Life cycle assessment key terms

The following are the main terms to understand when working with an LCA report. A complete list can be found at LifeCycleInitiative.org.

Embodied energy vs. operating energy

Embodied energy reflects the total energy used to bring a product into its current state. For example, a ceiling tile is shipped to a consumer. The ceiling tile was processed out of input materials at the manufacturing facility, and those input materials were extracted from raw materials, processed, and shipped to the factory. All of these activities require energy, and the sum of all that energy is the embodied energy in the ceiling tile.
Operating energy is the energy required to operate a system, such as the total energy consumed by a building during its lifetime.

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Functional unit

A quantitative expression of the product being studied, addressing the function, the quantity, the performance, and the time. The functional unit is the same across alternatives being studied. For example, the following functional units could be used:

Light Bulbs: in its LCA of light bulbs [PDF], DOE used 20 million lumen-hours as the functional unit since that was the average light output over the lifetime of a single 60W LED bulb in 2011. It would take 22 incandescent bulbs, or 3 CFLs to achieve the same lifetime light output
Floor Coverings: from the NIST BEES manual [PDF], the functional unit for floor covering alternatives is covering 0.09 m² (1 ft²) of floor surface for 50 years
Roof Coverings: Covering 9.29 m² (1 square, or 100 ft²) of roof surface for 50 years
Concrete Beams and Columns: 0.76 m³ (1 yd³) of product service for 50 years

Impact categories

Specific areas of ecosystem quality, resource use, or human health that are quantified in the LCA, such as Acidification, Eutrophication, Global Warming, Ozone Depletion, Human Health (Particulate), Human Health (Cancer), Human Health (Non-cancer), Eco-toxicity, Photochemical Smog Formation, and Resource Depletion (from EPA’s Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts, or TRACI).

Multi-attribute, single-attribute

Many product labels and certification programs certify products based on life cycle parameters and address many different environmental issues, making them multi-attribute programs. These parameters may include energy use, recycled content, and air and water emissions from manufacturing, use, and disposal. Others focus on a single life cycle stage or a single environmental attribute, such as water, energy, or chemical emissions that directly impact indoor environmental quality.

Product Category Rule

A Product Category Rule, or PCR, is set of rules and guidelines for developing EPD for a specific product or type of product. A PCR will specifically define a functional unit. While PCRs have been developed using international consensus processes, they can be industry-wide (for a given type of product) or for a specific product. PCR are particularly useful where the environmental impacts of products within a category group are to be compared.

Reference flow

The amount of product required to fulfill the product or service being studied, expressed as a functional unit. For example, if the functional unit is 1 m² of flooring that lasts 50 years, and two different flooring materials are considered, with A lasting 10 years and B lasting only 5 years, then the reference flow for A would be 5 m², and B would be 10 m².

ISO standards

The International Organization for Standardization (ISO) develops standards internationally agreed upon by experts. Examples of standards related to life cycle assessment include:

ISO 14040 and 14044 describe the basic framework for an LCA, including the goal and scope, the inventory, the impact assessment, the interpretation, the limitations, and guidelines for communication, with 14044 providing more detail about LCA technique.
ISO 14025 specifies how Type III environmental labels and declarations (Environmental Product Declarations) are created.
ISO 21930 describes the rules and guidelines for creating product category rules (PCRs) that are used for EPDs of construction products.
ISO 21931 and EN 15978:2011 define frameworks for assessing sustainability of buildings

System boundary

System boundary is defined as an interface between a product system and the environment or other product systems. It defines the activities and processes that will be included in each life cycle stage for the LCA analysis and those that will be excluded.