Refrigeration With No Electricity

Many people who’ve experienced blackouts know that power outages tend to be one of the first things to happen during small scale natural disasters. Power cables strewn across long distances can be vulnerable to all sorts of failure (e.g., downed trees in a thunderstorm, vehicle collision, transformer failure, tornadoes and hurricanes, etc).

In the modern world, our dependance upon electricity has caused us to forget useful skills and technology of centuries past. A prime example is the invention of electrical refrigeration. People switched from food preservation techniques like salting and canning to simply throwing food into the freezer. Electrical refrigeration made direct-to-home milk delivery a thing of the past. While modern refrigeration and freezing is certainly convenient, it creates a dependence upon the device and the electrical grid that powers it. What happens when the power goes out? The unit will only keep foodstuffs cold for a day or so before it is no longer a viable storage method.

There is some evidence that ancient civilizations were able to refrigerate their perishable goods by using evaporative cooling. A very simple evaporative cooler known as a botijo was used in Spain to store drinking water. The botijo jug was made of porous unglazed earthenware and placed outdoors. Over time, a small percentage of the water diffuses through the ceramic’s pores and evaporates, taking heat energy away with it. This has a net cooling effect on the remaining water and under ideal circumstances, the temperature can drop up to 50 degrees Fahrenheit from the starting temperature!

In the 90s, the technology was rediscovered by Mohammed Bah Abba who developed the idea of pot-in-pot refrigeration (or zeer pot). In his implementation, a small pot (glazed ceramic or metal) is placed inside a larger unglazed, porous ceramic pot. Sand is used to fill the space between. Water is poured over the sand until it is saturated and a wet towel is placed over the top of the apparatus. When the pot is left outdoors, direct evaporative cooling can reduce the temperature to the 40-50 degree Fahrenheit range. This is a very impressive feat when considering the design’s simplicity. If one were so inclined, the apparatus could be tinkered with by adding renewable energy powered ventilation fans to increase water evaporation — potentially bringing the interior pot’s contents to the mid 30s.

Here’s a useful chart that shows how effective these zeer pots can be:

(Source: Wikipedia)

Tagged in: alternative energy, bug out, food preservation, food security, natural disaster, public health