Keeping buildings cool is energy consuming and may call for innovative thinking to go beyond conventional, energy guzzling air-conditioning. Fortunately, researchers are actively exploring such options.
At the India Energy Week 2025 held in Delhi recently, a presentation by Sanjay Chhettri of Grant Thornton, an audit, tax and advisory services firm, highlighted the scope and application of earth-based solutions for cooling buildings.
The principle is simple. There is ‘cool’ available in many places — if you can tap it, you are in business. For example, Chhettri pointed out, the temperature 3 metres below ground is almost constant throughout the year. Why not make use of the temperature differential to cool or heat buildings?
If there are waterbodies near a building, use it. After all, the temperature of water at a depth will necessarily be lower. And then, the night air is cool.
Can you capture it, store it, and use it to cool the building during the day?
These ideas, of course, need to be engineered for practical application, but are slowly gaining ground.
Chhettri’s presentation mentioned several options, such as earth tube systems, direct ground cooling, geothermal cooling ponds, earth-sheltered buildings, borehole cooling, night purge ventilation, and ground source heat pumps.
Earthy solutions
An earth tube system essentially comprises pipes buried deep underground for circulating air.
These pipes are designed to pick up ambient air and circulate it through the cool underground before being used to flush out warm air from buildings. The system involves almost nil running expenditure.
Climateactionaccelerator.org explains the system thus: During the warm season, the ground is cooler than the ambient air. During the cold season, the opposite is true. This is due to the near constant temperature of the ground at a certain depth (around 2 metres).
Chhettri’s presentation highlighted two functioning systems in India to illustrate the use of earth-based solutions for cooling buildings.
The first is the air tunnel system at the Saint Methodist Hospital in Mathura.
The three-storeyed building features an 80-metre tunnel. Ambient air is let in at one end of the tunnel, the air is conditioned through earth pits and fed into the building. Chhettri said the system “has a cooling capacity of 512 kWhr and heating capacity of 269 kWhr”.
“Earth air tunnels can typically reduce air temperatures by 10-15 degress Celsius during peak summer months,” he said.
The other example is a resort in Rajasthan with earth-sheltered buildings.
The PEAK Resort and Spa in Udaipur has a system designed by Studio Symbiosis, where the villas are dug into the landscape on the slope of a hill, “drawing in southern cool winds”.
The wind movement is directed by constructing two buildings flanking the entryway, providing a wind tunnel effect.
Further, the villas are nestled within the dirt to form a heat sink, which cools them naturally during the burning desert daytime and warms them during the cold winter nights, according to information on the resort’s website. “Since each villa is surrounded by soil, heat gain and dissipation are regulated,” it says.
So, the message is clear. There are plenty of ways to cool buildings naturally, if you use your imagination. “Earth-based cooling methods are cost-effective, sustainable and suitable for India,” says Chhettri.