In recent years the main emphasis in reducing the carbon impact of buildings has been in reducing the energy used during occupation. This has been tackled in a number of different ways - improving the insulation in buildings to reduce heat loss or the need for cooling in hot weather, installing plant and equipment that uses energy more efficiently, rethinking the design of HVAC systems to use passive measures instead of mechanical systems.
Operational energy use for office buildings on a university campus have been benchmarked by Imperial College at 110-350 kWh/m2 Treated Floor Area/year . This covers heating, cooling, lighting, small power and ancillary building systems. Approximate figures for embedded energy in office buildings has been estimated at 1100-3300kWh/m2 (based on figures of 4-12 GJ/m2 quoted at an industry conference in 2004).
Hence to a first approximation, embedded energy is equivalent to 10 years of operating energy. As pressure continues to reduce operating energy then this multiple is likely to increase, and it will become more important to understand and then to reduce the embedded energy and CO2 emissions associated with manufacture and installation.
The difficulty with calculating specific figures for embedded energy and CO2 emissions is sourcing appropriate data. Ideally each component manufacturer would be able to quote the embedded energy and the CO2 emissions associated with each of their products. Contractors could be then combine these figures with other those for building materials and the construction processes to give an overall figure for embedded energy or CO2 emissions. In the benchmarking exercise in I3CON Work Package 4, we have used an elemental approach to calculate the carbon emissions in two different external cladding products. We have specifically not considered the or CO2 emissions associated with transportation or installation since these are so site specific.
The methodology we applied is as follows: