Air-con from the Earth

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Here Comes the Sun

It's a brave location for a university, 120 km from Delhi, across the Rajasthan border, where temperatures cross 48 Celsius in summer and drop below five degrees in winter. As I exit the Delhi-Jaipur highway, the modest NH8 gives way to an eight-lane 'expressway'. I'm in the Japanese industrial zone at Neemrana, Rajasthan, a short way away from the famous fort and palace in the Aravali mountain range, driving into the spanking new NIIT University (NU). The fort spans 25 acres; the university, a 100-acre 'green campus' at the foothills of the Aravalis. A sculpture of a Möbius strip, that symbol of elegant seamlessness, illustrates the Anaadi Anant motto--no beginning, no end. The 'seamless' campus will have  54 buildings, and accommodation for 5,000 students and 500 faculty members, costing over Rs 1,000 crore over 10 years.

NU is new: I was heading for the inauguration. What's really cool about it is the cooling (or heating, in winter): it's geothermal. A network of 'earth-air tunnels' over four meters below the surface works as a heat sink. The tunnels carry air that's pumped through them. The air gets cooled in summer, and warmed in winter, because several meters below, the temperature is far more consistent than on the surface. So when it's 45 degrees in the shade, it's under 30 degrees down there, so the air comes out cooler. The reverse happens in winter. (See NU's case study at http://bit.ly/earth-air)

Here's how NU's literature explains it, quoting a research paper from Tribhuvan University,  Kathmandu: “The thermal capacity of the earth is such that the day-night variations of surface temperature do not penetrate much deeper than 0.5 m, and seasonal variations up to a depth of about 4 meters. Beyond this depth, the earth's temperature, therefore, remains constant.”

That is a trifle oversimplified, and also assumes that four meters down, the earth is an infinite heat sink. Which is (nearly) true of the aggregate mass, but not for a localized area-which will gradually warm up a bit as you keep passing hot air from the surface through it (in summer)...and also warm up a few degrees in summer as surface temperatures stay in the forties.

A more accurate, and plausible, picture is here http://bit.ly/earth-temp. At soil depths greater than 9 to 10 meters below the surface, temperature is relatively constant at one location, though this “mean earth temperature” does vary from place to place.

Even so, the fact remains that in summer afternoons, the 'air from down there' could come up over 15 degrees cooler, and in winter mornings, perhaps 10 degrees warmer, than the surface air.

This is the air that NU is pumping through its buildings after de-humidification and dust precipitation. On that warm winter afternoon, it was certainly cooling effectively. At peak summer, it should help get the temperature down 10 or 15 degrees, the rest being handled through “booster chillers”. At a similar (but smaller) setup in TERI's 'green habitat' in Gurgaon, it reports temperatures of 20 Celsius in winter, and 28 to 30 Celsius in summer (http://bit.ly/teri-earth). NU claims its HAVC is the largest earth-air tunnel system in the world.

If this works, this will be a benchmark for large-scale cooling in campuses and buildings. It's green experiments like this-with major leaps of faith in investments-that are truly path-breaking, and help push interest in green tech from the domain of nice-to-do to makes-business-sense.

The author is chief editor at CyberMedia, publisher of 15 specialty titles including PCQuest.
You can reach him at pkr@cybermedia.co.in, twitter.com/prasanto.

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