> Jaali’s cooling feature relies on the Venturi effect in a similar way to an air conditioning unit. "When air passes through holes, it picks up velocity and penetrates afar. Due to the small apertures, air gets compressed and when released it gets cooler," says Pandya.
When the air passes through the holes, yes, it picks up velocity, but that velocity is lost immediately upon exiting so it can't penetrate further than if the restriction wasn't there. In fact it must lose some energy due to the restrictions so it will penetrate less and you can easily observe this when using a mosquito net in window.
Secondly the air is not compressed through the holes, the pressure actually drops as the speed increases. Unless I completely misunderstand the Venturi effect, in which case please correct me.
The purpose of the lattices is to let in air and light while restricting direct sunlight. That is important enough especially since it's passive, but shades are being used in modern buildings, it's not some lost art, and it is clearly nothing like AC. It's not even like modern ventilation or mobile shades which can let air only during the cool nights.
« One notable feature of the building is its application of a physics principle called the "stack effect", whereby the rotation angles of each brick in the jaali are designed to minimise solar radiation. »
As the air shrinks in volume (and as you say, speeds up) it goes up in temp. It dumps sone of that heat into the marble. So when it opens back up, it slows down and cools down. The material choice would seem to be very important. Marble and sandstone both have high thermal mass but low thermal conductivity.
> As the air shrinks in volume (and as you say, speeds up) it goes up in temp.
It does not shrink in volume, it does not compress, it only speeds up so the debit remains the same. If anything it would expand as an effect of the Venturi, because the pressure drops.
I was looking at a picture from the venturi in an AC loop where one side is higher because of the compressor and over restriction Yeah, venturi would seem to be a non-effect here.
I agree that the explanation given in the article seems wrong.
I think the correct way to reason is to consider the building as whole as a system.
There is pressure difference between two sides of the building, one in the sun and one in the shade. It seems that jaali is best understood as air flow diffuser. It reduces the overall air velocity flowing trough the building and decreases the pressure. It's a good at mixing air, thus temperature behind jaali is lower but not as much lower as it would be with solid sun shade.
Jaali probably just acts like an air shield (i.e. the air thrower above doors in shopping stores). This way you still get fresh air except lower rate of heat transfer.
We have this in our family home. Was not a fan of them because they collect all the dust but after reading this article they seem to have a very good use we never think about.
> Jaali’s cooling feature relies on the Venturi effect in a similar way to an air conditioning unit. "When air passes through holes, it picks up velocity and penetrates afar. Due to the small apertures, air gets compressed and when released it gets cooler," says Pandya.
When the air passes through the holes, yes, it picks up velocity, but that velocity is lost immediately upon exiting so it can't penetrate further than if the restriction wasn't there. In fact it must lose some energy due to the restrictions so it will penetrate less and you can easily observe this when using a mosquito net in window.
Secondly the air is not compressed through the holes, the pressure actually drops as the speed increases. Unless I completely misunderstand the Venturi effect, in which case please correct me.
The purpose of the lattices is to let in air and light while restricting direct sunlight. That is important enough especially since it's passive, but shades are being used in modern buildings, it's not some lost art, and it is clearly nothing like AC. It's not even like modern ventilation or mobile shades which can let air only during the cool nights.