The Persian ice houses, known as yakh-chal are ancient structures, used to store ice all year round with the purpose of preserving perishable foods but also for human consumption. The majority of ice houses used subterranean chambers to store ice or snow that had been collected from either neighbouring mountains or lakes during the winter months. These man-made underground chambers could reach a depth of 20 metres. The chambers are roofed with a domed structure that functions in parallel with a low wall and a shallow, long and narrow pool to create a passive cooling and an ice-harvesting system. The harvesting of the ice would take place daily during the winter. The process would consist of the pool being filled with fresh water every evening, which would freeze over night; the ice would then be collected in the morning and stored within the chamber.
The wall is constructed using adobe bricks, which provides a dense barrier to help shade the pool, which is positioned directly to the north of the wall. The winged open rectangular shape of the wall aids this shading process.
The height of the wall relates directly with the necessary level of shading and exposure of the pool required at different times of the year. The length of the pool often spanned up to 100 metres or more and 10 – 20 meters in width. Thus the height of the wall must be able to shelter the pool during the summer months from wind-induced convective heat gain and direct sunlight. It must also be able to shade the pool during the winter months to allow for ice to be created and harvested. It is essential however that the wall is not too high in order to allow the surface of the water to be exposed to the visible sky. This last factor impacts the amount of heat loss through radiation. To optimize this amount there needs to be exactly the right amount of exposure.
The construction of the main ice chamber consists primarily of mud bricks, similar to the wall of the pool. Straw or sawdust is then packed into the chamber to provide insulation enabling ice to maintain its frozen state during the summer months.
For the purpose of studying the structural and performative principles of the Persian ice houses the Meybod ice house in Yazd was used as a case study for which a series of environmental studies were carried out on. A thermal analysis of Meybod ice house was undertaken testing its performance over a three day period in winter. The results showed that the water in the pool remained below freezing while the ambient temperature was predominantly above 0°. The solar analysis proved the effectiveness of the winged shape of the wall. The Meybod ice house was designed with the appropriate dimensions to allow for complete shading from direct sunlight during the day and enough exposure to the sky during the night to facilitate efficient levels of ice production.
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