A water porter and his family filling a zeer clay pot with water from a water-filled animal skinCairo, Egypt c.1881
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A pot-in-pot refrigerator, clay pot cooler or zeer (زير) is an evaporative cooling refrigeration device that does not use electricity. It uses a porous outer clay pot (lined with wet sand) containing an inner pot (which can be glazed to prevent penetration by the liquid) within which water is placed. The evaporation of the outer liquid draws heat from the inner pot. The device can cool any substance, requiring only a flow of relatively dry air and a water source.
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Evidence shows that evaporative cooling may have been used in North Africa as early as the Old Kingdom of Egypt, circa 2500 BC. Frescoes show enslaved people fanning water jars, which would increase airflow around porous pots to aid evaporation and cooling the contents.