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Comment by motardo | Hacker News Reader

I would have thought these structures move air up and out by the [chimney effect](https://en.wikipedia.org/wiki/Stack_effect) instead of funneling air down as the article describes. I love my old house's double hung windows which also use the chimney effect for passive cooling by opening both sashes halfway. Cooler air comes in the bottom, and warm air goes out the top.

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> I would have thought these structures move air up and out by the [chimney effect](https://en.wikipedia.org/wiki/Stack_effect) instead of funneling air down as the article describes.

That's what wikipedia describes—pulling cooled air from underground qanats up through the house and out the tower. I was surprised to read in this article about air coming down through them. Now I don't know which one is correct.

Both, the tower doesn't have one opening on the bottom - it has two or four and they are separated by walls in the center. Wind is coming in from one direction and pushes cool air down into the building, hot air comes out the other side of the tower.

This article has a good visualization: https://surfiran.com/windcatcher-an-ancient-engineering-feat...

Wikipedia is equivocal about it (my highlight):

> The windcatcher can function in two ways: directing airflow using the pressure of wind blowing into the windcatcher, or directing airflow using buoyancy forces from temperature gradients (stack effect). The relative importance of these two forces has been debated.

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