Ihoyinyin

Ihoyinyin (Abuda: “ice pit”; iho meaning “pit” and yinyin meaning “ice”) is an ancient type of evaporative cooler used in Alero. Above ground, the structure has a domed shape, but has a subterranean storage space. It was famously used to store ice, but was often used to store food and keep it fresh as well. The subterranean space coupled with thick, heat-resistant construction material insulated to space year-round. Many that were built centuries ago remain standing and practically in use today.

Design and process
By 800 BC, Abuda engineers in what is now Alero had mastered the technique of using ihoyinyin to create ice in the winter and store it in the summer. In most ihoyinyin, the ice is created by itself during the cold seasons of the year; the water is channeled from the fenuko (subterranean aqueduct) to the ihoyinyin and it freezes upon resting inside the structure. Usually, a wall is also made along an east-west direction close to the ihoyinyin, and the water is channeled from the north side of the wall so that the shadow of the wall keeps the water cool in order for it to freeze more quickly. In some ihoyinyin, ice is also brought in from nearby mountains for storage or to seed the icing process.

The building allows cold air to pour in from entries at its base and descend to its lowest part, large underground spaces up to 5,000 m3 in volume. At the same time, the tall, conical shape of the building guides any remaining heat upward and outside through openings at the very top of the building, and through this active process, the air inside remains cooler than the outside. The ihoyinyin is built of a unique water-resistant mortar called lawam, made of sand, clay, eggwhites, lime, goat hair, and ash in specific proportions, that is resistant to heat transfer and is thought to be completely waterproof. This material acts as an effective insulation year-round, with the walls being at least two meters thick at the base.

More commonly ihoyinyin have access to a fenuko, and sometimes are equipped with a system of wind towers that can easily bring temperatures inside the space to frigid levels even in the Summer. Built of mud or mudbrick, in square or round shapes, ihoyinyin catch the slightest breeze by the vents at the top of funnel the cooling air down through internal, vertically-placed wooden slats to the water or structure below. Alternately, the ihoyinyin can function as a chimney, expelling warm air upward in order to pull cool air in from a base opening or a connected fenuko (the fenuko air being cooled by an underground stream). Many homes in older inland Aleri towns are equipped with such a system.

Ice created and stored in ihoyinyin is used throughout the year, especially during hot summer days for various purposes, including the preservation of food, to chill treats, or to make chilled desserts. One ihoyinyin near Tetmosi is located about 1.5 km from the city center. The building itself is 18 m high, and the massive insulation and continuous cooling water spiraling down its sides keep ice frozen throughout the summer. Today, the term ihoyinyin is also used to refer to modern refrigerators.