Zero Carbon v Carbon Neutral …. Definitions

Green Energy 3

There are three important points to note regarding the concepts of zero-carbon and carbon neutral developments.

The first point is that, there is a subtle, but important, difference between what zero-carbon and carbon neutral actually mean:

Zero-Carbon implies that the operation of a development does not produce Co2 emissions . Carbon-Neutral implies operation of the building produces CO2 emissions and that these emissions from the operation of the building should be taken into account.

Emissions produced from the operation of a carbon neutral building are offset.  It is the intent of the carbon neutral concept, that the building produce less C02 than a conventional building, rather than simply producing -and then offsetting -the same amount of carbon. This is practical – as it is likely to be easier and more cost effective to offset the minimum amount of C02 -and fulfill environmental and sustainability goals. Offsetting can be achieved by, for example, contribution of renewable energy produced on-site to the main power grid, by carbon sequestration on or off-site,  or by investment in renewable energy projects off-site.

The second point is alluded to in the previous: for both sorts of developments, carbon is calculated as the sum of the emissions produced by the operation of the building e.g. the energy required for space heating/cooling, water heating & lighting, but in the case of the a carbon neutral building the emission from  appliances use eg computers, fridges etc, are also taken into account. Recent clarifications in the UK is that Zero carbon is the minimum regulatory carbon required by the the building for function and includes space heating, water heating and lighting.  Appliances are not included in  this calculation. Zero Carbon is equivalent to Code for Sustainable Homes Level 5. Carbon Neutral is equivalent to Code for Sustainable Homes level 6. At the level 6 the emissions from house hold appliances are taken into account. It is  more expensive to achieve a Carbon Neutral building than a Zero Carbon building..

The materials and energy used in the construction or end-of-life phases of the building are not included in the assessments. The embodied energy in the building is therefore also excluded from the assessments. Further, the emissions necessary to travel to and from these developments are not generally included in the assessments.

The third point is that the most attention and effort to date has been placed on new residential developments. That is not to say that industrial or public buildings, or retrofitted buildings of any kind, cannot achieve zero-carbon  or carbon neutral status, but simply to note that the current focus of policy-makers and the public is on new residential housing stock .

Clarifications:

Low-Carbon Technologies …. -Air heat pump      -Ground heat pump,   -Combined Heat and Power (CHP),  – Biomass or waste boiler or stove

Zero-Carbon Technologies…..     – Solar thermal,   Solar PV   – Micro-wind,  Micro-hydro

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