Fresh water tank for fridge cooling - advice please

jeremyshaw

jeremyshaw

Well-Known Member
Joined
18 Apr 2005
Messages
885
Location
UK
Visit site
It seems to be increasingly common (in the Caribbean at least) to use a boat's fresh water tank to circulate the cooling water from a refrigerator system.

In hot climates the water temperature is about the same, and it saves a through-hull. It also saves cleaning and changing the filters, which just don't seem to last more than a few months.

So, my question, for those more savvy in these things than me, is whether I can relatively easily adapt my system.

Option A, the obvious way, is to put new feed and return connectors into the tank. But that is not easy to do.

Option B, the easy way, is to tap into the feed between the tank and the fresh water pump, and to put a couple of tees in there. But that won't work because it won't be circulating enough water, just what is in the hose loop.

Option C would be to take the feed off before the fresh water pump and tap the return into the tank filler. That way I still don't have to attack the tank itself but I can recirculate the whole tank worth of water. BUT when both pumps are running they will be 'competing' for the same supply from the same hose.

So my questions are:

A. Is this likely to be a problem, especially if the pumps have different flow rates. Or will it probably be OK given that the tank is about 2 foot above where the pumps would be, so there is a bit of head pressure.

B. Got a better idea?

Thanks
 
I don't like it.But I am intrigued..
It does seem a bit like putting a domestic fridge into a closed(warm,unvented) cupboard under the stairs.Once the few litres of water in the boats tank start to warm up-or are used up then what happens to the fridge pumps ability to remove heat..to where now?
Many parts of the world are cooler than the Caribbean seas.You would be denying yourself the benefits of that.
Would it be better to source high quality sea filters at a more reasonable cost possibly?
 
One concern would be the growth of bacteria, such as Legionella, in the cold water storage tank.

I know that the tank possibly goes above 20°C anyway but it is something to consider.
 
I've been doing a bit of research at the boat show for new units for my boat. I was told on several stands that the latest units are so effective that water cooling is no longer required, even in warmer climates. Much simpler!
 
Why would you want to drink warm water?!!! We keep water in the 'fridge to keep it cool in the Med/Caribbean. Seems a bit like seeking perpetual motion!!
 
This has been discussed ad nauseam on cruiser-forums. I still cant understand why you would want a system that requires water to be pumped to cool the refridgerant - it is a real waste of power. If you have to use this sytem then there are benefits in that you are in effect using a fresh water heat exchanger, but AFAIK noone has explored the impact of the additional heat into the fresh water tank, or what happens when you run short of water, let alone the health implications of running your drinking water through a non-health approved system.

IMHO the best sytem is the proper Keel Cooler system, where the refrigerant is pumped through a heat sink on the bottom of the boat, by the fridge compressor. Much more efficient even than an air cooled or pumped water cooled system.
 
When I first saw this thread I didn't reply because I thought I must have been missing something!

Surely, no matter how warm the Caribean water is this arrangement will inevitably end up with the water tank being warmer than the sea. It does seem self defeating.

Water cooling can be sorted out without needing an additional through-hull fitting.
 
Well, my query does seem to have provoked some debate . Sadly no answer to my actual question yet, but thanks for all the comments.

To clarify things, the system I am talking about is a holding plate system for a freezer, so it does need water cooling. I've put a new type evaporator in for the fridge which is air cooled which is great - the fridge is side opening so the original holding plae system wasn't really suitable. But dont have the amps to change the freezer over to a DC evaporator, nor want to chuck out a system that works perfectly well apart from this irritation.

I do have a genset, so I can crank up the plate twice a day, and I do have a 300 Litre stainless steel water tank. So that makes quite a big heat sink with good transmission of heat from the stored water. And I can easily vent the compartment where the tank is to help get out any excess heat.

Finally I have a big watermaker (a ludicrous 50 gallons an hour) so we never have problems with the tank getting low.

A particular problem is a situation like I have just now where I've parked the boat in Venezuela for a few months with my wife on board. We are on shore power so she'll have the freezer on 24/7 and I've found it hard to get her to understand the need to defrost the unit regularly. So the pump will be running a lot. This will clog up the filter faster than usual, as will the cruddy water in the marina.

As to the filters themselves, I'm on my third brand now - Shurflo. They are as good/bad as any, but the replacements are readily available and not too expensive. I'm told that the pump needs a fine mesh filter. I don't think there is a way to improve that aspect, though a keel cooler would undoubtedly be a good solution if I haul.

Bacteria: The water in the tank is always over 20C anyway, so I don't really see that this would create any additional risk. It's already a slightly higher risk than usual since we use mostly RO water, and we monitor it quite carefully - but our large production means we have large consumption (c20 gallons a day), so it turns over pretty quckly.

Regarding temperature, inside air temperature in the Caribbean is a little more than sea temperature, but of course water is a much more effective way to transfer heat. And the local experts tell me that the tank temperature won't be raised by more than 1C. It will have 12 hours to dissipate between charges.

So for these circumstances and for the sake of a few hours work, I think it's worth a try.

But, back to the original question, where is the best place to put the hoses - is my thinking right?
 
I was given to understand that the best refrigeration systems don't use a pump to run water through the heat exhanger, but allow the seawater to flow through either using the water flow past the boat, or convection. I was advised against using a pump, but to use a convection water cooled heat exchanger. (Either using an additional or existing hull skin fitting.) My reading of feedback from the ARC a couple of years ago, was that this was the only system, that was both power efficient and that would give good efficient service.

However at the boat shows last year, each refrigeration stand swore that their system was the only one that would work...
 
Sorry, I realised that. I was agreeing with you, not questioning you. Though it may have looked as if I was querying what you were saying. /forums/images/graemlins/crazy.gif
 
To test the theoretical in actual practise then.....If you were to tee off the tank outlet and return via a tee at the fill-inlet and hook that lot up for a week you could test the system without cutting additional holes in the stainless steel tank.And monitor the 300l tanks temp variations for a week...sounds ok so far to me,given the practical restrictions of harbouring in polluted marina waters.
Myself I always liked the 'no moving parts' concept of dumping excess solar and wind genorator volts straight into a supercooling holding plate at anchor.
By the way I always used to add a teaspoonful of bleach to the tank(100l) at each refill to deter bacterial build up. Let us know how it performs!
 
put a 'T' in the tank outlet before the pump increase the size of the hose between the tank and this 'T' put a NRV in between the 'T' and water pump use the otherside to feed the fridge then from the fridge take the pipe back to the water tank breather or where the water maker feeds the tank but put another NRV between the water maker and the 'T' you will use for this!!
you may need a filter somewhere in the return line to the tank!!
 
Jeremy,

I can't add to the previous postings which seem to answer your question.

However, I am intrigued with this as I don't understand why you would want to use the water tank for cooling rather than the sea.

Other than an arguable benefit of using freshwater it sounds like an inefficient method of cooling.

Am I missing something?
 
i still dont understand why we need to use water cooling, i worked in saudi arabia, angola, egypt and algeria, none of them the coolest places in the world and yet we never used water cooling for the condensers on any thing!!
saudi 130 deg in the shade at 1.00 pm angola 90 to 100 deg and humidity to die for, ok people say the rooms were air conditioned but even air conditioning was a room temp of 27 degrees C!! and the air conditioning condensers were in ambient temp. how hot is the inside of the boat !!! what is wrong with air cooling as long as plenty of air flow available.
stu
 
I've always understood that the advantage of water cooling was that it was a good way of removing the heat from the boat. If you use air cooling then, usually, the heat is simply being put into the cabin which isn't desirable, particularly in a hot climate.

Apart from that, sea temperature will usually be lower than air temperature and water is also a good conductoer of heat which will improve efficiency.

I don't know about air con, but assume that the condensers would usually be outside the cabin which would be different.
 
the point is that the condensers were in a high ambient temp and the systems worked satisfactorily, the point of the post is about efficiency not cabin temperatures.
stu
 
Tisme - I don't "want" to do it, it's been suggested to me by guys that seem to know that it is equally efficient.

As to 'arguable' benefit I think the benefit is real. Everyone I know who has seawater filters in the Caribbean finds them a a real hassle.

Back to the efficiency issue, I guess the real issue is the temperature of the return water. If it's 40C then it probably doesn't make much difference whether you are exchanging it with seawater at 25C or tankwater at 27C. If the difference is more marginal then there would certainly be an efficiency issue.

I guess only a trial will tell...
 
You must log in or register to reply here.

Share this page

Top