A yakhchāl ( 'ice pit'; ''yakh'' meaning 'ice' and ''chāl'' meaning 'pit') is an ancient type of ice house, which also made

ice Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 ° C, 32 ° F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally oc ...

. They are primarily found in the

Dasht-e Lut The Lut Desert, widely referred to as Dasht-e Lut (, "Emptiness Plain"), is a salt desert located in the provinces of Kerman and Sistan-Baluchestan, Iran. It is the world's 33rd-largest desert, and was included in UNESCO's World Heritage List ...

and Dasht-e-Kavir deserts, whose climates range from

cold Cold is the presence of low temperature, especially in the atmosphere. In common usage, cold is often a subjectivity, subjective perception. A lower bound to temperature is absolute zero, defined as 0.00K on the Kelvin scale, an absolute t ...

(BWk) to

hot Hot commonly refers refer to: *Heat, a hot temperature *Pungency, in food, a spicy or hot quality Hot or HOT may also refer to: Places *Hot district, a district of Chiang Mai province, Thailand ** Hot subdistrict, a sub-district of Hot Distric ...

(BWh) desert regions. In present-day

Iran Iran, officially the Islamic Republic of Iran (IRI) and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the nort ...

Afghanistan Afghanistan, officially the Islamic Emirate of Afghanistan, is a landlocked country located at the crossroads of Central Asia and South Asia. It is bordered by Pakistan to the Durand Line, east and south, Iran to the Afghanistan–Iran borde ...

, and

Tajikistan Tajikistan, officially the Republic of Tajikistan, is a landlocked country in Central Asia. Dushanbe is the capital city, capital and most populous city. Tajikistan borders Afghanistan to the Afghanistan–Tajikistan border, south, Uzbekistan to ...

, the term ''yakhchāl'' is also used to refer to modern

refrigerators A refrigerator, commonly shortened to fridge, is a commercial and home appliance consisting of a thermally insulated compartment and a heat pump (mechanical, electronic or chemical) that transfers heat from its inside to its external envir ...

. The structure typically had a domed shape above ground, a subterranean storage space, shade walls, and ice pools. It was often used to store ice, but sometimes was used to store food as well as produce ice. The subterranean space and thick heat-resistant construction material insulated the storage space year-round. These structures were mainly built and used since ancient times in

Persia Iran, officially the Islamic Republic of Iran (IRI) and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the nort ...

History

Records indicate that these structures were built as far back as 400 BCE, and many that were built hundreds of years ago remain standing, where Persian engineers built yakhchāls in the desert to store ice, usually made nearby. The ice created nearby and stored in yakhchāls is used throughout the year especially during hot summer days, for various purposes, including preservation of food, to chill treats, or making traditional Persian desserts like

faloodeh ''Faloodeh'' (, ), or ''paloodeh'' (, ), is a traditional Iranian cold dessert similar to a sorbet. It consists of thin vermicelli-sized noodles made from starch in a semi-frozen syrup containing sugar and rose water. ''Faloodeh'' is often ...

and

sorbet Sorbet (, ) is a frozen dessert made using ice combined with fruit juice, fruit purée, or other ingredients, such as wine, liqueur, or honey. Sorbet does not contain dairy products. Sherbet is similar to sorbet, but contains dairy. Etymolog ...

s. Although many have deteriorated over the years due to widespread commercial refrigeration technology, some interest in them has been revived as a source of inspiration in low-energy housing design and

sustainable architecture Sustainable architecture is architecture that seeks to minimize the negative environmental impact of buildings through improved efficiency and moderation in the use of materials, energy, development space and the ecosystem at large. Sometimes, su ...

. And some, like a yakhchāl in

Kerman Kerman (; ) is a city in the Central District (Kerman County), Central District of Kerman County, Kerman province, Kerman province, Iran, serving as capital of the province, the county, and the district. History Kerman was founded as a def ...

(over a mile above sea level), have been well-preserved. These still have their cone-shaped, eighteen meter high building, massive insulation, and continuous cooling waters that spiral down its side and keep the ice frozen throughout the summer.

Design

A yakhchāl's engineering is optimized to take advantage of the physics of

evaporative cooling An evaporative cooler (also known as evaporative air conditioner, swamp cooler, swamp box, desert cooler and wet air cooler) is a device that cools air through the evaporation of water. Evaporative cooling differs from other air conditioning sy ...

and

radiative cooling In the study of heat transfer, radiative cooling is the process by which a body loses heat by thermal radiation. As Planck's law describes, every physical body spontaneously and continuously emits electromagnetic radiation. Radiative cooling has b ...

, and the fact that the arid, desert climate is low in

relative Relative may refer to: General use *Kinship and family, the principle binding the most basic social units of society. If two people are connected by circumstances of birth, they are said to be ''relatives''. Philosophy *Relativism, the concept t ...

and

absolute Absolute may refer to: Companies * Absolute Entertainment, a video game publisher * Absolute Radio, (formerly Virgin Radio), independent national radio station in the UK * Absolute Software Corporation, specializes in security and data risk ma ...

humidity. The low relative humidity increases the efficiency of evaporative cooling due to the vapor pressure differential, and the low absolute humidity increases the efficiency of radiative cooling because the water vapor in the air otherwise inhibits it. In addition, in some desert climates, like those at high altitudes, temperatures drop below freezing at night. Their design is generally split into three areas: # The ice house or reservoir # The shade walls # The ice pits or pools However, they varied greatly, as some used all three components, whereas others were simply a large shade wall over a thin pool.

Ice house

Most yakhchāls operate like a traditional ice house. The tall, conical shape of the building is to optimize the

solar chimney A solar chimney often referred to as a thermal chimney is a way of improving the natural ventilation of buildings by using convection of air heated by passive solar energy. A simple description of a solar chimney is that of a vertical shaft util ...

effect, creating a convection current to guide any remaining heat upward and outside through openings at the very top of the building. Through this passive process, the air inside the yakhchāl remains cooler than the outside. At the same time, the building allows cold air to pour in from entries at the structure's base and descend to the lowest part of the yakhchāl: large underground spaces up to in volume. The yakhchāl is built of a unique water-resistant mortar called

sarooj Sarooj is a traditional water-resistant mortar used in Iranian architecture, used in the construction of bridges and yakhchāl, ancient Persian ice houses.lime, goat hair, and ash in specific proportions, is resistant to heat transfer and is thought to be completely water-impenetrable. This material acts as effective insulation all year round. The sarooj walls are at least two meters thick at the base. They also often have access to a ''

qanat A qanāt () or kārīz () is a water supply system that was developed in ancient Iran for the purpose of transporting usable water to the surface from an aquifer or a well through an underground aqueduct. Originating approximately 3,000 years ...

'' (Iranian aqueduct), and are sometimes equipped with bâdgirs (windcatchers or wind towers) built of mud or mud brick in square or round shapes with vents at the top which funnel cool air down through internal, vertically placed wooden slats to the water or structure below. A bâdgir can also function as a chimney, releasing warm air out the top and pulling cool air in from a base opening or a connected ''qanat'' (air in a qanat is cooled by the underground stream). It is this construction that allows the ice house of a yakhchāl to take advantage of evaporative cooling, keeping the structure cool to well below ambient temperatures. The ice inside the structure was often separated using wood and straw to separate the layers of ice and keep them from sticking to each other. Furthermore, most designs incorporated a hole at the bottom that would connect back to the qanat, or simply act as a well for drainage.

Shade walls

The temperature differences between shaded and non-shaded area in most areas where the yakhchāls were constructed often have temperature differences of nearly to cooler, making shade walls necessary for production and storage, as well as giving workers extra time to harvest ice. A wall is usually built in an east–west direction near the yakhchāl, often as high as and sometimes as high as to minimize convection losses as well as to provide shade. Due to their height, the base of the walls was often significantly thicker, and in some design the walls were arched and/or buttressed in order to support the load (as pictured at the yakhchāl at Sirjan). Water is often channeled from a qanat to a yakhchāl, which is used to fill the provisioning pools or used to power the evaporative cooling throughout the ice house. Incoming water is channeled along the north side of the wall so that radiative cooling in the wall's shadow pre-chills the water before it enters the yakhchāl (as pictured at the yakhchāl at Kowsar). Ice is then brought from either the ice pools covered by the walls, or from nearby mountains to be stored in the reservoir.

Ice pools

Many yakhchāls contained ice pools. These pools were constructed to either provision the yakhchāl with water needed for evaporative cooling, so that ice could easily be prepared and transferred to inside storage, or for the production of ice on site. Sometimes these pools were channels that were square in shape of dimensions roughly × with a depth of to , comparable to a

reflecting pool A reflecting pool, also called a reflection pool, is a water feature found in gardens, parks and memorial sites. It usually consists of a shallow pool of water with a reflective surface, undisturbed by fountain jets. Design Reflecting pools are o ...

. Often, no special material was used to finish the channel surface. By night time, the ice pools would often have a negative energy budget: * Heat conduction into the pool would be minimal due to the construction of the shade walls throughout the day and / or straw covering over the pool bed during the day. * Hot air convection towards the pools would be minimal, either by location or again due to the height and position of the walls. * Evaporation would take heat away from the pools, as with the rest of the yakhchāl. * Due to the low moisture content of the air, very little of the heat radiated upwards from the pool would be reflected back to the pool by the air above it, allowing the pool's heat to be largely emitted into space. This meant that ice pools could use the cold of the desert nights and/or radiative cooling to freeze water which would later be transported to storage as ice.

References

External links

* A TED talk on

. {{DEFAULTSORT:Yakhchal Cooling technology Architecture in Iran Iranian inventions Ancient history of Iran Persian words and phrases Ice trade Iranian architectural elements