The term ‘operational carbon dioxide (CO2)’ refers to carbon
dioxide emitted during the life of a structure or piece of
infrastructure, i.e. the CO2 associated with the use of the
building or structure.
In the case of a building it is closely related to energy use
such as heating and cooling and is often expressed as kg
CO2/m2.
For bridges it may be expressed as the total emissions of CO2 in
tonnes associated with all resurfacing, waterproofing, painting,
replacements and, where relevant, the effect of traffic disruption
during maintenance can also be included.
The term ‘embodied carbon dioxide (ECO2)’ refers to carbon
dioxide emitted at all stages of a product’s manufacturing process,
from the mining of raw materials through the distribution
process to the final product provided to the consumer. That is, it
can be calculated from its manufacture to the moment it leaves the
factory gate (cradle-to-gate); from manufacture through its
delivery to site (cradle-to-site); or from manufacture to its
eventual disposal (cradle-to-grave).
The embodied CO2 of concrete is often thought to be much higher
than other construction materials, when, in reality, the difference
is typically quite small, and becomes insignificant when compared
to, for example, a building's operational CO2 emissions.
Over the life of a building, the operational CO2 emissions have
far more environmental impact than the embodied CO2 of the
materials used to build it. Some 50 per cent of the UK's
carbon emissions are due to the energy used to heat, cool and light
buildings. It is essential, therefore, that energy consumption
during a building's lifecycle is taken into account when evaluating
construction materials. A building's environmental impact does not
stop once it has been built.
Commercial properties
Where the inherent thermal mass of concrete forms part of the
cooling strategy of a building, any additional embodied CO2 can be
offset many times over throughout the life of the building.
For more details on designing commercial properties using
thermal mass refer to The Concrete Centre publication
Utilisation of Thermal Mass in Non-residential Buildings.
Housing
Analysis of lifecycle CO2 emissions for a typical two-bedroom
semi-detached house, was carried out in an independent study by
Arup Research & Development in 2006.
The research compared lightweight timber homes with mediumweight
and heavyweight masonry and concrete homes and found the latter to
have the lowest total energy consumption and CO2 emissions over
their life, when embodied and operational emissions were
considered.
The savings were achieved through the use of the thermal mass of
the heavyweight structure for heating and cooling. These reductions
in the operational CO2 offset the slightly higher level of embodied
CO2 in a masonry house in as little as 11 years.
For further details refer to the full article in CQ Autumn 2006.