An ancient Persian ice house, used since the 1st millennium BC; the ancestor of the modern refrigerator. The ice created and stored in the yakhchāl was used to store food.
The yakhchāl is a dome, up to 18-metre (59-feet) high, completed by a large subterranean storage space, up to 5,000 m3 (180,000 cu ft) in volume. This allows cold air to pour in from entries at the base and descend to the lowest part of the structure, while the tall conical shape guides any remaining heat upward and outside through openings at the very top of the building. Through the active process the air inside the yakhchāl remains cooler than the outside. The yakhchāl is built of a thick (up to 2 metres (6.6 feet)) mortar composed of sand, clay, egg whites, lime, goat hair and ash, that is heat- and water-resistant.
The yakhchāl is connected to an aqueduct (“qanat”) and mainly built in high altitude deserts, in low humidity and low night temperature conditions, to promote the freezing of the channeled water.