Study Finds Occupancy Sensors Routinely Commissioned by Satisfied Contractors, but Suffer High Callback Rate

by Craig DiLouie, Lighting Controls Association

Posted July 2007

A new study conducted by ZING Communications, Inc., co-sponsored by the Lighting Controls Association and Watt Stopper/Legrand, suggests that electrical contractors routinely calibrate motion sensitivity and time delay settings in occupancy sensor installations; recommend occupancy sensors in a majority of lighting retrofit projects; select time delay settings that on average support optimal energy savings and lamp life; and are satisfied with occupancy sensor performance, ease of installation and commissioning, and customer/occupant acceptance.

However, the survey results also suggest that contractors nonetheless report a high rate of callbacks compared to previous research concerning other lighting technologies. The typical solution is to return to the job to adjust the time delay and sensitivity settings, according to the results. Respondents who report setting the time-delay of the installed sensors to 10 minutes or less also report a much higher rate of callbacks than those respondents setting a time-delay of 15 minutes or longer. This situation further suggests a strong potential for the utility of self-calibrating occupancy sensors. The ability of self-calibrating sensors to reduce callbacks has not been studied, however, creating a demand for further research.

Background

The first step in commissioning an occupancy sensor installation is to verify proper placement and, if applicable, orientation of the sensors, so that they match the specifications and construction drawings.

The second step in commissioning an occupancy sensor installation is to calibrate the sensor by adjusting its sensitivity and time delay settings. Calibration is a standard tool used in commissioning. Calibration means adjusting sensors from factory default settings to gain desired performance based on the actual conditions of the application. It should be coordinated with furniture placement, as occasionally furniture or equipment may be moved or relocated, which can affect sensor placement and/or orientation.

Sensitivity: The occupancy sensor’s sensitivity level indicates how much movement will cause the sensor to activate the lights. If you have too high a level of sensitivity, you can increase the possibility of false-on triggering. If you have too low a level, you can increase the possibility of false-off triggering. Sensitivity is also related to coverage; changing the sensitivity can result in changes to the coverage pattern.

Occupancy sensors are shipped with a factory setting for sensitivity, which can be adjusted in the field to fit the application need. The sensitivity adjustment allows the contractor to tune the sensor so that it responds appropriately to primary tasks in the space at the designed distance, while addressing possible sources of nuisance switching such as airflow. Setting the sensor at the most appropriate sensitivity setting will minimize the possibility of nuisance switching.

Time delay: The occupancy sensor’s time delay indicates how much time it will take to shut off the lights after the last motion has been detected. Longer time delays avoid continual on/off cycles of the lighting as people may go in out of the space frequently. Time delays also help to overcome brief periods of time when activity levels are low, as the sensor may not detect the occupant and therefore inadvertently switch the lights off. Factory settings can be adjusted in the field. The shorter the time delay, the greater the energy savings but also the shorter the lamp life, due to more frequent switching, which results in more wear and tear on the lamps. In many applications, time delays of no less than 15 minutes are recommended.

Self-calibrating Occupancy Sensors

As noted above, self-calibrating sensors were not included in the study, although the results suggest they may be useful to contractors seeking to reduce commissioning requirements, as self-calibrating sensors require little or no adjustment of their sensitivity and time delay settings. The sensor contains a microcontroller that continually monitors the space to identify usage patterns. Using this information, the sensor automatically adjusts its sensitivity and time delay settings for optimal performance based on these usage patterns. Over time, environmental conditions may change, but this type of sensor will continually adjust its operation to provide consistent service.

It is important to understand, however, that a self-calibrating sensor may inadvertently switch off lighting during the early stages of monitoring usage patterns. Re-triggering by detecting motion immediately after switching off the lights causes the sensors to adjust time delay, sensitivity, or both. This “learning phase” may result in callbacks by the owner if the owner does not understand the purpose of the self-calibrating sensor.

Time Delay versus Energy Savings

If the time delay setting for an occupancy sensor is shorter, energy savings will be maximized because the lights will be shut off for an overall longer period of time. In 1997, researchers studied energy savings potential for occupancy sensors in multiple space types and buildings and tracked energy savings versus time delay. The results are shown in the graphic below.

Graphic courtesy of New Buildings Institute

Shorter time delays, however, can increase the amount of switching of the lamps, which reduces their average rated life, as most wear and tear on the lamp is caused during startup. This does not necessarily mean lamp costs will be higher. The lamps may provide fewer burn-hours, but may not provide a shorter calendar life because they will be shut off for longer periods of time than if they were continuously operated. If the lamps must be replaced more frequently, the premium is typically less than the energy savings. After all, the primary cost of operating a lamp is energy, not the cost of the lamp.

Research has shown that sensible lamp life can be achieved with time delays of 15-30 minutes. Nonetheless, this is a factor that should be addressed in the economic analysis justifying the use of occupancy sensors. In addition, very short time delays can result in a higher incidence of nuisance switching, specifically the lights being switched off, in spaces with low levels of activity.

To optimize lamp life while maximizing energy savings, it is recommended that a minimum 15-minute delay setting should be used for occupancy sensors, that only ballasts that meet ANSI requirements for lamp ignition should be used, and that programmed-start ballasts should be used in applications with a high number of switching cycles per day and where lamp life is a primary concern.

Research Questions

A random sampling of typical factory settings for occupancy sensors indicates typical settings of 10, 20 or 30 minutes.

Manufacturers recommend that contractors commission the sensors upon installation, and reset the time delay to a setting appropriate for the application. In some cases, the exception is self-calibrating or “install and forget” sensors, which may be recommended to be installed as is with factory defaults (they automatically adjust their own time delay and sensitivity).

This raised the question: Do contractors typically commission sensors, and reset the time delay, and if so, what time delay settings are typically selected?

As the installed base of occupancy sensors rapidly grows, this question becomes highly relevant to the larger question of how much energy is being saved. A longer time delay (such as 30 minutes) reduces the possibility of nuisance switching, which can require further adjustment to the sensor settings, but also reduces energy savings.

Research Study Addresses Time Delay/Commissioning

In May 2007, ZING Communications, Inc. invited 450 electrical contractors to take an online survey asking them questions about occupancy sensor commissioning and performance. This population was pulled from the subscriber list of LightNOW and lightingCONTROL, two industry e- newsletters. Thirty qualifying respondents completed the survey, a 6.9% response rate. To qualify, respondents indicated they install lighting products in commercial projects in North America, and have installed occupancy sensors in the past. The results reflect, with a high degree of statistical accuracy, the views of the studied population. Note, however, this population has an inherent bias because it is constituted of subscribers to lighting newsletters, which brings up the possibility that the population is better educated about controls than other contractors. Keeping this bias in mind, the results are suggestive of the electrical industry.

Respondents were asked if they commission occupancy sensors after installation. For the purposes of this survey, commissioning is defined as calibrating the motion sensitivity and time delay settings of the sensor.

Nine out of 10 respondents (90.3%) report that they commission occupancy sensors after installation.

Respondents were then asked what time delay they typically set. Responses varied. About one-third of respondents (32.3%) report a 10-minute time delay as the typical setting, while about one-sixth of respondents (16.1%) respectively report selecting 5 minutes, 15 minutes and 20 minutes. More than one in 10 respondents (12.9%) select 30 minutes. Less than one in 10 (6.5%) typically don’t set the time delay, but retain the factory default setting. Discounting those that retain the factory default setting, the weighted average time delay for occupancy sensors installed by respondents is 13.5 minutes, suggesting that good energy savings are being realized.

Despite commissioning, the average respondent reports being called back on about one in five projects (18.7%) to make further adjustments or commissioning of occupancy sensors. This is about twice the callback rate that electrical contractor respondents reported in a separate 2005 survey about fluorescent dimming systems (9%), and more than twice the callback rate that electrical contractor respondents reported in another 2004 survey about all industrial/commercial lighting projects (7%).

The survey suggests that return visits to a site is a major problem with some contractors. Three responses—100%, 85% and 75%—increased the average callback rate (if these responses were removed, the callback would drop to 11%).

The survey further suggests that the time-delay settings of the sensors may be a factor. Respondents who report setting the time-delay of the installed sensors to 10 minutes or less also report a much higher rate of callbacks (22%) than those respondents setting a time-delay of 15 minutes or longer (14%).

When called back to resolve a problem with an occupancy sensor, nine out of 10 respondents (about 90%) say they adjust the time delay and/or sensitivity settings to correct the problem. About 10% of respondents say they typically replace the sensor. None of the respondents report moving the sensor as a solution.

Satisfaction with Sensors

Electrical contractors responding to the survey indicate they are more than somewhat satisfied, on a 1-7 scale, with 1 being “not satisfied,” 4 being “somewhat satisfied,” and 7 being “very satisfied,” with these attributes of occupancy sensors:

• Customer/Occupant satisfaction (5.66)
• Energy savings (5.59)
• Ease of installation (5.38)
• Reliability (5.31)
• Ease of application (selecting the right sensor, locating it, time delay, sensitivity) (5.14)
• Ease of commissioning (4.83)

In addition, all respondents report that their firms make recommendations on lighting equipment choices in lighting upgrade projects in existing buildings. The average respondent says his/her firm recommends occupancy sensors in 60.7% of the firm’s lighting upgrade projects in existing buildings.

Final Conclusions Suggested by Research

• The average electrical contractor is more than “somewhat satisfied” with occupancy sensor performance and ease of installation and commissioning
• The average electrical contractor regards his or her customers and associated occupants as more than “somewhat satisfied” with occupancy sensor performance
• The average electrical contractor is most satisfied with customer/occupant satisfaction and energy savings, and least satisfied with ease of application and ease of commissioning
• The average electrical contractor recommends occupancy sensors in a majority of lighting upgrade projects in existing buildings
• Occupancy sensors are typically commissioned in terms of calibration of motion sensitivity and time delay settings
• Time delays are, on average, set within an optimal range to maximize both energy savings and lamp life
• The average electrical contractor experiences a high callback rate for further adjustments to the sensor, which may argue for longer time delay settings (about one-third of respondents, for example, set the time delay at 10 minutes); a minimum of 15 minutes is recommended as a time-delay setting for occupancy sensors
• During callbacks, the contractor most often further adjusts the motion sensitivity and time delay settings to correct the problem
• Self-calibrating sensors have been designed to reduce both commissioning requirements and the callback rate; the utility of these devices need to be validated in further study

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