Refrigeration - Evaporator vs. Holding Plate

[RobMinton]

So I'm looking for the most efficient icebox conversion kit for the most reasonable cost. We'll be leaving after storm season this year for the Caribbean, Panama, and beyond so our primary cruising areas will be tropical/very warm. I've just started this bit of research and open to suggestions on the direction I should take our refrigeration, of which we don't require very much. But our existing icebox is about 9 CuFt. We don't require freezer space but evaporators do allow just enough space to freeze some cubes or whatever. We're a lower energy demand boat and hoping to keep it that way. I think a water cooled system is the way to go in the tropics. The cost of the evaporator systems vs. holding plate systems is very attractive. Can anyone lend advice or input on this? Thanks in advance!

[sailorboy1]

water cooled isn't any more efficient, it matter little in the topics if you are using 85 degree water or 85-95 degree air and once the water heat exchanger gets fouled it is all over

far as not needing a freezer, my freezer is at least as important as my frig, the freezer can store 4 weeks plus of meat and the frig just a couple

[a64pilot]

Stay away from water cooling and avoid a lot of maintenance and headaches.

[Typhoon]

It's a myth . If the system designed right . Water cooling is not needed, even in the hottest climates .

A bin evaporator would be your best solution . Keeps the box at fridge temperatures and you can make a few cubes at the same time , no extra energy lost . We build those .



Regards John

[Richard Kollmann]

Rob, a nine cu ft icebox conversion to a refrigerator in the tropics is pushing the envelope of your board DC electrical power grid. Worst case daily power consumption could reach 5000 BTU. After working with boat box refrigeration conversions for twenty five years I would recommend alternative energy from wind generator and Solar panel electrical. Thirty to fifty percent of refrigerator energy consumed in tropical climates is demand for cold liquids and maybe ice. In most cases available excess electrical energy is far more important than adding insulation.

[a64pilot]

I have 14 cu. ft. And it stays usually mid to low teens in the freezer and just above freezing in the fridge, so 33 or so.

However he said he doesn't want a freezer section, while I think that is a mistake, but it ought to significantly reduce energy consumption?

[RobMinton]

This is all really great input. I do like the idea of going with air cooled over water cooled for the simple fact of not having to install an additional thru-hull. But can you guys speak to the specific systems you're using?
We have 430ah of battery capacity and 280w of PV charging with another 140w panel on the way. I've got the amps to supply a decent refrigeration system (and possibly a small freezer section) but don't want to spend 2K if I can avoid it.
Our current 9 CuFt icebox is bigger than our demand for refrigerated space. So I could kill 2 birds/one stone by adding additional insulation to the icebox thereby increasing efficiency and reducing volume, which would call for a less robust system (less cost) with less energy demand.
Thoughts?

[john61ct]

I would not reduce the volume, if you need to add insulation do that from the outside.

Make a vented divider, the side with the evaporator functions as a freezer, "overflow" through the vent hole cools the fridge side.

Make the latter the size you need, fill up the freezer side with capped/glued 2" PVC "polar tubes" cut to fit, 85% full of seawater. Obviously make some freshwater ice if you enjoy that too, larger 2" blocks, also drinking water bottles 85% full.

Besides insulation, the key to efficiency is opening that box as infrequently as possible.

Keep a separate cooler for drinks, ice and current food supplies, maybe a couple days' worth. Ideally a well-insulated Yeti, Pelican etc.

Pack it so the frozen tubes sit **over** the contents, you can open that box all day long, keep the main fridge closed, except to replenish supplies every 2-3 days, swapping out the polar tubes.

[RobMinton]

This system makes a lot of sense. I'm interested to know if others have a variation and/or a refrigeration system spec to make this work for a 9 CuFt icebox in the tropics. Thanks for the input.

[Uncle Bob]

Rob, I installed an evaporator system, air cooled BD 50 comp, and if I was doing it again I would go for a holding plate. The evaporator ices up and fridge requires regular defrosting, moreso in the tropics so I am told.
Just my 2 cents worth. Cheers

[a64pilot]

Cold plate ice up too.
His problem I believe may be staying less than 2K.
I'd be looking for a dorm fridge or perhaps a Engle or other brand cooler.

[CLady]

I installed an Adler Barber evap unit, snugly lined the refrig unit inside surfaces with 1" closed cell insulation, and made the lid pretty air right to reduce increasing humid air flow that iced up in evap unit. In Hawaii there was minimal frosting up on evap unit. Plenty of ice cubes, frozen fish filets and 2 or less cyclone per hour of compressor.

[sailcrazy]

FWIW, we've spent our whole sailing "career" in the tropics, starting in the Philippines, to Singapore and Thailand, to the Medd, and now in the Caribbean. We use a holding plate system, one box for a freezer, one box for a refer, and a seperate, air cooled cool-box for drinks and backup for either the freezer or the refer. Our holding plates ice up, but require defrosting only about once each 3-4 months. And even though the cool box is not set to freezing temps, its evaporator ices up and requires defrosting about once each month or 2....but we're into it alot more than either of the other 2 boxes. Our holding plate system is water cooled, and the coolbox is air cooled.....they both work good and have for more than 15 years. Build and install what you're comfortable with, and what you want to work on to repair. For my money, I'd go with a water cooled system and holding plates.

[Rorzech]

A few points to keep in mind. The amount of frost build-up on the evaporator plates of any kind is determined by the relative humidity. The number of times you open the door. The quality of the door seal and any other air leaks in the box itself.
It takes energy to take humidity and convert it into frost. Also keep in mind when adding insulation, that the all so important vapour barrier is always on the warm side. For a cooler that means the outside.
Water vapour is a gas, and all gasses in the atmosphere have a pressure independent of each other, which means even though the air pressure inside and outside the cooler are the same , the vapour pressure isn't . Since the water vapour inside the cooler is turned to frost (a solid) the water vapour outside the cooler thinks there is a vacuum in side the cooler and its trying all it can to get inside the cooler through every pin hole available. So when you open the door to a nicely sealed cooler you have instantly equalized the vapour pressure so it doesn't really matter too much how long the door is opened for just the number of times it is opened. Kind of like , when you open the door ,it adds another layer of frost on the evaporator just like a tree adding another growth ring.Personally with the high efficiency compressors they have now, I prefer to run a 120 V fridge off an inverter. Have a static air cooled condenser out side the the hull/cabin and 6" solid closed cell foam for insulation.You can make a nice drying rack out of stainless 3/8" tubing as your condenser in a power vented closet.The more wet clothes and towels you hang on it the more efficient it gets. Evaporation is "cooling" Done right ,it will just sip electricity. If you have a good freezer then you'll have an endless supply of ice for your coolers. Having and endless supply of sunshine and fresh water is the next goal .Cheers

[Rorzech]

For your cool box. You should change thermostat to a "constant cut-in " thermostat. You can set it to the temperature that you desire and it will always cut in just above freezing temp giving time for the heat from your food to defrost it on every cycle.It turns it into "Auto Defrost" The thermostat capillary tube would be attached to your cold plate evaporator to sense the temperature. Simplest thermostat is the VT-9 it's universal designed to fit anything.