermostat than it is with airflow, and of course per volume water has a much greater ability to absorb heat so the engine itself can be smaller.
But aircooled motors work just fine and even in very high heat, ever seen a Deutz Diesel? Ever flown in a recip airplane?

Reference the heat pumps, I researched the most efficient systems available when I rebuilt my house, I ended up with three systems as that was most efficient with my usage. I have two wells on my property so a ground source heat pump would have been very easy to do without having to install a loop. Year round average temp here in South GA is 68F, so ground water is at 68F. Seemed a ground source would be a slam dunk as 68 degree water has plenty of heat for winter heating as well as summer cooling. I wanted a ground source unit, But guess what, the numbers don't support what would seem to be the most efficient, what in my case was most efficient is dual compressors in each unit, when the thermostat set point is more than 2 degrees off the actual temp, the small compressor kicks off and the big one kicks in, but the small one running pretty much continuously is more efficient than a larger one cycling on and off, cooling medium of the condenser had little if any effect. But what cinched the deal for me is the reliability of the air cooled over the ground source, ground source has a reputation of being troublesome. In 13 years only maintenance issue I've had with any of them is occasionally ants will get into the compressor relays
I'm no Engineer, but suspect 1 lb of air will absorb a very similar heat load that 1 lb of water will, just a incredible volume difference of course.

Now I'm sure there is a temp point that water cooling will be more efficient than air will be, assuming of course that the air is much hotter than the water, but what has that got to do with cruising? I won't cruise anywhere the air temp ever gets above the 90's, and honestly will probably be in search of cooler weather then, I'll never cruise with air temp regularly in the 100's, does anyone?
Right now, where I keep my boat, the water temp is 90f, it will get in the low 90's air temp wise during the day, and in the low 80's or high 70's at night, so do I want to cool my condenser with 80 degree air or 90 degree water?

But here truthfully is the rub so to speak, air cooled is all one little unit, take it out of the box it came in, connect DC power to it and your done, no external water pumps to mount, no hoses and clamps, no holes in the boat, and in my case it's in the lazarette, so the little noise from the fan, is inaudible. It works just as well as a water cooled unit, but is much more simple.

I think it's simply a design perspective, if your condenser is appropriately sized, it doesn't matter the medium used to cool it, but if it's not appropriately sized, it's not going to work well, regardless of the medium used to cool it.

[a64pilot]

Assume your compressor system pulls 4 amps at 13 V, that about 52 watts, so if it's 100% efficient in converting power to heat, then it's supplying 52 watts of heat, if it runs continuously and never stops.
1 Person apparently radiates 100W of heat on average, so your air cooled system is pumping the amount of heat into your cabin that 1/2 a person does, if it runs and never shuts off.
How much heat per hour do humans dissipate?

[jwcolby54]

Originally Posted by skipmac

I have seen this point mentioned a few times so conducted an experiment to see how much warmer it would actually get from an air cooled compressor.

My compressor is under the floors in a high section of the bilge.

I am going to point out:

1) Because you dumped the heat under the floor boards, the results would not be the same as dumping the air into the cabin. At least in my boat,that area is open into the engine compartment, so on my boat you would effectively be raising the temperature of the engine compartment, not the cabin. Don't get me wrong, that is a GOOD solution, but you are comparing apples to something else here.

2) The heat load may be dumped into different cabin sizes. My 33' boat has a very different cabin size than your 40' boat or someone else's 50' boat. The amount that the heat level rises is determined by a bunch of things including ventilation but it absolutely is also determined by the cabin volume of air.

3) The COST OF ELECTRICITY is what often matters (and does to me). You seem to think that 50 AH / day is remarkably low, yet for me that is my entire available energy budget for my single battery, drawn down to the 50% level on a daily basis.

I am going to suggest that the whole "save the OP from himself" thing is common on CF, and I am going to suggest that it is pursued to the bitter end, presenting the same opinions and arguments over and over, in the very same thread. In the end I need to HELP people trying to accomplish an objective, perhaps very very different from mine. It is perfectly fine to present alternatives. ONCE. However if the objective is to do any given thing, I eventually need to help them achieve that objective, not hound them into stopping asking for help in achieving their objective.

Take my own case. One of my biggest objectives is to minimize my electricity use. I have a much smaller boat and I cannot just throw diesel at electricity generation. I only have so much space for batteries. I only have so much space for solar. So I am going to perform an engineering evaluation of every single place I can save electricity.

Making my refrigeration more EFFICIENT (NOT measured in thousands of units sold!!!) is one of the major places to look. I either get that 50 amp hours a day down or I don't get refrigeration. I want refrigeration!

So if you wanted to help me, you would NOT simply rant on about how many units were sold to the US military and how many yachts have any given solution. I simply do NOT CARE about those two metrics. What I care about is calories (or BTUs) / watt. If an air heat exchange is the optimum solution for the calories / watt equation, then that wins and I go with that. Otherwise I keep looking.

And if it were my thread, and calories / watt was my objective, and I kept getting hounded (for example) by posts about the number of units sold to the military, then I would tend to go somewhere else looking for assistance, because those kinds of post are not helping me.

Just sayin'

[a64pilot]

From a pure efficiency perspective, you want to size your compressor so it's on an almost 100% duty cycle, or at least limit as much as possible the number of time it cycles per day.
Nothing I believe in a pure efficiency perspective will trump insulation, and of course not sharing a bulkhead with your engine compartment helps too.
So the most efficient would I believe a Vacuum paneled box, top opening with very good door seals and be kept full and never opened. Of course you have to open the thing, but keep that to as little as you can.
A way to get the thermal flywheel and reduce compressor cycling is a cold plate.

In my opinion, and I'm no Engineer nor a Physicist, just a dumb Arse mechanic, but type of cooling medium for the compressor isn't nearly as important as keeping the box as small as possible and as highly insulated as possible I wouldn't think.

[a64pilot]

I'd be willing to bet that from a financial perspective that the best / cheapest solution is another solar panel or two and another battery or two and a small 120V fridge, because going to a "marine" unit and building in a super insulated box will be extremely time consuming and awfully expensive as in thousands of $$$, and to be blunt, may not work all that much better than a small inexpensive fridge and beefing up your electric system would.

[colemj]

Originally Posted by jwcolby54

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.

I don't think you understood what I said. There is a temperature range that the refrigerant must be in for the compressor to function properly and efficiently. As long as that temperature can be met, there is no difference in how the cooling of the refrigerant is obtained.

Dipping the condenser in liquid nitrogen will not cool the fridge down any faster, and will actually be detrimental to its performance. If you don't believe me, then just consider the operating instructions and advise from manufacturers and professionals that in winter climates, one should decrease the airflow over the condenser coils to prevent over-cooling the refrigerant.

So now we are down to your implied argument of an insufficiently-designed small air cooled condenser against a properly sized water cooled one. What can I say to that? I could counter with an example of a properly-sized air cooled condenser against a too small water cooled one…

But the real fact is the brain-trusts designing all of these types of systems have already figured this out. Our air-cooled system is properly designed and installed to work in the temperature ranges in which we operate. I can promise you that adding a water-cooler to it will not cool our box any faster.

So I stand by my statement: "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"."

If you want to argue that the refrigerant reaches its liquid temperature milliseconds, or even seconds, earlier in a water cooled system over an air cooled one, then I guess you have a point.

Mark

[colemj]

The biggest bang on efficiency is insulation of the box. That is 90% of the equation. The other 10% is installation. If you had a perfectly insulated box, then you could get by with the worse installed and inefficient installation.

A properly-sized and installed air-cooled condenser will not be less efficient than a similar water-cooled condenser.

Where water-cooling helps in efficiency is when one cannot properly size or properly install an air-cooled unit. This is a valid point - where the point of "which is more efficient" is not valid.

It may be on a small boat, one has no choice but to mount a compressor unit in a small, hot, enclosed space with limited air exchange. In this case, it makes no sense to put the condenser in there with it - and water-cooling is a better option.

Mark

[jwcolby54]

Originally Posted by a64pilot

I'd be willing to bet that from a financial perspective that the best / cheapest solution is another solar panel or two and another battery or two and a small 120V fridge

I hear you, and you are correct. However what would be the best solution would be a small nuclear power plant.

My point is that those kinds of statements ignore a lot of things. The bigger the boat, the easier it is to "throw in a couple of more solar panels and batteries". I can completely cover the surface of my boat with solar and if the panels have even a small section shaded, then that entire panel goes down. So I spend bucks on 10 new panels and 4 of them actually work at any given time. There is a reason that solar panels tend to be on the back rail, and yep, panel shading (or lack thereof) is the reason.

Again, what is required is an analysis of a given case. What works (or even what is POSSIBLE) for you may be vastly different from my case.

[a64pilot]

Originally Posted by jwcolby54

Again, what is required is an analysis of a given case. What works (or even what is POSSIBLE) for you may be vastly different from my case.

Got it, maybe talk with Sailor Chic, I think she is is in a similar boat size wise, she is an Engineer where I'm not and she is frugal, or maybe better way to look at that is she has gone the efficiency as far as money is concerned, which is I think important.
It's one thing to get into esoteric discussions as to what's possible technology wise, but most of us live in a world where money spent is relevant too. Most of us can't spend ten times as much for say a 10% increase in efficiency, we have to determine "best bang for the buck" or at least I do.

I think that was your point about the nuke plant?