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Breeze-Powered Refrigerator

There’s more than one way to keep cool

Australian Curriculum links

  • Science > Physical sciences > Year 3 > ACSSU049
  • Science > Chemical sciences > Year 4 > ACSSU074
  • Science > Biological sciences > Year 5 > ACSSU043

You’ll need

  • One large terra cotta pot (must be terra cotta and unglazed)
  • One smaller terra cotta pot (may be glazed) that fits inside the larger pot leaving a gap of 2–5 cm
  • Sand
  • A funnel
  • Gaffer/waterproof tape
  • A thick cloth that covers the top of the large pot
  • A thermometer (two if you have one handy – a weather station with remote temperature sensor is particularly suited to this activity)
  • A jug

Try this

  1. Cover any holes in the base of the pots with gaffer tape
  2. Fill the base of the large pot with enough sand for the top of the smaller pot to sit level with the large pot.
  3. Sit the smaller pot in the large pot and fill the gaps between the two with sand
  4. Use the jug to water the sand. Make sure it damp but not muddy.
  5. Record the temperature on your thermometer and then place it inside the smaller pot
  6. Cover with a damp thick cloth and place in a breezy area.
  7. Leave for one hour then check the temperature inside the pot and compare to the temperature outside your pot.

Further investigation

  • Try placing your pot in different areas to compare its effectiveness. Does it work better in the sun or shade, still or breezy areas?
  • Try using other materials than sand.
  • What happens if you cover your pot in plastic wrap?
  • Try placing your pot in humid areas such as a bathroom, kitchen or laundry and then placing it in a dry area such as well-heated room or full sunlight.

What’s happening?

The pot you have made is called a zeer pot. It uses evaporative cooling to keep the inside pot much cooler. These pots are used in countries that don’t have electricity to keep food cool and safe from spoiling. As the breeze blows passed the outer terra cotta pot, some of moisture evaporates and reduces the temperature. This works because the outside pot is not watertight and the water is able to evaporate off it.

Real world links

Evaporative cooling is an ancient technology that was used by the Ancient Egyptians and other cultures. The Ancient Persians built special dome-shaped towers from bricks, called yakhchals, that were so effective that they could stop ice from melting in the desert during the middle of summer. These buildings aren’t the only things to use the power of evaporative cooling. Animals such as dogs pant, sheep use their noses to cool air and we use it when we sweat in the heat. You can read more about adaptations for living in a dry climate with this resource from the National Museum of Australia.