On Board Refrigeration

It seems that would be more efficient than just dumping hot air into the cabin (or more typically, behind the cabinets).

More efficient in this case does not mean lower run time , it just keeps perhaps unwanted heat out of the locker where the compressor package is.

Refrigerant needs to be cooled only so much after being pumped into a liquid , air or water does it.

Downside to water cooled is the time spend on the hard ,in a boat yard, sans refrigeration.

FF

Since I posted this blog entry I've added a remote bulb line thermostat and done some experimenting.
One More Time Around: Recreational Refrigeration
With the addition of the line thermostat I can make this little chest freezer a refrigerator, freezer or anything inbetween by simply setting a new temp on the add on thermostat.

I put a 5 gallon jug of water in the freezer and froze it into a solid brick. The brick will keep my beer cold for a week without turning on the power. This will allow me to eliminate buying ice for a cooler on shorter outings.

For longer times away from the dock, I'll determine how much generator runtime is necessary to 'recharge' the chest and what temp setting will be best - we regularly run the generator for a/c, coffee, microwave etc. Then I'll see if it's feasible to use the inverter to maintain the chest temp and use it's 130amp charger to bring back the inverter bank when i run the generator.

So many toys to experiment with...

I originally had decided on either a water cooled or a keel cooled freezer due to the apparent better efficiency, but this thread made me re-investigate my decision.
The result was a U-turn...

I will now go with a simple air cooled Nova Kool LT201F1, which has twin evaporator plates. It also has a 12' line between the evaporator and the compressor so it is possible to place the compressor in a convenient location away from cabins, bunk or heat sources.

The reason for the U-turn are the many references to leaks or other problems with the water cooled systems.

The brick will keep my beer cold for a week without turning on the power.

That must be an amazing box insulation..

At Adler Barbour the answer to electric (sail boat) refrigeration was a simple test.

Get a big hunk of ice , stick it in the box , and after a day or two , pull the ice and use a good scale and weigh it.

Plop it back in and wait 24 or 48 hours and then weigh it.

Loosing 2-3 lbs per day , electric will work, 5 lbs was the cut off to either re insulate the box , or go for a system with more holding capacity.

A battery can only hold so much energy (of reasonable size) so a eutetic (cold plate) system would be an easier choice to live with.

I chose 6 inches of freon blown urathine in sheets.Far better than pour in place.

With a 4000BTU plate ,28deg and 5500 Btu 0deg cold plate we get 4 days of service.

Our cruising rule is move at least every 3 days , with 2 hours of engine time for a complete cool down.

Biggest problem is the 28deg plate while cooling lowers the box temp enough to freeze vegetables. .An Igloo takes care of the delicate stuff.

In the Bahamas my bride joined in the middle of a bitch session where folks with stock production boat crap ice boxes and a couple of tiny batts were complaining about A-B refrigeration..

When she joined in and described how she had to pull the frozen milk out when lighting the Primus stove for AM coffee, she didn't get much sympathy!

~~~That must be an amazing box insulation~~~

The freezer is a top opening chest, so that helps.
Empty, the freezer will get to -40*. With the water in it for the brick it doesn't get quite that cold.



So now I've got it hooked up to a car battery via my Freedom 30 with the line thermostat, temp sensors in 3 places and a resettsble run timer.





I had the Freedom 30 already so I've got under $200 in this project so far. What does one of those cold plate jobbies run?

Eutetic solutions can be made at home using 50% salt and 50% water takes a while to freeze.

I haul a milk jug full to the boat in a cooler and just pop it into the fridge when I get aboard.
Chill's things off real quick. The fridge doesn't have to work so hard on the initial.

Eutetic solution. The stuff is great. Talk about a heat sink.
SD

Ahah, another variable to add to the experiment. I had tunnel vision because the basic plan was to use gallon jugs with tap water and drink it as it melted. With a permanent brick, I'm not limited to potable water.

The initial challenge is, How cold can I make the ice, or brine to start, without freezing my beer if the brew is added to the freezer/refrigerator after the power is off?

My wife has MS. She has a 'Cool Vest' that has rechargable packets that freeze at 40°. They are inserted in the vest to keep her cool on hot days when we're outside. They'll 'freeze' in about 20 minutes in a cooler. I've often wondered what else is 'out there' with similar properties for different temperatures that might be of recreational use.

We don't use the vest anymore because of the air conditioner and generator on the boat. And I put a window unit in the van rear window with a Honda 2000i on the back bumper so we can overnight even in the heat at Walmarts and rest areas while on the road.


I get more use out of it that she does...
One More Time Around: Family Road Trip to Ohio & Illinois from SC

Eutetic solutions can be made at home using 50% salt and 50% water takes a while to freeze.

Actually one can pick the temp the solution melts at , which is what keeps the boc at a stable temp.
The more salt the lower the temp, BUT the less capacity as salt takes up room too.

What makes a cold plate operate is the change of state , from a solid to a liquid.

Simply going to -100F below adds little time to the boxes holding time , its all in the melting.

The bad news is more eutetic capacity takes more more space out of the box .

Drinking the eutetic fluid , a gal of water is one cure , but Ice holds a box above 32F , fine for non frozen fresh food only.

FF

Big Thanks FF. You've given me a great head start.

A key point not noted above is that Danfoss "12v" compressors, while very good and efficient, are highly sensitive to voltage drop. One advantage of the 110(240)v/12v dual power systems is if the vessel has an inverter, the fridge will be running on the 110v circuit....and the internal conversion to "12v" actually puts out more like 13.2v and so the fridge operates well. But if the 110v side of the 110/12 auto-switch fails (which they commonly do) OR if the fridge is 12v only, then the fridge is highly dependent on the quality of the 12v supply. Running the 12v fridge power to the fridge via a circuit breaker on the main breaker panel often ends up with long cable runs and voltage drops. The fridge will run but it won't get as cold as it should and cycle times will be longer and amp consumption higher. Best practice is to run a dedicated cable from the House battery (or nearby bus) directly to the fridge (with an in-line fuse) to avoid volt drop

with the long refridgerent*runs from the compressor to the eutectic plates, all runing through the engine room, must be very inefficient.

NOT at all, the refrigerant is delivered as a liquid to the TX valve on the eutetic plate.

The theoretical loss of pumping a liquid thru 25 ft of copper tubing vs 5 ft is too small to contemplate.

FF

Aquabelle said:

A key point not noted above is that Danfoss "12v" compressors, while very good and efficient, are highly sensitive to voltage drop. One advantage of the 110(240)v/12v dual power systems is if the vessel has an inverter, the fridge will be running on the 110v circuit....and the internal conversion to "12v" actually puts out more like 13.2v and so the fridge operates well. But if the 110v side of the 110/12 auto-switch fails (which they commonly do) OR if the fridge is 12v only, then the fridge is highly dependent on the quality of the 12v supply. Running the 12v fridge power to the fridge via a circuit breaker on the main breaker panel often ends up with long cable runs and voltage drops. The fridge will run but it won't get as cold as it should and cycle times will be longer and amp consumption higher. Best practice is to run a dedicated cable from the House battery (or nearby bus) directly to the fridge (with an in-line fuse) to avoid volt drop

Click to expand...

I'm not convinced that that would be the "best practice". For starters, you certainly want (need) a convinient disconnect method. While removing the in-line fuse would disconnect the refrigerator, it would not be convenient in many cases.

I think the best practice is to check the voltage when the refrigerator is running and if there's an excessive voltage drop, find out why and correct the problem.

I would think (and hope) that the manufacturer of the refrigerator would take into account the possible voltage drop in the wiring when designing and manufacturing the refrigerator.

Fair point on the need for a switch if the fridge isn't being maintained 24/7...but no issue installing this on a direct-connect feed, in a convenient place. At least two major fridge manufacturers, Vitrifrigo & Isotherm, DO recommend direct-connection and make the point about sensitivity to voltage drop. But I also agree the voltage should be checked while fridge is operating and obviously, if it is remaining above 12v then no problem. Many people will, however be surprised to find just what voltage drop they do have if they have long cable runs to circuit breaker board and then aft (typically) to a fridge. Even small drops make a big difference to "12" volt compressor efficiency: the fridge will still work (which is why many folks don't pick up they have a problem of this origin) but the fridge cycles longer and doesn't get as cold as it should.