How Occupancy Affects Building Energy Use

occupancy cover

Getting to Know Your Building: Part 2

Buildings use more energy when they’re occupied. This may seem obvious, but it’s something our office (the Energy Conservation Office) investigates when looking for energy inefficiencies on campus. In particular, we make sure that buildings use less energy when unoccupied.



How do people impact building energy use?


People in buildings affect energy use mostly through lighting and plug loads. These plug loads include computers, copy machines, microwaves, coffee makers, and anything else plugged into an outlet. Looking at energy use throughout the day shows a direct correlation between occupancy and energy use. When people are in a building, the rooms are conditioned to a comfortable temperature and daily activities require electricity use.


The impact of people using energy in a building is why we emphasize the importance of people turning equipment off when it’s not needed, using computers that match the workload (the computing power of a laptop is typically sufficient for any kind of work that someone is doing), and using task lighting when possible.


Not everything is dependent on building occupants though, some things are automatic and/or programmed. Occupancy sensors are used in a handful of the buildings on campus to sense when someone is in a room and to run the HVAC system accordingly. For example, if you step out of your office for afternoon meetings the occupancy sensor will tell the HVAC system the room is unoccupied. Programming in the building automation system uses the lack of occupancy to save energy by adjusting the air flow.

How does a building operate when people aren’t there?

Building’s are usually deemed unoccupied in two ways: occupancy sensors or scheduled occupied hours. Information about the unoccupied hours of a building are important because a building can be tuned to use less energy during these unoccupied times.

People in the buildings can also affect plug loads at night, even when they’re not in the building. If computers and/or equipment are left on, or even if they’re put to sleep, they continuously draw power from the outlets. Equipment that can’t be turned off without being unplugged (such as microwave ovens) draw power 24 hours a day, often without the knowledge of the consumer. This electricity use also called a vampire load, is why it’s important to turn off everything you can when you leave for the night. To do this we suggest power strips, which can make it easy to turn off all equipment when you’re not using it.

The reason we mention this is because we’re seeing a fascinating disconnect between how much energy the building is using when no one is there. By looking at the Campus Energy Education Dashboard, or CEED, you can see that lots of buildings use a lot of energy (namely electricity) throughout the night.

If you want to help us out, you can use the demand graph on CEED to see how much electricity your building uses at night. If you think that your building is using too much, let us know!