Vacancy or Occupancy Sensors?

Technology changes very quickly even now in the construction industry.  A few years back, everyone was using Occupancy sensors to control lighting and save energy.  This has changed with recent updates to the IECC2012 energy code that we follow at work.  I am a coordinator for one of the many groups at ESD.  Our group deals with major office/lab renovations and retrofits.  Our group alone does hundreds of projects per year mainly in the downtown Chicago area.  The latest on basic lighting controls has seen the use of vacancy sensors more than occupancy sensing.

Occupancy sensors are an “auto-on” control that turns lights on in a room when a person trips the sensor.  That sensor could be an infrared, ultrsonic, or dual-tech (both), among others.  Now picture a typical, class A, office fit-out.  To maximize daylighting during the working hours, many glass partitions or sidelights (next to office doors) are used.  So if a private office has an occupancy sensor, someone outside in the hallway will trip the sensor when they walk by.  What was happening was that a person would turn on each office along a corridor just by walking outside of it.  An occupancy sensor will turn the lights off after around 30 minutes, but it would usually keep getting tripped.

Now take the vacancy sensor option.  Codes call for a “manual-on” system which is an occupancy sensor switched to vacancy mode.  The lights in the same private offices will remain off until someone goes into that office and toggles a manual, wall-mounted switch.  Now lights are turned on because they are actually needed and they will turn off at a set time once now movement or heat is detected in the room.  Another major difference is the placement of an occupancy versus vacancy sensor.  The vacancy sensor can be placed in a far corner so even if the lights are turned on manually, then the person leaves the office for the day, another person walking in the hall at a similar time will not turn the lights back on.  The occupancy sensor is usually placed by the doorway which means it is placed next to sidelights and glass partitions that have a clear view of a corridor.

Occupancy sensors are now mainly reserved for use in bathrooms and storage areas to automatically turn on the lights once someone enters.  Another note is that often the occupancy and vacancy sensor is the same sensor unit on a different setting.  This makes clear specifications and contractor coordination more important so that the correct use is installed.


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