Zero Carbon
Definition of Zero Carbon
A zero carbon development is one that achieves zero net carbon emissions from energy use on site, on an annual basis.
This is the accepted definition, although it could also be argued that the carbon equation should also factor in all the carbon emissions arising from the manufacture of the renewable energy equipment and possibly even the carbon footprint of the house itself. There is certainly a tendency for ‘zero energy’ houses to be high tech, state-of-the art, developments which undoubtedly leave a massive carbon footprint in their wake.
Usually, the definition allows for fossil fuels or other imported carbon based energy to be used on site, providing this is offset by an equivalent export of energy generated on site from renewable sources. For example, a tonne of imported coal may be offset by exporting the equivalent electrical energy generated on site from micro wind or solar PV or biomass. In practise, this is extremely hard to achieve.
The above definition of ‘zero carbon’ also does not cover waste or other environmental impacts of the building, the lifestyle of the occupants, or transport to and from the dwelling to access places of work, school, shops and essential services. Thus it is possible for a ‘zero carbon ’ household to still have an unacceptably high ecological footprint if the occupants of the building have to engage in a one or two hour commute to their place of work or indulge in the purchase of high embodied energy consumer goods.
Zero-Energy
The expressions 'zero carbon' and 'zero-energy' are used interchangeably by many people.
Low Carbon
There is no internationally accepted definition of what is meant by ‘low carbon’.
In Germany, a ‘low energy’ house is defined as one which requires less than 42kWh of heat energy per m² of floor area per annum (a house compliant with the 2002 Building Regulations in Ireland would be in the 55-70 kWh/m²/yr range).
An ultra-low energy or PassivHaus is defined as one which requires less than 15kWh of heat energy per m² of floor area per annum. These figures refer only to the energy required for space heating and do not cover energy required for domestic hot water supply.
For more information, see:
Low Environmental Impact Housing
