Factors contribute to the changes of LCA of wood products


Life Cycle Assessment (LCA) is a tool designed to quantify and evaluate a broad scope of environmental impacts from the selected life cycle of a given product. Life Cycle Assessment is one of the significant ways for the wood industry to promote the environment-friendly property of wood with scientific evidence. A classic LCA project is composed of three stages, define scopes and goals, provide Life cycle inventory (LCI), and procure lifecycle impact analysis (LCIA).

In the last report, we focus on reporting our Life cycle inventory for a wood chair produced in Indianan. In this report, we would like to discuss several factors that contributed to the changes in LCA. Choices of functional units, Geography factors, and Transportation are discussed below.

Figure 1. Exploded view of 14’’ chair components.
Choices of Functional Units

The functional unit is defined as the unit of comparison that assures that the products being compared provide an equivalent level of function or service. A careful selected functional unit will improve the accuracy of the LCA study and the usefulness of the results. For wooden chair comparisons, a single chair is fair enough as the functional unit, though it depends on the changes of parameters e.g., joint system or material types, the lifespan and prices differ. Another optional functional unit for multi-type material comparison is to apply an equivalent lifespan. Figure 2 is one comparison LCA study on three different material chairs. We assess the environmental impacts of wood, plastic, and aluminum chairs. Here the functional unit is the 20 years utilization of chair while the lifespan of a chair is estimated based on the cyclic loads of chairs, which are 20 years for a wood chair, four years for a plastic chair, and 6.4 years for an aluminum chair respectively. In this functional unit scenario, wood performs extremely better than other materials. If here quantity is used as the functional unit, then in some categories, wood becomes even worse than aluminum. These results also suggest that improve the strength and lifespan of products by adding no extra materials could somehow have a better environmental impact under some criteria.

Figure 2. A comparison LCA on three different chairs based on TRAIC 2.1.
Geography factors

The geography factors are important for wood furniture products LCA due to their less energy consumption during production. So the location of production may dominate the overall environmental impacts. Here we present a comparative LCA on Indianan hardwood chair verse Oregonian softwood chair, and the functional unit is one chair. The energy grades and wood species will affect the final outputs. Figure 3 is the result. We can see that in all categories, Oregonian softwood chair is better than Indianan hardwood chair. When lifespan is used as a functional unit, Oregonian softwood might be still better.

Figure 3. A comparison LCA on two different chairs based on TRAIC 2.1.

Above LCA studies do not consider the transportation of raw material and product distributions. In the real-world, most wood furniture in the US comes from China. Here we post a global warming potential (GWP) fitting based on our hardwood chair: $$ \text{GWP} = 0.0807\times T-26.22 $$

where $T$ represents good transportation with unit tkm. Here we assume that all transportation is based on trucks. The good transportation of a wood chair from China to the US is about 170 tkm, which releases almost half to the carbon storage in the wood. If the supply chains and wood products are more complicated, e.g., Canada produces raw softwood lumber, transport them to China, and transport back to NA after furniture production, then there might lead to positive GWP to the environment. So for wood furniture production, produce them locally might be the most way regarding LCA perspectives.