There two types of energy to consider in the lifespan of any building, the operational energy and the embodied energy. What are those two types?
Operational Energy Use
According to the U.S. Energy Information Administration (EIA) in 2023, residential buildings consume 15% of the total energy use (primary energy¹ plus secondary energy²) in the United States. Since most of our energy comes from burning fossil fuels, our energy consumption is tightly linked to our carbon footprint and the subsequent environmental impact.
The 15% represents the operational energy required to operate and maintain the home. Homeowners use this energy for space heating, water heating, air conditioning, refrigeration, cooking, and operating all the other appliances in our homes. About half that energy comes from the burning of fossil fuels in the home, mostly natural gas or propane. The rest of the energy consumed is mostly in the form of electricity, much of which still derived from burning fossil fuels.
Embodied Energy Use
The home’s operational energy consumption is important, but it’s only half the story. Before the first occupant has ever stepped foot inside the building, the construction process has consumed a significant amount of energy. Common building materials, such as concrete, steel, and glass all require enormous amounts of energy to manufacture. The manufacturing process includes extracting the raw materials from the earth, refining the raw material, and manufacturing it into useable building materials. Transportation (sometimes many thousands of miles) of those materials to the building site uses still more energy. The energy consumed prior to occupancy is referred to as embodied energy.
Operational vs Embodied Energy
Over the entire life cycle of a typical American home, the total energy consumption is the embodied energy plus operational energy. Typically, the embodied energy represents about 20% of the total energy consumed by the building during its useful life. Interestingly, for a highly efficient home, the embodied energy represents a much larger share of the total life-time energy consumption. This is because the operational energy consumption has decreased, often significantly.
For a typical American home, during the first year of the building’s life (during construction) all the energy consumed is embodied energy. Only after completion of construction we start using operational energy. At around the 5-year point the cumulative operational energy will exceed the embodied energy.
We need to tackle both the operational energy and the embodied energy consumption if we want to achieve a truly meaningful reduction in energy consumption.
[1] Primary energy: Energy sources that present in the natural world, the source can be either renewable or non-renewable. Examples include; coal, natural gas, crude oil, sun, wind, geothermal.
[2] Secondary energy: Energy derived from a primary source; secondary energy is a carrier of energy. Electricity is one of the most common secondary energy resources. Gasoline derived from crude oil is another very common secondary energy resource.