Yakhchāl

A yakhchāl (Persian for "ice pit") is a traditional ice house of the Iranian plateau. Above ground it appears as a tall, usually conical dome of earth; below ground it covers a deep storage pit where ice made or collected in winter was kept into the hot season. Records point to such structures as far back as about 400 BC.

The dome

The dome is the yakhchāl's roof and its cooling machine. Its tall, tapering form encourages warm air to rise and escape at the top, working like a solar chimney, while cooler air settles toward the pit. The Kerman yakhchāl is cone-shaped and about 18 m (59 ft) high.

Sarooj

Walls and domes were built of sarooj, a water-resistant mortar of sand, clay, lime, ash, goat hair and egg whites mixed in set proportions. Sarooj resists heat transfer, and walls were made at least 2 m (6.5 ft) thick at the base. Underground storage could reach about 5,000 m³ (180,000 cu ft).

Making the ice

Next to many yakhchāls ran long shade walls, often about 10 m (33 ft) and sometimes 15 m (49 ft) high, protecting shallow ice pools. Water, often brought by qanat, was let into the channels to freeze on clear winter nights, when dry air allows heat to radiate to the sky. Ice was also carried down from nearby mountains. Some sites used windcatchers (bâdgir) to draw air over the store.

Where they survive

Most examples are in the desert regions of the Dasht-e Lut and Dasht-e Kavir, at places such as Abarkuh, Meybod, Sirjan, Kowsar and Kerman. Many have decayed but some are well preserved. In modern Persian, and in Afghanistan and Tajikistan, the word now also means "refrigerator".