With the advancement of modern technologies serving humanity, we have air conditioning to cool us during hot seasons and heaters to keep warm in winter. However, our ancient ancestors were not as fortunate.
Whenever we complain about power outages on a sweltering summer afternoon, our parents often remind us, “When we were young, we didn’t even have a fan to use.” Air conditioning has only been around for about a century, so how did people in the past cool themselves?
Maintaining a comfortable ambient temperature is not only a luxury but also crucial for survival. There were times in history when electricity was not harnessed to power devices. Nevertheless, many civilizations developed strong cultural and architectural advancements very early on. As a result, people discovered simple yet profound lessons about thermodynamics, fluid mechanics, and HVAC.
Jaali
In ancient times, HVAC systems were integrated into architecture, with minimal reliance on equipment. For example, Jaali – a term from India referring to a lattice of stone or wood with perforations, placed in windows. Its intricate design is aesthetically appealing while also providing shade from the sun and rain. However, the most notable feature of jaali is its perforations, which help cool the air as it enters.
The holes in Jaali act like Venturi tubes, restricting airflow to lower its temperature.
Consider the difference when you blow air with your mouth wide open versus pursing your lips to blow air onto your hands; it’s clear that pursing your lips creates cooler air. This is a very simple application of the Venturi effect. When air passes through a constriction, its velocity increases, compensated by a drop in pressure. Since pressure and temperature are directly related, this leads to a decrease in temperature. The perforations in the jaali function like nozzles, constricting airflow and reducing its temperature in the process.
The Hawa Mahal in Jaipur is a great example of how Jaalis are used for cooling.
However, jaalis were primarily used in wealthier households. Common examples of jaali can be found in Indo-Islamic architecture, such as the Taj Mahal (Agra, India) and Hawa Mahal (Jaipur, India).
Thick Walls with Radiative Cooling
Thick walls provide radiative cooling. This type of cooling refers to the heat loss from the body to the surrounding environment through radiation. The walls designed to be thicker in structures like forts and palaces have greater thermal mass. This means they can absorb more heat emitted from bodies and objects within their range.
However, thick walls absorb and release heat slowly, causing discomfort at night. Therefore, the walls and floors of ancient palaces often had concealed water conduits. The flowing water would draw heat from the walls, keeping them cool.
Water conduits help cool the interior.
Modern techniques also utilize radiative cooling pipes within walls carrying cold water. This has reduced HVAC costs in facilities by over 25%. Infosys, a technology giant in India, is well-known for adopting radiative cooling methods as an alternative to conventional HVAC systems.
The ancient Romans used water conduits like sewers or underground channels to supply water for both utility and temperature regulation. Features like pools and fountains common in architecture from that period sourced water from these conduits.
Fountains and pools are an important part of Mughal architecture, cooling the air.
They also created simple heat exchangers to cool hot air. Pools and fountains would dissipate heat into the water upon contact. Fountains, screens, and pools were used either individually or in combination with other cooling methods.
Windcatchers are a great example of how to manage hot, dry air to keep homes cool. These structures protrude from a house, resembling a chimney.
Windcatchers extend from the roof and direct air into the house for cooling.
These structures have scoops and openings facing the wind, directing it into the home. Part of the wind’s heat is absorbed by the house’s walls due to thermal inertia. The base of the windcatcher, situated inside the house, guides the wind through damp screens and filters dust to further reduce temperature.
These systems were found in both affluent and common households. A classic example of traditional windcatchers is the Borujerdi House in Iran.
Stepwells can be found in arid regions of Gujarat and Rajasthan, India, to harvest and store water year-round. They are known for their unique inverted stair architecture, leading down several levels to the well.
Stepwells are complex architectural features with their own microclimate.
Stepwells have a stable microclimate; the bottom, near the water reservoir, is cooler than the surface by several degrees. The cross-section resembles a funnel, preventing excessive water loss due to evaporation while providing shade from the harsh sun.
Historically, these places not only provided water but also served as cool retreats from the extreme heat in arid regions. Notable examples of stepwells include Agrasen Ki Baoli in Delhi and Adalaj Ni Vav in Ahmedabad, India.
Common households in ancient times often used curtains and mats made from vetiver grass. The roots of vetiver grass, also known as Khus, were dried and woven into mats.
The roots of vetiver grass, also known as Khus, were dried and woven into mats.
This grass is known for its distinctive aroma and was often used to cool rooms in ordinary households. On hot summer days, water sprinkled on the mats would quickly spread due to capillary action. This water would absorb heat from the outside air and evaporate, cooling the air before it entered the room. This is an excellent method of humid cooling.
