Control Design Toolbox: The Lighting Controls Narrative

As demand for lighting controls continues to grow, advanced solutions are becoming increasingly specified while also becoming increasingly sophisticated. This increasing sophistication translates to greater owner benefit but can also pose greater risk of design and installation mistakes.

In a perfect world, designers create clear and detailed lighting control requirements that are easily installed by the installer and the owner. In the real world, however, the owner may not have clear expectations about their lighting. Further, the designer may not provide clear design intent, the installer may make errors and, if anything goes wrong, users will complain.

For the designer, the key is to clearly express the design intent, or the basis of design, so as to provide a common roadmap for the functionality of the lighting control system.

The question is: How?

While there is no standard for communicating design intent, designers have a number of tools at their disposal:

The written lighting control narrative describes the lighting controls, including a sequence of operation, or description of system outputs in response to various inputs. Device settings include occupancy sensor time delay and sensitivity adjustments, integrated dimmer presets, time schedules for relays, and other programming and calibration. Control zoning visually reveals what control devices control what loads. One-line wiring diagrams visually reveal how all of the control devices connect and their relationship to each other. Specifications and cut sheets describe the products used and desired baseline levels of performance. Lighting and electrical panel schedules assign loads to specific dimmers or switches in the panel. And performance testing criteria tell the commissioning authority and electrical contractor how and what to test the system for after installation, and criteria for acceptance.

The written control narrative could be considered most important because it informs everything else, and yet it is often missing in project documents. Going beyond what drawings can communicate, it provides a common guide and reference for the project. Specifically, it can be used to support contract document and specification preparation, provide clear direction during bidding to contractors and manufacturers, give the commissioning authority criteria for testing and accepting the control system, and tell the owner how their control system operates.

Designers benefit by accessing a common roadmap describing the lighting control system’s intended functionality, which increases the likelihood of satisfying the owner. Contractors and manufacturers have clear direction for bidding. Installers are less likely to commit costly errors. The commissioning authority knows what to test, how to test it, and criteria for acceptance. And the owner is more likely to receive a quality product, increasing the likelihood of acceptance.

This type of documentation may become common in the future as commercial building model energy codes address documentation and commissioning. ASHRAE/IES 90.1-2010 requires the following documentation be delivered to the owner within 90 days after acceptance of the control system: record drawings of the actual installation, submittal data for all controls, recommended schedule for inspection and recalibration, and a complete control narrative showing “how each lighting control system is intended to operate, including recommended settings.”

A basic control narrative might include at least two main elements. First, a general description of the project goals and delivered control strategies deployed to satisfy these goals. Second, a description of the control system and sequence of operations for each space type. The document may change or be fleshed out over time as the project moves from the pre-design (programming) to design (schematic design, design development, construction documentation) to construction and occupancy and operations, with changes reviewed and approved at each step.

Here is an example of very general project goals, including relevant codes, for a new office building:

“The lighting controls must meet the mandatory control requirements as defined in the ASHRAE/IES 90.1-2007 energy standard. Select control strategies implemented by the lighting systems go beyond these requirements to support LEED certification.”

Ideally, the owner will provide clear direction to inform the project goals. Following is a general description of the control strategies used in the project. Here’s an example:

“The interior lighting controls will enact two primary strategies intended to minimize energy consumption: 1) automatic shutoff via occupancy sensors in small, enclosed spaces and via a timeclock-based low-voltage control system in larger, open spaces, and 2) daylight harvesting in all spaces receiving high, consistent levels of daylight contribution, notably the main lobby and private and open office spaces. In certain spaces lacking daylight and where personal safety is an issue, such as corridors illuminated by electric lighting, select lights will remain ON at all times during normal hours of occupancy. In presentation spaces, notably the meeting and training rooms, flexibility will be provided to enable users to select preset light levels. Lighting controls will also turn exterior lighting ON/OFF using a photocell/timeclock based on curfew (grounds lighting) or dusk-to-dawn operation (security lighting).”

Following the project description is a lighting control system description, including a sequence of operations—a description of what the controls in each space do in response to inputs such as occupancy, time events or daylight levels.

This could take the form of a written description produced in a simple and consistent format; a matrix providing an at-a-glance view for each space type or each individual space (room numbers pulled from the drawings), an approach well suited to complex projects.

Back to our example, we will be deploying manual-ON, timeclock-OFF for general lighting in the open office spaces in our office building, and daylight harvesting dimming in perimeter zones receiving sufficient levels of daylight. The control narrative for the manual-ON and timeclock-OFF switching controls (code 2 under the “sequence of operations” column on the matrix) might read (adapted from the Department of Energy’s Commercial Lighting Solutions webtool):

“ON/OFF control of the general lighting in each open office area will be controlled by a combination of manual wall switches and timeclock schedule functionality residing in a low-voltage relay panel-based control system.

“Users entering the space at the start of business hours will turn the general lighting ON by control zone, with each zone being within 2,500 sq.ft. in area or per the local energy codes.

“At 6:00 PM, the control system will blink several times, warning users that the lights will turn OFF in five minutes. At 6:05 PM, the control system will turn the general lighting OFF. Users working afterhours may keep the lights ON, or turn the lights back ON, by toggling the manual wall switches, which function as a 120-minute override for the timeclock automatic shutoff system.

“After 120 minutes, the system will blink the lights again, and sweep them OFF five minutes later unless the override is again activated.”

Using this basis, we might add even more information—the more detail, the better:

“The control system shall be programmable at a microprocessor-based central processing unit (CPU). The system shall provide weekly routine and annual holiday scheduling and automatically adjust for leap year and daylight savings time. Each program shall not exceed 25,000 sq.ft. or one floor, whichever is smaller. The control system shall have 10-year nonvolatile memory that stores all schedules. The system shall be able to reboot the program and reset the time schedule and current time, without errors, following power outages up to 14 days in duration. The system shall export lighting energy consumption reports by space and zone. The control system shall operate independently of but be capable of communicating with the building automation system, if present.”

From there, we could also add performance testing and criteria for acceptance. For the above low-voltage relay control system, this might include ensuring that the general lighting in each zone turns OFF at the scheduled time, the sweep is properly preceded by a blink or other warning, and the overrides are properly zoned and working.

Finally, we could add references to other pertinent documents, such as wiring diagrams, control zoning and equipment specifications and cut sheets.

Producing a written controls narrative entails more effort at the front end, but can deliver strong project benefits. By providing clear expectations for lighting control system functionality, designers will more likely deliver a quality product, contractors will more likely provide an error-free installation and properly calibrate and program the system, the owner will more likely properly maintain it, and users will more likely accept it.