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Don Norwood
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4
Mar

Occupancy vs. Vacancy Sensors

By: Don Norwood

Occupancy sensors provide automated lighting control in enclosed offices, open work spaces, and shared amenity spaces; they are typically deployed with automatic on, automatic off, and time delay settings. When an occupant enters a controlled space, the occupancy sensor indexes lights to ‘ON’ without requiring manual operation of a wall switch. When the occupant exits, the sensor automatically indexes the lights back to ‘OFF’ after a programmed delay – typically between two and 15 minutes depending on user preferences.

Vacancy sensors take that control one step further with a manual on setting, as opposed to automatic on. When an occupant enters a space, they must physically change the lighting to the on setting. This allows the occupant to determine if overhead lighting is needed or if the ambient sunlight is sufficient. Like occupancy sensors, vacancy sensors also feature automatic off and time delay settings that respond to the occupant exiting the space. 

By adding a layer of user control, it is easy to see how vacancy sensors can provide additional efficiency simply by allowing occupants to turn on lights only when needed.

My colleague at GHT, Senior Associate Brian Redder, notes that occupancy sensors have recently been utilized to control HVAC systems as well. When a space is unoccupied, the sensor allows the temperature to drift a few degrees higher on warm days or lower on cold days – just enough to impact energy use without causing significant discomfort to an occupant that enters the space. The sensor will quickly return the space to the designated set point, or to the temperature requested on the connected thermostat control, when the space becomes occupied.

These subtle control changes can yield significant energy savings. They may seem insignificant on a zone-by-zone basis, but when applied over tens or hundreds of thousands of square footage, the cost benefits can quickly add up in the form of reduced electric utility bills. Have you used occupancy or vacancy sensors on a recent project? Let us know how the energy use was impacted in the comments below.