Metrics and boundaries are integral elements of the NZEB definition framework. Balance boundaries and metrics decide NZEB definitions. The four main metrics, corresponding to the four definitions are site energy, source energy, carbon emissions and energy cost.
NZEB metrics can measure energy in its primary and secondary form, environmental implications of energy use through emissions and cost of energy.
Primary energy is raw or source fuel for producing heat and electricity. It could also be termed as energy embodied or captured in fuels. Secondary energy is the energy product derived from primary energy, like grid supplied electricity.
Each metric has its benefits and drawbacks. Source energy and carbon emissions metrics are complex because they require complex conversion factors as energy use of the building is weighed against its impact at the source of generation and delivery distance. Conversely, they enable compensation of effect of building energy use on national or regional energy resources and environment.
Site energy and energy cost are simpler to evaluate but both cannot be used for energy accounting beyond the site.