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Old 20-11-2005, 14:23   #1
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Keel Coolers

Okay, I have come up with another advantage to having a keel cooler for refrigeration. When your boat is on the hard they still work. We have been in the yard for almost two weeks now, our refrigerator and freezer have been working like champs. The compressor stays on a little longer than if we were in the water. I think this is due to the heat disapation difference between water and air.

A small point, but valuable none the less.

Keith
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Old 21-11-2005, 11:37   #2
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Keith makes a valuable point

Being able to keep the refer up and running when on the hard is very nice. I have an old, relatively small, cold holding plate system. I discovered that I could merely run the water from the compressor into a 6 gal plastic jug stowed below. The heat capacity of 6 gal of water is sufficient to absorb the compressor heat removal from the plate so that the compressor still functions well. The compressor only comes on twice in 24 hours (once the plate is pulled down, of course) and the time that the compressor is off is sufficient for the plastic jug surface area to conduct the heat to the surrounding air and be sufficiently cooled before the next cycle, even in the tropics.
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Old 22-11-2005, 05:40   #3
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I've always been unimpressed with the idea of using raw water to cool a reefer system when fresh water from an onboard tank is available. And relying on fresh water makes use of the reefer possible while on the hard; in fact, we were just doing that in Lisbon last month while in a shipyard.

There are several types of custom built hardware that allow heat transfer using a thru-hull or external hull fitting...but I don't see the logic for incurring that expense when a few feet of vinyl hose and some 'T' fittings can provide infinite fresh water cooling from one of the boat's tanks. And isn't it on this BB somewhere that a contributor pointed out his new 2" ID Frigoboat thru-hull that incorporated cooling passages for his new reefer was not properly grounded and was about to fail due to galvanic corrosion?

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Old 23-11-2005, 04:36   #4
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After enlarging the holding plate on my refrigeration system, we increased the capacity of our existing air-air heat exchanger by adding a raw water cooling loop and running the refrigerant through a separate heat exchanger. A small pump was added with a relay switch that turns it on whenever the compressor runs, but can be switched off if desired. Raw water is drawn by tapping into the existing galley sea water supply... no added through hull needed.

So far so good, but I need to test it for another summer. The pump increases the energy draw, but improves the heat exchange efficiency especially with high ambient air temperatures, so hopefully itís a consumption wash. The larger holding plate does a much better job of chilling.

-Phil
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Old 23-11-2005, 08:38   #5
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It may be because of the differences in language, but IMHO there seems to be a lack of understanding of what a keel cooler is.

There are several technologies for getting rid of the heat from the compresor:

air cooling, where a motor has to spin a fan to blow air athrough the compresor. (not so good when ambient temperature is hot and needs the energy to power the fan)

Sea water cooling, where sea water comes in through a hull fitting and is pumped up to the compressor and used for cooling. (effective, but fouling can shut off the inlet, and extra power needed for pump)

Fresh water cooling, where fresh water goes through a heat exchanger of coils underneath the boat, and is pumped up to cool the compressor. (effective, and avoids the problem of fouled inlets, but does have risk of damage to the heat exchange coils, and the extra drag imposed by them)

Keel Cooler where the liquid used to cool the compressor is circulated through a sintered bronze block attached underneath the boat (similar to the ground used for SSB).


This is the most efficient type as it minimises the power consumption of the system. It is also the least vulnerable of any of the hull penetrating systems. Gets my vote.
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Old 23-11-2005, 09:36   #6
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This is the most efficient type as it minimises the power consumption of the system. It is also the least vulnerable of any of the hull penetrating systems. Gets my vote.
I'll second this. Just received by Figiboat system last week including the keel cooler.
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Old 24-11-2005, 05:59   #7
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"Fresh water cooling, where fresh water goes through a heat exchanger of coils underneath the boat, and is pumped up to cool the compressor."

Just for clarity's sake, let's make it clear to thread readers that there is no direct link between the choice of using fresh water to cool the compressor of a reefer system and a single specific method for how the fresh water is sourced. The latter depends on the design of the reefer system if equipped with water cooling.

'coils underneath the boat' means little to me, but most water cooling coils (thru which freon lines are routed) have in the past been mounted directly onboard the reefer platform. It's a relatively new concept to have the water cooling line run off the platform to a remote site (thru-hull or external cooler) and back. Whether this is 'better' or not is IMO more dependent on the locations of the water sources (fresh and raw) on a given boat and one's subjective preferences. I surely saw no inherent benefits in putting another hole in my boat when instead all I had to do was add a few feet of vinyl tubing and 2 'T's to the plumbing in one of my water tanks.

Jack
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Old 31-12-2005, 09:19   #8
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[i] I surely saw no inherent benefits in putting another hole in my boat when instead all I had to do was add a few feet of vinyl tubing and 2 'T's to the plumbing in one of my water tanks.

Jack [/B]
Hello Jack
Since I'm about to install a new Fridge/Cooling System and this interests me. Doesn't the Drinking Water heat up too much? How big is/are your tank(s)? What kind of pump do you use?

Wolfgang
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Old 31-12-2005, 09:39   #9
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I think Jack has missed out that the keel cooler illustrated in my last post, does not use a pump to circulate the freon, thus uses less electrical power than those water cooled versions that rely on a pump, or air cooled that need a fan. Dont ask me how it works cause I dont know, but suspect that the compressor is pumping the refridgerant round through the cooling cools and also through the keel cooler.
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Old 01-01-2006, 09:54   #10
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Wolfgag:

The short answer to your Q is 'No'. In fact, at one point on a previous boat - I've used this method on several - we got down to 1-2 gals of water in our keel tank yet fridge performance was not effected.

While in Trinidad, an 'engineer' on a Tayana 43 who was dissatisfied with his raw water cooling arrangement (he had two reefer systems) wanted to switch to fresh water but, like you, wondered about the system efficiency once the water volume in a source tank decreased. He sourced a 5 gal bucket of fresh water(which sat in his cockpit in the blistering sun) temporarily to measure the temp increase of the water and the most he could get it up was 5F. After a week's 'experiment', he shifted over to FW tanks sourcing both units.

The reason the water doesn't heat up is the huge heat transfer that occurs as your boat floats in an ambient medium (sea water temp) and all the materials between your fresh water supply and that ocean medium are sucking off the heat that is absorbed. To the extent your water tank(s) contact the hull's surface, this 'heat loss' will be greater; to the extent they are surrounded by air (800X less dense than water) the heat transfer will be slower.

Talbot, I wasn't commenting on the electrical performance of any given system; my points have been that using raw water as a cooling medium can be improved on, and the purchase of special thru-hulls or keel coolers seems an unnecessary expense. Just my opinion, of course.

Jack
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Old 01-01-2006, 18:01   #11
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Hi Jack,

I have to ask a couple of quesitons regarding your setup as well. Through the forum, I met a nice guy named Mark who is selling me a cold plate system.

It's currently cooled via salt water intake with through hull. After reading this thread, I really like the sound of your setup. Much more logical, and I have always hated drilling any new holes in hulls. Call it paranoia.

So given a standard salt water system, could I simply do away with the sea strainer and ciculate fresh water through it? How, exactly did you tee off your fresh water tanks to cycle water through a heat exchanger, and then return that water? Also, is the water taste affected by going through a heat exchanger? Mine's bound to have a lot of junk in it since sea water had previously been flowing through.i Any ideas on how to combat that?

Thanks in advance for any info. I really think this is an intelligent approach to this problem.

PS: My sea water (or soon to be circulating) pump has a throughput of 5 gals/min. Is this on the same order of what you have? I ask since I wanted to find out a little bit about the raising temp of the drinking/fresh water. Also, my tank is 55 gals.
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Old 02-01-2006, 07:01   #12
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My $0.02....

I would not want to drink water that had been directly exposed to a refrigeration heat exchanger. The materials used in those systems are NOT designed for potable water... so do we take a chance on the lead solder, etc used to construct them? Also would not want to taste the refigerant oil in my water should the heat exchanger leak... the higher relative pressure in the system would discharge the refrigerant & oil into the lower pressure coolant loop and your water tank.

So why not build a closed system? With good access to your water tank, take a small transmission cooler with a dense finned area and plumb it to the heat exchanger. This would require adding an inlet/outlet to your water tank, but it's still not another thru-hull.

It's entirely possible that even with an empty water tank the finned unit would provide enough of a temperature drop to support the system. They also make finned tubing sections that could be used in the run from the heat exchanger to the tank to help dissapate the heat.

For that matter - why not simply install one of those keel coolers into the water tank?? Assuming you have access near the bottom of the tank, one hole cut would be all that's needed. Just have to be careful about the materials they are made from - be sure they don't include some type of anti-fouling chemical or other material that would cause a health hazard.

For me a closed system would give me peace of mind. I've seen too much "interesting stuff" in refrigeration condensers to want to drink from them.
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Old 02-01-2006, 07:35   #13
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water temp

2 possible points

1) Using the holding tank to cool the fridge/freezer will increase the temp of the water in the holding tanks which will assist things to grow. Also the heat to be radiated will be on the inside of the boat.


2) Though we have a water maker on board we catch rain water and filter into the tanks. Many times the water is near ice cold and drinking from the tank is very refreshing.

Recommednation would be to enlarge an existing through hull and make a sea chest that many sources can be tapped. This reduces he need for more holes in the boat and still supplying the necessary water for a use and dump system which I beleive in the long hual would be a more efficent way to transfer heat from the system out of the boat.
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Old 02-01-2006, 07:56   #14
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Sean, if you are installing a system previously working with raw water, I'd suggest you do what the T43 owner did down in Trinidad: after install, temporarily run the system for a while from a remote source (5 gal bucket?). You could even add a bit of cleaning solution into the bucket's water initially, then change it out to solely fresh water. Then finish the install.

No, we've never found a problem with the water's taste being effected. Relative to Mark's concerns, we used this method on two different reefer brands and so the cooling (heat transfer) methods were different. In the first, the freon lines ran inside the water cooling lines; in the current one, the Isotherm's pump circulates water around the freon conduit. In both cases, a 'worst case' is that the freon leaks, you notice the box is not performing and, after discovering the problem, you make a note to flush the tank.

Re: the set-up, I just 'T'ed the FW supply line which ran nearest the compressor platform, adding water quality tubing plus an adapter (there was a dimension change) to a Shurflo strainer (a small device that Isotherm provides since they use a Shurflo pump). The strainer incorporates a fine mesh which IMO would be overwhelmed with raw water on occasion but works well with FW. I was cleaning the filter monthly while in London (terribly hard, solids-laden water...and that was after we used an activated carbon filter when filling our tanks) but found it didn't need cleaning once in 3 months once we were in Spain & Portugal. Bottom line: your water source(s) will shape your cleaning regimen. Once the circulated water does its cooling I routed the dischcharge via a similar hose to a 'T' on the vent line to the tank.

Isotherm intentionally throttles down the Shurflo's flow rate, as slower (to a point) is better re: heat transfer. This extends the life of the pump immensely, of course. I don't know what our pump's flowrate is; my guess is 1.5 gals/min. By coincidence the size of both tanks we've drawn on when using this method have been ~50 gals.

One 'operational' note: On the last boat we had only a single keel tank (our bladder tanks were separate and isolated) and so a freon leak into the tank would have left us with an awkward job of using the bladder tank water. IOW this wasn't an ideal arrangement altho' it proved not to be a problem for us in practice. On WHOOSH we have 3 FW tanks and for convenience the cooling water is drawn from the port settee tank. As a result, this is always the last tank we draw down and consequently our exposure to contamination from a leak is usually zero. I would think this approach would be available to most medium & larger boats these days.

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Old 02-01-2006, 08:45   #15
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There seems to be a slight misunderstanding of refrigeration in some of these threads. The cooling on a compressor system is not for the compressor but to cool the gaseous refrigerant after it exits the compressor. The cold returning saturated gas serves any necessary compressor cooling. Simple flow path is 1/ Hot gas exits the compressor 2/ Gas flows through the condensor (what is being called a cooler here) 3/ Condensed gas (liquid) refrigerant is now luke warm 4/ Liquid now passes through expansion valve and releases energy as it expands and vaporises (like turning liquid propane bottle upside down & cracking valve, it comes out a cold vapour) 5/ Vaporised liquid/gas passes through evaporator (the cold part inside the fridge or freezer) and absorbs energy (heat) from product or air in fridge. 6/ Gas returns to compressor.
The condensing part of this operation can be performed by water through a heat exchanger (the heat exchanger is the actual condensor in this system) or air blown across the condensor surface)
To my mind it is a waste of energy to provide a separate pump or fan for condensing when the compressor is already moving the refrigerant and there is a cooling medium available. Good quality, refrigerant compatible pipework in the water tank (or even fuel tank??) seems to me to be the answer to a lot of problems provided the heat build up was OK. Simply have the discharge (hot) pipework from the compressor run through a series of coils before it goes to the expansion valve, remove your existing condensor and sell on eBay for a fortune. Because the system would need to be evacuated, altered and then regassed by a technician this is not something you should try at home kids.
Mark, I accept your concerns about the effects of a leak but this would be mitigated by a professional installation with quality materials.
Any reason why it couldn't run through a fuel tank??
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