How Buildings Use Energy

In very broad terms, buildings use energy in two ways: (1) to power equipment that use energy (including lighting), and (2) to provide comfortable conditions for occupants inside the building. To operate lights and equipment, energy is independent of climate, with the exception of daylighting in buildings. When available, daylight will affect the energy used for lighting. Providing comfortable conditions requires energy use from furnaces, boilers, chillers, cooling towers, air conditioners, air circulation fans, exhaust fans, and/or pumps. These energy uses are highly dependent on climate conditions and building operation patterns and can change significantly from hour to hour or day to day.

In 2018, buildings accounted for 28% of all energy use in the United States (1).  This includes both residential and commercial buildings. The figure below shows type of energy consumed by each sector in the US.  The next sections will go in greater detail about the differences in energy consumption for residential and commercial buildings.

Residential Building Use

Energy use in residential buildings can be broken down into four main categories. The following graph was developed in 2015 by the U.S. Department of Energy and gives insight into how energy is sued in a typical residence both national, the pacific area (PAC) and California (CA). Changes in building systems and construction codes have reduced the energy used to heat and cool buildings in new construction. It is estimated by the California energy commission that Residences built to the 2019 standards will save 7% in energy compared to homes constructed to the 2016 codes.

Commercial Building Energy Use

Energy used for typical commercial buildings varies widely with space use (see Figure below).  This energy use can be broken down into ten major categories. The graph below was developed in 2012 by the U.S. Department of Energy and gives insight into how energy is used in commercial buildings nationally. Note that commercial buildings in California will use significantly less energy than the national average (especially for space heating and cooling) due to its moderate climate.

Next: Heat Losses and Gains