Why Embodied Energy Matters in Sustainable Building
Embodied energy is the total energy required of all activities to produce a product—from its raw material extraction to its transport, construction, and maintenance.
Now before explaining the technical aspects of embodied energy, it may be easier to understand the concept from something common. Let’s say you are making two cakes for a holiday meal: one a plain pound cake and the other a chocolate fudge cake with vanilla buttercream frosting and a chocolate ganache glaze, both made from scratch.
Already you know that the pound cake will require far less manual work than the chocolate cake. Yet the chocolate cake requires more work not only because it contains more ingredients but also because certain of its additional ingredients (chocolates, cocoa, cream, extract) have already required extensive processing before it ever reached the store.
When you’ve finished baking, your cakes are perfectly cooked masterpieces and wonders to behold. But that perfect picture of cakes betrays the overall work it took to:
- create each ingredient and fully transport it to where you found it
- get you to the grocery store and back home with your supplies
- prepare, bake, and finish your food creations
And in the end one cake cost far more work than the other. This is a representation of embodied energy.
Catherine Mohr on Embodied Energy (TED Talk - Excellent)
Initial and Recurring Embodied Energy
Typically embodied energy is understood in the context of buildings and the materials used to construct them. There are two forms of embodied energy: initial and recurring.
Initial embodied energy consists of energy used to acquire, process, and manufacture raw materials; transport them to a site; and construct a building. Two components of this energy are direct energy and indirect energy. Energy and fuel used to transport materials, products, and workers to a site and to construct a building is referred to as direct energy. Energy used to acquire, process, and manufacture materials, including their transport, is referred to as indirect energy.
Recurring embodied energy consists of energy used to maintain, repair, restore, or replace materials, components, or systems over the life of a building.
The term ‘embodied energy’ does not refer to any energy physically present in a material; instead, it does refer to the energy that has been used in the several processes involved in its lifecycle. The lifecycle of a product includes its raw material extraction, transport, manufacture, assembly, installation, disassembly, and deconstruction or decomposition.
Embodied Energy (MJ/kg)
How Embodied Energy is Calculated
Embodied energy is measured as energy required to produce a mass of material. Megajoules per kilogram (MJ/kg) is the formula most often used. A megajoule is one million joules, or the equivalent of a one-ton vehicle moving at 100 mph.
Calculations exists for each type of construction material. The higher the number, the more energy that is required to produce that material based on its processing and manufacture (called energy intensity); the lower the number, the less embodied energy. At right are an assortment of calculations based on several international sources.
Measuring embodied energy is very complex and precise energy figures are not only elusive, they just don’t exist. It is not logically possible to standardize extraction and manufacturing processes and distances to markets and sellers. Embodied energy for a product created and used in industrial Iowa, a land of rolling hills, could vary sizably for the same product created and used in Japan, where inhabitants are walled in by mountains.
Perhaps the biggest reason for the imprecise science is the lack of international consensus, for reasons just discussed and others. Methodology and concrete data for materials are all pending and keeps the larger science, sustainability and green building, waiting. Despite not having absolute values for materials, most products can be compared based on average values.
In the U.S. LEED (Leadership in Energy and Environmental Design), the nation’s premier green building organization and certifying agency, does rate embodied energy in its certification processes. LEED is a branch of the U.S. Green Building Council.
Did you know about embodied energy before reading this article?
Why Embodied Energy is Important
Embodied energy is important because of operating energy, the energy used to heat, cool, light, ventilate, and supply equipment and appliances. In fact, operating energy is usually the most significant aspect of total building energy. If a building’s thermal performance is bad, the embodied energy of a building can more than double over the lifecycle of the building.
When operating energy is efficient, however, embodied energy will replace operating energy as the most significant aspect of building energy. This means that less energy (and expenses) will be required to operate the building.
Was that confusing? Let’s simplify: The ideal is to have as little embodied energy in the materials that comprise a building but to have the energy therein be the most significant aspect of the building’s total energy use.
Recurring embodied energy is important here and relates to the building’s lifespan, and that depends on its durability. When durable materials and components are selected for a building, it will last longer.