160 Introduction to Renewable Biomaterials
25%, or adjusted according to some statistical measure associated with the value such as
standard deviation. Providing a range of values and understanding how different values
influence the results and eventually conclusions are far more valuable than providing
a static one-number answer without deeper insights into what is driving the overall
results.
In some studies, the goal may be to compare one product to another. This type of
study is referred to as a comparative LCA, and when a company wants to publically
communicate such results they must be first certified by through a peer-reviewed
process as defined by the ISO 14044 standards. In these types of studies, it is important
in the LCI phase to determine if the available data and models can reasonably calculate
the differences in environmental flows and impacts. To reasonably claim a difference
between flows for competing products, a general rule of thumb is that the values are not
significantly different unless they are at least 25% different. This 25% different rule is
often used as there is inherently uncertainty in the data, modeling, and other factors
that are not possible to completely model. This 25% rule at times could be too high and
a robust uncertainty analysis could be performed to further determine the certainty and
the probability that one product will produce lower flows and environmental impacts
than another.
Another important part of LCI interpretation is determining and communicating
the “hotspots” or process areas and process flows that influence the overall LCI
the most. For instance, in dried rough lumber production, the electricity used dur-
ing drying would be an energy use hotspot as well as a large contributor to GHG
emissions. Insights surrounding the hotspots are often some of the most important
and actionable information that is attainted by performing an LCA, and time should be
dedicated to understanding the driving factors behind the values of the most important
environmental flows.
For more information surrounding LCI methods, please refer to http://www.lcatextbook
.com and navigate to Chapter 5. This textbook provides additional details and resources
that could not be included in this brief introduction to LCA and is a free book available
to all.
5.3.2.9 Problems Set – Life-Cycle Inventory
Problem 1 A wood products production facility has emissions that contribute
to global warming (GWP) of 50,000 kg CO 2 eq day−^1. The production facility makes
1000 2×4in.^2 boards a day, 500 1×4in.^2 boards a day and 125 2×6in.^2 boards per day.
Prices ($) Weights (lb)
2 ×4in.^2 2.36 17
1 ×4in.^2 6.79 9
2 ×6in.^2 5.89 27
Using mass allocation methods, what is the GWP per kg of each product? Using
economic allocation methods, what is the GWP per board for each board type? Final
units are to be reported in kg CO 2 eq.
