For the adventurous folks , this was lifted from another board,
Free deck fridge that requires no electricity
All sailors should be aware that you can make a free off grid fridge that works well with no electricity. I'm sure anyone could make this for free if they desired.
The science behind these fridges has been cooling food and drinks for over 3000 years, and they are ideal for sailors because the wind, water, and sand required to operate it are easily at hand.
All you need is a couple of plastic bags, some sand, and some water.
It is called a "Zeer Pot Fridge", and I've linked several Youtube videos describing them below. You could build one in 10 minutes and cool your food by 40° (rough) without electrical power.
Typically it is built using pots instead of bags, but I wanted to emphasize the simplicity. I could make one with a few empty boxes and some sand.
If you want a secondary fridge on deck for your beer then a Zeer Pot maybe your answer. They would work great in wind on deck, but not so much in a cabin or galley.
Yet the cost is free for the electricity, and is free to build depending on what you want.. This is assuming you scrounged the necessary bags or boxes, but I'd advise a small investment.
There is probably a hundred Youtube videos on how to construct a Zeer Pot, but this is how Ice was kept frozen back in ancient Rome/Egypt/Mesopotamia. (kinda).
PLEASE SHARE THIS INFO SO OTHERS DO NOT NEED TO FUSS WITH ICEBOXES AS MUCH.
Okay... This is in Boat Design Section. This is because a) I see no refrigerator/galley section to the forum & b) an enterprising designer could build one or more into their ship once they understand the simple mechanics.
They normally require wind for evaporation, and water must be added from time to time. Oddly enough a lot of sailors have an unlimited supply of wind, water, and sand.
This is how the ancient Romans/Egyptians would refrigerate on their ships. It is simply a forgotten technology that keeps getting reinvented (long story).
I will link to a video on youtube, but find your own.. there are many.
This pot seems to use dirt instead of sand... Anything similar would work. Charcoal, sponge, etc. A person could put a few tiny flowers in the dirt section possibly. I wonder if that would aid evaporation? I mean the plant would suck away some of the water.
It works the same way your body cools itself. These clay pots are porous so help the liquids evaporate.
Even rich sailors might wish for a secondary deck fridge. Not exactly an Isotherm or your preference, but it's perfect for sailors and can cost less than a dollar if you want to be frugal.
NOTE: Fresh water evaporates quicker than salt water and is more effective, but ocean water would work in a pinch, but your beer would be a tad warmer. ALSO.. A round zeer pot fridge will cause the wind to circulate around the fridge easier, and this would also aid in the evaporation process that is required.
There are misconceptions about Zeer Fridges so make sure you understand the mechanics fully before building one. i.e. They won't work in your kitchen because they need wind/sun for evaporation. Some have also tried using other liquids such as alcohol which does evaporate quicker, but is more costly and loses some heat transfer values. Water is best. Porous containers (especially outer) is also advantageous. Bags would work in a pinch, but not advised for best results.
Clay pots are porous and allow evaporation. You may notice that the "Sudan Video" (first link) had the fridge suspended in the air. This allows water to evaporate through the bottom of these pots also. The interior pot is also clay and allows water to evaporate from the exposed fridge interior. If you could keep the interior walls clear a tad it would also aid them, but not necessary.
I've heard of people using screening to hold the outer sand. That certainly would be more porous and keep things cooler, but I've not tried that one yet.
This evaporation process is just a simplified process of what occurs in your fridge at home. Evaporated water takes a lot of heat with it.
If you are moved by this information.. please spread the word...
p.s. unrefrigerated eggs last up to 4 times as long if you coat them lightly with vaseline. An old time sailing trick. Eggs have pores that let in air and water. This is why Hard Boiled eggs weigh more.
Save some bilge-sucking scallywag from scurvy.