Re: Fridge/freezer cooling

Danny and Yvonne SIMMS

Hi Bill et al. Your post forestalled me. A win win using the copper coil idea. Since the SM water tank is in the keel it will achieve sea temp which would put it in the same efficiency as external keel tubing
 However I have operated Ocean Pearl for months at a time in tropical areas. My two fridges and one freezer are all air cooled and work well. If I wanted an improvement I would focus on insulation.
Kind Regards
SM 299
Ocean Pearl 

On 27/04/2022 03:01 Bill Kinney <cruisingconsulting@...> wrote:

I have never been a big fan of pumped cooling water for refrigerators.  The increased efficiency of cooling comes at a high cost of complexity and maintenance. But it is what you have to work with...

Switching to tank water is one of those situations where the benefits of the change are all up front, and the downsides are all potential and of unknown probability. Some more serious than others. The relative risk/benefit also changes based on how and where you use your boat.

The benefits of doing this are all listed in posts above, and are definitely nice to have.

The downsides:  

If you have a leak in your refrigerator cooling lines you have the potential to empty your entire tank of fresh water, and have no way of knowing it is happening. To be fair, this is about as likely as a salt water leak in the cooling circuit, which is arguably a more serious case, especially if you are not on the boat when it happens.

It is REMOTELY possible to have your refrigerant leak into your fresh water supply.  This is the reason (I believe) that the manufacturers of the cooling units recommend against doing this. I do not think refrigerant gas itself is so much an issue, but there is lubricating oil along with it that you would definitely NOT want to have in your drinking water. This is one of those unlikely, but serious, failure modes that are easy to dismiss, until they happen.

Having two pumps tee'd into one draw tube from the fresh water tank increases the opportunity for air leaks that can make priming difficult or impossible for both of them.  I would add a dedicated draw line for the cooling circuit, and add a return line that eliminated splashing into the tank.  The constant sound of that would drive me nuts!

This is a case where there is not a perfect answer. Neither arrangement is ideal.  The tank water case is certainly the better choice, right up until something goes very wrong and suddenly it is not.

There are alternatives, but they quickly get to be complex, and add their own difficulties and require a fair bit of engineering. With some cooling systems, it is possible to retrofit an air-cooled condenser.  This is arguably less efficient in very hot weather, but the difference in the real world is vanishingly small compared to an Amel's overall electric budget.

A not simple solution, but one that (I believe) would work, is to install a coil of copper tubing in the water tank and circulate a solution of non-toxic antifreeze through that.  It gives an extra barrier between contamination from the refrigerant, minimizes corrosion, and is easily maintained.  The most difficult part of the installation would be securing the copper coil in the tank.  This is probably what I would do if it was my boat. I think this has all the benefits of using tank water directly. Other than the design and install effort, I can't think of a downside to this, but I'm sure there are some...

It might be better to just add the plumbing parts to make it easy to flush the salt water cooling circuit with Barnacle Buster, or other product, to clean out the circuit on a regular basis.

I don't have a recommendation for you, just my thoughts for your decision.

Bill Kinney
SM160, Harmonie
Palmas del Mar, Puerto Rico

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