Life-Cycle Inventory of Hardwood Lumber School Chair


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).

Recent researches of LCA on wood mainly focus on investigating the (LCI) of composites materials, and few of them pay attention to final wood products. Here we post an LCA case study for a wood chair in Indianan. The design of this chair and manufacturing process has been thoroughly tested through laboratory modeling at Purdue’s Wood Research Laboratory and through a case study implementation of a manufacturing facility used to produce 50 furniture sets performed by Purdue Wood Research Laboratory in conjunction with the Institute of Technology of Costa Rica. Figure 1 is the exploded view of this 14’’ chair.

Figure 1. Exploded view of 14’’ chair components.
Scope, Goals and Functional Units

Our goal in this study is to 1) provide a production inventory for school furniture, 2) benchmark environment impacts of the well-studied wood chair in our lab. Figure 2 is a diagram of our production system boundary.

Figure 2. Production LCI system boundary. The dash line area are the main production process and bold black line area is the system boundary.

Material consumption

Laboratory testing of chair models shows that raw wood inputs for the chair, including waste wood not used in the final product, requires 496.8 in3 cutting units of lumber, or 3.45 board feet (BF). Only 56% of this lumber is found in the final product while rest are treated as wastes. Table 1 and Table 2 below are the details of raw material wood inputs and output.

Table 1. Major Material Inputs.
HardwoodStrehcher168 in3
HardwoodLegs160.8 in3
HardwoodSeat168 in3
Polyvinyl acetateGlue1.28 oz

Table 2. Major Material Outputs.
Waste HardwoodWood Wastes218.5 in3
Energy consumption

Table 3 is the operation times and energy consumption of each machine for producing a single chair. Here the energy consumption is computed based on the power of the machine and operation times. Generally, it is not easy to track idle power, so we assume that the idle power is half of the full power. Dust Collector contributes most to the energy consumption and achieves high uncertainty for mass production due to the nature of non-linearity in the mass production of wood products.

Table 3. Operation times and energy consumption of each machine for producing a single chair.
MachineCutting Time (s)Idle Time (s)Energy (kwh)
Band Saw87400.045
Radial Arm Saw28210.024
Table Saw6007920.103
Drill Press 6007920.103
Tenon Machine 2401390.048
Bent saw - trim 2001520.114
Orbital Sander 30 00.002
Hand Router 150 00.009
Dust Collector 150 1981.032