The traditional jaali—the intricately carved stone or wood latticed screen found across India's historic palaces, forts, and cenotaphs—is much more than a beautiful decorative feature. Long before the advent of electricity and modern HVAC systems, ancient Indian architects engineered these screens to act as highly sophisticated, passive zero-energy air conditioners.The secret to how a jaali cools a massive palatial space relies on two fundamental principles of fluid dynamics: the Venturi Effect and Joule-Thomson Expansion.
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| Jali window 11th Ce Ajitnath Jain temple Gujarat en.eikipedia.org |
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| Jaliwindows of India rprealtyplus.com |
Above image: Lattice stone or wood Screens known as jalis were used in Hindu ,Jain temple to reduce daylight entering the temple.They filtered and softened the light entering the inner part of the stuctures. The tradition of using jalis continued in later Indian architecture, including Hindu and Jain temples. Later designs of jalis were evolved, incorporating geometric and naturalistic patterns. The use of Jali became popular and expanded when Islamic architecture was used in places like Gujarat.During the Mogul time the adoption of jalis in Islamic buildings was widespread especially in Mausoleums highlighting the fusion of architectural styles and motifs from Hindu and Jain temples............
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| Jali stone trellis in a Hindu temple en.wikipedia.org |
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| Jali in the tomb of Mogul emperor Akbar en.wikipedia.org |
1. The Venturi Effect (Increasing Wind Speed)
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| Venturi effect and lattice window instagram.com |
Above image: The traditional Jaali is not only a design element in Indian architecture but also it is an ancient classic method in passive cooling particularly in Hindu and Jain temples in the earliest stage. By using the Venturi effect, these perforated screens naturally compress and cool the air as it passes through. The Physical benefits are: Privacy, natural ventilation and Natural ventilation, privacy, and casting shadow and allowing filtered light indoors during days...........
The first challenge in a hot, oppressive tropical climate is getting stagnant air to move. A jaali solves this through the Venturi Effect, which dictates that when a fluid (like air) passes through a constricted channel, its velocity increases.
A jaali acts as an array of hundreds of tiny Venturi tubes. When a gentle breeze hits the large exterior surface area of the palace wall, it is forced through the tiny, tapered geometric openings of the lattice screen.
The Physics:
According to the Continuity Equation ($A_1V_1 = A_2V_2$), as the cross-sectional area ($A$) of the opening decreases, the velocity ($V$) of the air must increase to maintain a constant mass flow rate.
The Result: A sluggish, barely noticeable outdoor breeze is mechanically compressed and accelerated as it passes through the stone holes, entering the royal living spaces as a high-velocity, refreshing gust of wind.
2. Joule-Thomson Expansion (Lowering Temperature)
Accelerating the air is excellent for creating a breeze, but how does the jaali actually lower the air temperature? This happens right as the compressed air exits the inner side of the lattice, behaving much like the nozzle of an aerosol spray can.
The Physics:
As compressed air is forced through the tiny apertures, it abruptly expands upon entering the wide, open volume of the palace room. This sudden drop in pressure causes the air molecules to spread out rapidly.
The Result: In expanding, the air performs work against intermolecular forces, which absorbs thermal energy from its surroundings. This thermodynamic process cools the air itself. You can experience this basic physics principle yourself: blow on your hand with your mouth wide open (the air feels warm), then purse your lips into a tiny circle and blow hard (the air feels noticeably cold).
The Macro System: Material and Moisture
The geometry of the lattice holes provided the fluid dynamics, but ancient architects paired this layout with two other natural elements to complete the palace cooling system:
ElementRole in Passive Cooling
Thermal Mass (Sandstone/Marble)Thick stone walls absorbed the intense heat of the day, delaying its transmission to the interior rooms. At night, the stone radiated this heat away, keeping the interior temperatures incredibly stable.
Evaporative Cooling (Water)Royal architects frequently placed channels of running water, fountains, or wet vetiver (khus) mats directly behind or beneath the jaali screens. As the high-velocity air rushed through the lattice, it absorbed moisture from the water, dropping the interior temperature by several additional degrees via latent heat of vaporization.
Through this brilliant convergence of geology and fluid mechanics, the jaali transformed scorching desert air into a cool, humidified breeze—keeping kings and queens comfortable in the height of summer using nothing but physics.
Chaudhary, D. R. (n.d.). Evaluating the impact of Jaali façades on building energy demand in Jaipur's hot semi-arid climate. MDPI Sustainability.
Joshi, P. (n.d.). Jaali - A study of passive cooling via 3D printed clay blocks (Thesis). Iowa State University Digital Repository.
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Lotankar, H. (n.d.). Evolution of Mughal fenestrations in 16th-17th century. International Journal of Innovative Science and Modern Engineering (IJISME), 4(2).
(Cited by: 2)
https://en.wikipedia.org/wiki/Joule%E2%80%93Thomson_effect
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