Seawater cooled refrigeration - which system is best

affinite

affinite

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I have a top loading coolbox on Canopus.
As we are based in Greece the existing 20 year old air cooled compressor has to work very hard in the summer and Im thinking of retiring it in favour of a seawater cooled unit.

My objectives are
1) Reduce/Remove constant fan noise
2) Reduce power consumption
3) Improve fridge efficiency

I know that this project should start with improving insulation and I will do that but there is only so much you can do to a built-in coolbox without extensive carpentry work.

I want to stick with 12v electric rather than mechanical belt driven compressor and Id rather not spend the earth, but Id like to know which the panel consider to be the best seawater cooling method

a) Keel cooler
b) Heat exchanger thing attached to galley waste thru hull fitting

Thx
 
Have 10 years experience of keel cooler for top loading fridge, its brilliant and generally operate the thermostat at its half setting which takes the temperature down to 0c. It will freeze liquid stored close to the cooling plate at half setting and certainly freeze liquid at above half setting still performing as new after 10 years.
I have no experience of the through hull galley waste fitting cooler, but thankfully was talked out of it when considering which cooler system 10 years ago. The keel plate is easily cleaned, my worry about the galley drain cooler was getting inside the housing to clean it properly.
 
affinite said:
I have a top loading coolbox on Canopus.
As we are based in Greece the existing 20 year old air cooled compressor has to work very hard in the summer and Im thinking of retiring it in favour of a seawater cooled unit.

My objectives are
1) Reduce/Remove constant fan noise
2) Reduce power consumption
3) Improve fridge efficiency

I know that this project should start with improving insulation and I will do that but there is only so much you can do to a built-in coolbox without extensive carpentry work.

I want to stick with 12v electric rather than mechanical belt driven compressor and Id rather not spend the earth, but Id like to know which the panel consider to be the best seawater cooling method

a) Keel cooler
b) Heat exchanger thing attached to galley waste thru hull fitting

Thx
Click to expand...

Have a chat with these people - www.penguinfrigo.co.uk
 
I have b). It works, but I can't compare it with a) because I've no experience of a).

This year I changed the anode on the sink waste for the first time in four years. It was about half wasted.

Apropos cleaning, the inside of the waste outlet where there's a heat exchanger coil has remained clean. Maybe being flushed with freshwater from the galley sink discourages growth?

All this, Solent waters, nowhere warmer.
 
Twister_Ken said:
I have b). It works, but I can't compare it with a) because I've no experience of a).

This year I changed the anode on the sink waste for the first time in four years. It was about half wasted.

Apropos cleaning, the inside of the waste outlet where there's a heat exchanger coil has remained clean. Maybe being flushed with freshwater from the galley sink discourages growth?

All this, Solent waters, nowhere warmer.
Click to expand...

I'm using the same system with comparable results in comparable environment. In the fridge we have one of those big blocks acting as a accumulator instead of a classic evaporator. This works very nicely unless you pack the frigde too full. Then the reduced airflow and the position of the thermostat leads to a overload on the compressor. This then switches off and needs to be reset. So we now take care of sufficient space in the box and all is well. Compared to the boat before that used a normal air-cooled condenser, the performance is much better, but I have no benchmarks.
 
Ours uses a standard Waeco fridge but with the Danfoss unis changed for one with a water cooled condenser. Seawater is pumped through using a Par Max 1 pump. Superbly simple and reliable, averages about 1 amp/hour throughout the summer in Greece.
 
vyv_cox said:
Ours uses a standard Waeco fridge but with the Danfoss unis changed for one with a water cooled condenser. Seawater is pumped through using a Par Max 1 pump. Superbly simple and reliable, averages about 1 amp/hour throughout the summer in Greece.
Click to expand...

Gosh, that's a meaty pump.
 
Just fitted an Isotherm unit, the one with the keel cooler sharing the sink waste. Not back in the water yet but here on the hard it was 27 degs ambient today, when we switched it on it cooled the fridge box (100lts) to 5degs C within two hours. We had ice cubes after three hours. That is on a fairly high setting (4) because we are not in the water but will obviously improve once we are back in tomorrow. It is virtually silent, very pleased so far.
 
pvb said:
Gosh, that's a meaty pump.
Click to expand...

It is but it runs slow. It has the standard voltage dropper from isotherm so it runs at half speed and current draw. It works out very economical and if the condenser leaks it's easy to fix as it is not buried in the hull under water. That's why I recommended we built that one for my dad (Vyv)
 
My Isotherm galley drain cooled unit continues work fine after 15 years - 9 of which serious cruising. Quiet and efficient. In my other, Caribbean based, boat there is an air cooled version. Also quiet and efficient - running 10 minutes an hour. This one has slightly better insulation. Insulation as ever is the critical factor
 
owen-cox said:
It is but it runs slow. It has the standard voltage dropper from isotherm so it runs at half speed and current draw. It works out very economical and if the condenser leaks it's easy to fix as it is not buried in the hull under water. That's why I recommended we built that one for my dad (Vyv)
Click to expand...

I have a good old fashioned difference of opinion... because:-

1. I believe it is always going to be more expensive (in energy) to pump sea water than to pass the refrigerant through a keel cooler.
2. I believe the likelihood of leaks from a non moving part like a phosphor-bronze keel cooler is much lower than a leak or failure of a moving item like a pump.

As our cruising all takes place in hot places, I have bought the Penguin Frigo keel cooled system, ripped out the existing fridge and rebuilt a new one insulating it with a minimum of 200mm closed foam insulation where possible and where not possible, because of space constraints, the equivalent insulation by the highly efficient but thinner Aerogel insulation.

Its too early to publish results as the work is only now nearing completion but I am hoping for a vastly reduced duty cycle despite incorporating a freezer in our design!
 
owen-cox said:
It is but it runs slow. It has the standard voltage dropper from isotherm so it runs at half speed and current draw. It works out very economical and if the condenser leaks it's easy to fix as it is not buried in the hull under water. That's why I recommended we built that one for my dad (Vyv)
Click to expand...

Owen - Why dont you pop over to see your Dad in Leros - say 1st week September
Oh and while your there could you just pop across the harbour where we will be moored and ..........
;)
 
pvb said:
Gosh, that's a meaty pump.
Click to expand...

??? It's tiny, the smallest one they make, only one valve chamber compared with three or four on the bigger domestic pumps. When Owen built the system we had a secondhand bigger pump with three chambers. Thinking we would save some power we changed to the small pump, but as they are only pumping to an open ended system they both use 0.5 amp when the fridge is running. The fridge uses between 3 and 4 when it is running, about a third of the time.
 
silver-fox said:
I have a good old fashioned difference of opinion... because:-

1. I believe it is always going to be more expensive (in energy) to pump sea water than to pass the refrigerant through a keel cooler.
2. I believe the likelihood of leaks from a non moving part like a phosphor-bronze keel cooler is much lower than a leak or failure of a moving item like a pump.

As our cruising all takes place in hot places, I have bought the Penguin Frigo keel cooled system, ripped out the existing fridge and rebuilt a new one insulating it with a minimum of 200mm closed foam insulation where possible and where not possible, because of space constraints, the equivalent insulation by the highly efficient but thinner Aerogel insulation.

Its too early to publish results as the work is only now nearing completion but I am hoping for a vastly reduced duty cycle despite incorporating a freezer in our design!
Click to expand...

I find it difficult to believe that the heat exchanger that forms a skin fitting for the galley sink can be as efficient as a pumped system but I accept that they work Ok. However, at the time that Owen designed mine there were several issues with galvanic corrosion of that heat exchanger, causing loss of the refrigerant and needing a haul out to repair. I understand that these problems have been rectified by close attention to materials and an anode is now fitted, but I still like the accessibility of my little pump.
 
It's a Danfoss BD35F with a water cooled condenser. I suggest you PM Owen to find the type number as there are many options. This replaced the original air cooled one on top of the Waeco fridge. Owen modified the switching a bit so the pump turns on when the fridge cuts in. Otherwise it has a Jabsco PAR MAX 1 pump running at 6 volts with a strainer immediately upstream.
 
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