Making Occupancy Sensors Work Properly
Cody Fincher, PE, CEM, LEED AP / Aug 9, 2018
Occupancy sensors (motion detectors to control lighting) have a reputation for being awesome… and for being a nuisance – It depends on who you talk to and their experiences with them. I love the occupancy sensor in my garage at home. Whenever I drive up or walk into the garage from the house, the lights turn on automatically. It is great when my hands are full and no way to flip the light switch. Plus, I know I’m not wasting energy because the lights turn off a few minutes after I leave! However,… I’ve also had some rough experiences with occupancy sensors. In addition to my experiences commissioning them, our company recently moved to a new office and had to “fight” with our occupancy sensors for several weeks. The primary issue was this: the lights were shutting off in our Principals’ offices while they were still there! As the senior electrical guy in the office, I knew where the blame would fall if we didn’t get the issues worked out quickly.
A little background — There are three common types of occupancy sensors: ultrasonic, infrared, and dual technology (combination ultrasonic and infrared). Ultrasonic sensors send out an ultrasonic signal and analyze the pattern of what is received. When someone walks through the space, the ultrasonic response is different, indicating that the space is occupied, and the lights need to be turned on. Infrared sensors monitor the infrared signal (surface temperature) of everything around it. When the infrared pattern changes, the sensor determines that the space is occupied and turns the lights on. The dual technology sensors have both ultrasonic and infrared capabilities to monitor occupancy in a space.
The sensors usually have two main adjustments: 1) sensitivity and 2) a time delay based on how long the lights remain on after motion is last detected. Additionally, the sensors often have an option to be setup in “Smart/Learning” mode, where the sensor adjust the time delays and sensitivities “automatically” based on what it detects over time. The dual technology sensors typically provide the best coverage and least likelihood of lights going off when they shouldn’t.
Occupancy sensors are usually setup to turn on and off automatically. However, this is not always the case. The sensors can be vacancy-type, which means the lights only come on once a person pushes a button. This avoids the lights coming on unnecessarily. The lights still go off automatically after the rooms are no longer occupied.
So, you may be wondering why we had such issues with the sensors in our office. Part of this was a result of some improper wiring by the electrical contractor, but a much larger part of the problem was that the sensors’ settings weren’t optimized. Our sensors were initially setup in the “Smart/Learning” mode (the default from the factory), but it turned out that the individuals in the offices did not move enough to actually be detected. Part of this was due to the style of sensor (infrared vs. ultrasonic) and it was also partly due to sensor location. We moved the sensors closer to their desks, but it did not solve the problem because the lights still kept going out! What finally had to do was take them out of “Smart/Learning” mode, and optimize the settings. We maxed out the time delays (30 minutes), and nearly maxed out the sensitivities. While the occupants weren’t moving enough every five minutes, they seemed to within every 30-minute time period (it must have worked because I am still employed, and the sensors have not been smashed with a hammer or thrown out a window!).
I tell this story not to imply that you should max out every occupancy sensor that you get (the one I have at my house is set to a very short time delay), but instead to emphasize the point that they do not necessarily work perfectly right out of the box. It’s worth mentioning that we had tested these occupancy sensors at project completion and found them functional. However, just because they work when you walk in doesn’t mean that they will work perfectly for the end-user. Occupancy sensors need to be adjusted and optimized based on the occupants. What works for one person/group won’t necessarily work for another.
It’s also important to make sure you have the correct style of sensor in your spaces. In our office, the sensors installed were infrared-style, which are not great at detecting small movements (sleeping Principals??… just kidding!). This was a big cause for our specific problem. However, infrared sensors typically are recommended for enclosed offices like these. I may sound like I am flip-flopping, but it is to emphasize the fact that the rules of thumb are merely recommendations, and do not guarantee perfect operation. The settings are very likely going to have to be tweaked!
On a new project, your facility operators should be properly trained at project completion on how to make adjustments to these sensors so that you can make these adjustments when needed. If you or your operators are not trained, be sure to ask your contractor about arranging training. Additionally, you should consider having your contractor and/or commissioning authority to come back after a few weeks/months of occupancy to help adjust the sensors.
Occupancy sensors can save a lot of energy, so don’t give up on them if they don’t work perfectly for you at first! Make adjustments based on the occupants, and make sure to point out to the design team during planning any rooms that may need to be extra sensitive so that the designer can plan for it accordingly. If someone tells you that they can setup your sensors perfectly the first time, be wary! There is a lot that a good engineer/ contractor/ commissioning authority can do, but it does not guarantee that there won’t be problems when you occupy your new or renovated space. Take the time required, and get the sensors optimized for your needs.