A green building is not glass

Since glass traps heat, buildings require more air conditioning. As a result, energy use goes up

Building green is definitely important. But it is equally important to know how green a green building is. 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 Bangalore 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 facade of a building. The facade, 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 the ECBC specifies. It goes on to set a wall-window ratio, and it 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 with glass. The ECBC then goes on to define the insulation and energy efficiency specifications of glass. Double-glazed or triple-glazed glass, which is solar reflective, is preferred since it provides superior thermal performance. In other words, it says glass is good, but it must be of high specifications to reduce the heat gain of a building. The ECBC, thus, endorses the extensive use of glass and promotes high-performance and expensive glass, which is manufactured by a few high-end firms.

Small wonder, then, that glass manufacturers are making hay while the sun shines. Incidentally (or not), Saint-Gobain Glass is a founding member of the Indian Green Building Council (IGBC), promoted by the Confederation of Indian Industry (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. Since glass traps heat, buildings require more air conditioning. Thus, energy requirement goes up. Second, 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 the Indian Institute of Technology, Delhi, in Jodhpur, Delhi and Chennai found that energy use increased with the increase in the glazed area, irrespective of the glass type used. The conclusion was that the glass curtain wall made of expensive reflective glass did nothing to cut energy costs 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, 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. Moreover, even if you use glazed or tinted glass, where 50 per cent of solar heat is 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 in. Buildings, then, need blinds to cut glare, which adds to the use of artificial light and increases energy costs.

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 the use of natural ventilation and breeze to reduce air-conditioning needs during certain periods of the year. In fact, glass necessitates air conditioning, as a result of which buildings become energy guzzlers. Ironically, these buildings still qualify for green tags when the air-conditioning system used in glass-cased constructions is more efficient. So, the principle is: build badly and then sugar-coat it. Clearly, we need more appropriate and inventive architecture.

What's worse, these codes are being pushed through government and municipal schemes without any evidence that green-certified buildings are actually working. Noida awards a five per cent extra floor area for green-certified buildings; the environment ministry gives fast-track clearance to such buildings. But the two main certificates - LEED and GRIHA, run by the IGBC and Teri, respectively - do not disclose data on the performance of the green buildings after they have been commissioned. So, even though ratings agencies say green-certified buildings save between 30 per cent and 50 per cent of energy and reduce water consumption by 20 to 30 per cent, they lack 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.

sunita@cseindia.org