BuildingGreen.com has a very good and useful piece about energy measurement from the December 2007 Environmental Building News.
The article, titled “Energy Metrics: Btus, Watts, and Kilowatt-Hours,” helps explain the differences between different terms such as kilowatt-hours (kWh) and British thermal units (BTU) and when and how they should be used. This is good information for everyone to understand, since we all use energy in our homes and workplaces. Practically anyone interested in improving energy efficiency in a building will be using these terms frequently and should have some understanding of the language.
Overall energy consumption of buildings, including both electricity and other fuels, is typically counted in million Btus per year (using the confusing Roman-numeral-based abbreviation MMBtu). To report energy use in way that is comparable from one building to another, we normalize by the building’s gross floor area, giving us energy numbers in thousand Btus per square foot per year (kBtu/ft2·yr). The average for office buildings in the U.S. is 91 kBtu/ft2·yr, or in metric units, 290 kWh/m2·yr.
I’ll note that none of the GreenBuildingElements writers are professional engineers, so we too may fall into the occasional mistake when writing about energy issues. Now, however, having this reference will be useful for all of us.
Image Source: BuildingGreen.com