In approximately 400 BC, Persian engineers developed sophisticated methods for preserving ice amid sweltering desert climates. During the winter, they would amass substantial quantities of ice from neighboring mountains and store it in structures known as Yakhchals, or ice pits. These ancient refrigeration units served the dual purpose of preserving ice for summer use and safeguarding food in the hot, arid environment of Iran. Additionally, the ice was utilized to produce refreshing delicacies for royalty during the scorching summer months and to craft faloodeh, a traditional Persian frozen dessert.
Above ground, these edifices featured remarkable large mud brick domes, with some towering as high as 60 feet. Below the surface, they contained expansive chambers, some as spacious as 5000m³, incorporating deep storage areas. The storage spaces frequently featured access to a Qanat, or wind catch. They were equipped with a system of wind catchers that effectively reduced temperatures inside the chambers to frigid levels during summer days.
Yakhchals are ancient constructions with extraordinarily robust mud brick walls, reaching up to two meters in thickness at their base. These walls are erected using a distinct mortar known as sārooj, which is composed of a precise blend of sand, clay, egg whites, lime, goat hair, and ash. This unique mortar exhibits high resistance to heat transfer and is believed to be entirely impermeable to water.
The design of the Yakhchal incorporates substantial insulation and a system of continuously circulating, cooling waters that enwrap its sides. This ingenious design ensures that the ice stored within it remains frozen throughout the scorching summer months. In these desert communities, the ice houses also include a trench at the base to collect any melted water from the ice, allowing it to refreeze during the cold desert nights. The harvested ice is then fragmented and transported to deep subterranean chambers. The trench continues to collect additional water, facilitating the repetition of the process and guaranteeing a consistent supply of ice despite the harsh desert conditions.
- Design of the structure: The Yakchal had a dome shape with thick walls made of bricks and clay. This construction helped maintain a cool temperature inside the vault.
- Water collection: During the winter, water was collected from rivers or melting snow in the mountains. This water was directed towards the Yakchal through canals.
- Freezing process: The water was distributed in small ponds or pools within the vault. During the night and in the coldest hours of the day, the water would freeze due to the low temperatures of the desert at night.
- Ice storage: Once frozen, the ice was cut into blocks and stored in the lowest part of the Yakchal, where the temperature was coldest. The dome shape and natural insulation of the walls helped keep the ice frozen for many months.
- Later use: During the summer, the stored ice was used to cool drinks, preserve food, or even for medical purposes if necessary. In short, the Yakchal took advantage of the natural cold of desert nights to create and preserve ice, using simple but effective storage and thermal insulation techniques.