Q&A for How to Make a Pot in a Pot Refrigerator

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  • Question
    Do I have to use clay pots or will PVC/metal cylinders work?
    Community Answer
    You cannot use PVC or metal containers because they don't allow evaporation like clay pots do, which is the whole point of the device. Clay pots allow evaporative cooling to take place because they are permeable to air.
  • Question
    Does this pot system use a lid, or just the cloth?
    Community Answer
    It can have an earthenware lid or a wet cloth, but both togther would be better to use.
  • Question
    As an artist, I can throw pots on a wheel; do they have to be that shape, or as long as they fit together and have a lip will it work?
    Community Answer
    Shape of the pots does not matter. But inner pot with small mouth covered with clay lid works tremendously well.
  • Question
    What type of sand should I use to fill in the gap?
    Community Answer
    You should use either fine sand or burlap. Charcoal will work even better than sand.
  • Question
    Does increasing outer temperature decrease the temperature inside the smaller pot?
    Community Answer
    This phenomenon is more related to the air humidity than its temperature. If you warm up the air without increasing humidity, the evaporation on the outer surface will increase and, therefore, the inside temperature will decrease. However, if air humidity is increased as well, it's the other way around.
  • Question
    Does it work in very humid tropical countries?
    Community Answer
    No, it will not work well in areas with lots of humidity because little evaporation takes place in humid environments.
  • Question
    Does it have to be water? Why not some other cold household liquid?
    Community Answer
    Water is the most basic liquid and generally the most abundantly available. Other liquids could also spoil or lead to bacterial growth or other issues after a while.
  • Question
    Can a plastic container be used?
    Community Answer
    No. See PVC answer. Pots have to be porous to allow for evaporative cooling.
  • Question
    If I glaze the pot to make it waterproof, do I glaze the inside or the outside of the pot?
    Community Answer
    Use unglazed pots. The reason this system works is because the pots are NOT waterproof.
  • Question
    Can I use water in the pot? And how warm/cool should the water be?
    Yannick Copin
    Community Answer
    The key point is not really the initial temperature of the water (see the Mpemba effect), but the fact that evaporation will take away a lot of (latent) energy from the system, therefore cooling it. Cooling down water is very expensive in energy (as much so as to warm it up), so the system would probably not be very efficient to cool down plain water within the central pot.
  • Question
    Where can I find clay pots?
    Community Answer
    Garden centers, WalMart, Amazon, Lowe's, Home Depot, etc.
  • Question
    What is the function of wet sand in the pot?
    Community Answer
    Water is the key element; the whole system relies on the chemical properties of water changing from a liquid to a gas. Any medium that increases the evaporation of the water will increase the cooling rate, hence the sand.
  • Question
    What is the purpose of cloth placed over the pot?
    Alexander Dorta
    Community Answer
    It keeps the water that evaporates inside the pot so it lasts longer; otherwise, the evaporated water would get out of the pot and it wouldn't keep it cool.
  • Question
    Does a pot refrigerator work indoors?
    Alexander Dorta
    Community Answer
    The pot does work indoors, but it does not work as effectively, depending on the warmth and humidity in your house.
  • Question
    Can I make this pot with other materials?
    Yannick Copin
    Community Answer
    The key aspect is the evaporation, which requires porosity of the clay. Any porous material should work.
  • Question
    Would circulating cool water continuously in the gap without sand, between the inner and outer pots cool effectively? This way there wouldn't be complete reliance on evaporation.
    Yannick Copin
    Community Answer
    This is evaporation that is taking energy from the system, not cold water per se.
  • Question
    What is the use of holes in the base of the pots?
    Community Answer
    Holes are not required. If there are any, you need to close them as water may enter the inner pot.
  • Question
    Community Answer
  • Question
    Do I have to make a hole in the bottom of both pots? Why is that necessary?
    Community Answer
    Read Step 2 more carefully. You do not need to make any holes in the bottom of the pots. If the pots already have holes in the bottom, then you need to fill them in.
  • Question
    In hotter climates, can I just dig a hole and bury the pot?
    Community Answer
    This pot system must have moving air circulating around it or it won't cool. That is its purpose and it would not work if it were buried. It performs like a swamp cooler. Shade the whole area where you keep the pot-in-a-pot refrigerator and it will work well. Note though, it is not suitable for humid regions.
  • Question
    Can I use concrete instead of clay material?
    Community Answer
    Yes, you can because of its porosity. This has been tested with a 8X8X16 block the size of a 4X8 X4high cooler.
  • Question
    If the outside air temp is x, what differential/cooling can be expected? Has anyone actually measured the inside/outside temperature differential?
    Community Answer
    Mine was about 15 degrees cooler, sometimes more. It depended on the humidity in the air. I mostly used it for fruits and veggies, but milk or cheese would be okay for 5 days or so.
  • Question
    Can I fill the outer pot with just water instead of sand soaked in water?
    Community Answer
    The sand retains the water. If you used only water, then everything would be wet and dripping.
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