Central Shanghai, 2010.

A recent article in the China Daily relates a disturbing new phenomenon in several Chinese cities directly related to the rapid pace of growth. Due to deficiencies in the manufacturing, installation, or maintenance of glass curtain wall systems, some glass has been reported to shatter and fall, sometimes from great heights. These 'glass bombs' have injured and killed several people, and in the case of Shanghai, they have led to an outright banning of the extensive use of glass curtain wall systems in the city. Ones first reaction may be to wonder whether that's going too far given the ubiquity of glass as a modern building material. In fact how would this affect the look of the city?

While the Newtonian embodied energy of glass may be on display in the spontaneous shattering of windows, the energy embodied in glass by the process of manufacturing may be a more compelling—if hidden—reason to limit it's use. While not the highest embodied energy material (this distinction goes to steel and aluminum, which are also required elements in a curtain wall), the manufacturing of glass requires roughly 10 times as much energy as one of the most common construction materials in China: concrete. The figure comes out to about 12-25 giga-joules of energy for 1 metric ton of glass. (1 joule = 2.7778×10-7 kilowatt-hours)

To make more sense of that figure I'll take an iconic new building on Shanghai's skyline as an example, the Shanghai World Financial Center by Kohn Pederson Fox, aka the Bottle Opener:

The building sports roughly 1.3 million square feet of insulating glass over its 101 story height. Some quick back-of-envelope calculations (this goes for most of the calcs here) puts the weight of that glass at around 3,925.5 metric tons. The above number for energy-required provides a range of which we will assume the higher end (energy efficiency in manufacturing is still relatively lower in China than the US). This facade would require roughly 98,000 giga-joules of energy to manufacture. To put that in approximate material terms, it would require either 3,500 metric tonnes of coal, 90.4 million cubic feet of natural gas, or 15,700 barrels of oil! This doesn't even address energy efficiency through heat loss and gain over the life of the building.

The above breakdown hints at China's mix of fossil fuels used in electric energy generation: 69% coal, 5% natural gas, 1% oil. With the effects of dwindling natural gas reserves, the caustic environmental effects of coal-fired generation, and peak oil production on the horizon, one may wonder whether a ban on excessive glass use is really a bad thing. In that case, Shanghai may become an urban laboratory for post-fossil fuel architecture.

The glass curtain wall really came to the pinnacle of its use in the 1970's through 90's (ironically weathering the oil shocks early in that period), and in many ways is synonymous with postmodernism. The use of mirrored glass particularly has been thoroughly explored by Reinhold Martin in Utopia's Ghost, where it suggests the triumph of Late Capitalism and globalization in the play of reflection and re-reflection in its surfaces—a kind of 'end of history' feedback loop that conceals the city (the outside) as much as it conceals the influence of capital (the inside). However, it is anyone's guess where the end of cheap abundant energy will leave the global networks of capital and culture. It would seem apropos that the threat of an end to such an arrangement, by challenging our taken-for-granted approach to energy, would submit the glass curtain wall to exposure.

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