Life cycle primary energy use and carbon footprint of wood-frame conventional and passive houses with biomass-based energy supply

In this study the primary energy use and carbon footprint over the life cycle of a wood-frame apartment building designed either conventionally or to the passive house standard are analyzed. Scenarios where the building is heated with electric resistance heaters, bedrock heat pump or cogeneration-based district heat, all with biomass-based energy supply, are compared. The analysis covers all life cycle phases of the buildings, including extraction of raw materials, processing of raw materials into building materials, fabrication and assembly of materials into a ready building, operation and use of the buildings, and the demolition of the buildings and the post-use management of the building materials. The primary energy analysis encompasses the entire energy chains from the extraction of natural resources to the delivered energy services. The carbon footprint accounting includes fossil fuel emissions, cement process reaction emissions, potential avoided fossil fuel emissions due to biomass residues substitution and end-of-life benefit of post-use materials. The results show that the operation of the building accounts for the largest share of life cycle primary energy use. The passive house design reduces the primary energy use and CO2 emission for heating, and the significance of this reduction depends on the type of heating and energy supply systems. The choice of end-use heating system strongly influences the life cycle impacts. A biomass-based system with cogeneration of district heat and electricity gives low primary energy use and low carbon footprint, even with a conventional design. The amount of biomass residues from the wood products chain is large and can be used to substitute fossil fuels. This significantly reduces the net carbon footprint for both the conventional and passive house designs. This study shows the importance of adopting a life cycle perspective involving production, construction, operation, end-of-life, and energy supply when evaluating the primary energy use and climatic impacts of both passive and conventional buildings.