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Good ventilation, he says, plays a crucial role in cooling a space. In a New Alipore bungalow, Bhattacharjee built windows on two opposite walls. While one of the walls has end-to-end windows, the other has smaller ones. When the windows on both sides are open, air flows freely, immediately cooling the space.
“Kolkata has a hot and humid climate. Consequently, fast air movement within rooms is essential. The prevailing breeze is from the south and south west – so I have located the bedrooms along the southern side. Large windows help draw the breeze into the rooms. There is also a patio fringing the bedrooms. Hot air escapes into the patio through the large windows, regains its speed and is cooled.”
Architects like Baroda-based Karan Grover use brick walls or jaalis as an effective way to cool a building. But in the CII Sohrabji Godrej Green Business Centre, Hyderabad, for which he won the Version 2 Platinum award for 2003 (given by the USGBC, the body that recognises structures that combine new technologies and materials with energy-efficient architecture), Grover also constructed wind towers and screen walls to reduce the ambient temperature by cooling the air as it passes into the circular structure.
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Cooled by up to 8 degrees Celsius, the air is supplied to air-handling units, substantially reducing the load on the air-conditioning. The indoor air is regulated to maintain the temperature-humidity ratio that is most comfortable. The building has only north and south openings, since these directions are the best for natural light and air.
In several of his projects, the architect has adapted traditional elements like the jaali, the courtyard and passageways that help in cooling the building, to modern structures. Grover prefers working with materials like mud, stone and brick, since “complete RCC buildings are so hot.” At the Uttarayan Art Centre in Jaspur, near Baroda, he has extensively used a mix of concrete and red brick throughout the building. The building façade has minutely-carved jaalis or little openings through which air passes, expands and ultimately cools.
Many Indian architects still resort to passive cooling methods. As Soumitro Ghosh, partner in Bangalore-based design firm Mathew & Ghosh says, “We look at designing a building’s surroundings to minimise summer sunlight striking external surfaces and to prevent heat re-radiation and reflection. Mitigation of undesirable summer sun and thermal impacts is achieved through the use of vegetation like deciduous trees, which interrupt the sun’s direct path, prevent reflection and keep the earth’s surface cooler.”
The use of wind towers, says Bhattacharjee, is the modern way of dealing with a harsh and hot climate. According to the International Journal of Sustainable Design, Jyotirmay Mathur (a mechanical engineer with the Malaviya National Institute of Technology, Jaipur) and Rajeev Kathpalia (an architect and urban planner who runs Vastu Shilpa Consultants in Ahmedabad) have developed a ‘solar chimney-wind tower concept’.
The duo claim that though this technique has been in use to keep the interior of buildings cool in summers, they have incorporated scientific and modern methods to add value to the older system. “The system combines a solar chimney and a wind tower. A stone-covered wind tower is used to push cool air inside the building, which pushes the hot air outside through the thermal conducting panels of the chimney,” says Kathpalia. This system is integrated into the building through roof-mounted thermo-siphon air panels.
In a Delhi residential building designed by them, they incorporated a multi-storey wind tower clad with heavy stone panels. The tower produces an upward draft of air drawn into the building passively, which is then cooled by the massive tonnage of stone classing.
The air flows through the rooms and corridors, accumulating heat as it does. The top of the building is vented with big black, thermally-conducting panels that help the hot air escape. According to Chicago-based architect Russell Gilchrist, who was in India for a lecture series, low-energy or green buildings the world over are using cooling towers or wind towers to reduce dependency on mechanical systems.
Gilchrist is part of a core team that designed Pearl River Tower in Guangzhou, a fast-growing Chinese city located about 100 miles from Hong Kong. “It has wind turbines built into two mechanical floors. There are two turbines per floor,” says Gilchrist, “and they reduce the wind pressure on a tall building, allowing for lesser use of concrete in the structure. The less concrete we use, the cooler the building is.”
The designers began by reducing the building’s energy consumption through a combination of site orientation, a high-performance building envelope and allowing more daylight to filter into the building. “By having an orientation towards the east, the tower takes advantage of midday sun while the effects of late-day sun on the larger, southern horizontal exposure are minimised.
The south facade’s low-E-glass, double-layer curtain-wall system reduces heat gain, which leads to less demand on the HVAC systems. Also, a glazed building allows more daylight to filter into the space,” says the architect.
There are other environment-friendly measures incorporated within the design. For instance, water and not forced air is used for cooling. A radiant cooling system allows for the building’s HVAC system to be 1/5th the normal size and also improves indoor air quality since the air is not recycled within the building.
Most modern cooling technologies like wind or cooling towers, says Gilchrist, are derived from the vernacular architecture of countries like China, India and the Middle East. “New technology and materials like heat-resistant bricks, heat-reflective glass and roofing may be an addition,” he says.
“But even today, many architects prefer deriving influence from traditional architecture, which used low-cost materials like brick, stone and amazing architectural concepts like verandahs and ventilation, to deal with harsh summers.”
In cities like Mumbai, Chicago or Beijing, however, constructing buildings with large ventilations or introducing courtyards, is impractical. That’s where modern-day technology like wind towers or new-age materials like heat-reflective glass come in use.
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