If you lived in ancient Persia, you could do a lot worse in trying to cool things down than by building a yakhchāl. Today we break down how the early fridges worked.See omnystudio.com/listener for privacy information.
Chapter 1: What is the main topic of this episode about ancient fridges?
Hey, and welcome to the Short Stuff. I'm Josh, and there's Chuck, Jerry, sitting in for Dave. And so this is Short Stuff, the How Do You Say This Again edition.
Yeah, I'm going to say it's spelled Y-A-K-H, you know, as most words are. C-H-A-A-L. I'm going to say YAKALS.
I'm going with the straight ahead yak chals. All right. Okay. So you say it your way throughout. I'll say it my way. And I'm sure I'll inevitably unconsciously start saying it your way.
We'll see. But what we're talking about is the promise from our refrigeration episode a little bit more on these ancient – basically ancient refrigerators or cooling systems. They were found across ancient Persia at least as old as 400 B.C. This is modern-day Iran.
Chapter 2: How were yakhchāls used in ancient Persia?
And this is – these are places where, believe it or not, the climate enables freezing of ice when you would not think you should be able to freeze ice.
Yeah, it's pretty amazing. And apparently still today in Iran, Afghanistan and Tajikistan, Tajikistan. Yeah, I said it right the first time. They call the refrigerators yakchals, which is how I would say it if I were in Iran. But that's the name for the fridge, which means that at some point someone in Iran has gone into a store and said, you got a smeg yakchal?
Yeah, exactly. Yeah. And these have been the fascination of like everyone from engineers to historians to physicists over the years because they're just so kind of confusing and how they actually work. And I'm still not entirely sure how it works. It seems to be a little magic involved.
Chapter 3: What materials were used to construct yakhchāls?
One thing I know goes a long way toward keeping this ice, and we got to say some of this ice is mined from the mountains and brought down and preserved. Some is made on site. We'll get to that. But one big factor is the insulation of the structure itself, which is made from a mortar called cerouge.
Is that how you're saying it?
Yeah. Sand, clay, egg whites, lime, goat hair, and ash. Mm-hmm. Quite a mixture.
Chapter 4: How did yakhchāls maintain ice storage through summer?
Some of these were several meters thick. Some of these yak chawls were. There was a study. We got some of this information from the engineering firm Max Fordham. And they did an analysis in 2018 of yak chawls and just how effective they might have been.
And they found that the walls of a yak chawl had the same insulative properties as a wall of concrete three inches thick surrounded by a one foot thick wrapping of styrofoam insulation. That's how effective these things were. Sand, clay, egg whites, lime, and goat hair, and ash. I was going to say, like, the secret is egg whites, but I don't know. You throw goat hair in there. Yeah.
Who knows what the secret is? I think the secret is the whole thing together, the whole ceruge mixture.
Yeah, probably so. So I mentioned that sometimes the ice was brought in from the mountains and kept there throughout the year. But usually what would happen is they would make ice. They would bring in water. They would divert water from an aqueduct. through these underground water channels called canots. And they would channel them to the north side of this wall.
It's another thing we haven't mentioned yet is they have these very, very high walls that act as shade for these channels to keep, you know, the wind off of it because stuff isn't going to freeze as fast if it's moving. So to keep the water still and to keep it cooler away from that sun.
Yeah. And so the channel has a little diversion into a trench or a pit or like a very shallow, like rectangular pond usually. And they'll divert water in there to fill it up. And then they let it freeze overnight. Over the course of a few nights, it'll continue to freeze and freeze and freeze in layers.
And what they're taking advantage of, you know, like when it snows and then the temperatures heat up and all the snow melts, but there's a little pile of snow like in a shaded corner of your yard that never gets direct sunlight. And it just takes forever to melt. They're taking advantage of the same thing.
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Chapter 5: What architectural features help yakhchāls preserve ice?
They're building that big old wall to keep it shaded and just let this ice grow and grow and grow. And then once it reaches, I think, 50 centimeters, which is like about a half a meter thick, then they'll cut it into blocks and they put it in the yak shell and they store it. Through summer, like this stuff will stay frozen for an entire summer.
So in that sense, these yak chawls are built to store cold throughout the course of a year. Even when the summer comes around, still cold.
Yeah. Another way that helps us out is that dome shape. It's not domed because they like domes, even though domes are nice. It's conical because that optimizes what's called the solar chimney effect. That's when you create a convection current, letting that heat go up, up, up, and out. through these openings at the top and bringing in that cool air from the bottom.
They also have wind catchers that they call badgers. And they actually take wind and direct it downward into the Yakchal Dome. And so the air that hits it is cooled by that ice and the air that's not cooled by it or cooled enough, like you said, that chimney effect takes it up along the curved sides toward the hole in the top and it says, see you later, don't come back.
That's right. And that feels like a good time for a break. And we'll come back and talk about what the heck they're doing with all this ice right after this.
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