Life cycle energy use of a zero-energy house

Taking the building sector’s huge impact on the environment into consideration, the European Union aims at ‘nearly zero-energy’ houses by 2021 through strict requirements for the (non-renewable) operational energy use. Although it is not included in current calculation methods, the life cycle energy use of buildings is an aspect of growing interest, encompassing both the operational energy use throughout the building service life and the life cycle embodied energy and end-of-life energy in building materials. This contribution examines the life cycle energy use of a zero-energy case study house by means of a life cycle energy assessment and contains a parameter analysis of its different components, such as the building construction and building services. The results show that, during its entire lifecycle, a zero-energy house uses 2 to 4 times less non-renewable energy than a passive house with identical floor plan and 3 to 5 times less than a house built according to standard building practice in Belgium. Secondly, the embodied energy in a zero-energy house with a passive building envelope proves to be equal to that in a zero-energy house with a standard building envelope. Thus, passive house requirements are not considered an essential criterion for zero-energy houses from life cycle energy point of view. On the other hand, the study reveals that the choice of building construction materials and building services are determining factors for the life cycle energy use, resulting in energy savings up to 35 kWh/year/m² for zero-energy houses.