The physics of geothermal energy is tweaked in many ways by modern air conditioning systems
Bangalore: The overgrowth of reeds at Good Earth Orchard, a colony of 60 homes in Bangalore, is actually part of a labyrinthine water-treatment system. Gallons of used water from the colony enter it every day to be pumped out for reuse a week later, good enough at least to water the bushes.
The system recovers about 80% of wastewater without using power or chemicals. A chamber skims off lightweight waste and settles the heavy parts. Another sealed chamber uses bacteria to break down organic waste. Finally, plants such as canna at the surface aerate the water through nitrogen fixation. All this happens without a single watt of power consumed, except for the irrigation pump. What you see on the surface is lush reeds speckled by red cannas, making it a rather pretty treatment plant.
Growing use of such technologies has put India on the green-building leaderboard with countries such as the US. “About 2-3% of all construction in India is green, as good as (in) the US. In the next two or three years, we want to bring it up to 10%, which will put us on top,” says S. Srinivas, principal counsellor the Indian Green Building Council (IGBC), a body that certifies green constructions.
Not all these technologies are 21st century innovations. Green construction in India uses a liberal mix of modern science and methods that are nearly 400 years old. Take wind towers, for example, a system used for decades by Arabs in West Asian deserts to keep buildings cool. The Confederation of Indian Industry’s (CII) Institute of Quality in Bangalore uses this technology to continuously supply air in the building. So do the office of the inspector general of police (IGP) in Gulbarga, and Aquamall Water Solutions building in Dehradun.
Wind towers are a series of concrete or fly ash towers. Every morning, these draw in hot air, which passes through channels splashed with water at night so cooled air is circulated through a building. The combination of increased airflow and contact with water brings down the temperature by 8-10 degrees Celsius, which in cities such as Bangalore does away with the need of air conditioning. “Warmer cities like Hyderabad can use hybrid systems,” says Srinivas.
Wind towers were often augmented in Persian architecture with geothermal systems that exploit the difference in temperature between the earth’s surface and 5-6 metres below. At this depth, across the planet, temperature is almost constant in a range of 10-15 degree Celsius. Towers connected to underground pipes would cool air even further beyond plain-vanilla wind towers.
The physics of geothermal energy is tweaked in many ways by modern air conditioning systems in Indian green buildings—another throwback to an ancient practice. Both cooling and heating can be achieved, though heating often requires a supplemental system. Geothermal systems are a major money-saver because almost 70% of the energy used by most buildings is for air conditioning.
“Geothermal systems haven’t really caught on in individual homes in India,” says Srinivas, “but corporations have started using it.” Dr Reddy’s Laboratories Ltd’s factory in Hyderabad is an example.
Conventional technologies have also kept pace. Efficiencies, or the ability of air conditioning systems to convert electricity into cooling power, are far higher today than a decade ago. “Today, we focus on part-load efficiency of an air conditioner when we certify a green building,” says Srinivas. Part-load refers to the time of the day when cooling requirements are not the highest. This is the case for most part of the day, and therefore, air conditioning efficiency during this time is more crucial than during peak-load hours.
Chandrashekar Hariharan, founder of Biodiversity Conservation India (Pvt.) Ltd (BCIL), takes another angle. BCIL uses ammonia-based air conditioning systems that are a lot less-polluting than the ozone-depleting chlorofluorocarbons used in regular air conditioners.
BCIL is an extreme example of using multiple micro-technologies to achieve tiny improvements that add up. Its complexes typically have banana and areca nut groves because of their high rate of water-vapour expiration.
The company also restricts the numbers of buildings on an acre of land depending on its water holding capacity. If the industry norm is about 90 houses per acre, BCIL would keep it at 46-48 because that is how much the rainfall on the land can sustain. “A patch of land is like your bank account,” says Hariharan. “Just like you cannot draw money without putting in, you cannot draw water without recharging it.”
BCIL only uses shallow wells instead of deep-water borewells. These are continuously recharged by rainwater.
Materials and designs at BCIL are also optimized to improve air quality. “Bangalore lies at about 13 degree north on the grid, the same latitude that passes through Mexico. Any building here would face the maximum heat on its south and west during the day. So we add more protection on these walls—non heat-transmitting materials and hollow bricks,” says Hariharan.
The use of fine controls and technologies cannot be emphasised enough. “This is why building management systems (BMS) have become so important,” says Srinivas. “They allow you to operate many energy-consuming devices in large buildings from a single switchboard. A chiller would be remotely shut down if not needed, and power would be switched off in rooms not used, for example.” An IGBC study shows energy savings from BMS can be up to 13%.
Over the years, with more green construction happening in India, an industry catering to this has sprung up. High performance glass, which can arrest almost 30% of heat in windows, is manufactured by Saint-Gobain and Asahi (India Glass Ltd), while waterless urinals, which use concepts of specific gravity, are manufactured by Parryware, Hindware, etc.
As demand grows, these technologies get cheaper. Waterless urinals now cost only Rs6,000 a piece compared with Rs15,000-16,000 some years ago. “It’s a virtuous cycle,” says an optimistic Srinivas. “As the tech gets cheaper, adoption rises.”
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