Defining net zero energy buildings

Worldwide increasing attention to energy consumption and associated environmental impacts thereof has resulted in a critical attitude towards energy usage of buildings. Increasing costs of energy and dependence on energy service providers add to this as well.

The built environment in general, and buildings in particular, are responsible for a considerable portion of energy consumed and would therefore be a prime attention area for energy efficiency interventions. The building sector can significantly reduce energy use by incorporating energy efficient strategies into the design, construction, and operation of new buildings and undertaking retrofits to improve the efficiency of existing buildings. It can further reduce dependence on fossil fuel derived energy by increasing use of on-site and off-site renewable energy sources.

Net Zero Buildings

The concept of a Net Zero Buildings is getting more and more attention and is currently being implemented in some form or the other in South Africa and other countries worldwide. Currently a limited number of building could qualify as Net Zero Buildings, but developments in energy saving and renewable energy technologies, building materials and construction techniques are advancing rapidly, enabling Net Zero to become a mainstream requirement for new developments.

As with any evolving field of attention, several definitions exist for Net Zero Buildings. However, it is commonly understood that a Net Zero Building combines a design to minimise energy requirements with the generation of energy by means of renewable energy technologies.

The NREL publication “Zero Energy Buildings: A Critical Look at the Definition” explores definitions in detail, and it suggests four ways in which net zero energy may be defined:

  • Net Zero Site Energy: A site Zero Energy Building produces at least as much energy as it uses in a year, when accounted for at the site.
  • Net Zero Source Energy: A source Zero Energy Building produces at least as much energy as it uses in year, when accounted for at the source. Source energy refers to the primary energy used to generate and deliver the energy to the site. To calculate a building’s total source energy, imported and exported energy is multiplied by the appropriate site-to-source conversion multipliers.
  • Net Zero Energy Costs: In a cost Zero Energy Building, the amount of money the utility pays the building owner for the energy the building exports to the grid is at least equal to the amount the owner pays the utility for the energy services and energy used over the year.
  • Net Zero Energy Emissions: A net-zero emissions building produces at least as much emissions free renewable energy as it uses from emissions-producing energy sources.

In general, when using the terminology “Net Zero Energy Building”, we are referring to a building for which the annual amount of energy used in its operations is equal to the amount of energy generated by the building. If the amount of energy produced by the building is exceeding the amount of energy used, we are talking about Net Energy Plus Buildings.

Source: Green Building Handbook Volume 5

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