Commissioning lighting occupancy sensors
- Learn energy codes and standards related to lighting and occupancy sensors.
- Understand the commissioning process for lighting and lighting controls.
- Know the role of the commissioning authority in the design of lighting systems
Many of us have seen or personally experienced a person frantically waving their arms in circular motions when the lighting turns off in a space controlled by an occupancy sensor. While this may seem comical at first, users in these spaces tend to get frustrated at the occupancy sensor and override it to avoid being left in the dark. Occupancy sensors then get a bad rap. Why did the occupancy sensor fail to keep the lights on?
Lighting uses approximately 20% of the total energy consumed in commercial buildings, according to the U.S. Department of Energy. There is great potential for energy savings by reducing the lighting levels or turning the lighting off when not needed.
Occupancy and vacancy sensors are devices that use sensors to detect when a space is unoccupied and accordingly automatically turn off (or dim) the lighting fixtures. This saves energy by turning the lighting off in a space or room if it is not occupied. The device can turn the lighting fixtures on automatically upon detecting the presence of occupants and thus is referred to as an occupancy sensor.
Vacancy sensors are like occupancy sensors and use similar sensor technology. However, vacancy sensors require the occupant to turn the lighting fixtures on in a room or space by pressing a manual switch, which typically is integral to the motion sensor. See Figure 1 for an example of a wall-mounted vacancy sensor with dual technology (passive infrared and ultrasonic). The button with the light bulb is pressed as a manual on to turn on the lighting fixtures manually.
Vacancy sensors should provide greater energy savings than occupancy sensors because they give the occupant a choice of whether to turn on the lighting fixtures. For example, if there is enough ambient light in an office with windows for daylight entering through the windows, the occupant may choose not to turn on the lights at all. Conversely, with an occupancy sensor, the lighting fixtures will turn on automatically regardless of how much daylight is in the room.
This article will use the term “occupancy sensors,” which can be either occupancy or vacancy sensors depending upon the owner’s project requirements.
Studies have shown that adding occupancy lighting controls can reduce lighting energy use 10% to 90% or more, depending on the use of the space in which the sensors are installed, according to the U.S. Department of Energy (see Table 1).
One study conducted by the U.S. Department of Energy on a university campus found that installing wired occupancy sensors to control lighting in more than 200 rooms in 10 buildings provided an annual cost savings of about $14,000 with a simple payback of 4.2 years.
Occupancy sensors are also mandated by energy codes. ASHRAE Standard 90.1-2010 and 2013: Energy Standard for Buildings Except Low-Rise Residential Buildings requires that lighting automatically turn off or be reduced in output in spaces/areas such as conference rooms, classrooms, breakrooms, storage rooms, private offices, etc., with a 30-minute maximum timeout setting, both for new construction and for major retrofits. Occupancy sensors help achieve this requirement.
It is important to understand occupancy sensors need to be commissioned to realize these savings in practice.
How does an engineer or commissioning agent commission occupancy sensors lighting controls? Fortunately, there are guidelines and processes: ASHRAE Guideline 0-2019: The Commissioning Process and ASHRAE Standard 202-2018: Commissioning Process for Buildings and Systems; the ACG (AABC Commissioning Group) Commissioning Guideline; and IES DG-29-11: The Commissioning Process Applied to Lighting and Control Systems.
The IES Lighting Handbook defines commissioning of lighting systems as “a systematic process that ensures that all elements of the lighting control system perform interactively and continuously according to documented design intent and the needs of the building owner.”
IES DG-29-11 breaks down the commissioning of lighting control systems into the following phases:
- Occupancy and operations.
The pre-design phase is when the commissioning team is formed and is led by the commissioning authority. The commissioning team, consisting of the construction manager, subcontractors and lighting engineer/designer, creates the commissioning plan, develops the owner’s project requirements and provides procedures to identify and track issues during the commissioning process.
The OPR should include performance requirements for lighting control systems. For example, a section of the OPR for occupancy sensors may state:
- Occupancy sensors shall be used to turn off lighting when a space/area is unoccupied. The sensors should be set for a maximum 30-minute timeout to shut off lighting.
- Occupancy sensors shall use vacancy mode to turn lighting on in enclosed private offices with automatic off.
- Occupancy sensors shall integrate with the heating, ventilation and air conditioning system and the building automation system in private offices to turn off lighting when unoccupied and provide code minimum ventilation levels.
- Daylighting harvest sensors shall be installed in all open office areas. Daylighting controls shall dim the lighting automatically to maintain a minimum of 30 foot-candles measured at the desktop height above finished floor.
In the design phase, the design engineer should complete the basis of design that explains the concepts that the engineer will employ to achieve the performance requirements of the OPR. For example, suppose the OPR states: “Vacancy sensors shall be used in all enclosed private offices.”
A BOD to achieve this OPR may state: “Vacancy sensors using passive infrared and ultrasonic, self-adaptive technologies shall be used in all private enclosed office. Sensors shall turn the lighting off within five minutes after an office is unoccupied.”
Typically, the contractual design phases of a project consist of schematic design, design development, construction documentation, construction administration and final punch list.
The schematic design contains an outline of the lighting control system to fulfill the OPR. The design development phase includes detailed drawings and specifications.
The construction documentation incorporates commissioning in the specifications. It is highly recommended that the commissioning specifications be incorporated no later than the design development phase. The specifications would be updated in the construction documents phase.
The specifications include lighting controls to be tested and roles and responsibilities of the commissioning authority and the contractor(s). Including these items helps reduce or even eliminate conflicts and issues during commissioning tasks such as functional testing. For example, a commissioning specification may state, “The contractor shall notify the commissioning agent in writing at least 14 days in advance of all pre-functional testing.”
The commissioning authority reviews the lighting control design documents to check compliance with the OPR and the commissioning plan. For example, the commissioning authority may check that occupancy sensors are located correctly in each space/area. Another example includes verification that occupancy sensors are located more than 6 to 8 feet from HVAC diffusers (especially for sensors that use microphonics).
Here are some typical occupancy sensor design items that should be reviewed by the commissioning authority:
- Occupancy sensors are not allowed to control lighting fixtures in electrical rooms as stated in the NFPA 70: National Electrical Code.
- Time delay setting of occupancy sensors stated in the specifications shall match the OPR. How long should the lighting fixtures stay on once no motion is detected? The less time the lighting fixtures stay on, the higher the savings will be. The commissioning authority should discuss this with the owner and the design team. With LED lighting now the standard and with frequent switching of LED lighting fixtures having little effect on the longevity of LED light sources, time delay settings should be 15 minutes or less. National Electrical Manufacturers Association guidelines recommend a 15-minute time delay. However, you may want to start with a 10-minute delay for greater energy savings and adjust to a longer time delay if occupants request it (refer to the U.S. Department of Energy).
- Location of occupancy sensors.
- Sensors should not be installed within 5 feet of HVAC supply diffusers.
- For enclosed spaces, locate a wall-mounted sensor where it will not be blocked when the door is open.
- Do not install sensors on an angled or inclined ceiling as they typically do not perform well when positioned at an angle.
- Verify that the type of sensor used will sense both minor and major movement.
- Restrooms should typically use ceiling-mounted ultrasonic sensors to detect movements in the stalls. Many lighting engineers/designers may use just one wall sensor to detect movement when an occupant enters a restroom, but this sensor may not detect an occupant in a restroom stall. It is good practice to have adequate lighting in restrooms in an unoccupied mode should the lighting be turned off at inappropriate times.
- Ceiling height should be considered when placing a sensor. Most sensors should not be installed with ceiling heights over 15 feet.
The commissioning authority always notifies the design team of issues discovered during the review of the documents. The design team should then reply formally to the commissioning authority’s comments and resolve all issues.
The construction administration phase involves training of the facility personnel on the operation and maintenance of the lighting and control system. A good example of a training program includes explanation on how occupancy sensors can be modified (e.g., change from occupancy to vacancy mode).
Also included in this phase is performance testing. For lighting control systems, the commissioning authority, electrical contractor, operators, manufacturer representatives and other stakeholders are typically present for the testing. A sample partial performance test for occupancy sensors may include verification that the lighting fixtures in a space turn on within 3 feet of entering a space in a private office.
The commissioning authority maintains an issues log that begins at the pre-design phase. The log includes details of each issue and who is responsible to resolve each issue one.
A systems manual, with specified sections provided by the construction manager, is handed by the commissioning team to the owner at the project turnover. The systems manual provides details, which are now described by LEED v4, on the operation and maintenance of the lighting controls. Also included are record drawings, submittals (shop drawings), the issues log, the OPR and BOD, as well as operations and maintenance manuals. Training should always include a review of the systems manual and its use in normal operation of the building.
The occupancy and operations phase begin at substantial completion. This includes providing completion of any deferred testing and training as well as maintaining the systems manual.
The commissioning requirements of Standard 90.1-2010 require that the construction documents identify who will conduct and certify the testing. All specified lighting controls and associated software must be calibrated, adjusted, programmed and assured to operate in accordance with construction documents and manufacturer installation instructions. Specific requirements are identified for occupancy sensors, programmable schedule controls and photosensors.
For example, at a minimum, the party conducting the testing must confirm that the placement, sensitivity and timeout settings for any installed occupancy sensors provide acceptable performance — for example, the lights must turn off only after the space is vacated and must turn on only when the space is occupied. Time switches and programmable schedule controls must be programmed to turn the lights off. And photocontrol systems must reduce light levels produced by the electric lighting based on the amount of usable daylight in the space as specified.
Standard 90.1-2010 requires a commissioning authority be engaged that is not involved in the design or construction team. The commissioning authority verifies that the lighting controls are adjusted, programmed and functioning in accordance with the design and the manufacturer’s installation instructions. The commissioning authority then submits documentation certifying that the lighting systems are in compliance with or exceed the performance requirements outlined for the project in the OPR.
Installing occupancy sensors and commissioning the devices have many benefits, including reducing operational and maintenance costs. And with properly designed and commissioned occupancy sensors, it’s time to say goodbye to days of people frantically waving their arms when the lights turn off.