Ancient-Indigenous Methods & Practices on Passive Refrigeration for Built Environment and Other Cooling Applications

Let me start by asking a simple question. “Do you feel comfortable standing directly under the scorching sun during summer, or would you rather stand under the shadow of a large tree?” A very trivial question, right?

Everyone knows that the latter will be the choice. Now, let me ask you one more follow-up question.

“Would you love it if there was a cool breeze blowing across while standing under the tree?”

I know what you are thinking. “Isn’t it so obvious? Who will not love a cool breeze while standing outside under a shade!”

This is the fundamental knowledge that we already have about passive refrigeration. We also know that such cooling is natural and effective, and on top of it, it is available free of cost to everyone. So, it is one of the examples of a sustainable (truly speaking) technology that already exists and was widely used in various forms before a generalised solution for refrigeration using burning fossil fuel was discovered and spread like wildfire or cell phone technology!

In the time of the grave crisis, we are facing today due to rapid climate change, which is the single most severe threat towards human existence on earth, this passive refrigeration technique could give rise to renewed hope in surviving under extreme conditions awaiting us in the near future. The cause of this rapid change in global climatic conditions is anthropogenic emission of greenhouse gases, including Carbon Dioxide and Methane.

Refrigeration through active systems such as vapour compression cycles, air cycles, etc., is contributing to large-scale emissions of greenhouse gases, including immense indirect emissions due to the consumption of electricity. Such systems are responsible for around 7-10% of emissions of greenhouse gases globally, out of which 80-85% are Carbon Dioxide emissions.

Therefore, it is apparent that eventually, we need to move away from such refrigeration systems or reduce their usage at large. Passive cooling systems based on our age-old, proven, and indigenous technologies need to be adapted widely, either standalone or hybrid, along with the current refrigeration systems. So, allow me to take you through what we already know about some of the passive systems. Such systems are simply defined as those that use naturally occurring processes to control or limit thermal energy (heat) entering the space being cooled and/or dissipate thermal energy (heat) generated inside, and while doing so, have little to no dependence on mechanical energy or electrical energy sources using conventional sources of energy including fossil fuels.

The techniques involved in such systems date back to the beginning of human civilisation. They were part of the vernacular architecture of almost all the regions with favourable climatic conditions. One such example can be found in the houses in ancient Iran and Iraq, as well as in Rajasthan in India, particularly in hot, arid areas. They used tall towers with air vents at the top of the buildings. Those are called the Badgirs in Persian and are shown in the image below. These systems drew cold air from the ground level by creating density gradients vertically by heating the air at the top and allowing it to flow out.

In another technique used for centuries in places like Rajasthan, roofs were cooled by painting them with lime. In this case, the property of high reflectivity of lime, which reflects most of the incident radiant energy from the Sun, was used. This simple method can produce a 4.5℃ lower temperature inside the houses than the outside air. Even roof treatments were not uncommon in India. In the eastern part of the country, in states like West Bengal, Odisha and Bihar, wet rice straws were used on the roofs during the summer. I still remember that during some summer mornings, I used to take one bucket full of water to the roof and spread it over the rice straws to make them wet!

This technique is nothing but evaporative cooling with insulation by providing thicker porous layers on top of the roofs. Traditionally, thick walls, lime as the binder, and rough outside wall surfaces with high albedo paints were common for houses in that part of the country. This was assisted by strategically planting trees with large canopies to provide shade. It was also common to have porte-cochères with high-rise roofs and high thermal storage materials on the roof, stairs and even in the parking area, as can be seen in the image below. All these served the purpose of providing cooler days with the help of nocturnal cooling and refrigeration storage using those storage materials.

Similar architecture can be found almost everywhere in the northern part of India. The difference that may be observed is the usage of materials. Almost all the materials used were locally available.

Passive refrigeration in ancient India was not only used for space cooling but also had applications in food preservation, cooling water, and even water conservation by reducing the high rate of water evaporation in dry and hot regions. Similar technologies date back to 300 BCE and can be found in countries including India, China and Türkiye. There are plenty of such methods that still exist and are just waiting to be explored.

Through India’s first BTech in Climate Change programme, Anant School for Climate Action helps students explore and even develop such solutions by equipping them with the right skills, knowledge and expertise.

The common factor in all these techniques is the use of locally available materials for building such passive refrigeration systems. Passive cooling, rooted in indigenous knowledge systems, has long been a sustainable approach to climate adaptation. Traditional methods like courtyards, wind catchers, stepwells and earthen materials effectively regulated temperatures but had limitations. Their success relied on local climate conditions, making them less effective in humid regions where evaporation is slow or in urban areas where heat retention is high.

Many techniques, such as thick mud walls and ventilated roofs, require large surface areas, limiting their use in modern dense spaces. Unlike mechanical cooling, these methods worked gradually, demanding careful architectural planning for airflow and shading. Additionally, the maintenance of organic materials like khus mats or thatched roofs required frequent upkeep. Air pollution and urbanisation now disrupt natural cooling, reducing the effectiveness of night radiation techniques like whitewashing rooftops.

However, blending traditional wisdom with modern materials, such as solar-assisted ventilation, reflective coatings and hybrid cooling systems, can help revive and enhance passive cooling for contemporary needs.

(The writer is Associate Professor and Director, Anant School for Climate Action, Anant National University)