Free Refrigeration In Hot Climates

Passive homes are a fairly recent trend in home building, but promise a future with minimal energy inputs in our day-to-day. One of the challenges in this year’s Hackaday Prize is to envision ways to add utility to earthen homes often used in refugee camps where there is a housing crisis. Adding passive utilities to these adobe buildings would be a fantastic upgrade, so [Cat] decided to tackle the challenge by creating a refrigerator that needs no electricity.

The the plan for the device works by using evaporative cooling to reduce the temperature in a small box which can be used for food storage. Of course, using evaporative cooling means that you need ready access to water and it likely won’t work in a humid or cool environment, but systems like these have been in use for centuries in plenty of places around the world. [Cat]’s plan is a little more involved than traditional methods of evaporative cooling though, and makes use of a specially painted chimney which provides the airflow when heated by sunlight.

The project is still in its infancy but it would be interesting to see a proof-of-concept built in a real-life passive house in an arid environment. Unfortunately, those of us in humid (or tropical) environments will have to look elsewhere for energy-efficient cooling solutions.

34 thoughts on “Free Refrigeration In Hot Climates

  1. Back in the 50’s in the desert SW, cars typically were not air conditioned to we used forced air evaporation coolers to keep the car’s interior bearable. The forced airflow through the cooler allowed it to continue working reasonably well while traveling through the gulf coast states.

    In looking at your idea, an unidirectional wind catcher base with turbine like blades would bring the incoming convective and wind driven air in and swirl it, tornado style through the evaporator then exhaust out the thermally augmented stack.

    As a second thought I wonder if the design could take advantage of the differential temperature convective wicking effect used in CPU coolers.

    1. By “differential temperature convective wicking effect” do you mean Heat Pipe?
      Using the latent evaporative pressure of water to move heat from a hot area of the pipe to a cooler area of the pipe.

      The smooth wall type (even DIY) could certainly be used as a “thermal diode” to transfer heat from inside the box to outside the box at a greater height, be it by having the raised end a chilled airflow or in chilled water. With a well insulated box, that would limit any heat from the air flow getting into the chilled box.

    1. You mean if everything becomes wet? The heat of vaporization for water (2260 j/g) is considerable and provided you don’t have 100% humidity, there will be cooling. It doesn’t cool the remaining water so much as leave the lower energy molecules behind. The heat sails up the chimney.

    1. The descriptions have some questionable thermodynamics “sometimes equipped with a system of bâdgirs (ancient design of windcatchers or wind towers) that could easily bring temperatures inside the space down to frigid levels even in summer days”. That and the rest imply the notion that wind = cold, which is certainly true for sweating humans feeling wind, but not true of the actual air temperature. First impression, the whole article needs examination.

      Maybe it is a giant Hilsch vortex generator, but I don’t think that works on such a grand scale and with velocity so low.

      1. Actually, shaped like that, with a hole in the top and well insulated, there’s a fair chance it works like a black body radiator in the cold winter nights, the cold source being the handful of degrees Kelvin of cosmic background.

        Haphazard natural “frost hollows” have been observed to go 15 degrees below the surrounding ambient in such conditions.

  2. Yes, I agree it would be “interesting to see a proof-of-concept,” but what I can instead offer you is a spoof of concept. Shouldn’t be that difficult. In this case even babies could offer proof of conception. Its probably in our genes.

        1. According to the article, a unit that can produce 60 kg of ice per day (“enough for 12 households”, based on a 5 kg ice block per household) costs about $7000 to build “if built in country where wages are low and transportation costs can be minimized.”

          Doesn’t sound all that attractive to me. Also see “The Mosquito Coast”.

  3. Some answers are in order eh?
    – Passive cooling: this is a bit more active. You are likely passively cooling now ;-) This harnesses the sun to some extent.
    – Iranian “refrigerator”: was used “to create ice in the winter and store it in the summer in the desert”. Not same market.
    – .. if everything around…: not true: evaporation will always suck heat. Black tube will heat inside air more than “around” so air will move; forcing evaporation, unless super humid.
    – Alternative/Ball: I looked into making either and realized I could not without specialized machinery and/or chemicals. Can you?

    I agree, it’s not for everywhere,everybody, etc.

    It will be useful in some places, not in others. Nobody complained that you can’t use skates in the ocean :-)

  4. People used to cut up naturally frozen lakes during winter and store the ice in thick walled ice houses to provide provide ice during summer months in some countries ( e.g. ).

    There is some evidence to suggest this happened long ago in some part of the Eastern Mediterranean (e.g. Damascus, Syria) where the temperature regularly drops below the freezing point of water during the winter months.

    1. A huge stack of ice blocks can resist melting for a long time. Years ago I saw an old photograph of an ice house that had burned. The outside was almost completely gone but the blocks of ice inside, separated by layers of sawdust were intact. IIRC the article with the photo said a new icehouse had been quickly built and most of the ice was saved to put in the new building.

  5. There are solar versions of the ammonia water refrigeration cycle (much like the Crossley icyball)

    Then there is the ammonia/calcium chloride adsorption refrigeration cycle, solar powered

    And there are descriptions of activated carbon/methanol refrigeration adsorption cycles too

  6. In addition to the solar water/ammonia cycle adsorption systems mentioned above, there are also calcium chloride/ammonia systems, like the following

  7. Any records about success of evaporative coolers in humid, tropical and subtropical areas were mostly people might congregate to survive in a crisis or emergency situation??

    Access to water is “vital”.

  8. Geez…nobody here has ever seen a gas powered refrigerator in a camper…uses a small flame to power a cycle based on ammonia. Not as super simple, but a solar conversion should not be out of the question….they just need a heat source for power.

  9. In short, the design has low efficiency single stage evaporative cooling, that doesn’t use all of the chilling produced.

    Cat needs to look at how evaporative coolers maximize the cooling potential of a given hot & dry air, as in, its temperature vs. humidity. “Shaggy Material” won’t perform well. You need to maximize the surface area of the water on the wet material and expose that to hot & dry air.

    In the design drawing, the hot & dry air is flowing past the shaggy-material. There will be latent evaporation from the water surface into the hot & dry air that is present. But chilling of the box is limited to the chilled water in the material/media touching the box.
    – Once that hot & dry air is turned into cooled & moist air, it needs to leave the material to let fresh hot & dry air in to continue the process, or the chilling is limited.
    – Also, that chilled & moist air is heavier than the hot & dry air flowing in below and past it – they’ll try and trade places.
    – The chilled air from the evaporative cooling is mixed with the hot air flowing past and lost out the chimney, throwing away the largest part of the chilling.

    1. Rather than that passive flow-by chilling, the rate of chilling can be greatly increased by having hot & dry air flowing through the wetting material/media. This efficiency is usually achieved by having the airflow go through a media pad from one side to another. Both the air is chilled and the water left on the media is chilled. Those are the two potential sources of cool for the heat within the box to conduct to. Chilled water flowing off the media can be collected and used to cool.

      To maximize chilling the box, get the heat from the box transfering to both the chilled air and the chilled water.

      Hot & dry air flowing through a media to get chilled is Single Stage evaporative cooling. Having a heat exchanger ahead of the hot & dry airflow, chilled by that chilled water (collected as it flows off the media), or by some of the chilled airflow, results is pre-chilling the incoming hot & dry air, for a Two Stage evaporative cooler. Some of that benefit can be achieved by irrigating the media pad with the chilled water, so while single stage, with the chilling of the water and from evaporative cooling, it’s much like a two stage, and it’s easier to reach the maximum chilling potential AND you use less water in evaporation.

      The most efficient media I know of is the blue Dura-Cool pad, which in single stage designs is capable of getting 95% of the evaporative cooling potential; Aspen pads are limited to 85%.

      (a possible enhancement to chilling a box, is to have the box sit in a pan, that fills with the chilled water flowing off the material/media fibres)

      With a material/media covered box, it would have to be kept wet. Anywhere the media gets dry will expose the box to the hot air.

      For efficiency, you need to separate the hot & dry airflow from the chilled cool & moist airflow.

    2. There’s a lot of potential for this in hot & dry areas. At least in day time.

      Without a lot of changes and attention to details, there should be a way to get as good as and even better than the performance of the wetted sand/pots used historically (and currently) in hot & dry climates. With some design enhancements, lower chilling and faster chilling should be achievable, but not at the rate of a fridge.

      The convenience of opening a door to access the chilled box like a modern fridge is nice, but the chilled air within falls out and is replaced by warmer air that contributes its heat to the chilled box. At the minimum, an insulated door that is well sealed. Better, like the pots, is have the opening on the top of the chilled box, so less chilled air inside it is replaced by warm air.

      A small VDC pump powered by a small cheap dedicated solar panel can easily handle keeping the material/media irrigated so chilling is maximized and there are no dry spots to pass/expose hot air. Should be under $30, possibly $20.

      So many things could be done with this.

  10. “Unfortunately, those of us in humid (or tropical) environments will have to look elsewhere for energy-efficient cooling solutions.” I.e. absorption or adsorption cooling. Water (in closed circulation also other other substances can be used) vapor is being ab-/adsorbed (i.e. by calcium chloride solution or silica gel), so it can keep evaporating. Used sorbent is regenerated in high temperature (i.e. by solar panel), releasing hot, concentrated vapor which can be condensed when it’s heat gets outside the building.

  11. Somebody gets excited about this ancient idea every few years.

    First, requires water but not electricity? You know what that means right? Have you ever experienced back pain? If no then be thankful. Very, very thankful. I wonder if the measurements done on the efficiency of this method include the muscle power used to pull a bucket of water up out of a deep well and carry it across a camp or village to one’s shelter?

    Second, works by evaporation. So you are trading temperature for humidity. This is not the way to become comfortable.

    Third, requires water but only works in non-humid environments. Consuming water in a non-humid environment is not the key to sustainability.

    So, sure. If you are experiencing a disaster or if you live in a place that really needs to build up it’s infrastructure this is good knowledge to have and may help you get by. This project, being about refugee housing is probably the perfect application for this technology. It is not a part of long term sustainable living.

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