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Embodied energy matters

Posted 17/08/2010 by RoseS

The news this week that China has overtaken Japan to become the world’s second largest economy has big implications. Over the next 15 years, the Chinese government expects an additional 350m people will be living in towns and cities in the country. And since a typical Chinese urban resident consumes three times as much energy as a rural person, the net result is likely to be a huge boost in energy consumption – a major driver behind China’s push for its cities to develop low-carbon action plans.

However, most of these action plans have so far looked at only how to reduce the growth of current energy consumption, according to a recent article by the US non-profit organisation the Post Carbon Institute (www.postcarbon.org/article/130761). This calculation ignores the ‘embedded energy’ used, for example, in creating a city’s streets, pavements, buildings and utilities etc and in manufacturing, transporting and selling the variety of goods and services that urban consumers buy, says the article author David Fridley.

Fridley reports a study on the Chinese city of Suzhou, with a population of 6m people located west of Shanghai, which reveals that the city’s total energy footprint was 111bn MJ/year – equivalent in energy to ca 18m bbl of oil. The study found that nearly three quarters of this energy is embedded in the consumption of goods and services and in the city’s infrastructure, while only 26% is operational energy used for transportation, lighting, heating and cooling or to run equipment.

Personal consumption of goods and services – particularly food – by individuals accounted for the largest energy footprint of the city at 59%. The study estimated the embodied energy in the food supply at nearly 41 MJ, or about 18 MJ/person/day; assuming each person consumes about 9 MJ of food energy/day this suggests that 2 MJ of energy is required to supply 1 MJ of food energy to each urban resident.

In the US, Fridley notes that the equivalent figure for energy input is about 10 MJ – a stark warning of the potential consequences of developing long distance or international food supply chains.

Increasing the lifetime of buildings from the current 30 years in China to the US average of about 75 years, or a UK average of over 100 years, could on the other hand significantly reduce the embodied energy of China’s buildings, the study indicates. It notes that ‘green’ buildings with low or net zero operational energy may not be green at all if the embodied energy of all the materials used in its construction are accounted for. And while buying energy efficient lighting or more fuel-efficient cars is significant, it points out that their contribution is relatively small.

Cath O’Driscoll - Deputy Editor

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