“A net-zero emissions building produces at least as much emissions-free renewable energy as it uses from emissions-producing energy sources”
Emissions of net zero energy emissions building are counted for the source energy and not site energy. To determine emissions output from a building, energy used in the building is multiplied by an emissions factor which weighs emissions resulting from transportation and at-source generation.
Carbon, sulphur oxides and nitrogen oxides are included in calculating emissions neutrality. Fuel used for generating electricity supplied by the grid determines the ease of achieving net zero emissions. Emissions from electricity supplied by a nuclear plant is different than that of hydro plant, which varies from a coal fired plant.
Net zero emissions building can be zero emissions on site or off site – they can produce the equivalent renewable energy on site or purchase it. On site emissions ZEB can produce renewable energy on its footprint or the site to gain emissions neutrality. If renewable fuels are bought to the site for production, emissions from transportation and fuel production must be factored in emission neutrality calculations.
Renewable energy credits can be purchased from an off-site source to offset energy use. Alternatively, a building is emissions ZEB if it uses grid supplied electricity from renewable sources like wind farms, hydro plants, and solar plants. However, this alternative is not practically possible as of now because of the limited generation capacity of wind farms and hydro plants. Most of electricity supplied to the national grid is generated by conventional coal fired plants. Additionally, electricity from various sources is mixed in the grid prior to supply. Determining emissions accurately is complex as this ratio of renewable versus non-renewable electricity in the grid (termed fuel mix) varies, and is seldom calculated by utilities. Information about generation mix in different regions is essential before attempting net zero emission buildings with any degree of accuracy.
Emissions ZEB is the most holistic model of evaluating and reducing impact of energy used by buildings. It factors pollution and emissions across different fuels, as across different regions.