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this article begins right, but then starts to read like it was copied from a book (mostly because it repeats what is said in the "introduction" as if it wasn't connected to it) I lack sufficient knowledge on this subject to make changes--164.77.106.16812:08, 13 November 2006 (UTC)[reply]
InMurray Leinster's the Planet Explorer he says the Babylonians were able to cool stuff to below ambient temperature via radiation to space at night by insulating it from ground heat and protecting it from convection currents. Is he just nuts? Is this an old theory that has now been discounted? thewind towers article says this is not possible, but it seems to make sense if you think about it really hard. Anybody know anything about this?Puddytang01:53, 17 April 2007 (UTC)[reply]
It looks true. It's circulating again, with a handful of sites making a big deal about it. Water freezes at night in the winter. A few intuitive optimizations can conserve ice, and help produce more ice, on more nights of the year. The Persians placed ponds for ice production next to the ice houses for easier transportation to storage. They must have placed the pool in the shadow of the ice house, so that it received less heat during the day. (I assume they kept some water in it during the day so that it stayed a little cooler by evaporation, to get a small head-start for cooling at night.)
The Persiansmight have discovered that low-lying water ismore likely to freeze at night in the winter. On cloudless, windless winter nights, water at or below ground level is more likely to freeze at night, even when elevated water does not freeze. That is, even when the ambient a few feet above ground is a few degrees above freezing, many surfaces radiate heat into the sky, become cooler than ambient, and produce some air that is (OH MY GOD) a few degrees below freezing, which collects at ground level and especially in depressions, depositinghoarfrost and freezing small puddles. SeeRadiative cooling#Nocturnal surface cooling. (Heat radiation from the water itself is probably minor to the effect.)
Knowing the explanation for the effect has no connection to exploiting it, but knowing more details of the effect is helpful in exploiting it.If the Persians noticed that low-lying water is more likely to freeze, they would optimize for it by placing the pond low (but that is kind of a "given"). We can look for other optimizations:If they knew that a small valley helped, they would try to place the complex at the bottom of a small valley (though a valley is also kind-of a "given", for availability of water, and more shade).If they surmised that heat from the ground countered the freezing, they might try to insulate the pond from the ground (as mentioned above) with straw, like they insulated the ice house. (If we tried this today, we might want to raise the pond a few inches above ground level, to let air cool it from below as well as above.)
This page independently credits radiation: "A clear night sky has a very low temperature, and on clear nights surfaces facing the sky radiate heat into the sky. In this way the temperature of the water in the pool could drop below the temperature of the air, and on cold nights it would drop below 0°C, thus creating ice."
This page incorrectly credits the yakhchāl: "Once water is stored inside the yakhchāl, it's able to freeze into ice because of the extremely low temperatures that the structure creates."
This is a great example. Of course it works! This is another great example of harnessing Passive energy. THere is an Ice Cave, the Bandera ice cave, that must work the same way as a natural formation.—Precedingunsigned comment added byMariecamille (talk •contribs)01:59, 2 June 2010 (UTC)[reply]
globalise and merge tags were placed on this article, but no discussions were started on the talk page. the reason given in the edit is that the article focuses "particularly on Iran, for no cost clear reason." Recognising the inherent selectivity of such a question, i disagree. My reasoning for why yakhchals are notable enough in their own right so as to warrant their own article separate from the generic ice house is the same reason whyEgyptian pyramids are not merged into themausoleum article. I will remove the tags... they should only be added back if engaging in discussion.Firejuggler86 (talk)10:54, 18 August 2020 (UTC)[reply]
This paper has an image of a map on page 4 of 7 that suggests a relationship with the type of ice house constructed in a place and where it lies in Iran. I am wondering if these places would also be considered yakhchāls, as they are pits with ice in them, just with different architecture around the pit.Robrobrob2 (talk)00:25, 25 September 2021 (UTC)[reply]
There's a lot of great things to add into this article fromthis paper regarding the physics of these places. Also, it would really be nice if there was a cc version ofthis picture that we could use in the ice pools section of the article. I might eventually get to adding the stuff from the paper into the text, but I don't have the skills to make the diagram.Fephisto (talk)03:53, 30 April 2023 (UTC)[reply]
Question: does Yakhchāl refer to just the adobe hut? Or does it refer to the entire complex (adobe hut+qanat+bâdgir+walls+ice pools)?Fephisto (talk)04:11, 30 April 2023 (UTC)[reply]
level-5 vital article is ratedStart-class on Wikipedia'scontent assessment scale.
Done, but maybe this source should be added, too?Fephisto (talk)15:44, 7 May 2023 (UTC)[reply]
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