In the hot, dry deserts of Ancient Persia in around 400 B.C.E, long before the invention of electricity, engineers mastered a sustainable technology to store ice throughout the scorching summer.
Yakhchāl were ancient evaporation coolers with a doomed shape above ground and subterranean storage space for ice, food, and other perishables. This effective method of storing ice in the middle of the desert may seem complex, but in reality, it was a simple technique that even the poorest could afford.
Ice was collected during winters from the nearby mountains and brought to the yakhchāl, and most also had qanats (underground channels) to carry water from nearby sources
Rising to about 60 feet in height, the structure of the yakhchāl above the ground was a massive mud brick dome. Bellow the ground there was an empty space up to 5000 cubic meters with very thick walls, measuring at least 2 meters at the base. The walls were made out of a type of mortar called sarooj; a mixture composed of sand, clay, egg whites, lime, goat hair, and ash in very specific proportions. This mortar was resistant to heat transfer and it was also thought to be completely waterproof.
The structure often contained a system of wind-catchers, which helped in bringing temperatures inside down to frigid levels during the summer.
Some of the yakhchāls that were built hundreds of years ago still remain intact. In present-day Iran, Afghanistan, and Tajikistan, the term yakhchāl is also used to refer to modern household refrigerators.