Life-Cycle Energy and Carbon Implications of Wood-Based Products and Construction

Abstract: Forests can be an important element of an overall strategy to limit the atmospheric concentration of carbon dioxide (CO2) that contributes to climate change. As an integral part of the global carbon cycle, forests remove CO2 from the atmosphere as they grow, and accumulate carbon in tree biomass. Using wood products made from sustainably managed forests can reduce net CO2 emission by substituting in place of fossil fuels and energy-intensive materials. In this thesis the mechanisms by which wood product substitution can affect energy and carbon balances are studied. These include: the energy needed to manufacture wood products compared with alternative materials; the avoidance of industrial process carbon emission from e.g. cement manufacture; the use of wood by-products as biofuel to replace fossil fuels; and the physical storage of carbon in forests and wood materials.A methodological framework is first developed by integrating knowledge from the fields of forestry, industry, construction, and energy. A life cycle perspective is employed encompassing the entire product chain from natural resource acquisition to material disposal or reuse. Analytical challenges that are addressed include the functional unit of comparison, the fossil reference system, land use issues of wood vs. non-wood materials, and the diverse phases of the product life cycle. The methodology is then applied to two multi-storey wood-framed buildings in Sweden and Finland, compared with two functionally equivalent buildings with reinforced concrete structural frames. The results show that less primary energy is needed to produce the wood-framed buildings than the concrete-frame buildings. CO2 emission is significantly lower for the wood-frame buildings, due to reductions in both fossil fuel use and cement calcination process emission. The most important single factor affecting the energy and carbon balances is the use of biomass by-products from the wood product chain as biofuel to replace fossil fuels. Over the life cycle of the wood-framed buildings, the energy of biomass residues from forest operations, wood processing, construction and demolition is greater than the energy inputs to produce the materials in the buildings. Realisation of this benefit is facilitated by integrating and optimising the biomass and energy flows within the forestry, industrial, construction, energy, and waste management sectors.Different forest management regimes are studied in an integrated carbon analysis to quantify the carbon flows and stocks associated with tree biomass, soils, and forest products. Intensified forest management that produces greater quantities of biomass leads to net CO2 emission benefits by augmenting the potential to substitute for fossil fuels and non-wood materials. The increased energy use and carbon emission required for the more intensive forest management, as well as the slight reduction in soil carbon accumulation due to greater removal of forest residues, are more than compensated for by the emission reduction due to product substitution. Carbon stock changes in forests and wood materials can be temporarily significant, but over the building life cycle and forest rotation period the stock change becomes insignificant. In the long term, the active and sustainable management of forests, including their use as a source for wood products and biofuels, allows the greatest potential for reducing net CO2 emission.Implementation issues related to the wider use of wood-based materials to reduce energy use and carbon emission are also explored. An analysis of the effects of energy and taxation costs on the economic competitiveness of materials shows that the cost of energy for material processing, as a percentage of the total cost of finished material, is lower for wood products than for other common non-wood building materials. Energy and carbon taxation affects the cost of wood products less than other materials. The economic benefit of using biomass residues to substitute for fossil fuels also increases as tax rates increase. In general, higher taxation of fossil fuels and carbon emission increases the economic competitiveness of wood construction. An analysis of added value in forest product industries shows that greater economic value is added in the production of structural building materials than in other uses of forest biomass. Co-production of multiple wood-based products increases the total value that is added to the biomass produced on an area of forest land. The results show that production of wood-based building material is favoured economically by climate change mitigation policies, and creates high added value within forest product industries.