Published on April 28th, 2018 | by James Ayre0
Yakhchāls, Āb Anbārs, & Wind Catchers — Passive Cooling & Refrigeration Technologies Of Greater Iran (Persia)
April 28th, 2018 by James Ayre
If you were indoctrinated into the western public education system anytime over the last few centuries, then you likely learned all about all of the amazing “inventions” that originated in Europe over the last half-millennia. If you later went on to give yourself an actual education, then you learned that much of what you were taught was bunk or propaganda.
The reality is that many of the technologies supposedly invented during the Renaissance in Southern Europe, and the centuries that followed in other parts of the continent, followed directly from or were exact copies of inventions from much earlier periods of time — many of which were imported into Europe from the Persian, Turkic, and Indian-subcontinent worlds, as well as cultures further east.
Guns, for instance, are known to have been developed first in what’s now China before then being spread widely by other groups — with the Mongols apparently being the ones to introduce guns and various other technologies to Europe and the Islamic world. If you were educated in the West anytime in recent history, though, you likely learned a very different and historically far less accurate version of events. (As an aside, the historical reality is that the Mongols were greatly outnumbered in essentially every battle with European and Islamic powers — by ratios of at least 5 to 1 in some cases. The situation occurred as it did simply due to the fact that the Mongols were far better at warfare and administration than their contemporaneous European counterparts.)
The situation regarding compasses, engineering techniques and designs, parabolic mirrors, various types of elegant mathematics, many architectural techniques, etc., is much the same — development elsewhere, followed by import to Europe without accreditation. That should sound familiar to those who follow the business sectors nowadays. What goes around, comes back around.
More to the subject at hand, though, there have been a great number of technologies related to renewable energy and passive building design in use throughout many parts of the world deep into history that remain something of an unknown to those in the modern western world, which seem worth highlighting here.
I’ll be focusing mostly just on Yakhchāls, Āb Anbārs, and wind catchers of various kinds in this piece. Enjoy.
Yakhchāls (Ice Pits) — Refrigeration, Ice Creation, & Air Conditioning Through The Use Of Wind Towers, Sarooj Insulation, & Underground Aqueducts
A Yakhchāl (“ice pit”) is a rather ingenious form of large evaporative cooler — based around the use of subterranean storage spaces, a large domed above-ground structure made with thick walls and outfitted with wind catchers (bâdgirs), which is shaded further by external walls, and connected to qanāts (a style of aqueduct used in the region).
Depending on the specific design utilized, and the needs of the specific region and application in question, such buildings can feature internal temperatures below freezing even during the height of summer.
To oversimplify, a basic design would be one whereby a system of wind catchers is used to draw/channel cool air into well insulated vents leading through underground cooled aqueducts (often coming from mountain snow melt) and into the subterranean space below the domed structure. This domed structure is itself often protected by external sun walls, and is made of a thick (at least ~2 meters) heat-resistant and water-impenetrable mortar made of clay, sand, egg whites, lime, ash, and goat hair (in specific quantities and processed in a specific way) known as sarooj. The open dome functions as a way of redirecting relatively warm out of the structure to be replaced by incoming cold air. The subterranean portions of the structures are filled with ice during the winter months by allowing water from the qanāts to flow into the structure and freeze. Taken as a whole the system is a very effective large-scale combination of the basic ice box/cellar tech in use in many parts of the world and an evaporative cooler relying upon underground aqueducts. As such they allow for the refrigeration and storage of perishable foods year-round on a near completely passive basis, and also for the year-round creation of frozen desserts (faloodeh’ etc.).
Designs vary quite a bit, though, as noted above — as yakhchāls are essentially relatively large engineering projects, so it made/makes sense to survey and design to specific and local needs. Some designs move cooled aqueduct water through the walls of the structure, for instance. Notably, some villages and ancient structures are/were cooled via connection with yakhchāls — as a sort of pre-modern form of very effective air conditioning.
Yakhchāls were already a mature technology in the Iranic (Persian) world circa ~400 BC — with origins stretching much further back into time, which remain somewhat murky.
As a final note here, the word Yakhchāl is now commonly used in the region to denote any type of refrigeration technology, rather than just the pre-modern passive buildings just discussed.
Āb Anbārs (Water Reservoirs) — Earthquake-Resistant, Contamination-Resistant, Temperature-Stratified Water Storage & Access
Āb anbārs (“water reservoirs”) are a type of earthquake-resistant, and temperature-stratified underground water storage system or cistern that has been used in region around what’s now Iran well into the distant past.
Owing to the underground design, āb anbārs can (and often have been) outfitted with access sites (faucets) at different depths of access stairway — allowing for easy on-demand access to water of different temperatures (owing to the passive stratification that occurs in large bodies of water). Given that some of these storage tanks are massive, the temperature differences in question can be substantial.
Āb anbārs in the Greater Iran region were generally built out of the same water-impenetrable mortar material known as sarooj that yakhchāls are/were made out of — with differences in “recipe” apparently varying based on local climate and aridity.
Notable here is this the bottoms of such structures were often lined with metals owing to reasons of structural support needs.
Owing to the way that access to the water in these structures was limited to external faucets (paired with drains and ventilation) located along underground stairways straddling the storage tanks, contamination risks were minimal — allowing for wide-sharing of water resources without risk of unintentional health hazards. Accompanying these design elements, a salty compound of some kind was usually used on the tank’s interior walls, to form a sort of surface on the top of the water column — further isolating the water from possible contamination.
Individual houses and compounds often had their own smaller āb anbārs, sometimes directly connected to the larger ones — with flow controlled by an official called a meerab.
Wind catchers were often used in conjunction with āb anbārs as a means of lowering water temperature and thus limiting risk of contamination, which also increased water storage capacity somewhat of course. And as ventilation is quite good, humidity doesn’t linger and dew doesn’t form, further limiting the potential for contamination.
Wind Catchers (Bâdgirs) — Downward Flow Designs, Upward Flow Designs, & Solar Chimney Designs
As noted earlier in the article, wind catchers (bâdgirs) were often used in Greater Iran as means of lowering the internal temperature of structures for various purposes (air conditioning, refrigeration, ice creation, etc.).
To provide a simplified explanation of the way the technology works — a number of different wind towers (usually 4, 8, or sometimes just 1) are built into or around a building (varying based on local wind patterns and dust potential) and used as a way of increasing ventilation, lowering building temperatures, and providing evaporative cooling.
There are 3 basic designs of Iranian style wind catchers: downward flow designs; upward flow designs (often in combination with qanāts access); and a sort of solar chimney design.
In downward flow designs, the intent is usually to provide internal cooling, and is used in combination with other strategies (high walls, close placement of buildings, courtyards to trap cool night air, etc.). In this case the wind catchers are placed so as to face the prevailing wind patterns, and to channel these winds downwards into the structure in question. This approach is quite old, and is known to have been used in ancient Egypt (and probably the older Indus Valley civilization as well).
In upward flow designs the intent is generally to draw air into the building in question up through nearby underground aqueducts (qanāts), via the placement of wind catchers facing away from the direction of the prevailing winds in combination with ground level air-intake opens elsewhere (which channel through the cold, underground aqueducts sometimes carrying snow or glacial melt). Often times these towers have movable openings or adjustable towers, so as to ensure that the placement is away from the wind. Alternately, multiple towers with sealable entrances can be used.
The general idea of these designs is to bring cold relatively humid air into the building which provides direct cooling as well as evaporative cooling. The buildings in question are of course already built with thick walls and a lot of thermal mass, so temperature is already being moderated considerably. You could think of such an approach as a combination of an underground “cool tube” and a swamp cooler.
In other designs the idea is often simply to provide a solar chimney effect. These designs were/are generally used in places without much wind and without access to qanāts. Basically, the idea is to provide an easy means of exit for hot air and to trap cooler night air. Such systems can work well in regions with cool night temperatures, but aren’t capable of providing cooling below that level. It should be realized, though, that underground structures with effective insulation (and or ice-storage) can trap winter temperatures year-round in the lower levels.
Such an approach would be much less effective in regions where ground temperatures are quite high (most of the humid tropical parts of the world, for instance). Alternately, such solutions are very well suited to many desert climates — most especially those in highlands and/or with access to mountains and snow or glacial melt.