A green facade | Centre for Science and Environment


Sunita Narain

Director General of CSE and publisher of Down To Earth, an environmentalist pushing for changes in policies and  practices and mindsets. More>>

A green facade

Building green is definitely important. But equally important is to know how green is a green building. Take the glitzy, glass-enveloped buildings popping up across the country. It does not matter if you are in the mild but wet and windy climate of Bengaluru or in the extreme hot and dry climate of Gurgaon, glass is the in-thing. I have always wondered how buildings extensively using glass could work in such varied climatic zones, where one needs ventilation. Then, I started reading that glass was green. Buildings liberally using glass were being certified green. How come?

Here the story becomes interesting. The Energy Conservation Building Code (ECBC) has specified prescriptive parameters for constructing an energy-efficient building envelope—the exterior façade of a building. The façade, based on the insulation abilities of the material used for roof and wall construction, will reduce heat loss. It will also reduce energy use if it allows daylight in. It is, therefore, important for any green building to have the right material for its exterior.

But this is not all that ECBC specifies. It goes on to set a wallwindow ratio and fixes the area of the building envelope that can be covered with glass at 60 per cent. This implies that a building can be green and energy-efficient if it is covered by glass. The code then goes on to define the insulation and energy-efficiency specifications of glass that should be used. In this way, double-glazed or triple-glazed glass, which is solar reflective, is preferred as it provides superior thermal erformance. In other words, glass built on certain superior and high specifications can reduce the heat gain of a building. ECBC, thus, endorses the extensive use of glass and promotes high-performance and expensive glass, which is manufactured by a few high-end companies.

Small wonder glass manufacturers are making hay in this sunshine. Saint-Gobain Glass incidentally (or not) is also the founding member of the Indian Green Building Council, promoted by industry association CII. The green code is built for their business to thrive.

This would still have been acceptable had this prescription worked. But first, builders cut corners in the use of expensive reflective material. Glass traps heat, therefore, buildings require more air-conditioning. Energy requirement goes up. Secondly, even when double- or triple-glazed glass is used there is evidence that in India’s extremely hot climate it does not work so well. A recent study by IIT-Delhi in Jodhpur, Delhi and Chennai found that energy use increased with increase in glazed area, irrespective of the glass type used in the building. The conclusion was that the glass curtain wall made of expensive reflective glass did nothing to cut energy costs as compared to ordinary glass.

We also forget that natural light in India is a glare, unlike in parts of the western world where glass is used to reduce energy use for lighting. So, even if theoretically the use of glass optimises daylight use, it remains a function of how much is used, where and how. For instance, the use of glass—of whatever glazing—in the south and west facades of a building will be bad in terms of thermal transfer. Then, even if you use glazed or tinted glass, where 50 per cent of solar heat gets reflected off the surface, 65 per cent of the visible light is transmitted into the building.

Heat transfer may be reduced but the harsh light filters through. Buildings then need blinds to cut glare, again adding to the use of artificial light and consequently raising energy cost.

What would work better is building protection against direct glare. Go back to the old fashioned methods of providing shades on windows. And do not build tight and sealed buildings, which do not optimise use of natural ventilation and breeze to reduce air-conditioning needs in certain periods of the year. In fact, glass necessitates air-conditioning, and buildings become energy guzzlers. The irony is that these buildings still qualify for a green tag when the air-conditioning system used in glass-cased constructions is more efficient. Build badly and then sugarcoat it, is the principle. Clearly, we need more appropriate and inventive  architecture.

What is worse, these codes are being pushed through government and municipal schemes without any evidence that green-certified buildings are actually working. Noida awards a 5 per cent extra floor area for green-certified buildings; MoEF provides fast-track clearance to such buildings. But the two main certificates—LEED and GRIHA, by IGBC and TERI respectively—do not disclose data on the performance of the green buildings after they have been commissioned. So, even though rating agencies say that green-certified buildings save between 30 per cent and 50 per cent of the energy and reduce water consumption by 20-30 per cent, they do not have corroborating data to verify the claim.

In this way we make sure that green is not so green. But it is definitely good for business, if not for the planet.

 

Recent Posts

Sunita Narain's picture
Down To Earth
30 September 2014
The myth of green building
Sunita Narain's picture
Down To Earth
16 September 2014
India's double challenge
Sunita Narain's picture
Down To Earth
1 September 2014
Green clearance test for NDA
Sunita Narain's picture
Down To Earth
16 August 2014
Chicken comes home to roost

Recent Comments

Comments

Follow us on 
 
 
 
 
 
 
 
 
 
 

 
 
 
 
 
 
gobar times