4 December 2012 — When India’s Northern Grid tripped on 30 and 31 July this year, the only detective work being carried out at the Central Bureau of Investigation headquarters in Delhi was how to keep cool.

The building, basically a glass envelope, quickly started to warm up and despite all that glass, not one window was designed to be opened.

One official, who did not want to be named, described it as “a nightmare”, reporter Disha Singh writes in her report, Reflections on glass, in this month’s Down to Earth website.

However Ms Singh found that despite many similar experiences, the use of glass in construction was gaining popularity in India.

“Industry is hard selling the material on the ground that glass contributes to aesthetics, energy efficiency, safety, security and comfort,” she says.

“Even Saint-Gobain Glass, the world leader in glass manufacturing, has a website glassisgreen.com. The company’s India unit is the founding member of the Indian Green Building Council.

“The website of another glass maker, AIS Glass, also highlights the green calibre of glass.”

Ms Singh said while glass gave a sense of open space and reduced the need for artificial light it also trapped heat and caused glare.

“To cut down heat and glare transmission, the glass industry has devised several technologies,” she writes.

“A typical version is double glazing with air gap in between for insulation. It is used in most high-rise buildings. An advanced version, triple glazing, is trying to find a foothold in India.

“A study by IIT-Delhi in the national capital city, Jodhpur and Chennai found that energy use increases with the increase in glazed area, irrespective of glass type, climate or orientation of the building.

For instance, glazing on the northern wall of a building allows the least gain in heat as compared to any other facade orientation. But if the glass wall covers more than 20 per cent of the south-facing facade, the building overheats even in winter.

Ms Singh writes that glass is not an environment-friendly material consuming a high amount of energy right from its manufacturing to transportation and installation.

“The embodied energy of glass is between 15.9 and 26.2 mega joules per kilogram; it is 1.06 MJ/kg for bricks.

“The embodied energy of glass increases considerably when used as double or triple glazing or when inert gases like argon replace the air gap to further improve performance.

“Glass also poses safety concerns. In 2011, Mumbai’s chief fire officer Uday Tatkare told a leading newspaper that buildings with glass facades are major fire hazards and hindrance in fire fighting.”

Finally Ms Singh says glass is also expensive when compared with other building material with a square metre costing between 1200 and 7000 rupees depending on the technology. A good quality brick wall costs less than 1000 rupees per square metre.

“Yet the obsession with glass is growing… instead of innovating designs to suit local conditions, identical glass buildings are being built.”

Meanwhile, a UK study of “The energy performance of two buildings with lightweight and heavyweight facades”, published in Adam Architecture, has found the latter offers reduced operating costs, 15-20 per cent with double-glazing, less risk of overheating and lower embodied energy in the materials used.

“The analysis shows that for the real benefits of such glazed façades (lightweight buildings) to be realistically achieved the building would need to be fitted with automated external blinds and automatic dimming lighting, both at extra expense,” the report says.

The report says the debate has continued to range between proponents of “modern” highly glazed building types and those of more “traditional” building types where areas of solid and glass are more evenly proportioned.

“It is often claimed that the so-called “passive solar” benefits of heat gains (through large areas of glass, with higher heat gains and better daylighting) more than offset the heat losses through the glass in the cooler months.

“The doubters would say that while this may be the case on certain days in spring and autumn, for most of the year the glass-dominated building is likely to require more heating in the winter and, potentially, more cooling in the summer.”

In the study the “heavyweight” building had punched windows to all four façades and a total glazed proportion of less than 40 per cent of the façade area.

The lightweight building had solid walls with punched windows to the east and west and glass façades to south and north.

Dynamic thermal simulation software was used to carry out the comparisons.

“The outcome of the analysis is, of course, sensitive to many different variables, not least of which are the weather, the orientation of the building and the use to which the building is put.

“For the purposes of the study, two building uses have been assessed with the same two building envelopes; a residential use and an office use. The office use has higher internal gains during the working day from equipment and people but is unoccupied for the rest of the time.

“The detailed assessments show, that in most analysed areas, Building Type A (the heavyweight building) has better energy performance and uses less energy than Building Type B (the lightweight building).

“Glass technology has improved very significantly in recent years, particularly with the introduction of selective coatings, but even the best glass still has a heat loss 10 times that of a highly insulated masonry wall and can still result in overheating, with no possibility of thermal mass.

“As we move towards zero-carbon buildings, type ‘A’ is more capable of further improvement; for example, use of new materials such as lime and hemp-based products.

“In the event of further global warming, type ‘A’ would provide greater thermal stability and would be less susceptible to additional solar gain.”