The Basics: Energy Terms and Units

Energy usage is tracked with a variety of units, including British Thermal Units (BTUs), therms, Joules (J), Calories (C), kilowatt-hours (kWh). A therm is a common measure of natural gas, commonly used for heating. ​

A kilowatt (kW) is 1000 watts, and both measure the rate of energy use, or how much energy is used per some period of time. A kilowatt-hour (kWh) is the amount of energy used over an hour's time if the rate of energy use is 1 kW. This is the preferred format for electricity usage, but since kWh, BTUs, and Joules all measure energy usage, we can easily convert between them all.

What is Energy Use Intensity?

Energy Use Intensity (EUI) is a way to measure the energy use per unit of area, often calculated with a year's energy use divided by the building's square footage (kBtu/sq.ft./year). It can be used to compare the energy intensity of any two buildings irrespective of their size and referred to as the "miles per gallon" of the building energy industry. Comparing a building's EUI to the average for a geographic area or specific space type is called benchmarking. 

Energy Use Intensity = Annual Energy Use (kBtu) / Building Square Footage (sq.ft.)

Different types of buildings will have different energy needs, so their average EUIs will also be different. Because of this, it is often most helpful to compare buildings of the same type or buildings against the average EUI of that type of building.

For example, dining facilities will have similar EUIs. Their EUI should be higher on average than a dormitory because they are likely in constant use throughout the day and using high amounts of hot water.

Energy Demand vs. Energy Usage

Energy Demand is the rate of energy consumption. When measuring electricity demand, the unit of measurement is a kW. 

Energy Usage is a quantity of energy used over a period of time. When measuring electricity use, the unit of measurement is a kWh. 

Seasonal Trends in Energy Use