Defining zero energy buildings - A life cycle perspective

A simple definition of a zero energy building (ZEB) is a stand-alone building which does not use any offsite energy source for its operation. The definition is easily extended to buildings with a net-zero annual on-site energy balance, where a building is connected to the electricity grid and annual energy use is the same as energy exported to the grid. In this paper we expand the ZEB definition adding a life cycle perspective including the embodied energy (cradle to site) of materials, which is considered as an additional off-site supply. The consideration of embodied energy adds a level that will help discern the life cycle benefits of different demand or supply side building design strategies to achieve ZEBs. Calculations of operational energy use and embodied energy for different house design options are presented, analyzing what options would move closer to this ZEB definition. Results show how the achievement of extreme reductions on energy demand by using high quantities of energy intensive materials are not an optimum solution over the life cycle of a building, active technologies becoming a better option after certain limits.