A typical yakhchal combined several engineering principles: 1. Evaporative cooling Water flowing through channels around the structure evaporated in the dry desert air. Evaporation removes heat from the remaining water, lowering the temperature of nearby surfaces. 2. Thermal mass and insulation The walls were built from a specialized mortar called sarooj (sand, clay, lime, egg whites, ash, and goat hair). This mixture created thick, highly insulating walls—often over two meters thick—that slowed heat transfer from the outside environment. 3. Subterranean storage Much of the ice storage chamber was built underground, where temperatures fluctuate far less than at the surface. This natural thermal buffering helped keep ice frozen for months. 4. Radiative cooling and night freezing During winter nights, shallow pools outside the structure allowed water to freeze when temperatures dropped below 0°C. Heat radiated away to the cold night sky, enabling ice formation even in climates with w...