n 400 BC Persian engineers had already mastered the technique of storing ice in the middle of summer in the desert.
The ice could be brought in during the winters from nearby mountains. But in a more usual and sophisticated method they had a wall made along east-west direction close to the Ice Pit (yakhchal).In winter the qanat water was being canalized to north side of the wall. The shadow of the wall makes water freeze more quickly so they could have more ice per each winter day. Then ice was being stored in a specially designed, naturally cooled refrigerators called yakhchal (meaning ice pits)