Keel Cooled Refrigeration in Freshwater Tanks?

[jwcolby54]

Originally Posted by colemj

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.

Mark

Mark come on, really? There absolutely is a difference in how the cooling is obtained.

Let's just take a ludicrous example to show how ludicrous your statement is.

I hire a thousand catholic school children to blow into tubes, collect the air and funnel that 10 miles through a hose to a refrigeration unit. You take a fan at the refrigeration unit and turn it on. Which is more efficient.

You just gotta get past "this works" and understand I am NOT disputing that it works. My ten thousand school children solution may work but it is decidedly NOT efficient.

So STOP already with "it works just fine, just make it bigger". It DOES work just fine. It simply is less efficient. I don't give a rats patuty how big you make the heat exchanger, you are NOT making it more efficient, you are making it LESS efficient because you have to use a bigger fan, requiring more electricity.

Take the heat exchanger, hang it on the end of your boat and use a blower from a swamp boat to cool it. Then you get to move the boat AND cool the refrigerator. That is more efficient, assuming you need to go somewhere.

Understand what efficiency means. Heat units moved per unit of electricity consumed. THAT IS IT.

Does your honkin fan and huge heat exchanger use less electricity to move the same amount of heat as a water pump moving water through the heat exchanger. Whichever solution uses less electricity is more efficient.

You know the answer, you just don't LIKE the answer. Which is fine, since you get to spec your solution.

And yes I understand the whole thing about matching the heat exchanger with the load. THAT is an entirely separate discussion.

[skipmac]

A few comments.

First, my <50 amphours/day is the worst case scenario, mid summer, inland Florida. Daily highs mid 90s, nighttime lows sometimes didn't reach the seventies. Winter when temps were 70s day, 50-60 night my power use was 20-25 amp hours/day.

Also I have a pretty large 9-10 cu ft box and a BD50 compressor. With a smaller box, a BD35 compressor and a well insulated box I would guess power use could be 30-50% less than I'm getting. That should be within most energy budgets.

Regarding the cabin temp increase from the air cooled system, I'm not sure I was clear in what I was trying to illustrate with my example. I understand the apples/oranges issue. My point, if the temp only increased a few degrees in a small, enclosed and covered space then I would extrapolate from this that the temps in a much larger, ventilated space would not increase a noticeable amount. Maybe not even a measurable amount.

Even a 30' boat the main cabin is going to be at least 5-6 times larger than my bilge area. So if the temp increased 5 degrees in a 60 cu ft area with no ventilation then the temp would certainly increase less than 1 degree in a 600 cu ft area even without considering ventilation.

This by the way, is not opinion but based on actual, real world tests and measurements on a real boat with a standard, off the shelf, marine refrigeration system.

Originally Posted by jwcolby54

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'

[colemj]

Originally Posted by jwcolby54

Does your honkin fan and huge heat exchanger use less electricity to move the same amount of heat as a water pump moving water through the heat exchanger. Whichever solution uses less electricity is more efficient.

You know the answer, you just don't LIKE the answer. Which is fine, since you get to spec your solution.

And yes I understand the whole thing about matching the heat exchanger with the load. THAT is an entirely separate discussion.

I'm beginning to think you have never actually seen an air-cooled Danfoss compresser/condenser. Those huge coil condensers you speak of are ~4" square and that honking fan is a 120mm computer case fan consuming 0.10A of electricity.

I promise you that the most efficient water pump you can find to circulate coolant consumes more than 10X the electricity.

Again, you are confusing efficiency by not recognizing that absolute efficiency doesn't matter in this application - the refrigerant only needs to be cooled to a specific temperature during a specific time. As long as this occurs, making it colder faster doesn't do any good. In fact, it can do harm and be less efficient.

If that temperature is met by a single pass through an air-cooled condenser, or a single pass through a water-cooled one, then there is no difference in how the cooling of the refrigerant is obtained.

Mark

[crazyoldboatguy]

I as the one who resurrected this thread with the admittedly outlandish suggestion to place the keel cooler in a fuel tank, rather than the fresh water storage tank. My reason for thinking that was because of the assertions by many that this could pollute the water in the tank from either a leak in the cooling circuit or from heating up the water to a point where algae, etc could proliferate.

Little did I know.

But, my specific issue remains. I plan on having 2 separate cooling units - 2 freezers, each cooled by a separate compressor. I will have ideal R30 insulation for both units. The volume is still to be decided - currently looking at somewhere near 5 cubic feet for each box. Both can be used as refrigerators if/when necessary. I will be using these units in an equatorial/tropical location but may well end up back in the Great Lakes - a temperate climate.

I tend to try to cover all bases, not always the best way to do things. I may end up on the hard while still needing refrigeration. Air cooled would handle that - so could a keel cooler in a fresh water storage tank. I can size the compressor for the load, per the specs provided by a manufacturer/seller. However, I need to get as much information as I can to see if it is practical and efficient. Please note - I own a 47' ketch rigged monohull. Solar panels are going to be a challenge. Not keen on wind power - high cost for the good ones and I just wonder when I will see the proper conditions to make it worthwhile. I am working on a towed/prop shaft generator as well.

But the key here is the size of the compression unit. I will likely go with an evaporator plate as I will be relying on solar/batteries, etc and not a generator or engine powered compressor. The batteries will be high up in a deep bilge - generating heat in a place I could use as a cooler air supply for a ducted system to cool off the condenser coils. I know using a cooling system that requires a pump or a fan impacts the need for electricity to power both - hence the focus on the keel cooler. I will have multiple fresh water storage tanks so could place each cooler in a separate tank.

I have attempted to contact Mr Kollmann thru his website to gain access to his blog for info but have not received a response. I bought the book and it is helpful but I can't ask a book questions and hope to receive an answer.

It is clear that the refrigeration discussion is as lively as the anchor discussion or monohull vs multihull issue is.

[colemj]

Another issue with putting a cooler in a diesel tank is that the engine(s) return hot diesel to the tank when running, so you have them also working against you in the heat load.

Mark

[crazyoldboatguy]

Originally Posted by colemj

Another issue with putting a cooler in a diesel tank is that the engine(s) return hot diesel to the tank when running, so you have them also working against you in the heat load.

Mark

Why didn't I think about that?

Ok, so my idea sucks. Kinda knew that from the start but all the responses clarify.

Keel cooler in a fresh water storage tank looks better all the time. For my application, anyway.

[donradcliffe]

The subject has been beaten to death in the usual CF fashion, but let me add my own 4 cents as a nuclear plant designer/heat transfer specialist:

1. The heat produced by the BD systems is about 300 BTU/hr, which as sailor chick says will heat 300 pounds of water one degree F per hour. Compare that with solar insolation in the tropics which will hit each square meter of your boat with about 1000 BTU/hr, and you will see why you should spend your time painting your hull and decks white and not worrying about the fridge exhaust.

2. The PO had installed a air-cooled system under one of the bunks, which used the system fan to draw up cooler air from the bilge and an exhaust grill to the main cabin. It worked with only one problem for 13 years in the tropics, and used about 50 amp-hrs/day to cool a double box with production insulation. The problem--the admiral blocked the air flow with some books.

3. I have no doubt that a fresh water tank system will work also, but my research showed that the liquid pump consumed more energy that the fan, and the pumps were less reliable than the fans.

4. There was a Practical Sailor experimental study which showed that air-cooled systems were more efficient than sea-water cooled systems until the air temperature exceeded 104 deg F, again due the pumping energy consumed. Of course, the sea water systems are much more failure-prone, and do not work in boatyards.

[Terra Nova]

Keel cooler in the sea, like Frigoboat does, is even better. And there is no water pump to power.

[crazyoldboatguy]

Originally Posted by Terra Nova

Keel cooler in the sea, like Frigoboat does, is even better. And there is no water pump to power.

Until you are on the hard in some boatyard having a refit.

I like the keel cooler in the fresh water storage tank. No pump or fan to power.

[a64pilot]

Originally Posted by Terra Nova

Keel cooler in the sea, like Frigoboat does, is even better. And there is no water pump to power.

I have heard quite a few problems here on this site with the keel coolers suffering from electrolysis and failures, some I'm sure from people that don't understand they need to be in the water to work etc., but I've heard of very few issues here about air cooled ones.
There may not be any more problems with the water cooled units, but there seems to be. Need a service professional with a lot of experience to chime in. I keep waiting for Richard to weigh in, but I think I know what he will say, I believe he has said it before.


Sent from my iPad using Cruisers Sailing Forum

[jcapo]

Originally Posted by crazyoldboatguy

Until you are on the hard in some boatyard having a refit.

I like the keel cooler in the fresh water storage tank. No pump or fan to power.

Until the water tank is empty.

[crazyoldboatguy]

Originally Posted by jcapo

Until the water tank is empty.

If my water tank is empty, I have more problems than with my fridge unit. Besides, if my water maker packs it in, I can simply fill my empty fresh water tanks with salt water, temporarily. Not only that, I have heard some folks mention they use the externally mounted fridge keel cooler system even while on the hard. Not as efficient but it still works. Why not use that in an empty fresh water tank?

[SV THIRD DAY]

Originally Posted by crazyoldboatguy

Until you are on the hard in some boatyard having a refit.

So true...
We are on week 5 on the hard with another 3ish to go and without a Cold Beer reward I would have throw in the towel about 6 days ago!

[skipmac]

Originally Posted by donradcliffe

The subject has been beaten to death in the usual CF fashion, but let me add my own 4 cents as a nuclear plant designer/heat transfer specialist:

1. The heat produced by the BD systems is about 300 BTU/hr, which as sailor chick says will heat 300 pounds of water one degree F per hour. Compare that with solar insolation in the tropics which will hit each square meter of your boat with about 1000 BTU/hr, and you will see why you should spend your time painting your hull and decks white and not worrying about the fridge exhaust.

2. The PO had installed a air-cooled system under one of the bunks, which used the system fan to draw up cooler air from the bilge and an exhaust grill to the main cabin. It worked with only one problem for 13 years in the tropics, and used about 50 amp-hrs/day to cool a double box with production insulation. The problem--the admiral blocked the air flow with some books.

3. I have no doubt that a fresh water tank system will work also, but my research showed that the liquid pump consumed more energy that the fan, and the pumps were less reliable than the fans.

4. There was a Practical Sailor experimental study which showed that air-cooled systems were more efficient than sea-water cooled systems until the air temperature exceeded 104 deg F, again due the pumping energy consumed. Of course, the sea water systems are much more failure-prone, and do not work in boatyards.

[crazyoldboatguy]

[QUOTE=donradcliffe;1907238]The subject has been beaten to death in the usual CF fashion, but let me add my own 4 cents as a nuclear plant designer/heat transfer specialist:


3. I have no doubt that a fresh water tank system will work also, but my research showed that the liquid pump consumed more energy that the fan, and the pumps were less reliable than the fans.



Re #3. Yes, the power consumed by a liquid pump would be more than that of a fan. The keel cooler uses no pumps whatsoever. The coolant is moved to the keel cooler and, after it is cooled, returns to the compressor. No pump is involved. The pump type cooler runs water (from whatever source you choose, seawater or from a fresh water storage tank) to the condenser where it circulates around the coolant tubes, taking off the heat, which is returned to the source water. Via a PUMP. The keel cooler does not use a pump to accomplish this.

Could amount to some power savings, no?